Pro VLA II
PROFESSIONAL TWO CHANNEL VACTROL/TUBE LEVELING AMPLIFIER

USERS GUIDE

IMPORTANT SAFETY INSTRUCTIONS READ FIRST
This symbol, wherever it appears, alerts you to the presence of uninsulated dangerous voltage inside the enclosure. Voltage that may be sufficient to constitute a risk of shock.
This symbol, wherever it appears, alerts you to important operating and maintenance instructions in the accompanying literature. Please read manual.
Read instructions: Retain these safety and operating instructions for future reference. Heed all warnings printed here and on the equipment. Follow the operating instructions printed in this user guide. Do not open: Aside from two vacuum tubes, there are no user serviceable parts inside. Refer any service work to qualified technical personnel only. Power sources: Only connect the unit to mains power of the type marked on the rear panel. The power source must provide a good ground connection. Power cord: Use the power cord with sealed mains plug appropriate for your local mains supply as provided with the equipment. If the provided plug does not fit into your outlet consult your service agent. Route the power cord so that it is not likely to be walked on, stretched or pinched by items placed upon or against. Grounding: Do not defeat the grounding and polarization means of the power cord plug. Do not remove or tamper with the ground connection on the power cord. Ventilation: Do not obstruct the ventilation slots or position the unit where the air required for ventilation is impeded. If the unit is to be operated in a rack, case or other furniture, ensure that it is constructed to allow adequate ventilation. Moisture: To reduce the risk of fire or electrical shock do not expose the unit to rain, moisture or use in damp or wet conditions. Do not place a container of liquid on it, which may spill into any openings. Heat: Do not locate the unit in a place close to excessive heat or direct sunlight, as this could be a fire hazard. Locate the unit away from any equipment, which produces heat such as: power supplies, power amplifiers and heaters. Environment: Protect from excessive dirt, dust, heat, and vibration when operating and storing. Avoid tobacco ash, drink spillage and smoke, especially that associated with smoke machines. Handling: To prevent damage to the controls and cosmetics avoid rough handling and excessive vibration. Protect the controls from damage during transit. Use adequate padding if you need to ship the unit. To avoid injury to yourself or damage to the equipment take care when lifting, moving or carrying the unit. Servicing: Switch off the equipment and unplug the power cord immediately if it is exposed to moisture, spilled liquid, objects fallen into opening, or the power cord or plug becomes damaged during a lightning storm or if smoke odor or noise is noted. Refer servicing to qualified technical personnel only. Installation: Install the unit in accordance with the instructions printed in the user guide. 1
IMPORTANT SAFETY INSTRUCTIONS READ FIRST... 1 INTRODUCTION.... 3 INSTALLATION..... 3
Unpacking....... 4 AC Power Hookup...... 4 Analog Audio Connections..... 4
FRONT PANEL CONTROLS and INDICATORS... 5
Power....... 5 Input Threshold Control..... 5 Ratio Control...... 5 Output Level Control...... 6 Attack Control....... 6 Release Control...... 7 Gain Reduction LED Meter..... 7 Bypass Switch...... 7 VU Meter...... 7 VU Meter Source Switch..... 7 LED Output Meter...... 8 The Link Switch...... 8

REAR PANEL I/O..... 9

Balanced Inputs...... 9 Balanced Outputs...... 10 I/O Level Switch...... 10

APPLICATIONS..... 11

Compressor/ Limiter...... 11 Stereo Mix and Mastering..... 11 Vocal and Instrument Leveling..... 11
WARRANTY INFORMATION.... 12 SERVICE..... 13 SPECIFICATIONS..... 14
FIGURE 1 Channel 1 Controls... 6 FIGURE 2 LED Output Meter and Link Switch... 8 FIGURE 3 Rear Panel.... 10

LIST OF FIGURES

INTRODUCTION
Thank you for purchasing Applied Research and Technologys Pro VLA II. Offering a superb level of sound quality, the Pro VLA II has a unique design that will enhance the sonic textures of your audio system for years to come. The Pro VLA II is one of the finest audio compressors available. Developed in partnership with studio and live-sound engineers, the Pro VLA II possesses a sound that is not available from any other compressor on the market - at any price! Unlike typical compressors which use solid state feed-forward circuitry to control level detection, the Pro VLA II is very musical. The nature of its operation is much like the way your eye adjusts to light. Just as your eye transparently adjusts to changes in light, the Pro VLA II adjusts to changes in signal level. The Pro VLA II was designed and constructed with the absolute best components, assuring a lifetime of quiet, reliable performance. The Pro VLA II offers: - Two channel opto-isolator (Vactrol)/tube-based leveling amplifier - Stereo linking of channels - Master Volume and Balance control in Link Mode - Hand selected 12AT7 Tubes - Vactrol - Analog Optical Isolators (AOI) - Non-VCA design = transparent, classic sound - VU metering of input and output levels - LED metering of output level with peak-hold function - XLR balanced inputs and outputs - 1/4 TRS active balanced inputs and outputs - Variable Threshold & Ratio controls - Variable Attack and Release controls - Variable Output Level rotary controls - 10 segment Gain Reduction LED array - 10Hz to 100KHz Frequency Response (+/-0.5dB) - >100dB Dynamic Range - Low noise (-99dBm A weighted EIN) - Internal power supply - 3 year parts and labor warranty

