Pro Channel

TUBE MIC PREAMP / COMPRESSOR / EQUALIZER

USERS GUIDE

Contents
FEATURES... 5 OVERVIEW.. 6 WHY USE AN EXTERNAL PROCESSING CHANNEL?.6 DESIGN NOTES....6 SETTING UP... 7 UNPACKING...7 AC POWER HOOKUP...7 AUDIO CONNECTIONS..7 INSTALLATION...8 SAFETY PRECAUTIONS...8 POWERING UP...8 FRONT PANEL CONTROLS AND INDICATORS.. 9 PREAMP CIRCUIT...9
Gain Control...9 Gain Switch....9 Phantom Switch....9 Phase Switch....10 Tube Drive/Gain Reduction Display..10 Preamp Output Control...10

COMPRESSOR CIRCUIT...11

Threshold Control....11 Ratio Control...11 Attack Switch....12 Release Switch...12 Type Switch...12 Comp Bypass Switch....12 Compressor Output Control..12 -2-
CLIP INDICATOR... 13 EQUALIZER CIRCUIT.. 13
Low Control... 13 Low Switch.... 13 Lo-Mid Control.... 14 Lo-Mid (X 10/Norm) Switch.. 14 Lo-Mid (Narrow/Wide) Switch... 14 Hi-Mid Control... 14 Hi-Mid (X 10/Norm) Switch... 14 Hi-Mid (Narrow/Wide) Switch... 14 High Control... 15 High Switch.... 15 EQ Byp Switch.... 15

MASTER CONTROLS.. 16

Master Output Control... 16 VU Meter.... 16 VU Meter Switches... 16 Power.... 16
REAR PANEL CONNECTIONS..17 INPUT AND OUTPUT CONNECTIONS.. 17
Input... 17 Output.... 17 XLR GND Switch... 17

LOOP INSERTS... 17

Preamp - Compressor Loop... 18 Compressor - EQ Loop... 18 Loop Connection Examples.. 18
APPLICATIONS...19 EQ TIPS.... 19
What is the best way to use EQ?... 20

SPECIAL EFFECTS... 21

GROUNDING...21 TUBE REPLACEMENT... 21 WERE ON-LINE!.. 22 WARRANTY AND SERVICE INFORMATION.. 22 LIMITED WARRANTY..22 SERVICE....22 BLOCK DIAGRAM.. 24 A R T PRO CHANNEL SPECIFICATIONS.. 25

Features

The Pro Channel is a unique product. It contains three independent, award-winning circuit designs: one of the finest tube microphone preamplifiers available, one of the finest optical tube compressors available, and one of the most flexible EQs youve ever used. Developed in partnership with studio and live sound engineers, the Pro Channel possesses a sound that is not available from any other product on the market at any price! The Pro Channel was designed and constructed with the best components, assuring a lifetime of quiet, reliable performance. The Pro Channel offers the following: The award winning A R T SOUND! Very low-noise, tube-based mic/line preamplification with discreet, Class-A solidstate input circuitry Both electro-optical and tube compressor designs Tube-based, semi-parametric, four-band equalization with selectable frequency ranges and Q Three hand-selected tubes VCA-less compressor circuitry (i.e., transparent dynamics control) Unique tube character and gain reduction LED metering Large 3 analog VU metering to monitor Output and Send points Bypassable compression and equalization circuitry XLR balanced inputs and outputs TS unbalanced inputs and outputs A rugged steel and aluminum chassis unbalanced insert points between the preamp and compressor and between the compressor and equalizer +48V phantom power Phase reversal Detented rotary controls Variable threshold and compression ratios Selectable attack and release time settings >90dB of dynamic range An internal power supply A five year warranty Designed in the USA -5-

Overview

Why use an external processing channel?
The best way to get a signal to tape is by using the shortest signal path. In most cases, the shortest path is as follows: mic to preamp to compressor to EQ to tape. (The signal doesnt even go through a mixer!) This isnt a new concept, but it has become more relevant with the availability of affordable mixing consoles. As their name implies, most affordable mixers are optimized for signal routing and general level mixing. However, they are not necessarily your best option for the actual recording of tracks. The simple truth is that the Pro Channel has a better sounding and more flexible collection of circuits. Mixer manufacturers need to make tradeoffs between price and performance. Imagine the price of your mixer if each channels EQ cost over $200 (were not talking to those of you who have a $250,000+ console)! For those of us on a budget, it just doesnt make sense to spend a ton of money on a Cadillac console when a budget mixer and a few pieces of external gear is more cost effective. Even those engineers who regularly work on big consoles use external EQs, compressors, and preamps! The goal of any recording is to get the sounds right before you commit them to tape. The Pro Channel helps you get it right so you dont have to fix it in the mix.

Design Notes

The Pro Channel is a multi-purpose tool for audio engineering and recording. Enclosed in a two rack space (2U) chassis are three independent circuits featuring a tube-based analog preamplifier, a VCA-less compressor (selectable between optical or tube control elements), and a semi-parametric, tube-based equalizer. The Pro Channel is designed to work seamlessly with any recording, soundreinforcement, or electronic instrument setup. A R Ts Pro Channel circuitry is a hybrid design utilizing the most advanced solid-state and tube technology. With a transformerless power supply, the Pro Channel maintains exceptional signal integrity and extremely low noise. Signal flow within the Pro Channel is from the preamp, to the compressor, to the equalizer (although you can change the order of the circuits by utilizing the insert points). While the preamp is always active, the compressor and equalizer may be individually bypassed. The preamplifiers active, balanced, solid-state input provides extremely low noise and excellent CMRR (Common Mode Rejection Ratio). The input has a high impedance, which prevents the loading of any device connected to it and makes the Pro Channel perfect for DI or line level applications. The preamplifiers second stage 12AX7a tube runs on a regulated DC voltage, providing an additional 20dB of gain. Our design enables the tube to overload before the input or output stage, allowing you to manipulate the tube gain to meet different sonic criteria. -6-
The compression circuit features a VCA-less design and utilizes either optical (Vactrol) or tube, dual triode electronics for superior musical performance. The compressor is soft knee by design. Although it is capable of providing a thoroughly squashed signal, it was designed to excel in areas where transparent and musical dynamics control is desired. The beauty of the optical design is its ability to apply heavy amounts of compression without pumping and breathing like VCA-based compressors. The tube compressor is capable of smoothly compressing fast-rising signal sources without undue side effects. In most cases you will hear the results of the compression without hearing the compressor. The tube-based equalizer was designed to help fix the instruments that give us headaches when recording (i.e., kick, snare, bass, toms, guitar amps, voice, etc.). The two sweepable parametric bands and selectable shelving bands have been optimized for musical instruments. The two sweepable bands overlap each other as well as the high and low shelving bands, providing you with the ultimate in flexibility. This EQ design gives you all the control you need to effectively dial in great sounds from even the poorest of sources.

Setting Up

Unpacking
Your Pro Channel was packed with care at the factory. The shipping carton was designed to protect the unit during initial shipment. Please retain this carton for use in transporting the Pro Channel, or in the unlikely event that you need to return your unit for servicing.

AC Power Hookup

The Pro Channel has an internal power supply designed to operate at 100 to 125VAC, 50 to 60Hz. Units manufactured for use outside of the United States have been modified to comply with the required electrical specifications. Under no circumstances should the power cable be altered. If the cable becomes cut or damaged, discontinue use and have it replaced before operating.

Audio Connections

Audio connections to and from the Pro Channel are balanced XLR (Pin 2 = Hot (+), Pin 3 = Cold (-), Pin 1 = Ground) and unbalanced (Tip = Hot (+), Sleeve = Ground). The insert points between the preamp and compressor and the compressor and equalizer are unbalanced (Tip = Hot (+), Sleeve = Ground) connectors. We recommend using only high-quality cables and connectors. -7-

Installation

The Pro Channel may be employed in a number of setups, including: between a microphone and a digital recorder, mixer, or analog recorder; in a mixers channel insert points; between a microphone and signal processors; and between electronic musical instruments (synthesizers, guitars, basses, samplers, acoustic instruments with pickups, etc.) and other gear.

Safety Precautions

WARNING: To avoid the risk of shock or fire, do not expose this unit to moisture. Do not remove metal panels or chassis parts. Removing any chassis parts exposes dangerous high voltages. There are no user-serviceable parts inside. Refer all servicing to qualified personnel. If your power cord becomes damaged, always replace it with the same type as originally equipped. Since the cord is detachable, it is possible to replace it with a cord configured for the wrong voltage. Always refer to the units rear panel to determine the correct supply voltage, and then choose an appropriate cord.

Powering Up

When the power switch is turned on, the VU meter illuminates. It is important to remember to turn the Pro Channel on before any monitoring levels or power amps are turned on. The Pro Channel has the ability to add over 80dB of gain to its input signal and can cause the unit to produce a thump on power up and power down. Like all tube-based equipment, the Pro Channel needs to warm up before being used. Allow one to two minutes for the tubes to reach their proper operating temperature. If the Pro Channel fails to power up when the power switch is turned on, check to see that its power cord is plugged into an active outlet. If the unit still fails to operate properly, turn it off and unplug it, and then consult your dealer or A R Ts Customer Service department.

