This symbol indicates that dangerous voltage constituting a risk of electric shock is present within this unit.
This symbol indicates that there are important operating and maintenance instructions in the literature accompanying this unit.
WARNING: This product contains a chemical known to the State of California to cause cancer and birth defects or other reproductive harm.
WARNING: Voltages in this equipment are hazardous to life. No user-serviceable parts inside. Refer all servicing to qualified service personnel. The safety certifications do not apply when the operating voltage is changed from the factory setting.
The Shure Model SCM810/E is an eight-channel automatic microphone mixer designed for use in sound reinforcement, audio recording, and broadcast applications. The SCM810 dramatically improves audio quality in any application where multiple microphones are required. Any low-impedance dynamic or condenser microphone (including wireless) can be used with the SCM810/E. Multiple SCM810 mixers can be linked to other SCM810/E mixers, as well as to Shure Models FP410, SCM410 and SCM800 mixers.
Each input channel has a two-band equalizer and three logic terminals. The equalizer reduces unwanted low-frequency audio pickup and makes different microphone types-lavaliers, boundary and handheld-sound similar. The logic terminals can be used to control external devices. The SCM810 operates on 120 Vac power; the SCM810E operates on 230 Vac power. Each mixer is supplied with a power cord, rack-mounting hardware, and a link cable.
The operating concept behind the SCM810/E Automatic Mixer is Shure's proprietary IntelliMix® circuitry. IntelliMix delivers seamless automatic mixing by combining three separate functions:
① Microphone Channel Gain Controls 1 - 8:
|Allows adjustment of microphone gain.|
② Input LED 1 - 8:
|Lights green when channel is active; lights red at 6 dB below clipping level.|
③ Low-Cut Filter 1 - 8:
|Recessed screwdriver adjustment provides adjustable low-frequency rolloff (high pass) to reduce undesirable low-frequency signals.|
④ High-Frequency Shelving Filter 1 - 8:
|Provides level boost or cut in mid/high-frequency region to compensate for off-axis tone coloration, or for cutting high-frequency sibilance.|
⑤ AUX Level Control:
|Sets the input level for aux-level equipment connected to the adjacent 1/4-inch INPUT phone jack or rear-panel 1/4-inch AUX input.|
⑥ Aux INPUT 1/4-inch Phone Jack:
|Mixes external auxiliary- or line-level sources into output. This out is not automatic. Signal appears at output of all linked mixers.|
⑦ MASTER Level Control:
|Determines the overall mix level.|
⑧ Output Level Meter:
|Nine-segment LED meter indicates peak output signal level. Last LED indicates limiter action.|
⑨ PHONES Control and 1/4-inch Phone Jack:
|Permits monitoring of mixer output through headphones. The PHONES knob controls headphones output level.|
⑩ POWER LED:
|Lights green when unit is powered.|
⑪ AC Power Connector and Rocker Switch:
|Connector supplies AC power to unit when plugged into a power source: the rocker switch turns the unit on.|
⑫ Microphone Logic:
|DB-25 male connector interfaces with each channel's GATE OUT, MUTE IN, and OVERRIDE IN logic terminals. See the Suggested Logic Applications section. NOTE: THIS IS NOT AN RS-232 PORT.|
⑬ DIP Switch:
|The 7-position DIP switch provides setup options for the mixer (see DIP Switches section).|
⑭ LINK IN/OUT Jacks:
|Allow multiple mixers to be stacked for additional inputs. Up to 50 SCM810 mixers can be linked.|
⑮ LINE OUTPUT Removable Block Connector:
|Active balanced line-level signal for connection to amplifiers, recorders or other mixers. Output can be modified to microphone level (see Internal Modifications).|
⑯ DIRECT OUT 1/4-inch Phone Jacks:
|Provides non-gated aux-level signal from each channel. Direct outs are wired pre-fader and pre-EQ. Can be modified for use as a gated channel output, send/receive insert point, or external speech gate for mixing consoles (see Internal Modifications section).|
⑰ AUX/D.O./D.O. Switch:
|Located behind the Line Output connector, this switch selects either aux input function or direct output function for channel 8 Direct Out jack. Left switch position is AUX IN; center and right positions are DIRECT OUT.|
⑱ INPUT 1-8 Removable Block Connectors:
|Active balanced microphone- or line-level inputs.|
⑲ Input 1 - 8 MIC/PHM/LINE Switch:
|Located behind the removable block connector, this switch selects operation at either microphone- level (left), microphone-level with 48 V phantom power (center), or line-level (right) signals.|
The rear-panel DIP switch provides the following setup options. The positions shown in bold type are the factory settings.
