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4. The heaters of the 12AX7 tubes used in the C-8 are returned to
ground through a hum reducing potentiometer in the power
amplifier. Heaters of tubes used in the C-8P are returned to
ground through a hum reducing potentiometer in the power
supply. This control requires an initial adjustment for mini-
mum hum, and should be readjusted each time one or more
tubes are replaced.
5. Grounding the turntable motor frame to the Audio Compensator
chassis near the input jacks may reduce the hum level on the
phonograph channels.
OUTPUT CONNECTIONS
Three outputs are provided: one auxiliary and two main outputs.
The auxiliary output may be used for recording tape from any source con-
nected to the Audio Compensator. The Selector switch, Bass and Treble
compensation switches, and Rumble Filter are effective at this output. Adjust-
ment of the Bass and Treble tone controls, Aural Compensator and Volume
control may be made for monitoring purpose and will not affect the recorded
signal. The auxiliary output delivers a signal of one volt.
All controls are effective at the main outputs, which are available at the
octal socket labeled "INTER-UNIT CABLE" between pins #1 and #2 (pin #1 is
ground), and at the RETMA pin jack labeled "MAIN OUTPUT". The inter-unit
cable connecting the C-8 to any McIntosh power amplifier uses the octal socket
output. The pin jack output may be used for driving a second power amplifier
if so desired.
The main and auxiliary output jacks are fed from cathode followers. The
input impedance of devices connected to these outputs should be 50, 000 ohms
or greater, and the capacitive reactance of audio cables connecting these
devices should not be less than 8, 000 ohms at 20, 000 cycles. This is the
reactance of a capacity of 1000 mmf. Audio cable having a capacity of 25 mmf
per foot may be 40 feet long.
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