INSTALLATION

The ART Pro VLA II may be used in a wide variety of applications and environments. In a rack-mountable, all-steel enclosure, the unit is designed for continuous professional use. Mounting location is not critical, however for greater performance reliability we recommend that you not place the unit on top of power amps, or other sources of heat and/or strong magnetic fields. The tube circuitry needs about a minute to warm up and stabilize from a cold power up.

Unpacking

Your Pro VLA II was packed with care at the factory. The shipping carton was designed to protect it during initial shipment. Please retain this carton for use in transporting the Pro VLA II when it is not installed in a rack, or in the unlikely event that you need to return your Pro VLA II for servicing. The shipping carton should contain: - The Pro VLA II - The owners manual - User Registration Card

AC Power Hookup

The Pro VLA II has an internal power supply designed to operate at 100 to 125VAC, 50 to 60Hz. Units manufactured for use outside of the United States of America 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 its use and have it replaced before operating the Pro VLA II. The power source must provide a good ground connection, and the ground pin on the mains plug should never be defeated.

Analog Audio Connections

Audio connections to and from the Pro VLA II are: Balanced input: [XLR] Pin 2 = Hot (+), Pin 3 = Cold (-), Pin 1 = Ground [1/4] Tip = Hot (+), Ring = Cold (-), Sleeve = Ground Balanced output: [XLR] Pin 2 = Hot (+), Pin 3 = Cold (-), Pin 1 = Ground [1/4] Tip = Hot (+), Ring = Cold (-), Sleeve = Ground Unbalanced 1/4 cables may be used with no damage to the Pro VLA II. We recommend using only highquality cables equipped with the appropriate connectors.
FRONT PANEL CONTROLS and INDICATORS
The POWER switch turns the power on and off to the unit. The Pro VLA II should be turned on with all monitor levels turned down to protect against any thumping caused by power up. Likewise, the Pro VLA II should be turned off after turning all monitor levels down. When the POWER switch is turned on, the VU meters will light. LEDs will light if its associated switch is in the in position. Power on the Pro VLA II before any monitoring outputs or power amps are turned on. Like all tube-based equipment, the Pro VLA II needs to warm up to operating temperature. The 12AT7 tubes will reach operating temperature within one to three minutes. During this warm-up period you may experience sound variations due to the bias of the tubes stabilizing. This is normal and the Pro VLA II will provide consistent results once the warm-up period is over. If the Pro VLA II 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 the ART Customer Service Department.

Input Threshold Control

The INPUT THRESHOLD control sets the point at which the Pro VLA II will act on a signal. Turning this control counter-clockwise lowers the threshold (adding more compression to a signal). Turning this control clockwise raises the threshold. Proper setting of the INPUT THRESHOLD control is dependent on the input signal. The output of a guitar can be 20dB to 10dB, whereas the level from an insert on a mixing console can be 10dB to +15dB. The easiest way to set the INPUT THRESHOLD control is to start with the control fully clockwise. Slowly turn the control counter-clockwise (lowering the threshold) until the yellow (0) LED light on the Gain Reduction meter begins to light. Next adjust the control (either lower or higher) for the desired amount of compression. Use the Gain Reduction meter as a visual guide to the amount of compression applied.

