REVISION C
BMX SERIES III CONSOLE
67
PACIFIC RESEARCH & ENGINEERING
4.2 MICROPHONE INPUT MODULES
This section describes the function and circuitry of the Microphone Input Module (PR&E #99-262) and
the Microphone Input Module With Sends (PR&E #99-252). See Chapter 7 for the module schematics.
4.2.1 Function
Both versions of the Microphone Input Module accommodate a wide range of input levels, permitting
the use of all contemporary microphones. Phantom powering for condenser microphones on both A and
B inputs is built into each Mic module (see Section 5.1 for details). Individual A and B input preamp
gain trimpots allow the module to handle nominal input levels from -60 dBu to -35 dBu.
The A/B input selector provides two microphone inputs per module, each with programmable monitor
mute selection for Control Room, Studio-1 or Studio-2. The mute circuitry incorporates an automatic
40 millisecond delay before the microphone is turned on, permitting “room reverb” to decay off-mic.
The PAN control allows for positioning of the microphone signal within the stereo sound field, and the
alternate action PGM, AUD and UTL buttons allow the module to be assigned to any or all of the console
stereo output buses.
4.2.2 Circuitry
NOTE: Except for the presence or absence of the Send circuitry, the two Microphone Input Modules
function identically. The additional Send circuitry is described at the end of the audio and logic circuit
descriptions.
AUDIO
Transformer-coupled microphone input preamplifier U1 utilizes variable feedback control to provide
an overall voltage gain range of 24 dB to 50 dB. Gain trim controls R9 and R10 adjust the preamplifier
gain for the A and B inputs respectively. The gain is adjusted to provide a nominal -10 dBu level to the
Patch Output. The Patch Input is buffered by balanced differential amplifier U2 operating at unity gain.
This amplifier provides input common mode noise isolation and signal drive to the mix fader, Cue relay
K3, and Talkback relays K4 and K5.
The mix fader “in-hand” attenuation is 15 dB, which is recovered by fader buffer amplifier U3 to the
–10 dBu internal system level. The output of U3 is routed to the pan pot and the pan INsert switch. The
left and right outputs of the pan circuit are buffered and amplified 3 dB by dual amplifier U4, and routed
to channel on/off relay K1, and Solo relay K6. The channel on/off relay routes the signal to the output
bus assignment button switches.
With Sends
PRE/post fader Send switch S5 gets its pre-fader input from balanced differential amplifier U2, and its
post-fader input from dual amplifier U4. The outputs of the Send PRE/post switch are controlled by dual