Specifications

to the COMPANDOR switching where the Compandor
can be inserted into the record program path. The
Compandor circuit is described later. The record
program then goes to the RECORD EXTERNAL
PROCESSOR jacks.
When an external processor is used, the record
program leaves the C40 through the EXTERNAL
PROCESSOR TO jack and returns via the FROM jack.
When a processor is not connected, the signal passes
directly through the jacks.
An equalizer amplifier with unity gain follows. A
pushbutton switch allows the 5 band equalizer controls
to be switched from the Listen program line to the
Record program line. This feature allows equalizing the
record signal before it is fed to a recorder.
The equalizer amplifier feeds to electronic interlock
switching and then finally to the record output jacks.
The switching is arranged so that if the Record input
selector is positioned to select the output of a recorder,
the Record program line will not feed the record output
jack connected to that recorder. This prevents recorder
feedback.
COMPANDOR
The Compandor will expand or compress the dynamic
range of the program material. The Compandor can be
switched to the Listen or Record program lines or turned
off. Program to the Compandor is applied to a voltage
controlled amplifier (VCA) which operates as a variable
gain block. Control voltages for this VCA are developed
from a sample taken from the left and right channel
input signals to the VCA. The electronic processing of
this sample is detailed. It includes band shaping,
logarithmic conversation, full wave rectification, level
setting, expansion or compression ratio regulation,
attach timing, and DC amplification. The resulting
processed voltage controls the gain of the VCA to cause
logarithmic gain expansion when expanding the program,
or the opposite, logarithmic gain compression when
compressing the program.
MONITOR AMPLIFIER
The monitor amplifier is a 20 watt per channel stereo
power amplifier. The monitor input selector switch
allows the amplifier to be driven from the LISTEN or
RECORD program lines or from an external input. It is
a push pull complementary class AB amplifier using a
differential input stage. The amplifier includes the
Mclntosh Power Guard* protection circuit. The Power
Guard circuit compares the amplifier output signal with
its input signal. If there is a difference between the
waveforms of these signals, Power Guard activates an
electronic attenuator at the input of the amplifier which
reduces the amplifier input level. This automatic control
system makes it impossible to drive the monitor amplifier
into clipping. Thus, clipping distortion and loudspeaker
damage due to clipping are eliminated.
(*protected by US Patent #4048573)
Issued by Engineering Department
May 4, 1992
Revised: May 26, 1992
October 6, 1992
C40 Product Preview Page 7
MclNTOSH LABORATORY INC., 2 CHAMBERS STREET, BINGHAMTON, NEW YORK 13903