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Alesis 1622

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FEATURES

16 INPUT CHANNELS WITH EQ - Plenty of inputs for keyboards, microphones, or effects 6 AUXILIARY SENDS - Sends signal to up to 6 outboard effects devices, or 4 outboard effects devices and 2 mono or 1 stereo headphone cue mixes 8 AUXILIARY RETURNS - Special dedicated inputs designed to blend the returns of any combination of 8 mono or 4 stereo outboard effects devices SOLO FUNCTION ON INPUT CHANNELS - Enables any overloads or unwanted background noise to be easily detected 2 SUB MASTERS - Makes it easy to control several input channels with just one fader (or two for stereo), or control record levels during multitrack recording CONTROL ROOM MONITOR SECTION - Sets a level for the control room monitor speakers that is independent of the main mix ELECTRONICALLY BALANCED MIC INPUTS - A feature normally found on consoles that are many times more expensive, this allows for both lower noise and greater headroom in the most critical stage of the console MIXDOWN TAPE DECK RETURN - Allows you to hear playback of your mix from the stereo mixdown tape machine just by flipping a switch INSERTS ON ALL INPUTS AND OUTPUTS - Allows for patching outboard signal processing devices such as EQ's, compressors, and effects directly into the signal path 8 DIRECT OUTPUTS - Allows for the quietest operation by bypassing unused electronics and sending the channel signal directly to the input of a Multitrack Tape Machine 2

DESCRIPTION OF CONTROLS

TOP PANEL
INPUT TRIM The INPUT TRIM is a variable gain control that allows the preamp stage of the mixer to boost the level of a mic or line level signal being fed into the input. The input section of any mixer is the most critical due to the high gain required to amplify such a low level signal (such as that of a microphone) to a usable level. If the gain is set too high, a hot signal from a synthesizer or loud vocalist will cause the input stage to overload and distort. If the gain is set too low, additional gain must be added at some other point in the mixer (such as the faders) which could cause excessive background noise at the output. EQ The equalizer, or EQ, section consists of simple bass and treble controls similar to that of a guitar amp or home stereo. EQ allows for any tonal shaping that might be required by a signal. For the technically minded, these are known as shelving equalizers and have turnover points at 10KHz and 100Hz. This means that the maximum boost or cut begins from 10KHz (and 100Hz for the low frequency EQ) and maintains this "shelf" or plateau from 10KHz to 20KHz. The frequencies below 10KHz are also affected, but less and less so as the frequency of the signal gets further away from 10KHz. See Figure 1

The SUB MASTER Faders can serve several different functions, depending upon the application. In sound reinforcement or in recording during mixdown, the SUB MASTER Faders will act as a group master for a number of input channels. For instance, if Input Channels 1 through 8 contained drum mics, and you wanted to control the overall level of the drums with just one fader, this could be achieved by assigning input channels 1 through 8 to the SUB MASTER ASSIGN, and then panning each channel either hard left or hard right (for mono). The SUB MASTERS could also be assigned in stereo by panning the input channels to any point in the stereo spectrum, in which case the composite signal will appear on both the right and left SUB MASTER faders. See Section 3. During recording, the SUB MASTERS can be used to mix several signals together onto a single track (or two tracks for stereo) by assigning those input channels to the SUB MASTERS and connecting the SUB OUT jack to the track that you wish to record on. See Section 3. SUB MASTER TO MASTER ASSIGN SWITCH This switch routes the signal on the SUB MASTERS to the MASTER Faders. MASTER FADERS The Left and Right MASTER Faders control the main output of the console to either the mixdown deck (in recording) or the sound system (in sound reinforcement). MAIN STEREO METERS The main STEREO METERS, each consisting of 7 green, 4 yellow, and 4 red LEDs, show the relative output levels of the MASTER Faders. The METERS will also show the level of any input channel that has its SOLO engaged. SOLO/POWER LEDS The SOLO LED lights whenever a solo is switched on. The POWER LED lights whenever AC power is connected to the unit.

BACK PANEL

MIC/LINE INPUTS Channels 1 through 16 can be accessed via a 1/4" phone jack. Normally, this would be used for line level signals such as synthesizers or tape machines but it is also possible to feed a microphone signal into this jack. In 4 or 8 track recording applications, channels 9 through 16 would normally be used for tape returns of tracks 1 through 8, while channels 1 through 8 would be used for mic or instrument inputs. MICROPHONE INPUTS Channels 1 through 8 contain an XLR jack which provides an electronically balanced input ideally suited for a microphone. This input is overridden should a plug be inserted in the corresponding Input phone jack (XLR #1 is defeated if a phone plug is inserted in phone jack #1). DIRECT OUTPUTS Channels 1 through 8 contain a DIRECT OUTPUT jack. Each channel routes its own input signal, after it has been amplified and EQ'd, to the Direct Output jack. This is generally used to feed a single track of a Multitrack Tape Deck. Because the Direct Output is the path with the least amount of circuitry and therefore the lowest possible background noise, it is most desirable to use when recording the signal of only a single channel. CHANNEL INSERTS Channels 1 through 16 each contain a stereo jack called an INSERT. This consists of an insert send (the tip of a stereo phone plug) and insert return (the ring of a stereo phone plug) and is used to insert an outboard effects device, such as a compressor, EQ, or chorus, directly into the 8

INSERT INTERFACING

Inserts are used to connect signal processing devices into the signal path of a channel. Normally, the device connected would be one that shapes the dynamics or tone of a signal, such as a compressor, gate, or EQ, rather than an effects device such as a reverb. It is also possible to insert one of these devices into the signal path of either the SUB MASTERS or MAIN OUTPUTS since they also have INSERT jacks available. This is desirable when either a group of instruments, or the entire mix, is to be processed. Any INSERT jack of the 1622 MIXER is a stereo jack containing both an input and an output (the output is the 1622's Send and the input is the 1622's Return). 1) To connect an outboard processor by way of the Insert requires a stereo plug to operate properly. 2) The tip of the plug is the Send and will be connected to the input of the effects device, and the ring of the plug is the Return and will be connected to the output of the effects device or processor. See Figure 9.

FIGURE 9

WIRING OF INSERT CABLE
SEND (TO INPUT) TIP (SEND)
RING (RETURN) RETURN (FROM OUTPUT)

HOW TO ADJUST LEVELS

In order to ensure the cleanest signal with the least amount of background noise (hiss and hum), it is extremely important for the proper levels to be maintained not only within the 1622 MIXER itself, but throughout the entire audio system. Therefore, it's best to observe the following guidelines when initially setting up your 1622 MIXER, and during daily use. A) MAINTAIN PROPER INPUT LEVELS - To set proper input levels on either a mic or line level signal, follow this procedure: 1) With mic or line level signal flowing through the channel, engage the channel SOLO. 2) Observe the SOLO level on the MAIN LED Meter. Adjust the TRIM control until the first red LED lights on the loudest peaks. If any distortion from signal overload is still heard (due to possible brief peaks that don't register on the meter), continue to decrease the TRIM control until the distortion goes away. See Figure 11. B) MAINTAIN PROPER FADER LEVELS - Ideally, both the input and output faders should be run at about the "0" position (about the 3/4 of the way up the fader travel) if possible. This position gives the greatest amount of headroom and lowest background noise. It also allows for any additional increase or decrease in level that might be required during mixing. Ultimately, the fader levels are dependent on the requirements of the mix; the 3/4 level is only a starting point. See Figure 10.

FIGURE 10

IDEAL FADER POSITION DURING RECORDING OR MIXING +10
-5 -10 -15 -20 -25 -30 -35

CHANNEL FADERS

C) MAINTAIN PROPER SYSTEM LEVELS - As a good rule of thumb, it is always best to try to run most volume level controls of your other equipment as well. This will 17
decrease the possibility of overload distortion and keep the amount of background noise to a minimum. SEVERAL CAUTIONS!! Even if you observe the above guidelines, it is still possible to run into some distortion in the following instances: 1) If a large amount of EQ is used, it may be necessary to decrease either the TRIM control, the Channel FADER, or both. The EQ is capable of adding quite a bit of gain and is a frequent cause of overload distortion problems. See Figure 11. 2) If several "hot" channels are assigned to a SUB MASTER, it is possible that the SUB MASTER will overload. Once again, it may be necessary to decrease either the TRIM controls, the Channel FADERS, or both, of each of the channels assigned to the SUB MASTER. See Figure 11.