NOTE: Switch positions and effects are shown in Figure 3 and also on the mixer label.
DIP SWITCH SW702 FUNCTIONS
|Switch Function||Manual/Auto||Last Mic, Lock-On||Hold Time||Off-Attenuation Level||Limiter Threshold||Link Local/Global|
|Switch Position Number||1||2||3||4||5,6||7|
|Switch Up||Auto||On||0.4 second||15 dB||5Up, 6 Up||=Limiter off||Global|
|5 Down, 6 Up||= +8 dBm|
|5 Up, 6 Down||= +16 dBm|
|5 Down, 6 Down||= +4 dBm|
|Switch Down||Manual||All mics off after hold time||1.0 second||∞ (completely off)||Local|
Manual/Auto: Automatic activation is defeated in the Manual position. In Manual mode, functions as a standard 8x1 mixer.
Last Mic Lock-On: Last Mic Lock-On feature keeps the most recently activated microphone turned on until a newly activated microphone takes its place. When defeated, microphones turn off after their preset hold time.
Hold Time: Adjusts the time an activated microphone (which is not locked on) remains on after the talker stops talking. Settings are 0.4 seconds or 1.0 second.
Off-Attenuation: Changes the off-attenuation level from 15 dB to infinity (∞). With the 15 dB setting, an unused microphone is 15 dB lower in level than when it is activated. With the ∞ setting, an unused microphone is completely off.
Limiter Threshold: Changes the output limiter threshold. Settings are OFF (factory setting), +16 dBm, +8 dBm, or +4 dBm (see Internal Modifications for other threshold settings).
Link Global/Local: Determines whether each linked SCM810 output contains only its own program output, or that of all linked mixers (see Mixer Linking for more information).
To mount the SCM810 in a standard 483 mm (19-inch) audio equipment rack, slide the mixer into the rack and secure it with the supplied Phillips head screws, as shown in Figure 4. Use all four screws.
Make audio connections as follows (see Figure 5).
The output limiter prevents distortion during loud program peaks without affecting normal program levels. This prevents overloading of the devices connected to the SCM810/E output.
Increasing the individual channel or Master Gain controls will increase the average output and, in turn, the amount of limiting. As supplied, the output limiter is defeated. However, you can change the limiter threshold so that the peak output level is +4, +8, or +16 dBm. Refer to the Internal Modifications section.
Low Cut Filter (High-Pass)
The low-cut (or high-pass) filter allows all frequencies above its cutoff point to pass from filter input to filter output without attenuation, while frequencies below the cutoff are attenuated (see Figure 6). The cutoff point is defined as the frequency where the signal has dropped 3 dB relative to the flat, or bandpass, region. Below the cutoff point, the filter exhibits increasingly more attenuation as the frequency diminishes. The rate at which this attenuation occurs is defined in decibels per octave (dB/oct). The SCM810 has a one-pole, low-cut (high-pass) filter of 6 dB per octave.
Low-cut filters are ideally used for attenuating, or rolling off, the audio signal where extraneous noise, excessive proximity effect, or other unwanted material is present. For example, the low-frequency vibration cause by footsteps and vehicle traffic can be transmitted through microphone stands to the microphone, and then into the sound system. These frequencies, typically ranging from 5 to 80 Hz, are generally not desirable.
The fixed-frequency equalizer produces a 6 dB boost or cut at 5 kHz and above (see Figure 7). High-frequency shelving is extremely useful for boosting flat frequency response, tempering very sibilant vocal microphones, or enhancing the sound of off-axis lavalier microphones.
When setting up a sound system which has an outboard equalizer or feedback controller in the signal chain, set the SCM810 to MANUAL. This activates all microphone inputs, so every possible feedback path is open. With the SCM810 in MANUAL mode, equalize the sound system and/or “Ring Out” the room to set the feedback controller.
After equalizing the sound system, set the SCM810 to AUTOMATIC mode. Remember that the input of an automatic mixer drops by 3 dB every time the number activated inputs doubles. When using an SCM810 in MANUAL mode, the master output drops by 9 dB when all 8 inputs are activated. Conversely, it will rise by 9 dB when switched back to AUTOMATIC mode.
NOTE: The SCM810/E mixer is fully automatic. For most applications, no additional adjustments are required.
If additional inputs are needed, more SCM810 mixers (as many as 50) can be “linked” using supplied link cables. Such a configuration can provide up to 400 microphone inputs.
