C11 STEREOPHONIC PREAMPLIFIER
GENERAL DESCRIPTION
The Mcintosh C11 Stereophonic Pre-
amplifier is a control center for any stereo-
phonic sound system. To increase the
enjoyment of stereo, this control center does
four jobs with precise control.
First, the control center amplifies weak
electrical impulses. As the record rotates on
the turntable, undulations in the grooves
move the pick-up stylus approximately one-
thousandth of an inch, in any direction, from
the rest position. From this slight mechanical
movement, the pick-up stylus generates a
weak electrical impulse on the order of a few
thousandths of a volt. To amplify and pre-
serve the information in such an electrical
impulse, the finest amplifier performance is
required.
Second, every sound system is used in a
different acoustical environment. The tone
balance of the music is affected by variations
The C11 Stereophonic Preamplifier com-
bines excellence in performance with ease of
operation. The controls used the most have
large diameter knobs. A new type of rocker
switch indicates those controls with simple
off-on functions. The C11 has an illuminated
front panel with light intensity control to
provide convenient reading under low-level
lighting conditions.
The C11 circuit consists of three amplify-
ing sections in duplicate for the left and right
stereo channels and a power supply. The
first section is the input preamplifier used to
amplify and equalize the input signals com-
ing from phonograph pickups, microphones,
or tape heads. Skillful layout, grounding, and
shielding for low hum pickups, metal film and
wire wound resistors, terminal boards with
high specific resistivity, low noise tubes and
extreme care in manufacturing combine to
achieve a new low in noise and hum.
The second amplifying section follows the
volume control, and thus it is impossible to
overload the circuit or any following circuits.
The same techniques as were used in the
preamplifier stage assure low hum and noise.
The bass and treble tone controls are feed-
back type circuits and operate in connection
in environment. Also, people listening to the
music have varying ideas of correct tone bal-
ance. To compensate for these conditions, a
high-quality control center is needed.
Third, there is a great variety of stereo-
phonic and monophonic records manufac-
tured today, both domestic and foreign. The
control center must accurately compensate
for the equalization introduced in the re-
cording process.
Fourth, with programs originating from
several sources such as tuners, records, tape
machines, microphones, etc., a control cen-
ter is needed to select and switch these
sources separately or in combination.
All of these jobs are performed with ex-
cellence by the C11 and yet this instrument
is simple to operate, easy to mount, and is
the finest in appearance.
with this section. Exceedingly low distortion
and correct frequency response are assured
using this arrangement.
The third section is the cathode follower
output. The sharp cut-off (18db per octave)
rumble and high frequency filters are asso-
ciated with this section. Output level set con-
trols are located at the input of the cathode
follower to allow simple balance of the entire
amplifying and speaker system. These con-
trols are conveniently accessible at each side
of the front panel under the end caps.
The power supply deserves special men-
tion. The power transformer is constructed
with "core" type grain oriented laminations
and magnetic shielding for low hum field.
Long life rectifiers, full wave rectification,
filter condenser sectionalizing and careful
grounding add to the hum free and long life
characteristics of the C11.
Special attention has been given to the
mechanical design also. The C11 may con-
veniently be installed in furniture cabinets,
custom built installations, or professional
relay racks. The tubes and the electrical con-
nections are conveniently located on the
back panel of the C11 for ready access.
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TECHNICAL DESCRIPTION
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