Front Panel Controls and Indicators

Preamp Circuit

Gain Control The Gain control sets the Pro Channels input gain. Turn the control clockwise to increase gain and counter-clockwise to decrease it. The front panel calibrations (-11dB to +30 dB) refer to the Gain Switch (see next section) in the Norm position with the input routed to the unbalanced input jack. Using the XLR (balanced) input connection results in 12dB more gain, thus making the control range from +1dB to +42dB. When setting the Gain control, refer to the first 10 segment Tube Character Array (directly under the VU meter) for a visual reference to the Pro Channels internal signal levels. Hint: The Pro Channels sweet spot is when all four of the yellow warm LEDs in the Tube Character meter are lit and the first red clip LED flashes occasionally. Gain Switch Use the Gain switch to add 20 dB of gain to the Gain controls range (described above). With the switch in, the gain range is +9 to +50dB using the unbalanced input (or +21 to +62dB using the balanced input). Note: With most microphone applications, youll find it necessary to use the Pro Channel with the +20dB gain switch in. (Use the setting that best fits your application.) Phantom Switch The Pro Channel can power any microphone needing +48 volts DC phantom power. Consult your microphones documentation to see if phantom power is required. Turning the Phantom switch on supplies power to pins 2 and 3 of the balanced XLR input jack. Note: Be sure to turn down or mute the output of the Pro Channel when turning phantom power on or off. Allow 30 - 45 seconds for the power to completely dissipate -9-
before disconnecting microphones. Another Note: Most dynamic microphones wont be affected or damaged if they are plugged into the Pro Channel when phantom power is turned on (we havent run across any). However, if the mic doesnt need it, dont use it. Some things are best left untested! Phase Switch The Phase switch is used to reverse the phase of the signal leaving the Pro Channels preamp section. The Phase switch reverses the polarity of the Preamp Output jack and everything after it in the signal chain. In the Normal position (out), the signal is inphase. In the Reverse position (in), the polarity of Pins 2 and 3 of the Output XLR jack (and the Tip of the jacks) are reversed and the signal is changed to 180 degrees out of phase with the input signal. In multiple microphone applications, mic placement can affect the phase of a signal. If two microphones pick up the same signal from different locations, the result can be a hollow or frequency-shifted sound; in some cases it may sound as if an instrument disappears completely. Depressing the Phase switch can remedy this problem. Note: In single microphone applications, switching the phase will produce no audible change in the output signal. Tube Drive/Gain Reduction Display The top LED display (directly under the VU meter) shows how the tube gain is affecting the input signal. These LEDs are calibrated with the tube circuitry to give you an accurate representation of the tubes output signal. The Tube Character LEDs measure the signal level before the Preamp Output level controluse them as a visual guide for setting the Gain control. The first four (green) LEDs are labeled Cln. The tube is producing a clean output when these are lit. The next four (yellow) LEDs are labeled Warm. This is the optimal operating range for the Pro Channels preamp. At this level, the tube is producing an output signal that most would term warm (or whatever youd like to call it simmering, toasty, etc.) Youll find the output signal has an enhanced bottom to low mid quality with smooth high frequency detail. The last two (red) LEDs are labeled Clip. The first red LED will light approximately 6dB before audible distortion occurs. If this light flickers, dont panic. The unique design of the Pro Channel allows the tube to distort well before any other gain stage. When a tube goes into distortion, its a gradual process and tends to sound pleasing for a range before it turns into a distortion box. You may also find that a clipped level is suitable for some applications. Preamp Output Control The Preamp Output control sets the output level of the preamp section. In most situations youll set this control around 12 oclock (or its 0 setting). The Preamp Output control has a range of no output (from its fully counter-clockwise position), to - 10 -

+10dB of gain (when turned fully clockwise). When setting up the preamp, start with the Preamp Output at its 0 position. Once you get the Gain control set the way you want it to sound, use the Preamp Output control to set the level out of the preamp (much like using the master volume control on a guitar amplifier). Use the Preamp Output control to recover gain when you have the Gain control set low for a clean sound. Likewise, you can use the Preamp Output control to decrease the level out of the preamp when youre cranking the Gain control up for maximum tube warmth. Dont be afraid to set the Preamp Output control very high if you desire a very clean signal, but with a good deal of compression. (See the next section.)

Compressor Circuit

Threshold Control The Threshold control sets the point at which the compressor acts on the input signal. Turning this control counterclockwise lowers the Threshold, adding more compression to a signal. Turning this control clockwise raises the threshold. The Threshold control is dependent on the Preamp Output control (or the output of a device plugged into the Comp In insert point). The easiest way to set this control is to start with it fully clockwise. After setting the Preamp Output level, slowly turn the Threshold control counter-clockwise, (lowering the threshold) until you see the yellow (0dB) Threshold LED light in the Gain Reduction display (below the Tube Character array). Now adjust Threshold (either lower or higher) until you have the desired amount of compression. (Use the Gain Reduction LEDs as a visual guide) Ratio Control The Ratio control sets the compression ratio (or slope) for the compressor circuit. At its minimum position, the compression ratio is an active 2:1, meaning that for every 2dB over the threshold the input signal rises, the compressors output will change by 1dB. This compression ratio is very mild and musical, and is ideal for smoothing all types of signals. At its maximum position, the compression ratio is greater than 10:1. This setting is typically called hard limiting as it allows only a 1dB change in level for any signal reaching 10dB above the set threshold. Hard limiting is ideal for applications where it is not desirable to exceed a certain level (i.e., mixing, popping bass, digital recording, etc.). - 11 -
Attack Switch The Attack switch selects the attack characteristics of both the tube and optical compressor circuits. The Fast position (in) allows the compressor to react quickly to fast-rising attacks. Note that the tube circuit has an inherently fast response and can be aggressive on signals with quick transients, such as snare drums. The Slow position (out) can be helpful in reducing compression artifacts for signals with very little high frequency content, such as piano or flute. Release Switch The Release switch selects the release characteristics of the compressor circuit. The Fast position (in) allows the compressor to recover quickly once the signal falls below the threshold. The Auto position (out) allows the compressor to adjust itself depending on the characteristics of the input signal. Use the Fast setting when the signal has repetitive, consistent characteristics, such as on kick drums, snares, and vocals. Use the Auto setting when the signal has varying characteristics, such as long decaying notes alternating with quick notes and mix material. Type Switch This switch covers one of the more unique features of the Pro Channel. In the Optical position (out), the Pro Channels compressor employs A R Ts award-winning Vactrol-based compression element from the Pro VLA. Switching to the in position engages the dual-triode, tube control element. This circuit is capable of considerably faster attack and release times than its optical counterpart. Experiment with the two types of compression to become familiar with how they react to different source material. Comp Bypass Switch A Bypass switch is included on the compressor circuit to enable you to remove it from the signal chain. In its Norm position (out), the compressor is active. When set to its Bypass position (in), signal passes from the preamp circuitry to the equalizer without compression and the adjacent red LED lights. Also, the Gain Reduction LED array operates as usual, though at a much dimmer level, to remind you that the compressor is out of the signal path. Use the Comp Bypass switch to achieve unity gain at the output of the Compressor. Unity gain is achieved when the compressors active level is the same as its bypassed level. Toggle the switch between Norm and Bypass while adjusting the Compressor Output level. Once the levels are the same (use your ears and the VU Output Level meter), youve reached the compressors unity setting. Compressor Output Control The Compressor Output control sets the output level from the compressor circuit. Typically, a compressors Output control is used to add gain to compensate for the amount lost due to compression. When the control is fully counter-clockwise, the output is off. Turning the control - 12 -

clockwise increases the level to a maximum of +20dB of gain. While you can use the compressor to add gain to a signal, it is better to add gain before the compressor for the best signal to noise ratio. If you want to use the compressor to add more gain, use the VU meter to monitor the Pro Channels output level, or use the meter on your recorder or mixer to make sure you wont clip the next piece of equipment in the chain.

Clip Indicator

The red Clip LED, located between the compressor and EQ sections, monitors the EQs level at several internal points. It will illuminate 6dB before the available headroom is exceeded. When the Clip indicator lights, the level into the equalizer is too high; turn down either the Preamp Output control, the Compressor Output control, or the output level of the device plugged into the Comp In insert point.

