1.3 Input Stage
The audio signals on DIN plug J303 pin 1 (left channel) and
pin 4 (right channel) pass through variable high pass filters
formed by C303, R315, R317 and C304 R316, R317 and buffer
amplifiers Z301 (5, 6, 7) and Z301 (3 ,2, 1) to DIN plug J303
pins 3 and 5. From pins 3 and 5, they can be returned to an
external power amplifier driving the satellite speakers. The
buffer amplifiers provide low output impedance, so cable capaci-
tances will not affect the treble response.
The audio signals on DIN plug J303 pins 1 and 4, or alternatively
on speaker plugs J301, J304, are summed by resistors R318, R319
into a first active low pass filter with kneepoint 138Hz and
8dB gain at 100Hz (when channels are in parallel).
The signal from the first low pass filter is passed via a
volume control R322 to a second amplifier stage Z301 (10, 9 ,8)
with 17dB gain.
1.4 Filter
The signal from Z301 pin 8 (test point C) passes a variable low
pass filter including R401, R402, R403, C401, C402 and Z401 (10,
9, 8), and then on to a fixed high pass filter with kneepoint
22.8Hz. The output terminal is test point (E).
Remaining components in the filter circuits are part of the
Ace-Bass amplifier, and is described in section 1.5.
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