To link multiple mixers, connect the LINK OUT of the first mixer to the LINK IN of the next mixer, and so on (see Figure 8). Leave the LINK IN jack of the first mixer and the LINK OUT jack of the last mixer unconnected.
As long as the link jacks of all mixers are connected (out-to-in, sequentially, leaving one Link In and one Link Out jack unconnected), the automatic mixing functions will be shared by all units. All input signals appear at all linked mixer outputs. There is no master/slave relationship.
The output controls and functions of each linked mixer are post-link and do not affect the signals appearing at other linked mixer outputs. Each mixer's Master level control only controls its own output. Each output can be used independently.
NOTE: The actual off-attenuation in the 15 dB switch position increases as more mixers are linked. This reduces excessive noise and reverberation contributed by the increased number of attenuated microphones. In a linked system, the Aux input of any mixer appears at each linked mixer's output. See Internal Modifications to defeat the linking of Aux signals.
IMPORTANT: When using the logic terminals on linked mixers, connect the LOGIC GROUND terminals of each unit together. Switching clicks may result if this is not done.
The Global/Local switch selects which input channels appear at that linked mixer's output. Set to the Global position, all input channels appear at that mixer's output. Set to the Local position, only its own eight input channels appear at that mixer's output. The Master level control, in any mode, only controls the level of its own output.
The Master level control is independent of the Global/Local switch. The output level of each mixer is affected only by its own Master control. All automatic functions (such as Last Mic Lock-on and MaxBus) are connected on all linked mixers and are not affected by the Global/Local switch.
An example of the possibilities of this setup is shown in Figure 9 Here two SCM810s are set to Local, and the resulting sound distribution provides local sound reinforcement while avoiding feedback. This is a simple “mix-minus” setup. The third SCM810 is set to Global and feeds a tape recorder, At the same time, the automatic functions (Last Mic Lock-On, etc.) remain common to all mixers. The following table summarizes the mixer settings.
|MIXER||Link Global / Local Switch||Audio Output Contains...|
|C||Global||A, B, C|
Additional link cables are available as Shure Part No. 95A1143 (305 mm-12 in.). Longer cables in a variety of lengths are available from Apple Computer as computer printer connections; they are variously referred to by Apple as “shielded serial cable with two mini DIN-8 connectors,” and “Apple System Peripheral-8 Cable.”
Knob, Channel Gain and Phones (white)
Knob, Channel Gain (blue)
Line (Power) Cord (SCM800)
Line (Power) Cord (SCM810E)
(typical, controls full clockwise)
|Low Impedance Mic (150 Ω)||80 dB||88 dB||34 dB|
|Line||40 dB||48 dB||-6 dB|
|Aux||44 dB kΩ||52 dB||-|
|Send/Return||20 dB||28 dB||-|
|Designed for use with||Typical||Output Clipping Level|
|Mic||19-600 Ω||1.6 kΩ||-15 dBV|
|Line||≤2 kΩ||10 kΩ||+22 dBV|
|Aux||≤2 kΩ||10 kΩ||+22 dBV|
|Send/Return||≤2 kΩ||10 kΩ||+18 dBV|
|Designed for use with||Typical||Output Clipping Level|
|Line||>600 Ω||60 Ω||+18 dBV|
|Headphone||8-200 Ω, 60 Ω recommended||300 Ω||+12 dBV|
|Direct Output||>2 kΩ||1 kΩ||+18 dBV|
|Send/Return||>2 kΩ||1 kΩ||+18 dBV|
<0.1%at +18 dBVoutput level, 50 Hz to 20 kHz(through 20 Hz-20 kHz filter); Input 1 and Master at 5, all other controls full counterclockwise)
|Equivalent Input Noise||-125 dBV(150 Ω source; through 400 Hz-20 kHz filter)|
|Equivalent Input Hum and Noise||-123 dBV(150 Ω source; through 20 Hz-20 kHz filter)|
|Output Hum and Noise||through 20 Hz-20 kHz filter; channel controls full counterclockwise|
|Master full counterclockwise||-90 dBV|
|Master full clockwise||-70 dBV|
>70 dB at 1 kHz
Mic/Line, Send inputs to all outputs are non-inverting; Aux input to all outputs is inverting
|HoldTime||0.4 ms (Switchable to 1.0 s)|
15 dB (switchable to∞)
Shorting outputs, even for prolonged periods, causes no damage. Microphone inputs are not damaged by signals up to 3 V; Lines and Monitor inputs by signals up to 20 V
|Low-frequency||6 dB/octavecut, adjustable corner from 25 to 320 Hz|
|High-Frequency||±6 dBat 5 kHz, ±8 dBat 10 kHz, shelvingat 5|
|Threshold||Switchable: off, +4, +8, +16 ( dBm at output)|
|Indicator||Lights red when limiting occurs|
Green on channel activation, red at 6 dBbelow clipping
46 V DC open-circuit through 6.8 k Ω series resistance per DIN 45 596
|SCM810||120 V ACratednominal, 50/60 Hz, 200 mA|
|SCM810E||230 V ACratednominal, 50/60 Hz, 100 mA|
|Operating Temperature||0° to 60° C (32° to140° F)|
|Storage Temperature||-30° to 70° C (-20° to165° F)|
44.5 mm H x 483 mm W 317 mm D (1¾ x 19 x 12½ in.)