FIGURE 11

POSSIBLE POINTS OF SIGNAL OVERLOAD
CHANNEL, SUB MASTER, AND MASTER INSERTS

CONTROL ROOM VOLUME

CHANNEL FADER MASTER FADER

SUBMASTER

APPLICATIONS

MULTITRACK RECORDING

Before we talk about the specifics of using the 1622 MIXER for recording, a brief discussion of multitrack recording is in order. 18
INTRODUCTION TO MULTITRACK RECORDING
The function of the 1622 MIXER, or any recording console for that matter, is to provide control of volume, tone, and spatial positioning of signals from microphones, electronic instruments, and tape machines, then to route these signals to a monitor system and tape recorder so they can be heard and recorded. Before the introduction of multitrack tape recorders, these signals had to be mixed together as a "live" performance. If the desired performance wasn't correct because of a musical mistake or balance problem, the performance had to be recorded again and again until the performance was deemed satisfactory. The introduction of multitrack tape machines changed this recording method forever. Most recording today has evolved into a multi step process. These are:
RECORDING (or Tracking) - Instead of needing an entire band available to capture a live

performance, recordings can be made one instrument at a time and constructed in a building block fashion. With the advent of drum machines and sequencers (such as the Alesis HR-16, HR-16:B, and MMT-8) it is possible to build an entire song before ever having to record on tape. Using this method of recording one instrument at a time also allows for fixing the mistakes (normally called "punching in") of an incorrectly played part. By "punching in", or replacing, the misplayed part, you can record a performance over and over again until it's perfect.
MONITORING - In order to properly record a performance, both the engineer, producer, and
all of the players must be able to hear the performance first. This is called Monitoring when listening to the speakers in a control room, and Cue when the musicians are listening to headphones while overdubbing. Monitoring is a more complex operation than it might seem at first glance since there are many mixes that can occur simultaneously. Often, there are 3 separate mixes (sometimes more) happening simultaneously in order to complete the task of just a simple overdub. The comprehensive systems and logistical layout of the 1622 MIXER will make it relatively easy for you to accommodate even the most complex monitoring requirements. The following are a few of the typical mixes that can occur during a session: MULTITRACK MIX The first mix would be the mix that is being recorded onto tape. This mix is derived from the channel faders and the direct outs (channels 1-8, typically) or the submaster outputs. These levels are normally adjusted so that the optimum signal level reaches tape in order to insure the least amount of noise and distortion. This level is usually about 0 VU (on the tape machine meters) although signal levels as low as -10 VU may be appropriate for instruments with high frequency transients, such as cymbals and snare drums. MONITOR SPEAKER (CONTROL ROOM) MIX If you were to only listen to the multitrack mix (see above), you would probably find that it would be terribly out of balance since the optimum recording level is the primary concern of that mix. Therefore, a second mix is required which is called the monitor mix. This is a separate mix which provides the engineer with a useful instrument balance and enables him to make changes and adjustments to the mix (such as muting or soloing channels) without disturbing the signals being recorded on tape. The 1622 MIXER can be configured to create a control room mix. See Section 2 - INTERFACING TO THE MULTITRACK TAPE RECORDER CUE MIX Many times a third separate mix is required as well. This mix is sent to the musicians headphones for overdubbing and is called a CUE mix. This mix can be radically different from what the engineer is listening to since the musician may need certain instruments louder or even absent in the mix in order to cue off of (hence the name). This mix is derived from the PRE-FADER SENDS, 19

The 1622 MIXER performs well in a Sound Reinforcement application. Here are some helpful hints to help you get the most out of your unit.
SOUND REINFORCEMENT APPLICATIONS IN MONO
Most sound reinforcement applications work best in mono. This is because so few members of the audience are actually seated in the ideal spot to hear the balance of a stereo sound system effectively. Also, a stereo sound system is much more difficult to mix, especially if you don't have a sound man. There are two ways to configure the 1622 MIXER in order to achieve a mono mix. METHOD A 1) Pan all of the input channels all the way to the left (or all the way to the right). See Section 1, PAN POT 2) A mono mix will now be present at the Left MASTER Fader (or Right MASTER Fader if all of the input channels were panned that way). This method will make RETURNS 6 and 8 unavailable (or 5 and 7 if all of the input channels are panned to the right) since these returns are dedicated to the right MASTER Fader. Use the following method if all 8 RETURNS are needed.
METHOD B 1) Pan all of the input channels to the center. 2) Use a Y cord from the MAIN OUT jacks on the backpanel. The output is now mono and all eight RETURNS are available for use. See FIGURE 14.

FIGURE 14

MONO OUTPUT FROM THE 1622 RETURNS MIXER FOR SOUND REINFORCEMENT USING ALL 8
INSTRUMENTS OR MICROPHONES
"Y" LEFT AND RIGHT TOGETHER FOR MONO IN

HOUSE SPKR AMP

MONITOR AMP

MONITOR SPKR

USING THE SUB MASTERS The SUB MASTERS are extremely useful in sound reinforcement work. A SUB MASTER can be very useful in controlling the level of several channels with the movement of only one fader. For example, if you wished to control your group vocals via a SUB MASTER, and the vocal mics were located on channels 1 through 6, do the following:
1) Raise the selected Channel Faders to the desired levels See Section 2, HOW TO ADJUST LEVELS 2) Unassign the selected Channel Faders by switching the "MASTER" assign switch to the "Off" position. See Section 1, MASTER ASSIGN SWITCH 3) Now assign the Channel Faders by switching the "SUB MASTER" assign switch to the "On" position. See Section 1, SUB MASTER TO MASTER ASSIGN SWITCH 4) Now assign the SUB MASTER by switching the "SUB MASTER TO MASTER" assign switch to the "On" position. The SUB MASTER fader will now control those channels assigned to it.
LINE INPUTS USED AS ADDITIONAL MIC INPUTS The 1622 MIXER is not limited to only 8 microphone inputs. Besides the XLR connections on Input Channels 1 through 8, Channels 9 through 16 may also be used as additional microphone inputs. This is accomplished by using the 1/4" plug as the microphone input and will require either an XLR to 1/4" adapter or a mic cable with a 1/4" plug on the end. See Figure 14.

USING THE SUB MASTERS FOR SEPARATE OUTPUTS There may be situations that call for a separate controlled output level beside the ones available from the MAIN OUTPUT, such as when the 1622 MIXER is used as an on-stage keyboard mixer. In this case, one set of outputs will feed the keyboard players on-stage amplifier, and the 2nd set of outputs will feed the house sound system. See Figure 15. In order to accomplish this, do the following : 1) Raise the Channel Faders to the desired levels 2) Assign the Channel Faders by switching both the "MASTER" assign switch and the "SUB MASTER" assign switch to the "On" position. 3) Now unassign the SUB MASTER by switching the "SUB MASTER TO MASTER" assign switch to the "Off" position. The SUB MASTER Fader will now separately control one set of outputs while the MASTER Faders will control the other.