Ratio Control

The RATIO Control selects the amount of compression applied to the input signal once that signal reaches or exceeds the threshold. This compression amount is expressed as a ratio of input to output. For example if a 4:1 compression ratio is chosen, for every 4dB over the threshold the input signal rises, the output level only rises by 1dB. In this case if the input signal increased 12dB over the threshold, the output level would only rise by 3dB. In general, compression ratios of 10:1 and greater are considered limiting. The range of the RATIO control is (2:1) to (20:1). The Pro VLA II may be used as either a compressor or a limiter with all of the following: - Multitrack recorder, DAT machine, hard disk recorder, or analog recorder. - In a mixers channel insert points. - Between a microphone preamp and signal processors. - Between preamplified electronic musical instruments (synthesizers, guitars, bass, samplers, acoustic instruments with pickups) and other line-level equipment.
FIGURE 1 Channel 1 Controls

Output Level Control

The OUTPUT LEVEL control serves two functions. The CH1 knob always controls the output level of CH1, but can also serve as a MASTER output level when the Link Mode is active. The fully counter-clockwise position of the knob mutes the output. The CH2 OUTPUT LEVEL control operates as a standard CH2 level control or as a BALANCE control when the Link Mode is active. In Link Mode when the BALANCE control is turned fully counter-clockwise the CH1 output is fully on and CH2 output is fully muted. When centered, both channels have equal gain. When turned fully clockwise the CH2 output is fully on and CH1 output is fully muted.

Attack Control

The ATTACK control sets the time it takes the Compressor/Limiter to respond to increases in signal level (by reducing gain). You can use this control to shape the front end of the dynamics envelope. One example is to listen to a snare hit and adjust the ATTACK control. A short attack makes the snare sound thin. As the attack time goes longer (the knob is turned clockwise) you should hear more of the thump in the compressed snare. The downside is that this creates an overshoot, (or transient), the length of which is the time set by the ATTACK control. Overshoots less than 1 msec. are very hard to hear even when they are clipped. If the ATTACK is set too fast, the gain may be reduced too much and thereby create a pumping sound1.

Pumping in a Compressor/Limiter sounds like the signal is muted when it shouldnt be. 6

Release Control

The RELEASE control sets the time the Compressor/Limiter takes to increase the gain after the input level drops. Longer settings maintain the dynamics of the input signal, while shorter settings reduce the dynamics. Shorter settings will also increase the apparent reverberation, and at extreme gain reduction settings, lead to breathing artifacts2

Gain Reduction LED Meter

The GAIN REDUCTION meter displays the Pro VLA II attenuation action. The meter covers a very large range while offering high resolution. The Yellow (0) LED illuminates when the input signal reaches or exceeds the compressor detector threshold setting (INPUT THRESHOLD control).

Bypass Switch

The Pro VLA II BYPASS switch physically connects the input jack to the output jack on each respective channel (also known as a hardwire bypass). The switch is lit when the unit is bypassed (unless power is off, yet the analog signal still passes from input to output).

VU Meter

The input or output levels of the Pro VLA II can be monitored by the analog VU meter. The VU METER switch selects the source of the audio for this meter. The ballistics characteristic of the meter provides an accurate indication of the average signal level. If you need peak level info (critical in digital systems) use the central stereo LED bargraph OUTPUT LEVEL meter.

VU Meter Source Switch

This switch selects either the input or output signal as a source for the analog VU meter, and lights when the input signal is selected. This function allows the user to compare the input vs. output level. This switch does not affect the LED bargraph meters audio source.
Breathing is the sound of the Compressor/Limiter turning up the gain so quickly you can hear breathing noises between words during vocal processing. 7
FIGURE 2 LED Output Meter and Link Switch

LED Output Meter

This meter displays both average and peak levels of the output signal. The LED labels indicate how far the output is away from full maximum output in dB. In each bargraph, a single LED is held on for a little over one second, displaying the peak level. Some peaks may not be audible, but can cause clipping in equipment following the Pro VLA II. Average levels are indicated by a histogram style display. The average levels displayed are similar to the VU meter when it is set to monitor the output level. 0 on the meter corresponds to an output level of +16dBu when the I/O level switch is in the +4 mode. When in the -10 mode, this level becomes +6dBu.

The Link Switch

The two channels of the Pro VLA II can be configured for stereo operation by depressing the LINK switch. Link Mode ties the output attenuation of both channels together onto the CH1 OUTPUT LEVEL knob, and moves all control over Attack and Release times to the CH1 set of controls. The CH2 OUTPUT LEVEL control becomes an output balance control. Link Mode ensures that each channel of the stereo input signal is processed identically to prevent any shifting or distortion of the stereo image. Bypass and meter-source select switch functions remain unchanged in link mode.

REAR PANEL I/O

The Pro VLA II XLR connectors follow the AES standard of: Pin 1 = Ground, Pin 2 = Hot (+), Pin 3 = Cold (-). The balanced 1/4 phone jacks are typical TRS connections: Tip - Hot (+), Ring - Cold (-), Sleeve - Ground.