Equalizer Circuit

The equalizer circuit in the Pro Channel is a tube-based, semi-parametric, four-band equalizer. All of the bands overlap, giving you the ultimate in flexibility. The normal bandwidth of each filter is purposely wide to provide a very musical sound. Low Control The Low control adjusts a shelving filter with a selectable corner frequency of either 40Hz or 120Hz. The two frequencies are selected with the Low switch (see below). The low shelving filter affects all frequencies below the corner frequency when applying boost or cut. In other words, cutting at 40Hz also cuts 30Hz, 20Hz, etc. The Low control has as range of 12dB. Low Switch The Low switch selects the corner frequency of the Low control. In the out position, the corner is at 40Hz. In the in position, the corner is at 120Hz. 40Hz is great for enhancing sub-low frequencies such as those in bass guitars and kick drums. Cutting 40Hz can also help to clean up mixes that sound muddy or loose in the low end. 120Hz is generally the low-end for vocals, guitars and toms. Boosting 120Hz can add - 13 -
weight or beef to a week vocal and cutting it can thin out a signal that takes up too much room in the low end. Lo-Mid Control The Lo-Mid control is a dual concentric pot (i.e., there are two controls one outer and one inner). The outer control is used to select a frequency while the inner one is used to apply boost or cut. The amount of boost or cut available depends on the setting of the Lo-Mid (Wide/Narrow) switch: 12dB for Wide and 20dB for Narrow. Bandwidths are approximately 1 octave and 1/3 octave, respectively. Also, the Lo-Mid control can cover two frequency ranges depending on the position of the Lo-Mid (X 10/Norm) switch; these ranges are 20Hz to 200Hz and 200Hz to 2KHz. Lo-Mid (X10/Norm) Switch The first Lo-Mid switch determines the frequency range covered by the Lo-Mid control (above). In its out position, the range is set at 20Hz to 200Hz. In its in position, the range is set at 200Hz to 2KHz. Youll notice that the Low and Lo-Mid control ranges overlap (meaning they cover the same frequencies); this is intentional and is one of the powerful features of the equalizer. Lo-Mid (Narrow/Wide) Switch The second Lo-Mid switch determines the width of the frequency band that the Lo-Mid control covers. In its Wide position (out), the Q is approximately 1.1. In its Narrow position (in), the Q is approximately 3.3. In general, youll find that the Wide setting yields the most musical, unobtrusive results. Conversely, Narrow is preferable for surgical cutting of a frequency band without affecting adjacent frequencies too much. Hi-Mid Control Like the Lo-Mid control, the Hi-Mid control is a dual concentric pot. The outer control is used to select a frequency while the inner control is used to apply boost or cut. The Hi-Mid control can cover two frequency ranges, depending on the position of the HiMid (X 10/Norm) switch; these ranges are 200Hz to 2KHz and 2KHz to 20KHz. Hi-Mid (X 10/Norm) Switch The first Hi-Mid switch determines the frequency range covered by the Hi-Mid control (above). In its out position, the range is set at 200Hz to 2KHz. In its in position, the range is set at 2KHz to 20KHz. Note: The Lo-Mid and Hi-Mid Frequency controls overlap in the 200Hz to 2KHz range. This feature allows either or both controls to be used in this range and is extremely useful if, for example, you want to cut at 200Hz and boost at 350Hz. Hi-Mid (Narrow/Wide) Switch The second Hi-Mid switch determines the width of the frequency band that the Lo-Mid control covers. In its Wide position (out), the Q is approximately 1.1. In its Narrow position (in), the Q is approximately 3.3. In general, youll find that the Wide setting yields the most musical, unobtrusive results. Conversely, Narrow is preferable for - 14 -

surgical cutting of a frequency band without affecting adjacent frequencies too much. High Control The High control adjusts a shelving filter with a selectable corner frequency of either 6KHz or 18KHz. The two frequencies are selected with the High switch (see below). The high shelving filter affects all frequencies above the corner frequency when applying boost or cut. In other words, cutting at 6KHz also cuts 7KHz, 8KHz, etc. The High Frequency control has as range of 12dB. High Switch The High switch selects the corner frequency of the High control. In the out position, the corner is 18KHz. In the in position, the corner is 6KHz. 6KHz is great for adding top end to guitars, snare drums and vocals. Cutting 6KHz can also help to take the edge off brittle or harsh sounding instruments. 18KHz may be used to add sizzle to cymbals and is generally referred to as the air band. While there arent many instruments that contain 18KHz information directly, many instruments and mixes contain upper harmonics that can add extra definition and space when boosted. Cutting at 18KHz can decrease hiss and noise. Note: The High and Hi-Mid controls intentionally overlap to give you greater flexibility. For example, on cymbals try boosting 18KHz with the High control while cutting 20KHz with the Hi-Mid control for a bright, yet noise-free result. EQ Bypass Switch A Bypass switch is included in the equalizer circuit to enable you to remove it from the signal chain. When set to its Bypass position (in), signal passes from the compressor circuitry to the output tube section with no equalization. The red LED lights when Bypass is engaged. In its Norm position (out), the equalizer is active. Use the EQ Bypass switch to compare your equalized and unequalized sound a reality check to make sure you are making an improvement! It may be necessary to adjust the Master Output control to balance the apparent level of the EQd and un-EQd signal.

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Master Controls
Master Output Control The Master Output control sets the final output level leaving the Pro Channel. When the control is fully counterclockwise, there is no output. Turning the control clockwise increases the output level to a maximum gain of +10dB. When setting this control, refer to the VU Meter (set for the Output optionsee below) or the level meter on your recorder or mixer. VU Meter A backlit, average reading VU meter can accurately monitor levels at several points in the Pro Channel. The 0VU level is calibrated to +4dBu at any of the internal points and at the Output connector. For the same calibration on the XLR output, a 600 load must be used otherwise the balanced output is 6dB higher (0VU = +10dBu). Note: When running the Pro Channel into a mixing console or recorder, always reference the meter on the mixer or recorder when setting output levels. Not all meters are calibrated the same and it is always best to look at the level entering the last piece of equipment in the chain. VU Meter Switches The VU Meter switches determine which point feeds the VU meter. The right-hand switch selects either the Pro Channels output or an internal point selected by the other switch. The left-hand switch selects either the preamp output or the compressor output. Note: When the right-hand switch is set to Output, the left-hand switch has no effect. Another Note: The internal level-monitoring points also correspond to the level at the Send jacks of the two insert loops. If you are using either of these jacks as your output to other devices, switch the VU Meter to monitor the appropriate point. Power The Power switch supplies and removes power from the Pro Channel. The Pro Channel should be turned on only after all monitor levels are turned down or off, to protect against any thumping caused by high gain settings. Likewise, the Pro Channel should be turned off after turning all monitor levels down. The Output Level VU meter is illuminated when power is on.

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Rear Panel Connections
Input and Output Connections
The Pro Channels XLR connectors follow the AES standard: Pin 1 = Ground, Pin 2 = Hot (+), and Pin 3 = Cold (-). The unbalanced phone jacks are the typical Tip = Hot (+) and Sleeve = Ground. Note: None of the Pro Channels circuitry is connected directly to the metal chassis. Either the input or output ground must be connected to another portion of the signal path in order to establish a ground reference. Input Only one Input jack should be used at a time. However, both inputs can be hard-wired without having to disconnect one while using the other (i.e., if no load is placed on the XLR input, the jack will function as if there was nothing connected to the XLR input). However, it is still preferable to disconnect any unused cables to avoid pick up of extraneous noise, hum, or RF interference. Output Both the balanced and unbalanced Output connections may be used simultaneously. This feature is particularly handy when using the Pro Channel as a direct box for instruments or line level signals. XLR GND Switch If you hear a hum when using the Pro Channels XLR output, a ground loop may be the problem. To remedy this problem, press the XLR GND switch in, to its Lift position, to disconnect the ground wire (pin 1) from the XLR output. This action interrupts the ground path and therefore breaks the loop.

Loop Inserts

Two signal loops are provided for the following applications: to connect external equipment to the Pro Channel, to use only specific individual circuits, or to take direct signal paths from specific sections. The connections are unbalanced (Tip = Hot (+), Sleeve = Ground). Both of the Send jacks may be used without interrupting signal-flow through the Pro Channel. The Return jacks break the signal-flow when a jack is inserted. - 17 -
The loops may also be utilized to re-patch the compressor and equalizer circuits in a different order (i.e., signal flow = preamp to equalizer to compressor). For information on how to do this, see Loop Connection Examples, below. Preamp - Compressor Loop A loop is provided between the preamps output and the compressors input. The Preamp Out (Send) jack takes its signal after the Preamp Output control. This jack may be used to send an unbalanced signal directly to an input of a recorder, mixer, or other piece of outboard equipment. The Comp In (Return) jack places its signal before the compressors Threshold control. This jack may be used to connect the output of a piece of equipment to the input of the Pro Channels compressor circuit. Since there is no Compressor Input Level control, equipment patched into the insert loop should have an Output control for setting proper levels. Compressor - EQ Loop A loop is provided between the compressors output and the equalizers input. The Comp Out (Send) jack takes its signal after the Compressor Output control. This jack may be used to send an unbalanced signal directly to an input of a recorder, mixer or other piece of outboard equipment. The EQ IN (Return) jack may be used to connect the output of a piece of equipment to the input of the Pro Channels equalizer circuit. Since there is no Equalizer Input Level control, equipment patched into the insert loop should have an Output control for setting proper levels. Loop Connection Examples To use only the Pro Channels preamp: Plug a mic, instrument, or line level signal into one of the Input jacks. Either connect the Preamp Out (Send) jack into the input of the next piece of gear, or bypass the compressor and equalizer circuits and connect either of the Output jacks to the input of the next piece of equipment. To use only the Pro Channels compressor: Plug a line level signal (such as a mixers Send) into the Comp In (Return) jack. Connect the Comp Out (Send) jack to the input of the next piece of equipment, such as a mixers Return. To use only the Pro Channels equalizer: Plug a line level signal into the EQ In (Return) jack. Connect either of the Pro Channels Outputs to the input of the next piece of equipment. To place the equalizer before the compressor: Plug a mic, instrument, or line level signal into one of the Input jacks. Connect Preamp Out (Send) to EQ In (Return). Connect the unbalanced Output to Comp In (Return). Use Comp Out (Send) as the main output to the input of the next piece of equipment. Dont forget that it is possible to use each section of the Pro Channel on a separate track. For example, the bass track can run through the compressor, the vocal track through the preamp, and the guitar track through the EQ all at the same time! - 18 -