FIGURE 15

USING THE SUB MASTERS OF THE 1622 MIXER FOR SEPARATE OUTPUTS

DRUM MACHINE

KEYBOARDS

HOUSE MIXING CONSOLE

STAGE MONITOR MIX FROM THE PRE-FADER SENDS It is possible to create up to two separate stage monitor mixes by using the PRE-FADER SENDS. Although it is possible to use the Post-Fader Sends as well, the Pre-Fader Sends are better suited to this application since any movement of the Channel Faders will not affect the Pre-Fader send level. See Figure 16. 1) On the Input Channels, turn SEND 1 and SEND 2 (for 2 separate mixes) or just SEND 1 (for a single, mono mix) until the desired balance is obtained. See Section 1, SENDS, and Section 3, HOW TO CREATE A CUE MIX 2) Use SEND MASTER 1 and 2 to increase or decrease the overall volume. 3) Usually, a 1/3 octave graphic equalizer is patched into the line to notch out feedback frequencies. The Alesis M-EQ 230 is a perfect unit for this application.
DEDICATED MIDI KEYBOARD MIXER
The use of the 1622 as a dedicated mixer in a MIDI keyboard setup is very similar to a sound reinforcement application except that the MAIN OUTputs will usually be in stereo rather than mono. See Figure 16. 30

FIGURE 16

THE 1622 MIXER USED AS A DEDICATED KEYBOARD MIXER

IN IN IN

MIXING CONSOLE OR SOUND SYSTEM

VIDEO POST-PRODUCTION

The 1622 MIXER can easily be used in editing bays or video post-production facilities. The availability of separate output jacks on the SUB MASTERS make the unit ideal for making simultaneous mix-minus feeds. A mix-minus feed, which is used for international versions of a film or video, is a separate mix containing all music and effects, but no dialog (which is usually dubbed in later). See Figure 17. To accomplish a mix-minus feed, do the following: 1) Raise the Channel Faders to the desired levels. See Section 2, HOW TO ADJUST LEVELS 2) Assign the Channel Faders by switching both the "MASTER" assign switch and the "SUB MASTER" assign switch to the "On" position. See Section 1 3) Unassign the Input Channels that contain the dialog (or any information not desired in the mix-minus feed) by switching the "SUB MASTER" assign switch to the "Off" position. 4) Now unassign the SUB MASTER by switching the "SUB MASTER TO MASTER" assign switch to the "Off" position. The SUB MASTER Fader will now separately control the mix-minus outputs while the MASTER Faders will control the full composite output. 31

FIGURE 17

USING THE 1622 MIXER FOR A MIX MINUS OUTPUT

CART MACHINES OUT

VTR'S OUT

MIX-MINUS

IN VTR

IN IN IN IN OUT OUT

MONITOR SPKR AMP

TROUBLESHOOTING

NO SOUND
NO SOUND WHEN CHANNEL IS SOLOED 1) Plug is inserted into LINE input, which has priority over MIC input. 2) Open circuit in the INSERT signal path. Remove plug from INSERT jack. NO SOUND WHEN MONITOR LEVEL TURNED UP 1) MONITOR MUTE is engaged. Switch to "Off" position. 2) SOLO is activated. If SOLO LED is lit, find the channel soloed and switch to "Off" position. 3) TAPE/MON Switch in the wrong position. Swith to MON position to hear the console signal. Switch to TAPE position to hear the mixdown tape deck.

OVERLOAD PROBLEMS

DISTORTION HEARD WHEN INPUT CHANNEL IS SOLOED 1) Input too hot. Decrease TRIM level. 2) Excessive use of EQ. Decrease TRIM level or EQ levels. 3) Cable fault. Check the cable from the mic or instrument. 4) Trouble at the source. Try a different mic or instrument. DISTORTION IS BEING RECORDED ONTO TAPE, BUT DISTORTION NOT HEARD WHEN INPUT CHANNEL IS SOLOED 1) SUB MASTER is overloaded. Decrease the fader levels of the channels assigned to the SUB MASTER. 32
2) Tape Machine input is overloaded. Set tape recorder input level control or SUB MASTER levels so that the meters of the tape deck hit 0 VU or less when recording. 3) Monitor input of the 1622 MIXER is overloaded. Decrease TRIM control or output of Multitrack Tape Deck. DISTORTION AT MIXDOWN MACHINE OR SOUND SYSTEM 1) Input Channel is overloaded. Solo each channel until distortion is found, then decrease either TRIM level or Fader level or both. 2) SUB MASTER is overloaded. Decrease the Fader levels of the channels assigned to SUB MASTER. 3) MASTER Faders are overloaded. If LED meters are in the red, decrease MASTER Fader level until distortion disappears. If LED meters are not in the red yet distortion is still heard, decrease all Input Channel Faders. 4) Overloaded Return. Decrease output level of effects device or decrease RETURN level. 5) Effects unit is overloaded. Decrease output of SEND MASTER level or input level of effects device. DISTORTION ON THE RETURNS 1) Overloaded return. Decrease output level of effects device or decrease RETURN level. 2) Effects unit is overloaded. Decrease output of SEND MASTER level or input level of effects device.

FIGURE 18

A TYPICAL BUSS LINE

BUSS LINE

TO OUTPUT JACK

BUSS MASTER OR SUBMASTER

Chorus - A popular signal processing effect, Chorus attempts to simulate the sound of a group of instruments by introducing minute changes in pitch and time. This is done by splitting the signal of an instrument into two parts. One signal remains unchanged while the second is slightly delayed in time and detuned in pitch. Compressor/Limiter - A compressor/limiter, which can be thought of as an automatic fader, very quickly reduces gain and attenuates the signal once it exceeds a predetermined level. The number of dB increase of the input signal needed to cause a 1 dB increase in the output signal of the compressor/limiter is called the "Compression Ratio". Thus, for a ratio of 4 to 1, an 8 dB increase of the input produces a 2 dB increase in output. A low compression ratio (2:1 to 8:1) causes the compressor/limiter to act in the compression mode. A compressor is usually used to even out the volume differences of an instrument or 36
vocal. A compression ratio of 10:1 or above changes the compressor into a limiter. A limiter is used to prevent short term peaks, which add little information to program material, from overloading amplifiers or tapes. The Alesis MICRO LIMITER is an example of a compressor/limiter. Cue Mix - The mix sent to musicians studio headphones is called the Cue Mix. This mix is usually different from the one that is being heard in the control room, since the musicians frequently require certain instruments to be of a different volume or absent altogether in order to "cue" off of. The 1622 MIXER is capable of supplying either 2 mono or 1 stereo Cue Mix. dBV - Decibels per Volt. This is a unit of measurement normally applied when measuring the inputs and outputs of most modern sound equipment. Technically speaking, this is measured when a low impedance source is fed into a high impedance input, as is the case in nearly all current sound equipment. +4dBV = 1.4 volts AC, 0dBV =.778 volts AC. Delay - An electronic effect in which the original signal is repeated and mixed back in with the original signal. Usually, the number of repeats and the length of time between the repeats can be adjusted. Also sometimes known as Echo. Direct Outputs - This jack contains the amplified (and EQ'ed) signal of only one channel, which has not been mixed together with other signals in the mixer. This is generally used to feed a single track of a tape machine. Because the Direct Output is the path with the least amount of circuitry and therefore the lowest possible background noise, it is most desirable to use. The 1622 MIXER has a Direct Output on each of the first 8 Input Channels. Distortion - Any deviation in the amplified signal from its original. Distortion may take many forms such as certain frequencies becoming louder or softer after being amplified (frequency response), unwanted signal artifacts when two or more signals are amplified at the same time (intermodulation distortion), or certain harmonics of a signal being favored over others (harmonic distortion). Echo - See Delay. Edit Bay - An Edit Bay is the equivalent of a video mixdown studio, where shots from different reels are assembled onto a master reel. At this point, video effects such as wipes and fades are also added. Effects - The term used for signal processing that is added to a signal to enhance its tonal quality. These effects may be reverb, echo, EQ, compression, chorusing, flanging, etc. Equalization (EQ) - Equalization is the ability to adjust the tonal balance of a signal. This can be of a very broad nature, such as the bass and treble controls of a home stereo unit, or of a finely tuned nature, such as a graphic equalizer. The 1622 MIXER has 2 bands of shelving type EQ (see shelving) per Input Channel. Fader - The Channel Fader determines the overall volume level of the channel. It is normally best to keep this Fader at about the 3/4 level for best headroom and lowest background noise. Feedback - Whenever a portion of an amplifier's output is returned to its input, and therefore reamplified, a loud howl called "feedback" is created. Most commonly, this occurs in sound systems when the output of the loudspeakers is picked up again and again by a microphone forming a feedback "loop". Flanging - First used in the sixties, "flanging" was achieved by the use of two tape recorders that would record and play back the same program in synchronization. By alternately slowing down one tape machine, and then the other, different frequency cancellations would occur. Since the slowing down of the tape machines was done by hand pressure against the flanges of the tape supply reels, the term "flanging" came into being. Today, flanging can be closely simulated by most outboard effects processors such as the Alesis MIDIVERB II, MIDIVERB III, 37

