Specifications

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 100 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 C712 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, and data ports are controlled by
logic circuits in the C712. The logic is changed by front
panel switches or by a microprocessor IR decoder. This
microprocessor IR decoder is programmed with exclusive
McIntosh software. It receives data from the front panel
or external sensors and provides the command signals
for input switching, data switching, and volume control.
Issued by Engineering Department:
December 21, 1992
C712 Product Preview/Page 5
MCINTOSH LABORATORY INC., 2 CHAMBERS STREET, BlNGHAMTON, NEW YORK 13903