Applications

The Pro Channels main application is as a processing channel for a microphone, instrument, or line level source. To use the Pro Channel as a mic or line preamplifier only, simply press the Bypass switches to bypass the compression and equalizer circuitry. Plug a microphone directly into either input and set the Input and Output controls to provide an appropriate level into the next stage of your system. The Pro Channel is ideal for use as a DI box. Plug your instrument into either Input and use the XLR, , or both outputs to connect to your recorder, board, or PA system. Experiment with different input level settings for distinct textures. The Pro Channel has enough gain to be used in front of a power amplifier. To use the Pro Channel as an instrument preamp, simply plug the instrument into the Input jack and connect the Output jack to the power amplifiers Input. See Loop Connections for further hook-up options and for using the Pro Channels individual sections. In most cases, the Pro Channel offers superior performance to your consoles on-board preamp. To use the Pro Channel instead of your consoles preamp, simply connect the Pro Channels Output to the Line Input of your mixers input channel. Note: You can connect the XLR Output jack of the Pro Channel to the XLR Input of your mixer, however most affordable mixers do not allow you to bypass their internal preamp when using the XLR jack. You will cause no harm to either unit when doing this, but you will probably experience slightly higher noise due to the fact that you are now preamplifying your mixers preamp. Note: Be certain that you do not connect the Pro Channels XLR Output to a mixer input that has Phantom Power applied.

EQ Tips

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What is the best way to use EQ? There are two schools of thought on EQ: 1) Use as much as you need to make things sound good. 2) Dont use any EQ. Most people follow the suggestion of if it sounds good, it is good. You need to use your ears and judge for yourself as their are no steadfast rules for EQing. Here are a few pointers to guide you: Always tweak the instrument you are EQing while listening to it in the mix. EQing an instrument when it is soloed doesnt give you a good representation of how it will sound when mixed with other instruments. Youd be surprised at how bad a killer guitar track can sound when it is isolated from the rest of the mix. Remember, what makes it killer is how it sounds in relation to the other instruments! Keep the big picture in mind. Most people think of EQ as boosting only (well just add a little EQ.). Many times a bad sounding instrument can be fixed by simply isolating the offending frequency and pulling it out. After you determine approximately where the problem area is in the instrument (highs, lows, mids), isolate the track and boost one of the mid bands. Slowly sweep through its frequency range. When the really nasty sound jumps out at you (youll know it when it happens) turn the boost back to 0 (12 oclock). Now put the track back into the mix and cut the frequency. Youll have to adjust the level of the instrument depending on how much you cut, but you should find that with the problem area pulled out, the instrument works better in the mix. When recording EQd instruments, make sure you have a good representation of frequencies on tape. Always monitor off-tape when recording to ensure that what youre hearing is what is on tape. When recording things like kick drums, make sure you have enough low end thud and high end click (if applicable) before you record. Recording guideline: You can always boost or cut frequencies after theyve been recorded, but you cant add frequencies that werent recorded! Also, if you get the right sound when you record the tracks, you shouldnt be spending a lot of time reEQing during the mix. When mixing, concentrate on blending tracks and the songs dynamics. If you find yourself EQing everything, take a break and come back to it later. Start mixing with a group of instruments such as the whole drum kit or guitars and bass, instead of listening to individual tracks. Mixing is the time for tweaking not applying a sonic re-design. Once again, if it sounds good, print it! Trust your ears never mind where the knobs are pointing.

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Special Effects
For industrial, metal, or just flavor textures, experiment with the Pro Channel. Overdriving the preamp, compressor, and equalizer circuitry can add interesting textures when blended with vocals and other instruments. Purposely placing signals out of phase can also yield interesting results. No harm will come to the Pro Channel with this type of experimentation. However, be sure to have output and monitoring levels turned DOWN before testing the sound. Remember, you have a great amount of gain available in the Pro Channel!

Grounding

Avoiding ground loops while several pieces of equipment are connected is one of the most common challenges in recording. For this reason, all ART recording gear does not have a direct connection between the audio circuit ground and the chassis ground. This technique enables the gear to be safely grounded through the 3-prong AC cord and also to the previous and next items in the signal chainwith optimum noise performance. At least one ground connection must be made between the Pro Channel and the rest of the signal chain. If you hear hum when using the Pro Channels XLR output, try pressing the XLR GND switch in, to its Lift position, to disconnect the ground wire (pin 1) from the XLR output.

Tube Replacement

The Tubes in your Pro Channel should last for many years. They are hand-sorted for optimal performance in our specific circuits. In the event that you need to replace them, A R T suggests that you do so with tubes available from A R T. These are matched to the Pro Channel and will yield consistent sonic results. You can replace the tubes with other brands, however A R T has no responsibility for the resulting sound quality; they may sound better, they may sound worse. The choice is yours. Unauthorized alterations to the Pro Channel also will result in voiding the warranty. A R T retains a policy of constant product improvement. A R T reserves the right to make changes in design or make additions to or improvements upon this product without any obligation, and to install the same on products previously manufactured. In other words, specifications are subject to change without notice.

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Were on-line!
For Product information, questions, applications, tips, answers and general discussion with ART employees, look for ART on the Internet. Email us at support@artproaudio.com and check out our Web Site at www.artproaudio.com.
Warranty and Service Information

Limited Warranty

Applied Research and Technology(A R T) will provide warranty service for this unit in accordance with the following warranty statement. A R T warrants to the original purchaser that this product is free from defects in workmanship and materials for a period of five years from the date of purchase. A R T will, without charge, repair or replace, at its option, defective product or component parts upon prepaid delivery to the factory service department or an authorized service center, accompanied by proof of purchase date in the form of a valid sales receipt. EXCLUSIONS: This warranty does not apply in the event of misuse or abuse of the product or as a result of unauthorized alterations or repairs. This warranty is void if the serial number is altered, defaced, or removed. A R T reserves the right to make changes in design and make additions or improvements upon this product without any obligation to install the same on products previously manufactured. A R T should not be liable for any consequential damages, including without limitation to damages resulting from the loss of use. Some states do not allow limitation of incidental or consequential damages, so the above limitation or exclusion may not apply to you. This warranty gives you specific rights and you may also have other rights which vary from state to state. For products purchased outside the United States, an authorized distributor of Applied Research and Technology will provide service.

Service

The following information is provided in the unlikely event that your unit requires service. 1) Be sure that the unit is the cause of the problem. Check to make sure the unit has power, all cables are connected correctly, and the cables themselves are in working condition. You may want to consult with your dealer for assistance in troubleshooting or testing your particular configuration.

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2) If you believe the ART unit is at fault, go to www.artproaudio.com. You may contact Customer Service for more assistance, or directly request a Return Authorization for service in the resources area of the website. 3) If you are returning the unit for service, pack the unit in its original carton or a reasonable substitute. The original packaging may not be suitable as a shipping carton, so consider putting the packaged unit in another box for shipping. Print the RA number clearly on the outside of the shipping box. 4) Include, with your unit, a note with the RA number and your contact information including a daytime phone number, preferably attached to the top of the unit.
Fill in the following information for your reference: Date of purchase ___________________ Purchased from Serial number ___________________ ___________________

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A R T Pro Channel Specifications
Dimensions Weight Maximum Gain Dynamic Range Frequency Response Low-Cut Filter Input/Output Connections Insert Connections Input Impedance Output Impedance Maximum Input Level Maximum Output Level Equivalent Input Noise Phantom Power Compression Ratio Attack Time Release Time Maximum Compression EQ Frequency Bands Low Shelf Low-Mid Sweepable Low-Mid Q High-Mid Sweepable High-Mid Q High Shelf Boost/Cut per Band 6.5"D x 19"W x 3.50"H 12.0 lbs. XLR to XLR: 83dB, to : 65dB >100dB (20-20KHz) 20Hz to 20KHz (0.5dB) Single-Pole Variable: -3dB@10Hz to 250Hz XLR balanced and unbalanced unbalanced 1.67K (XLR), 1M (), 10K+ ( inserts) 600 (XLR), 300 (all ) +15dBu (XLR), +21dBu () +27dBu (XLR), +22dBu () -130dBu (XLR to XLR, A wtd) +48V DC (switchable) Variable: 2:1 to >10:1 Fast: 2ms (optical), 0.5ms (tube) Slow: 15ms (for 20dB of comp) Fast: 300ms Auto: 100ms-3sec (program dependent) 30dB (optical), 23dB (tube)
40Hz, 120Hz 20Hz to 200Hz, 200Hz to 2KHz (Shift out / in) Wide, Narrow (Q=1.1 / 3.3) 200Hz - 2KHz, 2KHz - 20KHz (Shift out / in) Wide, Narrow (Q=1.1 / 3.3) 6KHz, 18KHz Low, High: 12dB Lo-Mid and Hi-Mid: 12dB (wide), 20dB (narrow) Total Harmonic Distortion (THD) <0.1% (typical) Tubes Three (Hand-Selected) Power Requirements 100-125 VAC, 30W