or QUADRAVERB. The effect of flanging, either electronically or mechanically done, is achieved by slightly delaying a signal, then constantly varying the amount of time delay. The delayed signal is then mixed back with the original signal to produce the "swishing" or "tunneling" sound. Gate - See "Noise Gate". Graphic Equalizer - Seen on sound systems, some home stereos, and many guitar type amplifiers, this device gets its name from the fact that the control settings actually form a graph of the frequency spectrum. While shelving equalizers work on broad sections of the frequency bandwidth, a graphic equalizer divides the frequency spectrum into sections called bands which are normally measured in musical octaves. An example of a graphic equalizer is the Alesis MEQ 230. Ground Lift - An adapter for an AC line plug that converts it from 3 pin operation to 2 pin. This is frequently used to avoid ground loops (see Ground Loops). Ground Loops - When a sound system or recording system has a loud hum or buzz, a Ground Loop is usually the cause. Ground Loops are created by having more than one ground point in a sound system. (See Section 5 - GROUNDING). Headroom - The amount of available operating level before a circuit is overloaded and begins to distort. For example, the nominal operating level of the 1622 MIXER is +4dBV and the maximum output level is +20dBV which means that there is 16dB of headroom available. If the nominal operating level is -10dBV and the maximum output level is +20dBV, then there is 30dB of headroom available. High Impedance - Any impedance which is 10,000 ohms or more is considered a High Impedance. The inputs of most audio devices are High Impedance. All inputs except the microphone inputs of the 1622 MIXER are High Impedance. Inserts - Inserts are used to connect signal processing devices into the signal path of a single channel. Normally, this is a device that shapes the dynamics or tone of a signal, such as a compressor, gate, or EQ, rather than an effects device such as a reverb. An insert consists of both an input and an output and is used to place an outboard effects device, such as a compressor, EQ, or chorus, into the signal path of only that channel. Each Input Channel, the Sub Groups, and the Master Outputs of the 1622 MIXER have inserts. LED - LED is an abbreviation for Light Emitting Diode and is commonly used as an indicator on audio and musical equipment. Line Level - The output of most mixers and outboard equipment, which may be nominally 10dBV or +4dBV, or approximately.1 to 1 volt AC. Because the signal level is so high, costly low noise precision amplifiers are no longer required. See "Nominal Level" Low Impedance - Any impedance 1,000 ohms or lower is considered to be Low Impedance. The outputs of most audio devices and electronic musical instruments are Low Impedance. Most microphone inputs are Low Impedance. The microphone inputs of the 1622 MIXER are Low Impedance. Mix-Minus - A mix-minus feed, which is used for international versions of a film or video, is a separate mix containing all music and effects, but no dialog (which is usually dubbed in later). See Section 3, VIDEO POST PRODUCTION Mixer - A unit which blends several audio sources, such as microphones, tapes, records, or CDs, together in a single mono or stereo output. Mixing Console - A Mixing Console blends several audio sources together with the capability of routing different mixes to several different output combinations. 38

Monitor - In recording, Control Room Monitors are the primary speaker for listening to either a performance or tape playback. In sound reinforcement, a Monitor is a separate on-stage sound system intended only for the performer so he can hear himself. MultiTrack - A tape machine that has 4 or more independent recording tracks, and is capable of recording on any channel while remaining in sync with previously recorded tracks. Mute - To turn off or disengage. On a mixing console, a Mute switch is an On/Off switch for a particular function. The 1622 MIXER has a Mute switch for each of its 16 inputs. Noise Gate - As the name suggests, a noise gate is sort of an electronic fence gate. When there is enough pressure on the gate (the signal is loud enough), the gate will open to let the signal through. You can control how much level it will take to open the gate (or how much pressure), how long the gate will stay open, and how fast it will close. Because of this amount of control, a Noise Gate such as the Alesis MICRO GATE can be set to eliminate any noises, clicks, or buzzes which might be a component of the signal by closing the gate (turning off) either when a signal is not present, or when the signal drops below a preset threshold (or pressure). The Noise Gate will not actually eliminate all noise that is a component of the signal, just the noise that exists when the signal is not present. It can also be used for a variety of special effects such as gating the reverb on a snare drum to achieve the popular 80's style drum sound effect, or tightening up the sound of a live drum kit by suppressing leakage between drum mics. Nominal Level - Typical operating level. This is usually -10dBV for semi-pro and stereo equipment, and +4dBV for professional quality equipment. The 1622 MIXER can accommodate either. Outboard - Refers to any piece of equipment that is connected to a mixing console but not an integral part of it. Overdubbing - A basic process of multitrack recording, Overdubbing is the recording of a new part in sync with previously recorded material. Pan Control - The Pan Control determines the spatial positioning of a signal and places it anywhere between the left and right speakers. Patchbay - Refers to a row of jacks that are permanently connected to various pieces of equipment. This allows immediate access to inputs and outputs for fast and easy interconnection. See Section 2, INTERFACING WITH THE MULTITRACK TAPE DECK VIA A PATCHBAY Patching - The process of interconnecting one piece of equipment to another. PFL - Stands for Pre-Fader Listen. A type of solo, PFL allows the engineer to listen to the signal as it enters the console but before it travels through much of the circuitry of the console. Thus, if an overload occurs , the engineer can easily tell at what point in the signal path. The 1622 MIXER uses a Pre-Fader Listen scheme in that the Fader position has no bearing on the volume of the soloed channel because the Solo signal is taken from before the Channel Fader in the signal path. Phase Cancellation - The change in timbre that occurs when a signal partially cancels itself out. This frequently happens when a sound appears at a microphone at the same time as its reflection. Phone Plug - See 1/4" plug Phono Plug (RCA) - A connector commonly found on hi-fi equipment and semi-pro audio equipment. Although inexpensive, RCA phono plugs are not used in professional applications since the connectors don't lock together and are subject to frequent accidental unplugging. 39

Sub Master - A Sub Master (sometimes called a "SubGroup" or "Group") is used to control the level of several channels with the movement of only one fader. The 1622 MIXER has 2 Sub Masters. Tape Returns - Inputs on a console specifically dedicated to receiving the signal from a tape deck. This may either be from a Mixdown Tape Deck (cassette, two track, DAT), or Multitrack Tape Deck. Transients - Extremely brief, high output audio signals, usually the attack portion of a signal. For example, when looking at a signal meter, even though the meter of a signal may indicate an acceptable level, the transient portion of the signal (such as a cymbal crash) can very briefly rise far above what the meter is capable of reading, causing a moment of overload and therefore, distortion. Trim - A control on a mixer or console that sets or "Trims" the gain of the microphone preamp. There is a Trim control on each Input Channel on the 1622 MIXER. TRS - A stereo phone plug is also commonly known as a TRS plug because of the arrangement of construction; i.e. T stands for tip, R for ring, and S for sleeve. See Figure 9. Unbalanced Line - A circuit that uses a single wire to carry the signal voltage. Although unbalanced circuitry is simpler to build than balanced equipment, unbalanced lines are more susceptible to outside induced hum and noise. This is not a problem at line level where the signal is strong and the induced hum and noise is weak. But weak microphone level signals would suffer from outside induced hum and noise. This is why balanced lines are nearly always used for microphone level signals. See Figure 19. VU - VU stands for Volume Units, which is one common standard of measurement of metering on professional audio equipment such as tape recorders and consoles. XLR - A mating male and female jack and plug used for balanced operation and normally found on professional audio equipment. These are desirable because of their locking feature (making them difficult to accidentally disconnect) and sturdy construction. Most professional applications use the 3 pin type which are a requirement for balanced operation (see Balanced), although others with more pins are used for other applications. The 8 microphone inputs of the 1622 MIXER use XLR type connectors.See Figure 19.