Balanced Inputs

The Pro VLA II provides both an XLR and 1/4 input jack. Both jacks are balanced. The 1/4 jack can be used with unbalanced signals by simply plugging in an unbalanced cable. The inputs are designed for use with line level signals ranging from 30dBm to +20dBm. While it is possible to plug an instrument directly into the Pro VLA II, it is desirable to run the instrument into a preamp ahead of the Pro VLA II. This will provide a stronger signal and will keep noise to a minimum. Microphones must connect through a microphone preamplifier (like the ART MPA GOLD) before connecting into the Pro VLA II. The input impedance of the input 10K Ohms. NOTE: The Pro VLA II has a passive (hardwire) bypass. This means that the bypass works even if the power is OFF.

FIGURE 3 Rear Panel

Balanced Outputs
The analog output of the Pro VLA II is available on both a 1/4 TRS balanced jack and an XLR jack. This output is active pseudo balanced. The output has a 100 Ohm impedance into a balanced or unbalanced load. The LED and analog VU meter monitor the level present at this output. 0 VU on the analog VU meter corresponds to +4dBu (about 1.23 Volts RMS). 0 on the LED bargraph OUTPUT LEVEL meter corresponds to an output level of +16dBu into a balanced load.

I/O Level Switch

The Pro VLA II can be optimized for either professional (+4dBu) or consumer (-10dBV) I/O levels. When the switch is depressed the unit is in professional levels mode. This shifts the levels such that 0 VU on the meter corresponds with +4dBu on the input or output. When set to the -10 mode, 0 VU corresponds to about 10dBV. NOTE: +4dBu is equivalent to +4dBm into a 600 Ohm balanced load.

APPLICATIONS

Compressor/ Limiter
The main application of the Pro VLA II is to control the dynamic range of an audio signal. Plug a line level (post preamplifier or other gain stage) source into either input, and set the threshold and output controls to provide the desired amount of compression to the input signal.

Stereo Mix and Mastering

Because of its low noise and excellent tonal qualities, the Pro VLA II is ideal for processing mixes when recording to DAT, hard disk or analog recording devices. Used as a mastering device, the Pro VLA II is capable of adding warmth and impact to the overall signal level. Pro VLA II is ideal for live use as well.

Vocal and Instrument Leveling
The musical nature of the Pro VLA II makes it ideal for use on a wide range of instruments and vocals. Place the Pro VLA II into a channel insert, after a preamplifier, or in line with the direct output of a mixer channel. Adjust the controls of the Pro VLA II to achieve the desired amount of compression.

WARRANTY INFORMATION

Limited Warranty:
Applied Research and Technology will provide warranty and service for this unit in accordance with the following warrants: Applied Research and Technology, (ART) warrants to the original purchaser that this product and the components thereof will be free from defects in workmanship and materials for a period of three years from the date of purchase. Applied Research and Technology will, without charge, repair or replace, at its option, defective product or component parts upon prepaid delivery to the factory service department or 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. ART 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. ART shall not be liable for any consequential damages, including without limitation damages resulting from loss of use. Some states do not allow limitations 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 have other rights, which vary from state to state. For units 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. 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.

SPECIFICATIONS

Input Impedance
Balanced/Unbalanced...10K Ohms

Maximum Levels

Range Switch....+4dBu/-10dBV selectable Inputs....+20dBu (in +4dBu mode) / +10dBV (in 10dBV mode) Output....+20dBu (R load > 10K, 0.1%THD)
Output Gain... +20dB max Frequency Response..10Hz to 100KHz (+/- 0.5dB) Dynamic Range...>100dB (20-20KHz) THD @ 0dBm Out:...<0.1% (typical) Equivalent Input Noise (EIN)
+4dBu mode...-99dBu ('A' weighted) -10 dBV mode...-107dBu ('A' weighted)
Attack Time... 0.25msec. to 50msec. variable Release Time...150msec. to 3 sec, variable Slope...Variable: 2:1 to 20:1 Max. Attenuation...30dB Dimensions... 3.50 H x 19.0 W x 9.17 D Weight...10.5 lbs. Power Requirements... USA 105 to 125 VAC / 60 Hz Export units configured for country of

destination.