(Export units configured for country of destination)
The Pro Channel was designed and developed in the United States of America.
1999-2008 Applied Research and Technology

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www.artproaudio.com

support@artproaudio.com

Pro Channel Tube Mic Preamp / Compressor / Equalizer

215-5004-102

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APPLIED RESEARCH & TECHNOLOGY, Inc. 215 TREMONT STREET ROCHESTER, NEW YORK 14608 USA (716) 436-2720 Voice (716) 436-3942 Fax Internet http://www.artroch.com E-mail: art@art.com
Pro Channel Professional Tube Mic Preamp, Compressor & Equalizer

215-5004-100

Pro Channel
PROFESSIONAL TUBE MIC PREAMP, COMPRESSOR & EQUALIZER

USERS GUIDE

Contents
FEATURES... 4 OVERVIEW.. 5 WHY USE AN EXTERNAL PROCESSING CHANNEL?..5 DESIGN NOTES...5 SETTING UP... 6 UNPACKING....6 AC POWER HOOKUP...6 AUDIO CONNECTIONS...6 INSTALLATION...6 SAFETY PRECAUTIONS...7 POWERING UP...7 FRONT PANEL CONTROLS & INDICATORS.. 7 PREAMP CIRCUIT...7
Gain Control....7 Gain Switch....8 Phantom Power Switch....8 Phase Switch...8 Tube Drive/Gain Reduction Display...9 Preamp Output....9

COMPRESSOR CIRCUIT...10

Threshold Control....10 Ratio Control...10 Attack Switch...10 Release Switch...10 Type Switch...11 Compressor Bypass Switch...11 Compressor Output Level Control...11
CLIP INDICATOR...12 EQUALIZER CIRCUIT...12
Low Control...12 Low Shift Switch...12 Lo-Mid Controls....12 -2-
Lo-Mid Shift x 10 Switch... 13 Lo-Mid Wide/Narrow (Q) Switch... 13 Hi-Mid Controls.... 13 Hi-Mid Shift x 10 Switch... 13 Hi-Mid Wide/Narrow (Q) Switch.. 13 High Frequency Control... 13 High Shift Switch... 14 EQ Bypass Switch.... 14

MASTER CONTROLS...14

Master Output Level Control.. 14 VU Meter.... 15 VU Meter Switches... 15 Power.... 15
REAR PANEL CONNECTIONS..15 INPUT AND OUTPUT CONNECTIONS... 15
Input.... 16 Output.... 16

LOOP INSERTS... 16

Preamp - Compressor Loop... 16 Compressor - EQ Loop... 16 Loop Connections... 17
APPLICATIONS...17 EQ TIPS.... 18
What is the best way to use EQ?... 18
SPECIAL EFFECTS.... 19 GROUNDING... 19 TUBE REPLACEMENT..19 BLOCK DIAGRAM...20 A R T PRO CHANNEL SPECIFICATIONS.21 WERE ON-LINE!...22 WARRANTY AND SERVICE INFORMATION.22 LIMITED WARRANTY... 22 SERVICE.... 23

Features

The Pro Channel is a unique product. It contains three independent award-winning circuit designs: one of the finest tube microphone preamplifiers available, one of the finest optical tube compressors available, and one of the most flexible EQs youve ever used all in one unit. Developed in partnership with studio and live sound engineers, the Pro Channel possesses a sound that is not available from any other product on the market at any price! The Pro Channel was designed and constructed with the best components, assuring a lifetime of quiet, reliable performance. The Pro Channel offers: The award winning A R T SOUND! Very low-noise, tube-based mic/line preamplification with discreet, Class-A solidstate input circuitry Both electro-optical and variable-mu compressor designs Tube-based semi-parametric, four-band equalization with selectable frequency ranges and Q Three hand-selected tubes VCA-less compressor circuitry (i.e., transparent dynamics control) Unique tube character and gain reduction LED metering Large 3 analog VU metering to monitor Main Output or Insert Send points Bypassable compression and equalization circuitry XLR balanced inputs and outputs TS unbalanced inputs and outputs A rugged steel & aluminum chassis unbalanced insert points between the preamp and compressor and between the compressor and equalizer +48V phantom power Phase reversal Over 80dB of gain Detented rotary controls Variable threshold and compression ratio Selectable release time settings >90dB dynamic range An internal power supply A five year warranty Designed and manufactured in the USA

Overview

Why use an external processing channel?
The shortest signal path is the best way to get a signal to tape. In most cases, the shortest path is: mic to preamp to compressor to EQ to tape deck. The signal doesnt even go through the mixer! This isnt a new concept, but it has become more relevant with the availability of affordable mixing consoles. As their name implies, most affordable mixers excel in signal routing and mixing capabilities. However, they are not necessarily your best option for the actual recording of tracks. While their onboard circuitry is nearly always clean and quiet, the simple truth is that the Pro Channel has a better sounding and more flexible collection of circuits. Mixer manufacturers need to make trade-offs betweeen price and performance. Imagine the price of your mixer if each channels EQ cost over $200 (and were not talking about those of you who have one of those $250,000+ consoles)! The use of external processing (equalizers, preamps and compressors) has sonic and practical benefits when you consider that most recording is done one or two channels at a time. For those of us on a budget, it just doesnt make sense to spend a ton of money on a Cadillac console when a budget mixer and a few pieces of external gear is more cost effective. Even those engineers who regularly work on big consoles use external EQs, compressors and preamps! The goal of any recording is to get the sounds right before you commit them to tape. The Pro Channel exists to help you get it right so you dont have to fix it in the mix.

Design Notes

The Pro Channel is a multi-purpose tool for audio engineering and recording. Enclosed in a two rack space (2U) chassis are three independent circuits featuring a tube-based analog preamplifier, a VCA-less compressor switchable between optical or variable-mu control element, and a semi-parametric, four-band, tube-based equalizer. Used as a direct recording channel, a mic/line preamp, or a DI (direct) box, the Pro Channel is designed to work seamlessly with any recording, sound-reinforcement, or electronic instrument setup. A R Ts Pro Channel circuitry is a hybrid design utilizing the latest, most advanced, solid-state and tube technology. With a transformerless design, the Pro Channel maintains exceptional signal integrity and extremely low noise. The compressor circuit follows the preamp and the equalizer follows the compressor (although you can change the order of the circuits by utilizing the insert points). While the preamp is always active, the compressor and equalizer may be individually bypassed. The preamplifiers active balanced solid-state input provides extremely low noise and excellent CMRR. The input has a high impedance, which prevents the loading of any device connected to it and makes the Pro Channel perfect for DI or line level applications. The preamplifiers second stage 12AX7a tube runs on a regulated DC voltage providing an additional 20dB of gain. Our design enables the tube to overload before the input or output stage. This allows you to manipulate the tube gain to meet different sonic requirements. The compression circuit features a VCA-less design and utilizes either optical (Vactrol) or variable-mu dual triode electronics for superior musical performance. The compressor is soft knee by design. Although it is -5-
capable of providing a thoroughly squashed signal, it was designed to excel in areas where transparent and musical dynamics control is desired. The beauty of the optical design is its ability to apply heavy amounts of compression without pumping and breathing like VCA-based compressors. The variable-mu compressor is capable of smoothly compressing fast-rising signal sources without undue side-effects. In many cases you will hear the results of the compression without hearing the compressor. The tube-based equalizer was designed to help fix the instruments that give us the most headaches when were recording: kick, snare, bass, toms, guitar amps, voice, etc. The two sweepable parametric bands and selectable shelving bands have been optimized for musical instruments. The two sweepable bands overlap each other as well as the high and low shelving bands, providing you with the ultimate in flexibility. This EQ design gives you all the control you need to effectively dial in great sounds from even the poorest of sources.

Setting Up

Unpacking
Your Pro Channel was packed with care at the factory. The shipping carton was designed to protect the unit during initial shipment. Please retain this carton for use in transporting the Pro Channel, or in the unlikely event that you need to return your Pro Channel for servicing.

AC Power Hookup

The Pro Channel has an internal power supply designed to operate at 100 to 125VAC, 50 to 60Hz. Units manufactured for use outside of the United States have been modified to comply with the required electrical specifications. Under no circumstances should the power cable be altered. If the cable becomes cut or damaged, discontinue use and have it replaced before operating the Pro Channel.

Audio Connections

Audio connections to and from the Pro Channel are balanced XLR (Pin 2 = Hot (+), Pin 3 = Cold (-), Pin 1 = Ground) and unbalanced (Tip = Hot (+), Sleeve = Ground). The insert points between the preamp and compressor and the compressor and equalizer are (Tip = Hot (+), Sleeve = Ground) unbalanced connectors. We recommend using only high-quality cables and connectors.