4.3 kg (9 lb., 9 oz.)
For additional service or parts information, please contact Shure's Service department at 1-800-516-2525. Outside the United States, please contact your authorized Shure Service Center.
SCM810: Listed by Underwriters Laboratories, Inc.; cUL Certified (Canada). SCM810E: Conforms to European Union Directives; Certified to EN60065; Eligible to bear CE Marking; Conforms to European EMC Directive 2004/108/EC; Meets Harmonized Standards EN55103-1:1996 and EN55103-2:1996 for residential (E1) and light industrial (E2) environments.
This product meets the Essential Requirements of all relevant European directives and is eligible for CE marking.
The CE Declaration of Conformity can be obtained from: www.shure.com/europe/compliance
Authorized European representative:
Shure Europe GmbH
Headquarters Europe, Middle East & Africa
Department: EMEA Approval
75031 Eppingen, Germany
Phone: +49-7262-92 49 0
Fax: +49-7262-92 49 11 4
The SCM810's Advanced Functions are recommended only for those who are technically knowledgeable and familiar with audio electronics.
The logic functions of the SCM810 expand the mixer's range of installation and control options. Logic can be used for everything from simple cough switches to elaborate computer-controlled room systems. (Shure's AMS Update publication contains additional applications of advanced logic. This publication is available by contacting Shure's Applications Group.) The following logic functions are available for each channel:
GATE OUT: Follows channel gating and goes to logic “low” (sinks current) when microphone is gated on. 500 mA of current sinking ability is provided (see Figure 10A).
MUTE IN: Applying logic “low” (from GATE OUT or a switch closure to logic ground) gates channel off (see Figure 10B). Channel output drops to -.
OVERRIDE IN: Applying logic “low” (from GATE OUT or a switch closure to logic ground) forces channel on (see Figure 10B). Factory setting provides that when both Mute and Override are activated, Mute takes precedence (see Internal Modifications for Override precedence).
LOGIC GROUND: Logic ground is distinct from the SCM810 audio ground. Make all logic ground connections to this pin, including power supply ground of external logic circuitry. To avoid switching clicks, do not connect logic ground to audio, chassis or rack grounds. Logic controls are accessed at the DB-25 multi-pin connector on the rear panel (Figure 11). The pin connections are given in the following table.
|Logic Function||Input Channel||Connector Pin No|
|GATE OUT1 GATE OUT 2 GATE OUT 3 GATE OUT 4 GATE OUT 5 GATE OUT 6 GATE OUT 7 GATE OUT 8||12345678||1 15 4 18 7 21 10 24|
|OVERRIDE IN 1 OVERRIDE IN 2 OVERRIDE IN 3 OVERRIDE IN 4 OVERRIDE IN 5 OVERRIDE IN 6 OVERRIDE IN 7 OVERRIDE IN 8||12345678||14 3 17 6 20 9 23 12|
|MUTE IN 1 MUTE IN 2 MUTE IN 3 MUTE IN 4 MUTE IN 5 MUTE IN 6 MUTE IN 7 MUTE IN 8||12345678||2 16 5 19 8 22 11 25|
This section contains suggestions on the uses of the SCM810's logic capabilities. Note that uses of these functions are not limited to the listed applications. The user is limited only by individual imagination and creativity. For additional suggestions and solutions to installation problems, contact Shure's Applications Group.
In the following paragraphs, the wiring diagrams refer to the DB-25 connector pins shown in Figure 4.
The talker can turn off his or her microphone during coughing or private conversations by installing an SPST pushbutton switch between the MUTE IN and Logic Ground pins for each channel to be modified (see Figure 12- Channels 1, 2 and 3 modified). When a channel is muted, no audio is passed. (See “Dead Zone on MUTE IN Defeat” in Internal Modifications section for more information on MUTE IN logic).
