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BMX SERIES III CONSOLE
The -10 dBu output of U602B is routed to the bandpass filter circuit and to filter in/out switch S601A.
The highpass filter is a three-pole, 18 dB/octave design, using U603B and its related components. The
output of the highpass filter is applied to a lowpass filter, also a three-pole design, using U603A and
associated parts. The 3 dB points of the resulting bandpass filter are slightly below 300 Hz and slightly
above 3400 Hz. The output of the filter is connected to filter in/out switch S601A.
The signal, as chosen by the filter in/out switch, is connected to output amplifiers U604A and U604B.
The first stage operates at a gain of 4 dB and the second, inverting stage, at unity. The input to output
gain of the push-pull pair is 10 dB, resulting in an output level of 0 dBu.
4.9 SEND AND RETURN MODULE
4.9.1 Function
The Send and Return Module contains both the two Send amplifiers and the stereo Return circuits. The
Send portion of the module contains the mixing and output amplifiers for the effects/foldback channels.
The Return signal may be assigned to the PROGRAM, AUDITION or UTILITY output buses.
4.9.2 Circuitry
SEND AUDIO
NOTE: The two Send output circuits are identical, thus only Send-1 is described.
The Send-1 bus signal is summed and inverted by amplifiers U101A and U101B, which are operating
at unity gain. The output of U101B is routed through Send on/off relay K100 and the front panel SEND–
1 master fader to balanced line output amplifiers U102A and U102B. Amplifier U102A operates with
a gain of 22 dB while inverting amplifier U102B operates at unity. Therefore, the total voltage gain
from input to balanced output of the line amplifiers is 28 dB. This gain provides a master fader "in-
hand" attenuation of 10 dB for an output level of +4 dBu.
The output of U101B is also connected to solo relay K1A. When energized, this relay routes the pre-
fader signal to both of the stereo SOLO buses via resistors R321 and R421.
SEND LOGIC
NOTE: The logic circuitry for the two Send circuits are essentially identical. For clarity and simplicity,
only the circuitry for Send-1 is described below.
Pressing the Send ON button will pull down the input to inverter U3B, which will deliver a high output
to S1A and the input of U8C. If S1A is as shown, pin 2 closed to pin 4, the high output from U3B will
be applied to the input of U6D. Each time the ON button is pressed, bistable U5A will be toggled by
the positive-going signal applied to its input, and its output will change state. The output of bistable
U5A is connected to one input of gate U4A. A high at any input to this device will cause a high at its
output. This high is applied through inverter U7B to ON lamp drive transistor Q3, and to transistor Q2
PACIFIC RESEARCH & ENGINEERING
REVISION C
78
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