Specifications

MONO
The mono button adds the left and right program
signals together to provide a monophonic signal at the
MAIN or BALANCED OUTPUTS. MONO does not affect
the TAPE outputs.
POWER
The red button turns the C712 on. The panel will
illuminate to indicate the program source that has been
selected and special operating modes.
HEADPHONE JACK
The C712 has sufficient built-in power capability to
feed a low impedance dynamic headphone connected
to the HEADPHONE jack.
REAR PANEL INFORMATION
The C712 has 3 groups of audio connectors on the
rear panel, INPUTS, PROCESSOR and OUTPUTS.
The AUDIO INPUTS are PHONO, AUX, CD 1, CD 2,
TUNER, TAPE 1, TAPE 2, and VIDEO.
PHONO and AUX are combined on one position of
the selector switch. The user must decide which way
he will use the inputs. A moving magnet phono
cartridge may be plugged into the PHONO input or any
high level source into the AUX. However the insertion
of an RCA plug into the AUX jack switches the phono
preamp off. Only one input may be used at a time.
The PROCESSOR connectors are for the PROCESSOR
IN and OUT.
The OUTPUTS are TAPE 1, TAPE 2 and MAIN.
XLR connectors are provided for L & R BALANCED
outputs.
One unswitched and one switched AC outlet is
provided for program source equipment.
REMOTE CONTROL
An "F" connector is provided for an external sensor.
A 1/8 inch phone jack for each input selection
provides serial data outputs for control of other
equipment.
A 1/8 inch phone jack is provided for POWER
CONTROL of high power Mclntosh power amplifiers.
TECHNICAL DESCRIPTION
ELECTRO-MAGNETIC SWITCHING
All signal switching in the C712 is done by
ELECTRO-MAGNETIC methods. ELECTRO-MAGNETIC
switching is an old and proven technology that has been
blessed with modern materials and manufacturing
methods.
Each switch consists of a glass tube that is filled
with an inert oxygen-free atmosphere and sealed with
tiny leads protruding from either end. These leads
extend into the tube and overlap one another with a
separation of a few thousandths of an inch. The leads
are made from a ferrous material that is influenced by
a magnetic field. They are first plated with gold as a
base material, then with rhodium and ruthenium.
Ruthenium is the best contact material known. The
glass assembly is then placed in the center of a multi-
layer coil of copper wire. The entire assembly is molded
together in a tough shock absorbing plastic. The switch
and coil connectors extend from the bottom in the form
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.
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. Open loop gain of this
integrated circuit is 100,000. With high open loop gain,
a large amount of negative feedback can be used around
the phono amplifier to further reduce noise and
distortion. The feedback network also 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 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. The gain of the amplifier is 40dB at 1000Hz.
The phono amplifier has a very wide dynamic range.
At 1000Hz, the phono input circuit will accept 90
MclNTOSH LABORATORY INC., 2 CHAMBERS STREET, BINGHAMTON, NEW YORK 13903
C712 Product Preview/Page 4