The chairperson can, by activating a switch, silence all other microphones and be heard without interruption. For operation in this mode, connect all the MUTE IN pins together except that of the chairperson's channel, and wire an SPST pushbutton or toggle switch between those MUTE IN and Logic Ground pins (see Figure 13-the chairperson is shown as Channel 1). An alternative to a switch is to connect the chairperson's GATE OUT to the MUTE IN of other channels. When the chairperson's microphone activates, all other microphones mute.
Remote Channel-On Indicators
Remote indicators can be used to indicate when a talker's microphone is on. Connect the LEDs and a 5-volt supply to the GATE OUT pins as shown in Figure 14 (Channels 1, 2 and 3 shown modified). To avoid switching clicks in the audio output, do not ground the power supply negative terminal in the audio system or rack ground.
IMPORTANT: If a single cable is used for the microphone audio signal and the LED dc power, separate shielded pairs must be used. Failure to carry the dc power on a shielded pair may result in audible clicking due to capacitive coupling between the dc power lines and microphone lines.
Disabling the Gating Function (Bypass)
To keep certain microphones on at all times, wire the desired microphone channel's OVERRIDE IN pins together to the Logic Ground pin. The selected channels now function as they would in a non-automatic mixer (see Figure 15-Channels 1, 2 and 3 modified).
Inhibiting Gating for Unwanted Sounds
As described in the Operating Principles section, MaxBus attempts to activate only one microphone per sound source. Muting a microphone channel prevents its audio from appearing at the mixer's output. However, the muted microphone still communicates with other mic channels via MaxBus. A sound source picked up by a muted microphone will not activate other microphones.
Sound sources that may cause unwanted microphone channel activation include:
The SCM810 can prevent these and similar sounds from activating microphones by taking the following steps.
-or-connect the unwanted sound source directly into a Mic/Line channel input.
Some applications require a loudspeaker to be placed near each talker to provide audio reinforcement, or to permit telephone conversation or conference monitoring. Each loudspeaker can cause feedback unless it is automatically switched off when the talker near it speaks. To provide this function, connect the GATE OUT terminal of each channel to a separate loudspeaker muting relay as shown in Figure 17 (Channels 1, 3 and 5 shown modified). Recommended relays are Omron G6B-1174P-US-DC12, Potter & Brumfield R10-E1Y2-V185, or equivalent (available through Digi-Key and Newark Electronics).
NOTE: A diode across each relay coil is required to suppress inductive voltage spikes which may damage the SCM810.
An existing sound system using 24-volt relays can be used with the SCM810 without modification if the relay coil current draw is under 500 mA.
In normal operation, when several people talk, each microphone gates on so that no speech is missed. In “filibuster” action, a microphone that is gated on prevents other microphones from gating on. Once a microphone has gated on, other microphones cannot gate on until the talker has paused long enough for that microphone to gate off. Thus the person talking has the floor and cannot be interrupted.
To establish this function, first perform the internal Mute to “Inhibit” modification (see Internal Modifications). Then connect all the MUTE IN pins of the modified channels together, all the GATE OUT pins of the modified channels together, and the GATE OUT pin of one modified channel to the MUTE IN pin of another modified channel (see Figure 18- Channels 1, 2 and 3 modified). Turn the Last Mic Lock-On switch (SW702, position 2) to off.
NOTE: To prevent high-frequency oscillation, do not wire a channel's GATE OUT pin to its own MUTE IN pin unless the Mute to “Inhibit” change has been made.
See Internal Modifications.
Diode Isolation of Logic Controls
Two or more control functions using the same logic pins can be isolated with diodes. In this manner a channel can be muted by an overall group mute switch, or by its own cough button (see Figure 19-Channels 1, 3 and 5 modified).
External Logic Devices
SCM810 logic levels are directly compatible with TTL and 5-volt CMOS logic families. For information on logic gate use, refer to the TTL Cookbook and CMOS Cookbook, both by D. Lancaster, Howard Sams Publishing Co.
Mixer logic may be used with 15-volt CMOS logic if a pull-up resistor is used with each GATE output (see Figure 20-Channel 1 modified).
Digital Controls or Microcomputers
The SCM810 logic pins can interface with custom-designed digital control circuitry or microcomputers for unlimited possibilities of system control functions.
NOTE: Remove AC power before opening the unit.
WARNING: All modifications must be performed by qualified service technicians.