Installation

The Pro Channel may be employed in a number of setups including: Between a microphone and a mixer, digital multi-track recorder, DAT machine, hard disk recorder, or analog recorder. In a mixers channel insert points. Between a microphone and signal processors. Between electronic musical instruments (synthesizers, guitars, basses, samplers, acoustic instruments with pickups) and other gear. -6-

Safety Precautions

Warning: To avoid the risk of shock or fire, do not expose this unit to moisture. Do not remove metal panels or chassis parts. Removing any chassis parts exposes dangerous high voltages. There are no user-serviceable parts inside. Refer all servicing to qualified personnel. Note: If your power cord becomes damaged, always replace it with the same type as originally equipped. Since the cord is detachable, it is possible to replace it with a cord configured for the wrong voltage. Always refer to the units rear panel to determine the correct supply voltage, and choose an appropriate cord.

Powering Up

When the power switch is turned on, the VU meter will illuminate. It is important to remember to turn the Pro Channel on before any monitoring levels or power amps are turned on. The Pro Channel has the ability to add over 80dB of gain to its input signal. This can cause the Pro Channel to produce a thump on power up and power down. Note: Like all tube-based equipment, the Pro Channel needs to warm up before being used. Allow one to two minutes for the tubes to reach proper operating temperature before using. If the Pro Channel fails to power up when the power switch is turned on, check to see that its power cord is plugged into an active outlet. If the unit still fails to operate properly, turn it off and unplug it. Then consult your dealer or A R Ts Customer Service department.

Front Panel Controls & Indicators

Preamp Circuit

Gain Control The Gain control sets the Pro Channels input gain. Turn the control clockwise to increase gain and counter-clockwise to decrease gain. The front panel calibrations (-11dB to +30 dB) refer to the Gain Switch in the Norm position (see next section) with the input routed to the unbalanced input jack. Using the XLR (balanced) input connection results in 12dB more gain, thus making the control range from +1dB to +42dB. Selection of the gain range is made with the +20dB gain switch. When setting the Gain control, refer to the upper 10 segment Tube Character -7-
Array (under the VU meter) for a visual reference to the Pro Channels internal signal levels. Hint: the sweet spot for the Pro Channel is when all 4 of the yellow warm LEDs in the Tube Character Array are lit. Gain Switch Use the Gain switch to set the range of the Gain control depressing the switch adds 20dB to the gain range described above. With the switch in, the gain range is +9 to +50dB using the unbalanced input (or +21 to +62dB Balanced). Note: With most microphone applications youll find it necessary to use the Pro Channel with the +20dB gain switch in. Use the setting that best fits your application. Phantom Power Switch The Pro Channel can power any microphone needing +48 volts DC phantom power. Consult your microphones documentation to see if phantom power is required. Turning the phantom power switch On supplies power to pins 2 and 3 of the balanced XLR input jack. Note: It is best to have phantom power turned off when connecting microphones to the Pro Channel. Note: Be sure to turn down or mute the output of the Pro Channel when engaging or disengaging phantom power. Additionally, when disengaging, allow 30 - 45 seconds for the power to completely dissipate. Most microphones will make a sound like air leaking from a tire when phantom power is disconnected, but some can make some very nasty low rumbles and whines as well. Another Note: MOST dynamic microphones should not be affected or damaged if they are plugged into the Pro Channel when phantom power is turned on (we havent run across any). However, if the mic doesnt need it, dont use it. Some things are best left untested! Phase Switch The Phase switch is provided to reverse the phase of the signal leaving the Pro Channels preamp section. The Phase switch reverses the polarity of the Preamp Output jack and everything after it in the signal chain. In the Normal (out) position, the signal is in-phase. In the Reverse (in) position, the polarity of Pins 2 and 3 of the Output XLR jack (and the Tip of the jacks) are reversed and the signal is changed to 180 degrees out of phase with the input signal. In multiple microphone applications, mic placement can affect the phase of a signal. If two microphones pick up the same signal from different locations, the result can be a hollow or frequency shifted sound. In some cases it may sound as if an instrument disappears if it happens to be 180 degrees out of phase. Depressing the Phase switch can remedy this problem. Likewise, if a microphone cable is wired incorrectly, the signal will be also out of phase. Note: In single microphone applications, switching the phase will produce no audible change in the output signal.

Ratio Control The Ratio control sets the compression ratio (or slope) for the compressor circuit. At its minimum position, the compression ratio is an active 2:1. This means that for every 2dB over the threshold the input signal rises, the compressors output will change by 1dB. This is a very mild and musical compression ratio, which is ideal for smoothing all types of signals. At its maximum position, the compression ratio is greater than 10:1. This is typically called hard limiting as it allows only a 1dB change in signal level for any signal reaching over 10dB of the set threshold. This setting is ideal for applications where exceeding a certain level is not desirable (i.e., mixing, popping bass, digital recording, etc.) Attack Switch The position of the Attack switch selects the attack characteristics of both the variblemu and optical compressor circuits. The in (Fast) position allows the compressor to react quickly to fast-rising attacks. Note that the variable-mu circuit is inherently faster responding, and can be aggressive on signals with quick transients, such as snare drums. The out (slow) position can be helpful in reducing compression artifacts for signals with very little high frequency content (piano, flute, etc.). Release Switch The position of the Release switch selects the release characteristics of the compressor circuit. The in (Fast) position allows the compressor to recover quickly once the signal falls below the threshold. The out (Auto) position allows the compressor to adjust itself depending on the characteristics of the input signal. Use the Fast setting when the signal has repetitive, consistent characteristics (kick drum, snare, vocals, etc.). - 10 -
Use the Auto setting when the signal has varying characteristics (long decaying notes alternating with quick notes, mix material, etc.) Type Switch This switch covers one of the more unique features of the Pro Channel. In the out position (Optical), the Pro Channels compressor employs the award-winning Vactrolbased compression element from our Pro VLA. Switching to the in position engages the dual-triode variable-mu control element. This circuit is capable of considerably faster attack and decay times than the optical circuit. However, when the Attack & Decay times are set to very long time constants, the shared detector circuit will dominate, and the two types will behave in a very similar manner. Experiment with the two types to become familiar with how they react to different source material. Compressor Bypass Switch A Bypass switch is included on the compressor circuit to enable you to remove the compressor from the signal chain. When set to its in (Bypass) position, signal is allowed to pass from the preamp circuitry to the equalizer circuit with no compression. The LED will glow red when Bypass is engaged. In its out (Norm) position, the compressor is active. Also, when the compressor is bypassed the gain reduction LED display (under the VU meter) will still operate, but at a much dimmer level. This is to remind you that the compressor is out of the signal path, but still gives you an indication how much compression will result when the compressor is engaged. Use the Bypass switch when setting the compressors output level to achieve unity gain. Unity gain is achieved through the compressor when the active level is the same as the bypassed level. Toggle the switch between Active and Bypass while adjusting the Compressor Output level. Once the levels are the same (use your ears and the VU Output Level meter), youve reached the unity setting for the compressor. Compressor Output Level Control The Compressor Output level control sets the output level from the compressor circuit. Typically, the output level of a compressor is used to add gain to compensate for the amount of compression applied to a signal. The output level is set to achieve unity gain (no apparent level change when the compressor is active or bypassed). See Compressor Bypass Switch for more details on achieving unity gain. When the control is fully counter-clockwise, the output is off. Turning the control clockwise increases the level to a maximum of +20dB of gain. While you can use the compressor to add gain to a signal, it is better to add gain before the compressor for the best signal to noise ratio. If you want to use the compressor to add more gain, use the VU meter to monitor the Pro Channels output level, or use the meter on your recorder or mixer to make sure you wont clip the next piece of equipment in the chain.

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Clip Indicator
The Clip LED, located between the compressor & EQ sections, monitors the EQ section at the input, plus several internal points. It will illuminate 6dB before the available headroom is exceeded. When this Clip indicator lights, the level into the equalizer is too high. Turn down either the Preamp Output control, the Compressor Output control, or the output level of the device plugged into the compressor return insert point.