APPENDIX

There may be situations that arise that the 1/4" type outputs of the 1622 MIXER must be interfaced to a balanced XLR type input. This is fairly easy to do and will have no effect on the performance of the unit. There are two methods to accomplish this since there is currently no adhered to international standard. METHOD A The published Audio Engineering Society standard for the pin out of an XLR connector is: Pin 1 Pin 2 Pin 3 Ground + -

To change this connection from balanced to unbalanced, simply solder pins 1 and 3 together. See Figure 17A. This convention is followed throughout most of the world, except for the United States. If you are connecting the 1622 MIXER to a device of European origin, chances are it is probably wired this way. Check your owners manual to be sure. METHOD B The typical way that an XLR connector is wired in North America is: Pin 1 Pin 2 Pin 3 Ground +
To change this connection from balanced to unbalanced, simply solder pins 1 and 2 together. See Figure 17B. This convention is followed only in the United States. If you are connecting the 1622 MIXER to a device made for the American market, chances are it is probably wired this way. Check your owners manual to be sure. If you have chosen the wrong method of wiring, DON'T WORRY since you cannot harm your 1622. The audio quality may suffer slightly, however, due to possible phase cancellation. If you are unsure, try both ways and chose the one that sounds best!

FIGURE 19

WIRING OF UNBALANCED XLR
METHOD A - EUROPEAN EQUIPMENT

HOT SHIELD 3

METHOD B - AMERICAN EQUIPMENT
Aux Returns, 13 Aux Send Master, 13 Aux Sends, 8, 13, 25, 32 Auxiliary Sends, 6, 7, 48
Insert Return, 12 Inserts, 12, 17, 26, 36, 43
Line Input, 36 Line level, 18, 44, 47 Low Impedance, 44
Balanced, 15, 16, 40 Buss, 7, 10, 13, 28, 40
Channel Fader, 7, 8, 19, 25, 27, 31, 32, 34, 35, 42, 47 Compressor, 12, 13, 14, 26, 40, 44 Cue mix, 6, 25, 41, 48 Cue, 21
Main Insert, 14 Main Out Level Selector, 14 Main Outputs, 13, 14, 24, 26, 30, 31, 33 Master Assign, 27 Master Faders, 8, 9, 10, 11, 25, 27, 29, 32, 34, 35 Mix-Minus, 33, 44 Mixdown Deck, 13, 14, 24, 28, 48 Mixdown, 22, 28 Monitor Defeat, 9, 13 Monitor Mix, 21 Monitor Mute, 36 Monitor Out, 14 Monitor Volume, 9 Monitor, 13, 25, 28, 29, 44 Mono, 10, 29 MultiTrack, 45, 48 Mute, 7, 45
Direct Outputs, 12, 23, 24, 41 Distortion, 18, 35, 41
Effects Device, 12, 44 Effects Returns, 9 Effects Sends, 25 Effects, 7, 13, 22, 25, 28, 35, 42 EQ, 6, 12, 19, 22, 26, 28, 35, 42, 44

Feedback, 32, 42

Noise Gate, 45 Nominal Level, 45

doc1

ALESIS RA-100

Reference Manual

CHAPTER 1 GETTING TO KNOW THE RA-100
1.1 INTRODUCTION...1 Principal Features...1 Unpacking and Inspection...3 About This Manual....4

CHAPTER 2 INSTALLATION

2.1 REAR PANEL CONNECTIONS..5 2.2 POWER CONSIDERATIONS...5 Fuse....5 The AC Cord....5 Electrical Service to the RA-100...6 2.3 OPERATING ENVIRONMENT..6 Thermal Considerations in Rack Mounting..6 Mounting on a Shelf or in a Non-Rack Enclosure..7 Avoiding Electromagnetic Interference..8 2.4 INPUTS...8 Input Jack Characteristics..8 Cables....8 Cable Wiring Tips...9 Adapting the RA-100 to Balanced Lines...9 2.5 OUTPUTS....11 Connector Options...11 Output Cables...11 Connecting Cables to Push Connectors..12 The Importance of Speaker Polarity..13
CHAPTER 3 USING THE RA-100
3.1 FRONT PANEL CONTROLS...14 Volume Controls...14 On-Off Switch....14 Mute Switch...15 Clip Indicators....15 3.2 CHECKING FOR PROPER POLARITY..15 3.3 CHOOSING THE CORRECT SPEAKERS..15 3.4 ABOUT GROUND LOOPS...16
CHAPTER 4 TYPICAL APPLICATIONS
4.1 STUDIO MONITOR AMP...18 4.2 SOUND REINFORCEMENT...18
4.3 KEYBOARD AMPLIFICATION SYSTEM..19 4.4 GUITAR AMPLIFICATION SYSTEM..20 4.5 BIAMP SOUND REINFORCEMENT...21
CHAPTER 5 MAINTAINANCE/SERVICE
5.1 GENERAL INFORMATION...22 Cleaning....22 Maintenance....22 Refer All Servicing to Alesis...22
CHAPTER 6 TROUBLESHOOTING
Hum....23 No Volume...23 Distorted or Low Level Sound...23 Thin Sound/Sound that Changes Unpredictably in a Room.23

CHAPTER 7 SPECIFICATIONS

DO NOT REMOVE THE RA-100 TOP COVER. THERE ARE NO USER SERVICEABLE PARTS INSIDE. REFER SERVICING TO A QUALIFIED REPAIR TECHNICIAN.
CHAPTER 1: MEET THE RA-100

1.1 INTRODUCTION

Principal Features
Congratulations on your purchase of the Alesis RA-100 Reference Amplifier. With all the wondrous advances in both analog and digital electronics in the past few years, its easy to forget that an audio chain is only as good as its weakest link. With low-cost digital devices now offering sound quality unheard of only a few years ago, Alesis has applied its expertise toward creating a sonically accurate, stable, and affordable stereo power amplifier thats suitable for the digital age. Optimized for studio monitoring applications and moderate-power live performance setups, the amps main features include: 100 watts per channel into 4, 75 watts per channel into 8 Dual clipping indicators alert you of any type of non-linear operation, not just clipping Output short circuit protection to minimize down time and protect the amplifiers circuitry Massive, conservatively rated, custom-designed extruded heat sinks (individual for each channel) for cool operation No ventilation fan is needed, allowing for quiet operation and reduced ambient noise in the studio Extremely low noise and distortion; suitable for quiet applications such as recording studios, church installations, and museums However, some of the RA-100s most important features are hard to put on a spec sheet. In a quest for a musical sounding power amp that can stand up to a tough life on the road as well as continuous operation in the studio, Alesis has made some changessome minor, and some very significantto the standard power amp. The RA-100 doesnt produce any audio transients during power-up or 1
power-down. Nonetheless, theres a 2-second mute on power-up to compensate for any pieces of equipment plugged into the RA-100 that produce transients upon power-up, and receive power at the same time as the RA-100. Also, because the amp doesnt produce power on/off thumps itself, the mute circuit can be pre-power amp. This allows simpler circuitry than what would be required for shutting down the power amp stages. The RA-100s power supply has plenty of reserve capacity to handle percussive transients, but if someone kicks the RA-100s plug out of the wall, you want all amplification to cease immediately. Therefore, if the amp senses any loss of power, it instantly mutes the audio. Because power-up and -down are noiseless, the on/off switch doubles as a mute or panic button. The output stage uses full complementary-symmetry circuitry throughout. Although there are cheaper ways to design an output stage, this time-tested approach is generally considered superior to non-complementarysymmetry types. The output devices are rated at 30 Amps of peak current, and boast a 20 MHz FT (transition frequency) for superior bandwidth. Extremely good stability with reactive loads (e.g., speakers and crossovers). Stable operation is essential when presented with the changing load characteristics of typical speakers; the RA-100 uses several stabilization techniques to maintain consistent feedback network characteristics. Alesis recognizes that amplifiers will sometimes be driven into clipping even though this is not good practiceduring a recording session or under the pressures of live performance. As a result, a great of deal of research went into creating the best possible clipping entry/recovery characteristics. Amps with lots of overdrive and saturation tend to create overshoot and ringing during the clipping process, which degrades the sound; the RA-100 has been designed so that it exhibits very little saturation, even when overloaded. As a result, it enters and exits clipping very cleanly. Clean clipping allows the RA-100 to be driven harder, which makes the overall perceived sound louder. Monitoring a sine wave being clipped confirms this action. With the RA100, the amp will follow the original input signal as soon as clipping ceases (a). With some conventional amp designs, the signal will hang at the clipped level for a while before catching up with the input signal (b. This saturation-caused overshoot can sometimes sound worse than the clipping itself. s

