BMX SERIES III CONSOLE
REVISION B
213
PACIFIC RESEARCH & ENGINEERING
NOTE: When the mic module is turned OFF, there is a one-second delay in the cassette machine toggling
from the record mode to the pause mode. This allows for the recording of the voice-to-music transition.
Another method of connecting the cassette skimmer is to connect it to the Control Room Monitor Module.
When this is accomplished, the tape machine will be placed in record whenever the Control Room speakers
mute.
For a schematic of this interface, see Section 8.6.
CIRCUITRY
Power is applied to the interface through input connectors J1 through J4 and diodes CR2, CR4, CR6 and
CR8. This arrangement allows any or all of the four inputs to be used. The ON TALLY voltage is routed
through diodes CR1, CR3, CR5 and CR7 to the “fast attack/slow release” circuit comprised of R1, R2,
CR9, R3 and C5.
When ON TALLY voltage is applied, C5 is charged quickly through CR9 and R3. When ON TALLY
voltage is removed, C5 is discharged slowly through R2 and R1. Schmidt inverter squares up and inverts
this signal and sends it to monostables that generate the PLAY and PAUSE pulses for each cassette
recorder. U2 generates pulses for Cassette 1 and U5 generates pulses for Cassette 2.
U2A and U5A are configured to trigger on the “falling edge” of the inverted ON TALLY voltage, which
indicates the beginning of cassette skimming and cassette RECORD. U2B and U5B are configured to
trigger on the “rising edge” of the inverted ON TALLY voltage, which causes the cassette to PAUSE.
Grounding the SKIM DISABLE input on J5 disables the PLAY and PAUSE pulses for Cassette 1, and
grounding the SKIM DISABLE input on J7 disables these pulses for Cassette 2.
Each of the four monostables generates a 0.1 second pulse governed by the time constant of C7/R6, C8/
R9, C10/R14 and C11/R17. Each monostable is connected to an opto-isolator to eliminate any audio or
logic ground loops. Opto-isolators U3, U4, U6 and U7 are driven by transistors Q1, Q2, Q3 and Q4.