Equalizer Circuit

The equalizer circuit in the Pro Channel is a tube-based, semi-parametric, four-band equalizer. All of the bands overlap, giving you the ultimate in flexibility. The normal bandwidth of each filter is purposely wide to provide a very musical sound. Low Control The Low control adjusts a shelving filter with a selectable corner frequency of either 40Hz or 120Hz. The low shelving filter affects all frequencies below the corner frequency when applying boost or cut. In other words, cutting at 40Hz also cuts 30Hz, 20Hz, etc. The Low Frequency control has as range of 12dB. Two ranges are selected with the Low Shift Switch: 40Hz or 120Hz. 40Hz is great for enhancing sub-low frequencies such as those in bass guitars and kick drums. Cutting 40Hz can also help to clean up mixes that sound muddy or loose in the low end. 120Hz is generally the low-end for vocals, guitars and toms. Boosting 120Hz can add weight or beef to a week vocal and cutting it can thin out a signal that takes up too much room in the low end.
Low Shift Switch The Low Shift switch selects the corner frequency of the Low Frequency control. In the out position the corner is at 40Hz. In the in position the corner is at 120Hz. Lo-Mid Controls The Lo-Mid control is a dual concentric pot (there are two controls one outer and one inner). The outer control is used to select a frequency while the inner control is used to apply boost or cut. The amount of boost or cut available depends on the setting of the Wide/Narrow (Q) switch: 12dB for Wide and 20dB for Narrow. Bandwidths are approximately 1 octave and 1/3 octave, respectively. Also the Lo-Mid control can cover two frequency ranges depending on the position of the Shift x 10 switch. These ranges are 20Hz to 200Hz and 200Hz to 2KHz. - 12 -
Lo-Mid Shift x 10 Switch The Lo-Mid Shift x 10 switch determines the range over which the Lo-Mid frequency control will cover. In its out position, the range is set at 20Hz to 200Hz. In its in position the range is set at 200Hz to 2KHz. Note: Youll notice the Low Frequency and Lo-Mid Frequency controls overlap (meaning they cover the same frequencies). This is intentional and is one of the powerful features of the equalizer circuit. Lo-Mid Wide/Narrow (Q) Switch The Lo-Mid Wide/Narrow switch determines the width of the frequency band that the Lo-Mid control covers. In its out (Wide) position, the Q is approximately 1.1. In its in (Narrow) position, the Q is approximately 3.3. In general, youll find that the Wide setting is most appropriate for boosting a band with the most musical, unobtrusive results. Conversely, Narrow is preferable for surgical cutting of a frequency band without affecting adjacent frequencies too much. Hi-Mid Controls Like the Lo-Mid Frequency control, the Hi-Mid control is a dual concentric pot (there are two controls one outer and one inner). The outer control is used to select a frequency while the inner control is used to apply boost or cut. The Hi-Mid control can cover two frequency ranges depending on the position of the Shift x 10 switch. These ranges are 200Hz to 2KHz and 2KHz to 20KHz. Hi-Mid Shift x 10 Switch The Hi-Mid Shift x 10 switch determines the range over which the Hi-Mid Frequency control will cover. In its out position the range is set at 200Hz to 2KHz. In its in position the range is set at 2KHz to 20KHz. Note: The Lo-Mid and Hi-Mid Frequency controls overlap in the 200Hz to 2KHz range. This feature allows either or both controls to be used in this range. This is extremely useful if, for example, you want to cut at 200Hz and boost at 350Hz. Hi-Mid Wide/Narrow (Q) Switch The Hi-Mid Wide/Narrow switch determines the width of the frequency band that the Lo-Mid control covers. In its out (Wide) position, the Q is approximately 1.1. In its in (Narrow) position, the Q is approximately 3.3. In general, youll find that the Wide setting is most appropriate for boosting a band with the most musical, unobtrusive results. Conversely, Narrow is preferable for surgical cutting of a frequency band without affecting adjacent frequencies too much. High Frequency Control The High Frequency control adjusts a shelving filter with a selectable corner frequency of either 6KHz or 18KHz. The high shelving filter affects all frequencies above the corner frequency when applying boost or cut. In other words, cutting at 6KHz also cuts 7KHz, 8KHz, etc. The High Frequency control has as range of 12dB. The two ranges are selected with the High Shift switch. 6KHz is great for adding top end to guitars, snare drums and vocals. Cutting 6KHz can also help to take the edge off brittle or harsh sounding instruments. 18KHz may be used to add sizzle to cymbals and is - 13 -

generally referred to as the air band. While there arent very many instruments that contain 18KHz information directly, many instruments and mixes contain upper harmonics, which can add extra definition and space when boosted. Cutting at 18KHz can decrease hiss and noise. High Shift Switch The High Shift switch selects the corner frequency of the High Frequency control. In the out position the corner is 18KHz. In the in position the corner is 6KHz. Note: The High Frequency and Hi-Mid Frequency controls overlap. This feature gives you the ultimate in flexibility. For example, on cymbals try boosting 18KHz with the High control while cutting 20KHz with the Hi-Mid control for a very bright, yet noise-free result. EQ Bypass Switch A Bypass switch is included in the equalizer circuit to enable you to remove it from the signal chain. When set to its in (Bypass) position, signal is allowed to pass from the compressor circuitry to the output tube section with no equalization. The LED will glow red when Bypass is engaged. In its out (Norm) position, the equalizer is active. Use the EQ Bypass switch to compare your equalized and un-equalized sound a reality check to make sure you are making an improvement! It may be necessary to adjust the Master Output control to balance the apparent level of the EQd and un-EQd signal.

Master Controls

Master Output Level Control The Master Output control sets the final output level leaving the Pro Channel. When the control is fully counterclockwise, there is no output. Turning the control clockwise increases the level of the output to a maximum of +10dB of gain. When setting the Output Level control, refer to the VU Meter (set for the Output option) or the level meter on your recorder or mixer. - 14 -
VU Meter A backlit, average reading VU meter is provided to accurately monitor levels at several points in the Pro Channel. The 0VU level is calibrated to +4dBu at any of the internal points, or at the Output connector. For the same calibration on the XLR output, a 600 load must be used, otherwise the Balanced Output is 6dB higher (0VU=+10dBu). Note: When running the Pro Channel into a mixing console or recorder, always reference the meter on the mixer or recorder when setting output levels. All meters are not necessarily calibrated the same and it is always best to look at the level entering the last piece of equipment in the chain. VU Meter Switches The VU Meter switches determine which point feeds the VU Meter circuit. The righthand switch selects either the Pro Channels Output, or an internal point selected by the other switch. The left-hand switch selects either the Preamp Output or the Compressor Output. Note: When the right-hand switch is set to Output, the left-hand switch has no effect. Another Note: The internal level-monitoring points correspond to the level at the Send jacks of the two insert loops. If you are using either one of these jacks as your output to other devices in your chain, switch the VU Meter to monitor the appropriate point. Power The Power switch supplies and removes power from the Pro Channel. The Pro Channel should be turned on only after all monitor levels are turned down, or off, to protect against any thumping caused by high gain settings. Likewise, the Pro Channel should be turned off after turning all monitor levels down. The Output Level VU meter will illuminate when power is on.

Rear Panel Connections

Input and Output Connections
The Pro Channels XLR connectors follow the AES standard: Pin 1 = Ground, Pin 2 = Hot (+), Pin 3 = Cold (-). The unbalanced phone jacks are the typical Tip = Hot (+), Sleeve = Ground. Note: None of the Pro Channels circuitry is connected directly to the metal chassis. This means that either the input or output ground must be connected to another portion of the signal path in order to establish a ground reference. - 15 -
Input One input jack per channel should be used at a time. However, because of its design, the Pro Channel can be hard-wired without having to disconnect the XLR inputs when using the jacks. If no load is placed on the XLR input (no instrument or microphone connected), the jack will function as if there was nothing connected to the XLR input. However, it is still preferable to disconnect any unused cables to avoid pick up of extraneous noise, hum, or RF interference. Output Both balanced and unbalanced output connections may be used simultaneously. This is particularly useful when using the Pro Channel as a direct box for instruments or line level signals. Note: If you experience a hum when using both output connectors simultaneously (one to the console and one to an instrument amp), a ground loop may be the problem. To remedy this problem, disconnect the ground wire (pin 1) from the XLR cable plugged into the Pro Channels output (or use a ground-lifted audio cable). This interrupts the ground path and therefore breaks the loop.

Loop Inserts

Two signal loops are provided to connect external equipment to the Pro Channel, to use only specific individual circuits, or to take direct signal paths from specific sections. The connections are unbalanced (Tip = Hot (+), Sleeve = Ground). Both of the send jacks may be used without interrupting signal-flow through the Pro Channel. The return jacks break the signal-flow when a jack is inserted. The loops may also be utilized to re-patch the compressor and equalizer circuits in a different order (i.e., signal flow = preamp to equalizer to compressor). Preamp - Compressor Loop A loop is provided between the output of the preamp circuit and the input of the compressor circuit. The Preamp Send jack is located directly after the Preamp Output level control. This jack may be used to send an unbalanced signal directly to an input of a recorder, mixer or other piece of outboard equipment. The Compressor Return jack is located directly before the Threshold Control of the compressor circuit. This jack may be used to connect the output of a piece of equipment to the input of the compressor circuit in the Pro Channel. Since there is no input level control to the compressor in the Pro Channel, the piece of equipment patched into the insert loop should have an output level control. Compressor - EQ Loop A loop is provided between the output of the compressor circuit and the input of the equalizer circuit. The Compressor Send jack is located directly after the Compressor Output level control. This jack may be used to send an unbalanced signal directly to an input of a recorder, mixer or other piece of outboard equipment. The EQ Return jack is located directly before the input of the equalizer circuit. This jack may be used to connect the output of a piece of equipment to the input of the equalizer circuit in the Pro Channel. Since there is no input level control to the equalizer in the Pro Channel, the piece of equipment patched into the insert loop should have an output level control. - 16 -

Loop Connections To use only the preamp of the Pro Channel: Plug a mic, instrument, or line level signal into either of the Input Jacks. You can use either of the following for an output: Plug the output from the Preamp Send jack into the input of the next piece of gear, or Bypass the compressor and equalizer circuits and connect either of the Output Jacks to the input of the next piece of equipment. To use only the compressor circuit of the Pro Channel: Plug a line level signal (or a send from a mixer) into the Compressor Return Jack. Connect the Compressor Send jack to the input of the next piece of equipment (or the return of a mixer). To use only the equalizer circuit of the Pro Channel: Plug a line level signal (or a send from a mixer) into the EQ Return Jack. Connect either output from the Pro Channel into the input of the next piece of equipment (or the return of a mixer). To place the equalizer circuit before the compressor circuit: Connect the Preamp Send to the EQ Return. Connect the unbalanced Output to the Compressor Return. Use the Compressor Send as the main output to the input of the next piece of equipment. Dont forget that it is possible to use each section of the Pro Channel on a separate track. For example, the bass track can run through the compressor, the vocal track through the preamp, and the guitar track through the EQ all at the same time!

