Technical Description - McIntosh C32 Owner's Manual

Technical Description

The dual program line control begins at two stereo
selector switches feeding from a common group of input
sources (PHONO PREAMP, TUNER, AUX, TAPE 1, 2, or 3)
to two separate stereo high level amplifiers. One of these
is the LISTEN amplifier, the other is the RECORD amplifier.
The LISTEN amplifier provides signal processing by high
and low pass filters, five equalizers, loudness compensation
and a logarithmic expander. The other, the RECORD am-
plifier, feeds the selected signal to the tape record output
connections.
A stereo monitor amplifier in the C 32 feeds HEAD-
PHONE, MONITOR and LINE OUTPUT. The input to the
MONITOR AMPLIFIER can be selected from either LISTEN
or RECORD program lines.
Phono Preamplifier
Each phono preamplifier circuit uses four specially se-
lected low noise transistors arranged in very low impedance
configuration. To achieve low noise a 68 ohm feedback
termination is used. As a consequence, the preamplifier
must be capable of operating as a power amplifier to drive
this low impedance with low distortion. The actual power
output capability of this stage is more than 100 milliwatts.
The C 32 is engineered to follow the RIAA equalization
curve precisely. One percent resistors and five percent
capacitors are used to ensure exact equalization of the
playback signal to the RIAA curve.
Input Selector Switching
A l l input switching is done electronically, using Field
Effect Analog switches (FET). The mechanical LISTEN and
RECORD switches on the front panel are simple, single deck
switches that are self cleaning and extremely reliable. They
switch small DC voltages which turn the FET Analog
switches on or off. The design eliminates degradation of
frequency response or noise pickup.
Mode Selection
The LISTEN signal, as it leave its input selector switch
is connected to the MODE SELECTOR switch. The configura-
tion of this switch permits combining the L and R programs
and connecting to LEFT or RIGHT outputs. This procedure
reveals system imbalance of less than a decibel, thus pro-
viding the means for very precise system balancing. LEFT
input to both L and R outputs and RIGHT input to both
L and R outputs is also provided again affording the same
degree of precision in balancing input signals. The switch
also provides STEREO REVERSE and MONO positions.
Precise Tracking Volume Control
The volume control is designed and manufactured for
Mclntosh Laboratory. It is a step attenuator which has left
to right tracking accuracy within 1 dB throughout its entire
range. Such extremely accurate matching is achieved
through electronically controlled laser 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 accuracy
is not degraded with use as in ordinary volume controls.
Loudness Compensation
In the past, loudness controls have typically used simple
passive circuits connected to a tap on the volume control.
As a consequence, compensation accuracy was dependent
on many variables such as speaker efficiency, amplifier
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