No speaker stress during shutdown. With traditional protection circuitry, the act of clamping the output devices to a safe value can make the amp unstable with particular notes that interact with the speaker resonance, thus producing oscillation or motorboating. This could damage your speakers. The RA-100 uses an elegant clamping design that observes the load at all times but also integrates the signal characteristics into the clamping action. Thus, the clamping action is gentle and, after clamping to the maximum current encountered in normal operation, will slowly (over 1 to 2 seconds) clamp based on the load and signal characteristics. If the source of the problem (e.g., a short across the speaker terminals) is removed, the signal recovers instantly. Alesis also recognizes that whatever else, the show must go on. As a result, under conditions of extreme abuse (such as ultra-low speaker impedances or mounting that allows for no ventilation), the RA-100 will limit its signal rather than simply shut down. Taken to an extreme, this will produce distortion but sound will still come out. To acquaint yourself with the RA-100s operation, and to use it properly in various applications, carefully read this manual. Power amplifiers are highcurrent devices that are the next-to-last link in the audio chain. Proper attention to cabling, power distribution, ground loops, and other topics covered in this manual is vital to have the RA-100 live up to its full potential. As always, we welcome your suggestions and comments concerning this product, or any other product in the Alesis line.

Unpacking and Inspection

Your new Alesis power amplifier was carefully packed at the factory, and the container was designed to protect the unit during shipping. Please retain this container in the highly unlikely event that you need to return the RA-100 for servicing. Upon receiving the RA-100, carefully examine the shipping carton and its contents for any sign of physical damage that many have occurred in transit. If you detect any damage, do not destroy any of the packing material or the carton, and immediately notify the carrier of a possible claim for damage. Damage claims must be made by you. If you picked up your amplifier directly from an Alesis dealer, contact the dealer. The shipping carton should contain: This instruction manual 3

Alesis RA-100 power amp with the same serial number as shown on the shipping carton Power cord. Four stick-on rubber feet (for shelf mounting, to prevent the RA-100s bottom surface from scratching the shelf) Alesis warranty card. It is important to register your purchase; if you have not already filled out your warranty card, please do so now.

About This Manual

The manual presents information in a logical order. Chapter 2 covers installation, and Chapter 3, how to use the RA-100. Chapter 4 covers several typical applications. The manual closes with information on maintenance/servicing, troubleshooting, and operating specifications. Please remember that a power amplifier is a high-current, high-power device and should be treated with respect and care. Even if you are an audio veteran, we urge you to read the entire manual to make the best use of the RA-100.

CHAPTER 2: INSTALLATION

2.1 REAR PANEL CONNECTIONS
The following diagram shows the various rear-panel components. Please refer to this diagram during the procedures described in this chapter.
Fuse: 5 Amps Left Push Clip Outputs Right Left Phone Input Plug Output
(A spare fuse in included in the fuse holder)

AC Line Cord Jack

Right Phone Plug Output

Left Input

Right Push Clip Outputs

2.2 POWER CONSIDERATIONS

Replace with a 5 Amp, slow-blow type only; use of any higher amperage value will void the warranty. FUSES ARE FOR YOUR PROTECTION NEVER SUBSTITUTE A FUSE OF A HIGHER RATING, OR BYPASS IT.

The AC Cord

The RA-100s IEC-spec AC cord (do not substitute any other AC cord) is designed to feed an outlet that includes three pins, with the third, round pin connected to ground. The ground connection is an important safety feature designed to keep the chassis of electronic devices such as the RA-100 at ground potential. DO NOT OPERATE ANY ELECTRICAL EQUIPMENT WITH UNGROUNDED OUTLETS. PLUGGING THE RA-100 INTO AN UNGROUNDED OUTLET, OR LIFTING THE UNIT OFF GROUND WITH
A THREE-TO-TWO WIRE ADAPTER, CREATES A HAZARDOUS CONDITION. ALESIS CANNOT BE RESPONSIBLE FOR PROBLEMS CAUSED BY USING THE RA-100 OR ANY ASSOCIATED EQUIPMENT WITH IMPROPER AC WIRING.

Electrical Service to the RA-100
Although the RA-100 has a maximum audio output rating of 200 watts total into 4, this does not represent the total current consumption since there are certain inefficiencies inherent in linear amplifier design. As a result, the fuse is rated at 5 Amps, implying that the maximum current the RA-100 can draw is around 500 watts. However, in typical studio applications the average power consumption will be much less. However, when multiple devices are plugged into a single AC outlet, the possibility of overheated connections can exist. Electrical standards have taken enormous strides toward increased safety over the past few decades thanks to circuit breakers, ground fault interrupters, and improved wiring and insulation materials. Unfortunately, some clubs are situated in older buildings whose wiring may not meet current safety standards, or have wiring that has deteriorated over the years. Make sure the circuit supplying power to the RA-100 can supply enough current to run it properly. If the circuit has to supply other high-powered consumption units such as refrigerators, coffee pots, toasters, air conditioning, or stage lighting, plug the RA-100 into a different circuit with a lesser load.
2.3 OPERATING ENVIRONMENT
Thermal Considerations in Rack Mounting
The RA-100 can be mounted in an equipment rack (taking up 2 rack spaces), placed on a shelf, tucked away in a vocal booth, etc. When you install it, keep in mind that heat is the major enemy of electronic equipment. Fortunately, the RA-100s protection circuitry will not allow the unit to run hot enough to damage any of the circuitry. However, sustained high-temperature operation sufficient to cause limiting will adversely affect the sound quality for as long as the excessive temperature conditions exists. The RA-100 has extensive heat sinking to minimize overheating, as well as eliminate the need for a ventilating fan. The latter feature is crucial for the 6
cramped control rooms typically found in smaller studios; any fan noise would interfere with the mixing or monitoring process. The RA-100 should be installed so that its heat sinking is allowed to do its job. Please observe the following: The RA-100 is designed to perform properly over a range of ambient temperatures from 0 C to +50 C (32 F to 122 F), in up to 80% noncondensing humidity. These are not absolute limits, but Alesis cannot guarantee that the RA-100 will meet its published specs if operated outside of these ranges. If necessary, use a fan to blow air over the RA-100 and promote cooler operation. Prevent the side heat sink fins from becoming obstructed. There should be enough airspace around the amplifier for it to breathe. Always allow adequate ventilation behind the RA-100. Do not seal any enclosure that holds the RA-100. Never throw a coat or other flexible fabric or covering over the top of the amp when its in use. You may wish to leave an empty rack space above or below the amp to promote good air flow. Due to the RA-100s weight (13.5 lbs.), its a good idea to mount it in the bottom of the rack frame.