Applications

The main application of the Pro Channel is as a processing channel for a microphone, instrument or line level source. To use the Pro Channel as a mic or line preamplifier only, simply press the Bypass switches to bypass the compression and equalizer circuitry. Plug a microphone directly into either input and set the input and output controls to provide an appropriate level into the next stage of your system. The Pro Channel is ideal for use as a DI box. Plug the instrument into either input and use the XLR, 1/4, or both outputs to connect to your recorder, board, or PA system. Experiment with different input level settings for different textures. In most cases the Pro Channel offers superior performance to the on-board preamp on your console. To use the Pro Channel instead of your on-board preamp, simply connect the output of the Pro Channel to the line input of your mixers input channel. Note: you can connect the XLR output jack of the Pro Channel to the XLR input of your mixer, however most affordable mixers do not allow you to bypass their internal preamp when using the XLR jack. You will cause no harm to either unit when doing this but you will probably experience slightly higher noise. This is due to the fact that you are now preamplifing your mixers preamp. Note: Be certain that you do not connect the Pro Channels XLR Output to a mixer input that has Phantom Power applied. The Pro Channel has enough gain to be used in front of a power amplifier. To use the Pro Channel as an instrument preamp, simply plug the instrument into the Input jack and connect the Output jack to the input of the power amplifier. See Loop Connections for further hook-up options and for using the Pro Channels individual sections. - 17 -

EQ Tips

What is the best way to use EQ? There are two schools of thought on EQ: 1) Use as much as you need to make things sound good. 2) Dont use any EQ. Most people follow the suggestion of if it sounds good, it is good. You need to use your ears and judge for yourself as their are no steadfast rules for EQing. Here are a few pointers to guide you. Always tweak the instrument you are EQing while listening to it in the mix. EQing an instrument when it is soloed doesnt give you a good representation of how it will sound when mixed with other instruments. Youd be surprised at how bad a killer guitar track can sound when it is isolated from the rest of the mix. Remember, what makes it killer is how it sounds in relation to the other instruments! Keep the big picture in mind. Most people think of EQ as boosting only (well just add a little EQ.). Many times a bad sounding instrument can be fixed by simply isolating the bad frequency and pulling it out. After you determine approximately where the problem area is in the instrument (highs, lows, mids), isolate the track and boost one of the mid bands. Slowly sweep through the frequency range. When the really nasty sound jumps out at you (youll know it when it happens) turn the boost back to 0 (12 oclock). Now put the track back into the mix and cut the frequency. Youll have to adjust the level of the instrument depending on how much you cut, but you should find that with the problem area pulled out, the instrument works better in the mix. When recording EQd instruments, you want to make sure you have good representation of frequencies on tape. Always monitor off tape when recording. This ensures that what youre hearing is what is on tape. When recording things like kick drums, make sure you have enough low end thud and high end click (if applicable) before you record. Recording guideline: You can always boost or cut frequencies after theyve been recorded, but you cant add frequencies that werent - 18 -
recorded! Always be prepared for the drummer who says he loves the John Bonham kick drum sound (lots of low end power and ambiance) that you got when recording but during the mix decides he wants to sound like Metallica (more click than punch). If you get the sounds right when you record the tracks you shouldnt be spending a lot of time re-EQing during the mix. During mixing you should be concentrating on the blending of tracks and the dynamics of the song. If you find yourself EQing everything, take a break and come back to it later. Start mixing with a group of instruments (the whole drum kit or guitars and bass) instead of listening to individual tracks. Mixing is the time for tweaking not applying a sonic re-design. Once again, if it sounds good, print it! Trust your ears never mind where the knobs are pointing.

Special Effects

For industrial, metal, or just flavor textures, experiment with the Pro Channel. Overdriving the preamp, compressor and equalizer circuitry can add interesting textures when blended with vocals and other instruments. Placing signals purposely out of phase can also yield interesting results. No harm will come to the Pro Channel with this type of experimentation. However, be sure to have output and monitoring levels turned DOWN before testing the sound. Remember, you have a great amount of gain available in the Pro Channel!

Grounding

Connecting several pieces of equipment (from several different manufacturers) together without ground loop problems is one of the most common challenges in recording. For this reason, all ART recording gear does not have a direct connection between the audio circuit ground and the chassis ground. This enables the gear to be safely grounded through the 3-prong AC cord, and also to be grounded to the previous and/or next item in the signal chain for optimum noise performance. It also implies that at least one ground connection must be made between the Pro Channel and the rest of the signal chain that it is connected to.

Tube Replacement

The Tubes in your Pro Channel should last for many years. They are hand-sorted for optimal performance in our specific circuits. In the event that you need to replace them, A R T suggests that you do so with tubes available from A R T. These are matched to the Pro Channel and will yield consistent sonic results. You can replace the tubes with other brands, however A R T has no responsibility for the resulting sound quality. They may sound better, they may sound worse. The choice is yours. Please realize that unauthorized alterations to the Pro Channel will result in voiding the warranty.

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Block Diagram

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A R T Pro Channel Specifications
Dimensions Weight Maximum Gain Dynamic Range Frequency Response Low-Cut Filter Input / Output Connections Insert Connections Input Impedance Output Impedance Maximum Input Level Maximum Output Level Equivalent Input Noise Phantom Power Compression Ratio Attack Time Release Time Maximum Compression EQ Frequency Bands Low Shelf Low-Mid Sweepable Low-Mid Q High-Mid Sweepable High-Mid Q High Shelf Boost and Cut / Band 6.5"D x 19"W x 3.50"H 12.0 lbs XLR to XLR 83dB to 65dB >100dB (20-20KHz) 20Hz to 20KHz (0.5dB) Single-Pole Variable -3dB@10Hz to 250Hz XLR balanced & unbalanced unbalanced 1.67K - (XLR), 1M - (), 10K+ inserts) 600 (XLR), 300 (all ) +15dBu (XLR), +21dBu () +27dBu (XLR), +22dBu () -130dBu (XLR to XLR, A wtd) +48V DC (switchable) Variable: 2:1 to >10:1 Fast: 2ms (optical), 0.5ms (vari-mu) Slow: 15ms (for 20dB of comp) Fast: 300ms Auto: 100ms-3sec (program dependent) 30dB (optical), 23dB (vari-mu)

40Hz / 120Hz selectable 20Hz to 200Hz / 200Hz to 2KHz (Shift out / in) Wide / Narrow selectable (Q=1.1 / 3.3) 200Hz - 2KHz / 2KHz - 20KHz (Shift out / in) Wide / Narrow selectable (Q=1.1 / 3.3) 6KHz / 18KHz selectable Low, High: 12dB Lo-Mid & Hi-Mid: 12dB (wide), 20dB (narrow) Total Harmonic Distortion (THD) <0.1% (typical) Tubes Three Hand-Selected Power Requirements 100-125 VAC, 30W
(Export units configured for country of destination)
A R T retains a policy of constant product improvement. A R T reserves the right to make changes in design or make additions to or improvements upon this product without any obligation to install the same on products previously manufactured. In other words, specifications are subject to change without notice.

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The Pro Channel was designed and manufactured in the United States of America. Applied Research and Technology, Inc. (716) 436-2720 (Phone) 215 Tremont Street (716) 436-3942 (FAX) Rochester, NY 14608 USA

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For Product information, questions, applications, tips, answers and general discussion with A R T employees look for A R T on the Internet. Email us at art@artroch.com Check out our Web Site at: http://www.artroch.com
Warranty and Service Information

Limited Warranty

Applied Research and Technology, Inc. (A R T) will provide warranty service for this unit in accordance with the following warranty statement. A R T warrants to the original purchaser that this product is free from defects in workmanship and materials for a period of three years from the date of purchase. A R T will, without charge, repair or replace, at its option, defective product or component parts upon prepaid delivery to the factory service department or an authorized service center, accompanied by proof of purchase date in the form of a valid sales receipt. EXCLUSIONS: This warranty does not apply in the event of misuse or abuse of the product or as a result of unauthorized alterations or repairs. This warranty is void if the serial number is altered, defaced or removed. A R T reserves the right to make changes in design and make additions or improvements upon this product without any obligation to install the same on products previously manufactured. A R T should not be liable for any consequential damages, including without limitation damages resulting from the loss of use. Some states do not allow limitation of incidental or consequential damages, so the above limitation or exclusion may not apply to you. This warranty gives you specific rights and you may also have other rights, which vary, from state to state. For products purchased outside the United States, service will be provided by an authorized distributor of Applied Research and Technology, Inc. products.