Note: 0 dBu = 0.775 VRMS, 0 dBV = 1 VRMS
ART maintains a policy of constant product improvement. ART reserves the right to make changes in design, or make additions to, or improvements upon, this product without any obligation to install same on products previously manufactured. Therefore, specifications are subject to change without notice. Vactrol is a registered trademark of PerkinElmer Optoelectronics
www.artproaudio.com E-mail: support@artproaudio.com
2007 Applied Research & Technology 213-5004-100 e

PRO VLA

PROFESSIONAL TWO CHANNEL VACTROL/TUBE LEVELING AMPLIFIER

USERS GUIDE

TABLE OF CONTENTS
Introduction Registration Features Overview Setting Up Unpacking AC Power Hookup Audio Connections Installation Safety Precautions Powering Up Front Panel Controls and Indicators Power Threshold Control Ratio Control Output Level Control VU Meter Input/Output Switch Attack Time Switch Release Time Switch Bypass Switch Stereo Link/Dual Mode Switch Gain Reduction Meter VU Level Meter Rear Panel Connections Input Output Applications Tube Replacement Warranty Information Service Information PRO VLA Specifications On-line Information 14 14

212-5004-101

Introduction Thank you for purchasing Applied Research and Technologys PRO VLA. Offering a superb level of sound quality, the PRO VLA has a unique design which will enhance the sonic textures of your audio system for years to come. Registration If you havent done so already, please take the time to fill out the User Registration Card for your purchase. Having you in our data base allows us to keep you informed of updates, application notes, and new product introductions. It only takes a moment and will ensure you are constantly up to date with your purchase. Fill in the following for your future reference: Date of purchase: ___________________ Purchased From: ____________________ Serial Number: 212-________
Features The PRO VLA is one of the finest audio compressors available. Developed in partnership with studio and live sound engineers, the PRO VLA possesses a sound that is not available from any other compressor on the market - at any price! A member of the A R T Reference Series, the PRO VLA was designed and constructed with the absolute best components, assuring a lifetime of quiet, reliable performance. The PRO VLA offers: - Two channel Opto-isolator (Vactrol)/tube-based Leveling Amplifier - Stereo linking of channels - Hand selected 12AX7 Tubes - Vactrol - Optical electronic isolators - Non-VCA design = transparent, classic sound - VU metering of input and output levels - XLR balanced inputs and outputs - 1/4 TRS active balanced inputs and outputs - Variable threshold ratio - Auto and Fast attack and release settings - Variable Threshold rotary controls - Variable Output level rotary controls - 10 segment Gain Reduction LED Array - 10Hz to 20kHz Frequency Response (+/-0.5dB) - >100dB Dynamic Range - Extremely low noise (-99dBm A weighted) - Internal power supply - 5-year parts and labor warranty - Designed and manufactured in the USA
The PRO VLA is member of A R Ts Reference Series of professional signal processing products.

OVERVIEW

Design The PRO VLA (Vactrol-based Leveling Amplifier) is a multi-purpose tool for audio engineering and recording. Enclosed in a 2U (3.5 high) rack-mountable chassis are two independent channels of analog compression designed to work seamlessly with any recording, sound-reinforcement, or electronic instrument setup. A R Ts PRO VLA circuitry is a hybrid design utilizing the latest and most advanced solid state and tube technology. Using a transformerless design throughout, the PRO VLA maintains exceptional signal integrity and extremely low noise. Its VCAless design utilizes optical electronics (Vactrol) coupled with a 12AX7 vacuum tube gain stage for superior musical performance. The PRO VLA is a soft knee leveling amplifier by design. Although it is capable of providing a thoughougly squashed signal, the PRO VLA was designed to excel in areas where transparent, expressively musical dynamics control is desired. Application Compression is used to alter the dynamic range of a signal. In recording and live sound situations, compression and limiting is necessary to manage sounds with wide dynamic ranges. Dynamic Range is measured as the difference between the loudest and softest level of a signal. (i.e. from a scream to a whisper). Once a signal rises above or falls below the set threshold (selectable signal level), the compressor automatically changes its gain to raise or lower the overall signal level. Think of this as manually moving a fader up and down to try to keep a signal at a consistent level. Limiting can be described as a ceiling. When using a limiter, once the signal level reaches the threshold, it is unable to go any louder - it is limited to a desired level. In addition to making signal levels more manageable, it is common practice to apply compression or limiting to a signal to make it louder or more in-your-face. The benefit of using the PRO VLA for these applications is in its design. By utilizing opto-electronics, the PRO VLA allows you to add more compres-

sion without sounding like youre squashing the daylights out of the signal. Unlike typical compressors which use VCAs to control level detection, the PRO VLA is very musical. The nature of its operation is much like the way your eye adjusts to light. Just as your eye transparently adjusts to changes in light, the PRO VLA adjusts to changes in signal level.

