Instruction manual

AMS-1027 AMPLIFIED SPEAKER STATION
3-3
rise, which decreases the audio level of the VCA. For the standard
volume/balance configuration, the right hand control board is plugged into J18.
To implement the optional A volume/B volume configuration, the right hand
control board is plugged into J16. For instructions, see “Vol/Bal to A-Vol/B-Vol
Retrofit Instructions” on page 1-6.
LIMITING CIRCUITRY
The output of the four VCAs are summed into IC8A and IC8B where the audio
waveform’s conversion to voltage takes place, and the rectified output from each
of these stages is the input to a corresponding non-inverting section of IC3A and
IC4A. These non-inverting sections develop limiting control voltages for each
VCA section. A voltage above 2 volts across D2 and D6 will cause a lower gain in
the corresponding section of the VCA.
HEADPHONE AND SPEAKERS
The output of the four VCAs (IC8A and IC8B) is also the input circuitry for the
headphone amplifier as well as the input of the speaker amplifiers, through IC7.
Signals from IC8 are passed through IC10 (highpass filters A and B) for the side
speaker amps, IC12A and IC11B. The input and output of these filters are
summed through resistor packs SP9 and SP8 into the VCA (U4) on pin 10. Due
to the inversion of the highpass filters, this allows a corresponding lowpass to be
derived. The control signal for this phase is derived from IC4B, which is rectified
from the output of IC9, which is used as the bass summing amp. The output of
the driver stage goes to IC11A and IC12B to drive the center woofer speaker.