Cable Wiring Tips

If you decide to wire your own cables, Alesis recommends that you use two conductor shielded cable (even in an installation that uses unbalanced wiring) with either a braided or foil-type shield. Connect one conductor to the phone jack tip connection to carry the hot signal, and the shield connection to the sleeve. The other conductor should also connect to the shield since it is not good practice to depend on the shield wire itself to complete the signal connection. This is because the shield wires are more subject to breakage, especially in portable installations, than the more protected internal insulated wires. By using a second safety conductor for ground, the worst that could happen with a broken shield would be a rise in noise or hum due to the lack of shielding. If the ground connection were completely lost, there would be either extremely loud hum or major loss of audio.
Adapting the RA-100 to Balanced Lines
With long cable runs (e.g., over 6 meters/20 feet) in noisy electrical environments, the cable itself can act as an antenna and pick up RF fields, AC hum, or other types of interference. To avoid these problems, many professional studios and live sound companies use balanced line connections. The average application will probably not require balanced lines, so try unbalanced connectors first and convert to balanced line operation only if warranted. Balanced lines carry a pair of signals, each out of phase with respect to the other but otherwise identical. To be converted back into a single, unbalanced line, both balanced lines feed a differential amplifier input or transformer that responds to the difference in levels between signals. Thus, the out-ofphase signals are recombined into an unbalanced signal, but interference induced into the cable will not be out of phase. Since there is no difference between these signals, the differential amplifier or transformer will reject the interference to a great degree. This tendency to ignore interference is called Common Mode Rejection. To adapt a balanced line output to feed the RA-100, you have four options. Balanced line to unbalanced line transformer. These commonly available audio accessories have a balanced line input, usually in the form of an XLR connector, and an unbalanced line output, usually in the form of a 1/4" phone jack. The same transformer can also convert unbalanced signals to balanced signals. Advantages: High signal carrying capacity, no power required, generates no hiss. Disadvantages: Inexpensive transformers may color the sound due to frequency response irregularities and can pick up hum due to inductive nature of transformers. Very high-fidelity models are expensive. Active balanced-to-unbalanced converter. This uses an active electronic circuit to convert balanced lines to unbalanced lines, but does not work in the other direction. Advantages: Good frequency response specs, no inherent hum pickup, less expensive than transformers. Disadvantages: Requires power, generates some noise. 1622 mixer. Inputs 1-8 of the Alesis 1622 mixer include balanced line inputs as well as direct-to-tape unbalanced outputs and unbalanced signal send points. You can plug a balanced line signal into the balanced XLR input, then patch either the direct out or send connection to the RA-100. Advantages: Available free if you have a 1622, flat frequency response, no inherent hum pickup. Disadvantages: Generates some hiss, optimized primarily for low level signals. Wire your own adapter. It is possible to feed just one of the balanced lines, 10

along with ground, into the RA-100. The following diagram shows an adapter that assumes pin 2 of the XLR connector is hot. Female XLR Connector 2 shield (no connection) If pin 3 is hot, then do not connect pin 2 to anything, and connect the wire from the 1/4 phone jack tip to pin 3 of the XLR female connector. If your system uses stereo phone jacks to carry balanced line signals (the tip and ring should carry the in-phase and out-of-phase signals, respectively, although this may be reversed in some systems), then an adapter is not necessary. Simply plug a stereo cord from the balanced phone jack into the RA-100s input; it will ignore the ring connection and amplify only the tip connection. Advantages: Inexpensive, simple. Disadvantages: No inherent hum and noise rejection; defeats advantages of balanced line operation 1/4 inch phone jack

2.5 OUTPUTS

Connector Options
The RA-100 is intended to drive loads of 4 or greater. There are two speaker connection output options for each channel: 1/4" mono phone jack, and push clip terminals (red = hot output, black = ground). Push connectors are the preferred choice for permanent installations. There is greater surface area contact than with phone connectors, thus promoting a better electrical connection between the speaker wire and amplifier. Phone jack connections are used for sound reinforcement or any situation when quick setup and breakdown are important. You are also less likely to accidentally reverse the wires if they are permanently connected to phone plugs.

Output Cables

Speaker cables must deliver large amounts of peak current to a speaker. To complicate matters further, a speaker represents an inductive load, and is more difficult to drive than a purely resistive load. Speakers are also very low impedance devices. Any resistance between the amp output and speakers will degrade the damping factor, efficiency and ultimately, the sound quality. Therefore, the cables you use between the RA-100 and its speakers are very 11
important. Alesis recommends stranded, rather than solid, cables for flexibility and ease of installation. However, solid cables are equally usable. Never use guitar cords as speaker cables. Because they lack sufficient currentcarrying capacity, the amp and speakers will not perform properly and the sound may be degraded. If you make your own cables use electrical zip cord, which is designed to handle several amps of current, or heavy-gauge speaker cables if possible/affordable. In any event, the thicker the cable, the lower the resistance and the better the current-carrying capability. Standard hookup wire is not acceptable; the minimum acceptable wire type is the common zip cord used to connect AC to appliances. The following table relates the wire gauge to the how many feet of cable is required at different impedances to produce a 1 dB power loss. The lower the resistance, the better. For cables run up to about 25 feet, 16 to 18 gauge wire is satisfactory. Cable length that produces 1 dB of power loss wire gauge 22 at 4 feet 30 at 4 meters 9 at 8 feet 60 at 8 meters 18

CHAPTER 3: USING THE RA-100

3.1 FRONT PANEL CONTROLS

The following diagram shows the various front panel controls, as described next.

Volume Controls

These regulate the input signal going into the RA-100. Always turn the volume controls all the way down (counterclockwise) when making input or output connections to the RA-100. Power should be off as well. Its also good practice to turn the volume controls all the way down when turning on power just in case a signal source feeding the RA-100 is live.

On-Off Switch

Press the upper half of this rocker-type switch to turn the amplifier on, and the lower half to turn the amplifier off. Upon turning on the amplifier, the green power indicator LED will light. Note that in direct sunlight, this light may not be easily visible. WHEN TURNING ON AND OFF THE GEAR IN A SYSTEM, IT IS IMPORTANT TO TURN ON THE POWER AMP LAST AND TURN IT OFF FIRST. Devices that are amplified by the RA-100 may generate thumps or other transients on power-up; if the RA-100 is on, these transients could be of sufficient amplitude to damage your speakers, especially if system levels were inadvertently set too high. Conversely, some units also create transients when turned off. For this reason, the RA-100 should always be turned off first. However, Alesis realizes that in many applications the RA-100 power switch will be left on and the RA-100, along with other gear, will be switched on by a master AC switch. As a result, there is a brief delay to allow other equipment in your system to settle down after receiving power. After this delay, during which the other units will have presumably made all the noises they were going to make, the RA-100 will be ready for operation. 14

Mute Switch

Because turning the RA-100 on and off generates no spikes within the amplifier, the power switch doubles as a mute switch or panic button. For example, if there is a serious feedback problem, you can simply turn off the RA-100, then chase down the source of the problem.

Clip Indicators

These improve on conventional clipping indicators by showing whenever any conditions occur that could lead to non-linearity, such as an extremely out-of-spec load (e.g., too many speakers connected in parallel or a short across the speaker terminals). Even if the problem occurs for only a few microseconds, a pulse-stretching circuit will allow the LED to light long enough for you to see that a problem is occurring. Because of the RA-100s ability to enter and exit clipping with as few audible artifacts as possible, you may not hear any distortion even if the indicator flashes. In general, a few flashes every now and then will not be a problem. However, if the LEDs flash often or remain on for any extended period of time, then turn down the volume controls to reduce the signal level going to the RA-100. If this doesnt solve the problem, check your output cables and speakers.

3.2 CHECKING FOR PROPER POLARITY
To check for correct speaker polarity, briefly connect the + terminal of a 1.5V battery to the speaker cables hot or + lead, and the batterys - terminal to the speaker cables cold, ground, or - lead. You will hear a pop from the loudspeaker as you connect the battery, and another as you disconnect it. Observe the direction of the speaker cone movement. If the speaker cables are wired in the common manner (and the speakers themselves are not mislabelled), the speaker cone will move forward (toward you) when you connect the battery and away from you when the battery is disconnected. If the speaker cone moves in the opposite direction, reverse the wires going to the speaker and re-test for proper polarity. Always check your speakers' polarity as not all manufacturers follow the same wiring convention.
3.3 CHOOSING THE CORRECT SPEAKERS
Near-field monitoring through reference speakers has become the preferred way to monitor and mix music. With near-field monitoring, small speakers are placed so that they are a few feet from the engineers ears. As a result, room acoustics become less important since the primary acoustic interaction involves direct sound from the speakers rather than reflected sounds from the room. Since few home and project studios have good acoustics, near-field monitors can provide realistic monitoring in a small space at relatively low levels. Near-field monitors offer other advantages compared to large studio speakers, including smaller size, lower cost, and easier transportability to other studios for reference purpose. Because of its moderate power rating, excellent fidelity, and lack of a noisegenerating fan, the RA-100 Reference Amplifier excels in driving reference near-field monitor speakers in smaller studios. However, you should choose speakers that can handle the power the RA-100 can generate. Speaker wattage ratings are often confusing, and standards by which ratings are obtained vary from manufacturer to manufacturer. If a speaker can handle 100 watts RMS continuous power, it should be able to handle the RA-100. However, under conditions of clipping or other abuse of the RA-100, damage to speakers is possible. For best results, use speakers designed for medium- to high-power applications.