SETTING UP

Unpacking Your PRO VLA was packed with care at the factory. The shipping carton was designed to protect it during initial shipment. Please retain this carton for use in transporting the PRO VLA when it is not installed in a rack, or in the unlikely event that you need to return your PRO VLA for servicing. The shipping carton should contain: - The PRO VLA - The owners manual - User Registration Card AC Power Hookup The PRO VLA has an internal power supply designed to operate at 100 to 125VAC, 50 to 60Hz. Units manufactured for use outside of the United States of America 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 its use and have it replaced before operating the Pro VLA. Audio Connections Audio connections to and from the PRO VLA are balanced XLR (Pin 2 Hot (+), Pin 3 Cold (-), Pin 1 Ground) and active balanced 1/4 TRS (Tip = Hot (+), Ring = Cold (-), Sleeve = Ground). Unbalanced 1/4 cables may be used with no damage to the PRO VLA. We recommend using only high-quality cables equipped with the appropriate connectors. Installation The PRO VLA may be employed in a number of setups including: - Between a microphone preamplifier and a mixer, digital multi-
track recorder, DAT machine, hard disk recorder, or analog recorder. - In a mixers channel insert points. - Between a microphone preamp and signal processors. - Between preamplified electronic musical instruments (synthesizers, guitars, bass, samplers, acoustic instruments with pickups) and other line level equipment. Note: the PRO VLA should be securely mounted in a standard 19 rack.
FRONT PANEL CONTROLS & INDICATORS
Power The Power switch supplies and removes power from the unit. The PRO VLA should be powered on with all monitor levels turned down to protect against any thumping caused by gain settings. Likewise, the PRO VLA should be turned off after turning all monitor levels down. Threshold Control The Threshold control sets the point at which the PRO VLA will act on a signal. Turning this control counter-clockwise lowers the threshold (adding more compression to a signal). Turning this control clockwise raises the threshold. Setting the Threshold control is dependent on the input signal. The output from a guitar might be -20dB to -10dB, where the level from an insert on a console might be -10dB to +15dB. The easiest way to set the threshold control is to start with the control fully clockwise. Slowly turn the control counter-clockwise (lowering threshold) until you see the yellow Threshold LED light. Now adjust the control (either lower or higher) until you have the amount of compression you desire. Use the Gain Reduction meter as a visual guide to the amount of compression applied. Ratio Control The Ratio Control selects the amount of compression applied to the input signal once that signal reaches or exceeds the threshold. This compression amount is expressed as a ratio of input to output. For example if a 4:1 compression ratio is chosen, for every 4dB over the threshold the input signal rises, the output level only rises by 1dB. In this case if the input signal was 12dB over the threshold, the output level would rise by only 3dB. Generally compression ratios of 10:1 and greater are considered limiting. The range of the Ratio control is 2:1 to 10:1. The PRO VLA may be used as either a compressor or limiter.

SAFETY PRECAUTIONS

Warning: To avoid the risk of shock or fire, do not expose this unit to moisture. Do not remove metal panels from chassis parts. Removing the chassis from its cabinet parts exposes dangerous high voltages. There are no user-serviceable parts inside. Hazardous voltages are present inside the chassis. Refer all servicing to qualified personnel. Caution: If your power cord becomes damaged and must be replaced, always replace it with the proper type (3 prong).

POWERING UP

When the power switch is turned on, the VU meters will light. LEDs will light if its associated switch is in its in position. Power on the PRO VLA before any monitoring levels or power amps are turned on. Like all tube-based equipment, the PRO VLA needs to warm up to operating temperature. The 12AX7 tubes will reach operating temperature within one to three minutes. During this warm up period you may experience variations due to the THD of the tubes stabilizing. This is normal and the PRO VLA will provide consistent results once this warm up period is over. If the PRO VLA 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.
Output Control The Output control sets the output gain of the PRO VLA. When the control is fully counterclockwise, the output level of the PRO VLA is attenuated by -83dB. Turning the control clockwise adds gain (sometimes called make-up gain). Since levels can be decreased when compression is applied, the PRO VLA has the ability to apply gain to bring the processed signal back up to unity (same as input level). To properly set the output level, adjust the Output Control while switching between Active and Bypass. When these two levels are equal in volume, the output control is set properly. VU Meter - Input/Output Switch The VU Meter Input/Output Switch toggles the VU meter between displaying either input or output signal levels. The Input setting is the signal entering into the PRO VLA. The Output setting is the signal (post-process) leaving the PRO VLA. In stereo applications, place one switch in the Input position and one switch in the Output position. This enables you to see both levels at a single glance of the meters. Note: The Zero (0) level of the VU meter is calibrated at +4dBm when using the XLR connectors into a 600 Ohm load or - when using the 1/4 outputs into a high impedance load. Attack Time Switch The position of the Attack Time switch selects the attack characteristics for the channel of the PRO VLA. Attack Time refers to how quickly compression is added after the input signal rises above the Threshold. Since different signals have different attack characteristics, it is important for a compressor to have different settings which allow the action of the compressor to sound more natural. The out position is the Auto setting. The Auto setting is a program dependant attack time with 20ms being the slowest the PRO VLA will take to achieve 20dB of compression. In other words, the Attack Time circuitry in the PRO VLA is designed to adapt to the signal characteristics of the signal you are processing. The in position is the Fast setting. This setting has a fixed attack time of 2ms. The Fast setting is ideal for punchy, repetitive signals. Release Time Switch The position of the Release Time switch selects the release char-

