MPA-‐2 Operating Manual Ver. 1.2 2016
9
General Unit Operation
The operation of the MPA-2 Microphone Preamplifier is fairly straightforward. Both
channel A and Channel B are identical in operation.
All controls and adjustments are done on the front panel. Gain control is accomplished
by means of a front panel rotary encoder that adjusts the gain from 20dB to 70dB in
2dB steps. The gain setting is displayed on the dual 7 segment front panel LED.
All front panel controls are handled via a microcontroller that handles all functions on
the main audio board as well as the display and switch functions on the front panel.
Once you power up the MPA-2 the unit will stay in mute for 10 seconds to allow the
unit to stabilize. The unit will also mute for one second when you switch in any of the
options such as +48V, Pad, LoZ, Polarity. This is to avoid any loud popping on the
output. The same is true when you switch out any of the options, the unit will again
mute for one second.
All the front panel power supply LED’s should be illuminated. If one if the LED’s are out
contact the factory as the unit may require service.
All pushbutton functions will illuminate the pushbutton to an on state. Once the function
is no longer enabled the pushbutton LED will extinguish. All LED’s have a small standby
current applied so they will appear very dim but never totally go out. The Mute
pushbutton will flash while the unit is booting up at startup.
It will take at least 20 minutes for the MPA-2 to fully come up to operating
temperature. At that time all output offset voltages as well as the internal servos will
have had enough time to settle.
The front panel LED meters read the MPA-2 output as it relates to balanced operation.
The peak LED is factory set to come on at +24dBu (Balanced out). There is a 2 second
hold on this LED. VU meters have a damped response for average level.
The MPA-2 uses a 2 dB step for gain change. *Because this is a step gain control
there will always be a small step click when changing gain.
The front panel optical encoder controls will rotate without hitting a stop. Once you
reach the full 70dB gain spinning the encoder will not increment the display any longer.
The same holds true for the minimum gain setting.
There are no internal user adjustments or settings.
For unbalanced operation follow the instructions on the rear panel. DO NOT GROUND
PIN 3. FLOAT THIS PIN FOR UNBALANCED OPERATION. USE PIN 2 AS THE OUTPUT.
Recall last front panel settings. If the unit loses power the MPA-2 will power back up
and retain the last known setup on the front panel. This includes gain setting and all
front panel switch settings.