This section describes SCM810 modifications that can be made using solder “jumpers” on the printed circuit board; the pads where jumpers may be used are placed close together so that a single solder drop functions as a jumper. Note too that:
To gain access to the main printed circuit board, remove the 8 Phillips head screws securing the top cover, and remove the top cover. Most modifications can be made from the top of the main board.
Short jumper X901. Remove resistors R900 and R909.
The Master gain control can be disabled so it cannot be tampered with. The following table indicates the resistor value to be used for the desired gain.
|Master Section Gain||Resistance|
|-6 dB||5.1 kΩ|
|6 dB||20 kΩ|
Remove resistor R9230. Install new resistor at jumper X914.
All three threshold settings (+16, +8 and +4 dBm) can be changed. To shift the threshold down by 6 dB, resistor Rwill be 82 kΩ. To shift the limiter thresholds up by 6 dB, R will be 330 kΩ.
Remove resistors R9177 and R9180. Install new resistor R at jumper X907.
With linked mixers, the Aux input from a modified mixer does not link.
Remove resistor R9024.
A channel's Direct Out phone jacks can be changed from pre- to post-fader.
Short jumper X106. Remove resistor R1011.
Changes a channel's 1/4-inch Direct Out jack to a post-fader insert point. Send is tip of phone jack; return is ring. Insert jacks are useful for inserting line-level signal processors into a channel. For instance, a parametric EQ or compressor/limiter can be inserted into a channel for additional processing.
Short jumpers X101, X102, X105 and X106. Remove resistors R1011 and R1020.
This post-fader, post-EQ channel output is gated, but without NOMA. In this mode, if the Local/Global switch is in “Local”, a manual mix of channel inputs is present at the Line output. The Off-Attenuation level of the Gated Direct Out signal is infinite.
Short jumpers X104 and X906 (in Master section). Remove resistor R1011.
The SCM810 can be used in conjunction with large mixing consoles to provide automatic mixing for talk shows, panel discussions, and news shows. Large consoles have channel insert jacks so that external signal processing devices can be patched into individual channel signal paths. With this modification the SCM810 can be placed into unbalanced insert jacks, and the SCM810 used as a high-quality, external, 8-channel speech gate. This arrangement allows the operator complete control of each channel via the console's input control strip, while the SCM810 keeps the number of open microphones to a minimum.
In this operational mode:
Short jumpers X103, X107, X108 and X906 (in the Master section). Remove resistors R1011, R1019, and R1020.
With this modification and when both MUTE IN and OVERRIDE IN logic are grounded for a channel, the Override mode will take precedence (as supplied, the MUTE IN takes precedence over OVERRIDE IN).
Short jumper X114. Remove resistor R1046.
As supplied, MUTE IN is intended for use as a momentary cough button or privacy function (mute when necessary). However, if the MUTE IN is intended to be used so that the talker must unmute microphones to enable speech pickup (unmute when needed), this modification is needed. This removes the muted channel from the MaxBus which eliminates “dead zones.” A dead zone is an area in which a microphone picks up a talker through a muted microphone and other microphones do not activate for that talker.
Short jumper X115.
As supplied, a channel will mute when its MUTE IN terminal is grounded. The mute function can be changed to “Inhibit” by an internal modification for each channel. After the modification, a logic “Low” at the MUTE IN terminal prevents that channel from gating on if it is off, but allows it to remain on if it is already on. IMPORTANT: To prevent high-frequency oscillation, never connect a channel's GATE OUT to its own MUTE IN unless the “Inhibit” modification has been made.
Short jumper X111..
This modification should only be performed with the Change MUTE IN to Inhibit modification described above.
Short jumper X113. Remove resistors R1046 and R1058.
This modification changes the off-attenuation level from -15 dB to a selected value. Select from the following resistor values.
|Master Section Gain||Resistance|
|10 dB||18 kΩ|
|20 dB||50 kΩ|
|30 dB||150 kΩ|
Remove resistors R9088 and R9145. Install new resistor at jumper points X904 and X908.
In addition to the dip switch SW702 options of 0.4- and 1.0-second hold time, the hold time can be increased to 1.5 seconds. (More than 1.5 seconds is not recommended.)
Install a 470 kΩ resistor across jumper points X902. Move DIP switch down to 1.0-second position.
The hold time can be decreased from the factory preset of 0.4 seconds to 0.3 seconds. (Less than 0.3 seconds is not recommended.)
Install a 2 MΩ resistor at jumpers X903.
If desired, these functions can each be remotely controlled with an SPST switch.