What the Front Panel controls Do
and How to use Them
INPUT SELECTOR
The INPUT SELECTOR is a five position switch that
connects the chosen input program to the proper circuits
in the C 27.
AUX 1: Connects to the high level input, any output
from a high level program source requiring flat amplifica-
tion. Such a source could be a television set, playback from
another tape recorder, an additional tuner, etc. In the
AUX 1 position the gain is 20 dB to the MAIN outputs,
0 dB to the TAPE outputs. The input impedance is 100 k
ohms.
AUX 2: Same as AUX 1 but for a second high level
program source.
TUNER: Connects the output from any AM, FM or MPX
FM tuner to the high level input stage. In the TUNER posi-
tion the C 27 has flat amplification. There is 20 dB of
gain to the MAIN outputs, 0 dB to the TAPE outputs. The
input impedance is 100k ohms.
PHONO 1: Connects the output of any magnetic phono
cartridge to the low level input stage. The response has
been shaped according to the RIAA standard to compensate
for the characteristics of a magnetic phono cartridge. The
gain at 1K Hz is 62 dB to the MAIN outputs, 42 dB to the
TAPE outputs. The input impedance is 47k ohms and
100 pF.
PHONO 2: Same as PHONO 1 but for a second phono
system.
MODE SELECTOR
L to L & R: Connects the left input to both loudspeak-
ers. R to L & R: Connects the right input to both loud-
speakers. Stereo Rev: Connects the left input to the right
loudspeaker and the right input to the left loudspeaker.
Stereo: Connects the left input to the left loudspeaker
and the right input to the right loudspeaker.
Mono (L + R): Adds the left input and the right input
and then connects the L + R program to both loud-
speakers.
L + R to L: Adds the left and right program together
and connects the combined program to the left loud-
speaker only.
L + R to R: Adds the left and right program together
and connects the combined program to the right loud-
speaker only.
PRECISE TRACKING VOLUME CONTROL
The VOLUME control is a precision step attenuator
which has left to right tracking accuracy within 1 dB
throughout its entire range. Such extremely accurate match-
ing is achieved through electronically controlled trimming
of the resistance material deposited on pairs of printed
circuits. Since the switch commutator touches only contact
pads and not the actual resistance element, tracking ac-
curacy is not degraded with use as in ordinary volume
controls. Clockwise rotation increases volume. The VOLUME
control in the C 27 has been designed and manufactured
for Mclntosh Laboratory.
FILTERS/SPEAKERS
The small center knob of the concentric FILTER/
SPEAKERS control shapes the C 27 frequency response to
reduce or filter objectionable low frequency noise and/or
objectionable high frequency noise. The large outer knob
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