Audio-Technica SMARTMIXER AT-MX351 User Manual

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Adjusting ”Off” Attenuation
In instances when the number of microphones in use is high, it may be necessary to increase 
the amount of “off ” attenuation per microphone to keep the total ambient noise level low. 
There are “off ” attenuation adjustments inside the unit. To adjust the “off ” attenuation of 
channel 1, unplug the unit, remove the top cover and locate the trimpot designated on the  
circuit board by “VR3” (Figs. 4 and 5, page 11). It is factory set at approximately 8 dB, the 
attenuation at the middle of the control’s rotation. When the control is turned fully counter-
clockwise, “off ” attenuation is approximately 20 dB. Conversely, when the adjustment is 
turned fully clockwise, “off ” attenuation is approximately 6 dB. VR6, VR9 and VR12 control 
“off ” attenuation for channels 2, 3 and 4 respectively.
Changing the settings of the switches designated on the circuit board by “SW5,” “SW11,” 
“SW17” and SW23” will extend the range of “off ” attenuation to –40 dB for channels 1, 2, 3  
and 4 respectively.
Preamp Outputs
Each microphone channel has an independent unbalanced preamp output that is separate 
from the main mixer output. This is helpful when it is necessary to record the output of each 
channel, whether or not it is the active mixer output (as is required, for example, in some 
courtroom proceedings). As set at the factory, no gating is applied to these outputs. To gate 
these outputs, unplug the unit, remove the top cover and locate the switches designated on  
the circuit board by “SW6,” “SW12,” “SW18” and SW24” (Figs. 4 and 5, page 11). Change the 
switch position(s) to “Gating” for channels 1, 2, 3 and/or 4 respectively, as desired.
Input Limiters
Independent, adjustable limiters are available on all mic channels. To adjust the limiter 
threshold of channel 1, unplug the unit, remove the top cover and locate the trimpot designated 
on the circuit board by “VR2” (Figs. 4 and 5, page 11). It is factory set at approximately 0 dB 
RMS. When the control is turned fully counter-clockwise, limiter threshold is approximately  
–10 dB RMS. Conversely, when the adjustment is turned fully clockwise, limiter threshold  
is approximately +10 dB RMS. VR5, VR8 and VR11 adjust limiter threshold for channels 2, 3 
and 4 respectively.
Changing the settings of the switches designated on the circuit board by “SW4,” “SW10,” 
“SW16” and SW22” will turn off the threshold-limiting function on channels 1, 2, 3 and 4 
respectively.
Force-on/Force-off
To activate force-on/force-off, install a closure between the appropriate pin and Ground 
Reference on the External Control connector on back of unit.
12
External Control Connector Pinout
Pin 1 
Channel 1 force off 
Pin 8 
Channel 4 force on
Pin 2 
Channel 2 force off 
Pin 9 
Channel 1 TTL out
Pin 3 
Channel 3 force off 
Pin 10 
Channel 2 TTL out
Pin 4 
Channel 4 force off 
Pin 13 
Ground reference
Pin 5 
Channel 1 force on 
Pin 14 
Channel 3 TTL out
Pin 6 
Channel 2 force on 
Pin 15 
Channel 4 TTL out
Pin 7 
Channel 3 force on