acteristics for the channel of the PRO VLA. Release Time refers to how quickly the channel returns to unity gain (no compression) after the input signal falls below the Threshold. Again, since different signals have different decay characteristics, it is important for a compressor to have different settings which allow the action of the compressor to sound more natural. The out position is the Auto setting. The Auto setting is an automatically adjusting (sometimes called program dependent) release time with a range of 100ms to 3 seconds. The in position is the Fast setting. This setting has a fixed release time of 300ms. The Fast setting is ideal for punchy, repetitive signals. Use the auto setting when the signal has varying characteristics (long decaying notes alternating with quick notes, mix material, etc.). Bypass Switch A Bypass switch is included on each channel of the PRO VLA to enable you to remove the unit from your signal chain. When set to its in position, the channel of the PRO VLA allows signal to pass from the input jacks to the output jacks with no processing. The LED will illuminate to inform you the channel is bypassed. In its out position, the PRO VLA is active and the input signal is processed. Use the Bypass switch when setting the PRO VLAs Output Level to achieve unity (no boost or cut) gain. Unity gain is achieved when the active level is the same as the bypassed level. Stereo Link/ Dual Mode Switch The PRO VLA may be used as two independent channels of compression/limiting or as a stereo processor. When the Stereo Link/Dual Mode switch is in its out position, the PRO VLA operates as two independent channels. With the switch in its in position, the PRO VLA is a stereo unit. In this Linked mode the Threshold, Ratio, Attack and Release controls of channel #1 are used to control both channels of the PRO VLA. Youll notice these controls on channel #2 are inactive when the Stereo Link/Dual Mode switch is in. This design is common among professional compressors. It ensures that each channel of the stereo input signal is processed identically to prevent any shifting or distortion of the stereo image. The Output controls remain independent in the Link Mode to allow for level matching. The LED will light when the switch is in the in (linked) position.
equipment. Gain Reduction Meter Each channel of the PRO VLA has a ten segment LED gain reduction meter. These meters provide a visual indication of how much compression is taking place. The right-most LED in these meters is the Threshold LED. The Threshold LED will light when the input signal reaches the level set by the Threshold control. The range of the meter is -1dB to -30dB. VU Level Meter Each channel of the PRO VLA has a backlit VU meter showing either the input or output level (switch dependant). The zero (0) level is calibrated to +4dBm (with a 600 ohm load on the XLR output or a high impedance load on the 1/4 output). Use the VU meter to view input (unprocessed) and output (processed) levels. The meters are active when the PRO VLA is in bypass. Do not use both inputs on a channel at the same time. Outputs The outputs of the PRO VLA are active balanced. You may use these in unbalanced configurations without harm to the output circuitry. Use the unbalanced 1/4 jack for sending your signal to amps, processors or other unbalanced configurations. Use the XLR output to send signals to equipment which accepts XLR connections. Both outputs may be used at the same time. **Note: If you experience a grounding hum when using both output connectors simultaneously, a ground loop may be the problem. To remedy this problem, disconnect (lift) the ground wire (pin 1) from the XLR cable plugged into the PRO VLAs output. This interrupts the ground path and therefore breaks the loop.

