Specifications

At 1000Hz, the phono input circuit will accept 90
millivolts without overload, a voltage far greater than
the output of any current magnetic phono cartridge
Phono input overload, therefore, is virtually impossible.
A signal level of 10 millivolts at the phono input at
1000Hz will produce 1 volt at the tape output. The tape
output has a source impedance of 600 ohms, designed
to operate into a load impedance of 10,000 ohms or
greater
LOUDNESS AMPLIFIER
At the input to the high level or loudness amplifier,
the signal passes through the mono switch, then
through the volume control, and into the loudness
amplifier 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
volume control position and differences in input level
The C38 uses active loudness control circuitry An
integrated circuit operational amplifier is used here It
has two feedback loops One feedback loop has flat
response The other feedback loop has loudness
compensation. A potentiometer is placed between these
two feedback loops making is possible to select any
combination of the two from a flat response to full
loudness compensation. The overall gain of the
loudness stages is 20dB and is not affected at mid
frequencies by the position of the loudness control.
TONE CONTROL AMPLIFIER
The tone control amplifier uses high technology
integrated circuit operational amplifiers. Its output stage
has been optimized for the best transient performance
and minimum distortion Another operational amplifier
is arranged in a circuit configuration that is equivalent
of a series turned circuit The series tuned circuit is
inserted via a control potentiometer into either the input
or feedback circuit of the operational amplifier, thereby,
providing a boost and cut capability of 12dB. The
overall gain of the stage is 0dB When the potentiome-
ter is at its center detent position, the tone control
elements are removed from the signal path.
CONTROL LOGIC
All inputs, outputs, CD, Tuner, SCR, and Video
selector lines are controlled by logic circuits in the C38
The logic is changed by front panel switches or by two
microprocessor IR decoders, one for LISTEN (A) and one
for RECORD (B) These microprocessor IR decoders are
programmed with exclusive Mclntosh software. They
receive data from the front panel or external sensors
and provide the command signals for input switching
and volume control A third microprocessor decodes
the CD1, CD2 and TUNER function commands.
SYSTEM EXPANSION
Audio buffers and data switches feed a 25 pin
subminiature "D" connector for system expansion
through CR10s.
Issued by Engineering Department
March 23, 1992
Revised: September 30, 1992
MclNTOSH LABORATORY INC., 2 CHAMBERS STREET, BINGHAMTON, NEW YORK 13903
C38 Product Preview/Page 6