REVISION C
BMX SERIES III CONSOLE
79
PACIFIC RESEARCH & ENGINEERING
to drive Send on/off relay K100. The output of U4A also drives inverter U7C, which activates Send-
1 ON Tally transistors Q4 and Q5.
Note that the circuit, as described, is an alternate-action system in which the Send is switched on when
the ON button is pressed, and is switched off when the ON button is pressed again. If switch S1A is
set to connect pin 2 to pin 3, the bistable is removed from the circuit. Under this condition the Send
will be switched on only while the ON button is held down. The remote ON function operates in a
similar manner, using U3D as an input buffer and S1B to determine the choice between alternate action
and momentary control.
The SOLO function operates in a similar manner except that the switching is always alternate-action.
The input buffering is done by U3F and the toggling by U9A. The output of U9A at pin 2 is applied
to SOLO lamp driver Q1. The output of U9A pin 1 operates SOLO relay K1. The output of U9A pin
1 also drives OR gate U4C. Any logic high at the input to this gate results in a high output, which pulls
down the SOLO BUS via transistor Q6. Operating the SOLO button again will toggle bistable U9A
to turn off the SOLO mode. If a local or remote Send ON button is pressed, a high will be delivered
to one of the inputs of U8C. Either of these highs will cause a high on the output of U8C, which will
reset the SOLO bistable to the “off” condition.
RETURN AUDIO
NOTE: The stereo return circuits consist of two identical sets of circuitry. For clarity and simplicity,
only the left channel is described below.
The input signal is buffered by balanced differential amplifier U300B, operating with a gain of -8 dB.
The output of U300B is routed through the front panel INPUT MODE switch, MIX level control, and
buffer to the PAN control and pan insert switch. The output of the pan circuitry is buffered by U302B,
and then connected to channel on/off relay K300 and SOLO relay K301. The output of channel relay
K300 is connected to the stereo mix bus assignment buttons, while the output of SOLO relay K301 is
routed through resistor R320 to the SOLO LEFT BUS terminal.
RETURN LOGIC
Pressing the local RETURN ON button causes the output of U10F to go high. This high is connected
through gate U6A to the input of bistable U12A, which causes the bistable to toggle. The output of
U12A pin 1 will go high. This high is inverted by U7F to operate the remote “on” lamp via Q14 and
Q15, inverted by U10E to energize ON relay K300 and the ON tally via Q13, and routed through gate
U11B to turn off remote “off” tally drive circuit Q16 and Q17. Pressing the ON button again toggles
U12A, causing pin 1 to go low and drive remote “off” lamp drive circuit U11B, Q16 and Q17. The
additional circuitry around remote tally drive circuits is for short-circuit protection on the external lines.
Unlike the module’s controls, the remote controls are not alternate action, but are independent “on” and
“off” controls. Pressing a remote ON button causes a high output from U10B, which is routed to U11C.
If U12A is in the off state (pin 2 high), then U11C will deliver a high at its output. This will toggle
U12A via U6A. Pressing the remote ON button again causes no further action because U11C pin 10