REAR PANEL CONNECTIONS APPLICATIONS
Its easy to interface the PRO VLA with other equipment. Balanced XLR and balanced 1/4 phone, input and output connectors are located on the rear panel. The PRO VLAs XLR connectors follow the AES standard of: Pin 1 = Ground, Pin 2 = Hot (+), Pin 3 = Cold (-). The balanced 1/4 phone jacks are typical TRS connections: Tip - Hot (+), Ring - Cold (-), Sleeve - Ground. Input The PRO VLA provides both an XLR and 1/4 input jack. Both jacks are balanced. The 1/4 jack can be used with unbalanced signals by simply plugging in an unbalanced cable. The inputs are designed for use with line level signals ranging from 30dBm to +20dBm. While it is possible to plug an instrument directly into the PRO VLA, it is desirable to run the instrument into a preamp before the signal runs into the PRO VLA. This will provide a stronger signal and will keep noise to a minimum. Microphones must be run into a microphone preamplifier (like A R Ts PRO MPA) before being run into the PRO VLA. Use the XLR input for use with equipment that provides an XLR output. Use the 1/4 input jack for balanced or unbalanced 1/4 Compressor/ limiter The main application of the PRO VLA is to control the dynamic range of a signal level. Plug a line level (post preamplifier or other gain stage) source into either input and set the threshold and output controls to provide the desired amount of compression to the input signal.
Stereo mix and mastering Because of its low noise and excellent tonal qualities, the PRO VLA is ideal for running mixes through before recording to DAT, hard disk or analog recording devices. Used as a mastering device, the PRO VLA is capable of adding warmth and impact to the overall signal level. The PRO VLA is ideal for live use as well. Vocal and instrument levelling The musical nature of the PRO VLA makes it ideal for use on a wide range of instruments and vocals. Place the PRO VLA into a channel insert, after a preamplifier, or from a direct output of a channel of a mixer. Adjust the controls of the PRO VLA to achieve the desired amount of compression.
Tube Replacement The two 12AX7A tubes in your PRO VLA have been specially selected and sorted to specific operating tolerances. The origianl tubes should provide years of trouble-free performance. In the event they need to be replaced, we reccommend replacing them with tubes available from A R T. We cannot guarantee consistent performance from offthe-shelf replacements.

For units purchased outside the United States, service will be provided by an authorized distributor of Applied Research and Technology, Inc.

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 supplied, all cables are connected correctly, and the cables themselves are in working condition. 2) If you find the unit to be at fault, write down a complete description of the problem, including how and when the problem occurs, and a description of your complete setup before calling Customer Service. 3) Call our Customer Service department for a Return Authorization (RA) number or questions regarding technical assistance. Customer Service hours are 9:00am to 6:00pm Eastern Time, Monday through Friday. 4) Pack the unit in its original carton or a reasonable substitute. The packing box is not recommended for a shipping carton. Put the packaged unit in another box for shipping. Print the RA number clearly on the outside of the shipping box. Print your return shipping address on the outside of the box. 5) Include with your unit: a return shipping address (we cannot ship to a P.O. Box), a copy of your purchase receipt, a daytime phone number, and a description of the problem. Keep your manual! 6) Ship your unit to: APPLIED RESEARCH AND TECHNOLOGY, INC. 215 TREMONT STREET ROCHESTER, NEW YORK 14608 ATTN: REPAIR DEPARTMENT RA#_______________________
WARRANTY AND SERVICE INFORMATION
Limited Warranty Warranty service for this unit will be provided by Applied Research & Technology, Inc. in accordance with the following warrant statement. Applied Research & Technology, Inc. (A R T) warrants to the original purchaser that this product and the components thereof will be free from defects in workmanship and materials for a period of five years from the date of purchase. Applied Research & Technology, Inc. will, without charge, repair or replace, at its option, defective product or component parts upon prepaid delivery to the factory service department or 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 or make additions to or improvements upon this product without any obligation to install the same on products previously manufactured. A R T shall not be liable for any consequential damages, including without limitation damages resulting from 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.

A R T PRO VLA SPECIFICATIONS
Dimensions Shipping Weight Input Connections Output Connections Input Impedance XLR, 1/4" Output Impedance XLR, 1/4" Maximum Input Level, XLR Maximum Input Level, 1/4" Maximum Output Level, XLR 19W X 6.5D X 3.5"H 9 Lbs balanced XLR & 1/4" TRS balanced XLR & 1/4" TRS 20K ohms, 1M ohms (unbal.) 600 ohm, 300 ohms (unbal - 600ohms bal.) +21dBm +21dBm +27dBu (RL = 100Kohms, THD = 5%) +21dBu (RL = 600ohms, THD = 5%) Maximum Output Level, 1/4" +21dBu (RL = 100Kohms, THD = 5%) Frequency Response 10Hz to 20kHz (+/-.5dB) Dynamic Range >100dB (20-20kHz) THD @ 0dBm out: <0.1% (typical) Equivalent Input Noise (EIN) XLR to XLR -99dBm ('A' weighted) 1/4" to 1/4" -97dBm ('A' weighted) Attack Time Fast 2ms, Slow 15ms (for 20dB compression) Release Time Fast-300ms, Slow 100ms-3sec. Slope Variable: 2:1 to >10:1 Max. Attenuation 30dB Power Requirements: 100-125VAC, 25W - (USA) Internal fuse. Other power requirements 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. Therefore, specifications are subject to change without notice. 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. Check out our Web Page at: http://www.artroch.com 1996 Applied Research and Technology, Inc.