3.4 ABOUT GROUND LOOPS

A hum or buzz may be introduced into some audio systems by a phenomenon known as a ground loop. This can occur if a piece of equipment sees two or more different paths to ground, as shown below. shielded cable Device A path 1 Device B
path 2 To AC power service
One path goes from device A to ground via the ground terminal of the threeconductor AC power cord, but A also sees a path to ground through the shielded cable and AC ground of device B. Because ground wires have a small amount of resistance, small amounts of current can flow through ground and generate a voltage along the cable shield. This signal may end up getting induced into the hot conductor. The loop can also act like an antenna into which hum is induced, or can even pick up radio frequencies. Furthermore, many components in a circuit connect to ground. If that ground is dirty and contains noise, it might get picked up by the circuit. Ground loops cause the most problems with highgain circuits, since massive amplification of even a couple millivolts of noise can give an audible signal. Most ground loop problems can be solved by plugging all equipment into the same grounded AC source. However, it is important to make sure that the AC source is not overloaded and is properly rated to handle the gear plugged into it. For really tough cases, you may need to break the connection that causes the loop condition. Although some do this by using a ground lifter and breaking the AC ground, THIS IS A DANGEROUS OPTION WHICH YOU SHOULD NOT USE because it sacrifices the safety factor the AC ground wire provides. In the previous diagram, a better option would be to interrupt the cable shield. There are two ways to do this: one is to simply break the shield at some point, usually by disconnecting it from ground at one jack. (The other end should remain connected so that the shielding properties are retained, even if there is no direct path for ground.) The other is to use a transformer as mentioned in section 2.4, Adapting the RA-100 to Balanced Lines, to provide isolation in the audio line between the two pieces of gear. Transformers generally have no ground connection between the input and output connections.
CHAPTER 4: TYPICAL APPLICATIONS

4.1 STUDIO MONITOR AMP

1622 Mixer

RA-100 in out out in

Monitor Outputs

Near-Field monitors

In the studio, the RA-100 is ideal for driving near-field or other reference speakers. In this example, an Alesis 1622 mixer feeds the RA-100, which provides power amplification. The RA-100 outputs feed a set of near-field monitor speakers.

4.2 SOUND REINFORCEMENT

For auditorium and live music use, the RA-100 has sufficient power to drive a set of small-to-medium size club speakers. The hookup diagram is the same as above, with an Alesis 1622 mixer feeding the RA-100, and the RA-100 driving the speakers. Biamplification often provides better live sound and greater efficiency by splitting the audio signal into two different channels. One channel drives a low frequency speaker system and the other, a high frequency speaker system. See Section 4.5.
4.3 KEYBOARD AMPLIFICATION SYSTEM

Quadraverb Outputs

Inputs

RA-100 in in

A stereo keyboard feeds the Alesis QuadraVerb, which provides reverberation and other signal processing effects. The QuadraVerb outputs feed the RA-100, which then drives a set of small-to-medium size club speakers. With multiple keyboard setups, you may need a mixer to combine the keyboard outputs into a single stereo feed. The Alesis 1622 Mixer is ideal for this type of application. The QuadraVerb can either process the 1622s outputs on the way to the power amp as shown, or be inserted into the 1622 and use the 1622s send/return effects capabilities. In this case, the 1622 master outputs would go directly into the RA-100. Remember that synthesizers require full-range speakers to accommodate the extremely low and high frequencies some keyboards can generate.
4.4 GUITAR AMPLIFICATION SYSTEM

MIDI Foot Pedal

Quadraverb GT MIDI In

RA-100 in

Outputs in

Speakers

Many guitarists now use rack mount, component systems for greater flexibility compared to all-in-one amps. In this system, a guitar goes through a QuadraVerb GT to provide distortion, chorusing, reverb, and other effects. Its outputs feed the RA-100, which then drives a set of small-tomedium size club speakers. Note that mono sound sources should plug into the right QuadraVerb GT input jack, as show in the diagram. An optional MIDI Program Change footswitch calls up different programs in the QuadraVerb GT.
4.5 BIAMP SOUND REINFORCEMENT

Low Frequency Speakers

Low Frequency Outputs

High Frequency Outputs

Ins Crossover High Frequency RA-100 in out out in
Ins High Frequency Drivers

Low Frequency RA-100

Biamplification splits a signal into two separate lines. One carries low frequency signals and the other carries high frequency signals. Each split feeds its own power amp and set of speakers. The main advantages of biamplification are greater efficiency and lower intermodulation distortion since low frequency speakers need not carry high frequencies (and high frequency speakers wont receive low frequencies). In this setup, an Alesis 1622 mixer feeds a crossover that generates the separate high and low frequency splits. The low frequencies go to one RA-100 which drives the low frequency speaker system; the other RA-100 handles the higher frequencies and drives a set of high frequency speakers.
CHAPTER 5: MAINTENANCE/SERVICE

5.1 GENERAL INFORMATION

Cleaning
Disconnect the AC cord, then use a damp cloth to clean the amplifiers metal and plastic surfaces. For heavy dirt, use a non-abrasive household cleaner such as Formula 409 or Fantastik. DO NOT SPRAY THE CLEANER DIRECTLY ONTO THE FRONT OF THE UNIT AS IT MAY DESTROY THE LUBRICANTS USED IN THE SWITCHES AND CONTROLS! Spray onto a cloth, then use the cloth to clean the unit.

Maintenance

Here are some tips for preventive maintenance. Do not remove the RA-100 top cover. There are no user serviceable parts inside. Refer servicing to a qualified repair technician. Periodically check the AC cord for signs of fraying or damage. If you use the push connector output terminals, check that the cables are securely in place and that no strands short to the chassis or any other terminal. Periodically rotate the volume controls (make sure power is off). In many applications the volume controls will be set to a particular point and not adjusted. Occasional rotation of the volume controls will minimize buildup of dust on the potentiometer wiper, thus minimizing scratchiness as the unit gets older. Place a dust cover over the RA-100 when it is not in use.
Refer All Servicing to Alesis
Alesis has spent a great deal of effort researching power amplifier reliability. We believe that the RA-100 is one of the most reliable amplifiers that can be made using current technology, and should provide years of trouble-free use. WARNING: The full AC line voltage, as well as high voltage/high current DC voltages, are present at several points within the chassis. Service on this product should be performed only by qualified technicians. THERE ARE NO USER-SERVICEABLE PARTS INSIDE.
CHAPTER 6: TROUBLESHOOTING

Begin the troubleshooting process by re-reading the manual to make sure you didnt miss some important point regarding the units operation. After that, try the following techniques for specific problems.
Turn down the volume controls. If the hum goes away, then the source of the hum is either in a unit feeding the RA-100, or in the input cables feeding the RA-100. Check your cables and other units. If the hum persists, there may be a ground loop. Follow the advice given in section 3.4. Also, check to see that the RA-100 is not situated near other devices with large external hum fields. If a loud hum continues, there may be a problem within the RA-100.

No Volume

Turn up the volume controls with no signal feeding the RA-100, and listen very carefully to the speakers. If you hear any hum or noise, no matter how low level, then the RA-100 is receiving power and the problem probably lies in the equipment or cables feeding the RA-100. If the speakers are absolutely dead and make no noise whatsoever, check the speaker cabling.
Distorted or Low Level Sound
If either of these problems occurs after the RA-100 has been on for a long time and running under a heavy load, it is possible that the output protection circuitry has kicked in. Let the unit rest for a minute by turning off the power and see if the problem goes away. If it does, check for thermal problems such as obstructed air flow around the unit. Bad cables can also cause distorted or low level soundyet another argument for using the best cables you can afford.
Thin Sound/Sound that Changes Unpredictably in a Room
This is generally the result of mismatched speaker polarity. Refer to section 3.2 for information on how to test for proper polarity. 23
CHAPTER 7: SPECIFICATIONS

 

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