Specifications

of printed circuit board terminals.
When a DC voltage is applied to the coil, current
flows and creates a magnetic field. The force of the
field causes the leads to bend and contact one another
inside the sealed glass tube. The inert gas eliminates
corrosion of the contacts, which insures a low
resistance, distortion free switch.
SURROUND SOUND PROCESSOR
The internal surround sound processor is made up of
three sections. First is an LSI integrated circuit that
takes a DOLBY SURROUND signal and decodes it to 4
channels, LEFT FRONT, CENTER, RIGHT FRONT and
SURROUND. The signal from the LEFT, CENTER and
RIGHT are added together then put through a low pass
filter to form the SUBWOOFER channel. The
SURROUND signal is fed to a digital TIME LINK delay
circuit, a 7kHz low pass filter and finally to a DOLBY
B type noise reduction section. It is then split into L
& R surround channels. Connectors are provided for
the future addition of THX processing.
PHONO AMPLIFIER
The phono amplifier uses a high technology integrated
circuit operational amplifier. Its differential input stage
has been optimized for low noise and low distortion
performance. The feedback network provides precision
RIAA frequency compensation. The network uses 1 %
metal film resistors and 5% polypropylene film
capacitors. To achieve low-noise performance it is
essential that the feedback network have a very low
impedance. As a consequence, the preamplifier must
be capable of operating as a power amplifier to drive
this impedance. The actual power output capability of
this preamplifier stage is more than 100 milliwatts, a
great margin beyond that which is required.
Input sensitivity of the phono amplifier is 2.5 millivolts
and the gain is 40dB at 1000Hz. It has a very wide
dynamic range. The phono input circuit will accept 60
millivolts without overload.
VOLUME CONTROL
A superior surround sound system requires a super
precision volume control. Tracking accuracy must be
near perfect or the audio image will shift as the control
is moved. Mclntosh engineers have designed a micro
processor controlled volume system that retains the
familiar VOLUME CONTROL KNOB but provides "State
of the Art" performance. All SIX channels track within
one quarter of a dB throughout most of their range. 256
steps are provided for excellent resolution and each
channel has ± 12dB of trim. The control microprocessor
also drives a two digit display that indicates % of
volume and the amount of trim used for system
calibration. The gain of the volume control section is
20dB.
LOUDNESS AMPLIFIER
At the input to the high level or loudness amplifier,
the signal passes through the mono stereo 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 C39 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 gain of the loudness
amplifier is 0dB.
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 the
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
potentiometer is at its center detent position, the tone
control elements are removed from the signal path.
CONTROL LOGIC
All inputs, outputs, CD, Tuner, and Video selector
lines are controlled by logic circuits in the C39. 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.
C39 Product Preview/Page 8
MclNTOSH LABORATORY INC., 2 CHAMBERS STREET, BINGHAMTON, NEW YORK 13903