McIntosh C-11 Owners manual

STEREO

TABLE OF CONTENTS

PREAMPLIFIER

GENERAL DESCRIPTION 1
TECHNICAL DESCRIPTION 1

Mechanical Specifications 2
Electrical Specifications 2

FRONT PANEL FACILITIES 2
BACK PANEL FACILITIES 5
INSTALLATION 6
CONNECTING 8

A-C Connections 8

Input Connections 9

Output Connections 10

Loudspeaker Phasing Connections 11
Ground Connection 11

OPERATING INSTRUCTIONS 11

Balancing a Stereo System 11

Adjusting Phase 12

Listening to a Stereo Record 12
Adjusting the Balance Control After the

System has been Balanced 12

Adjusting for Special Effects 12

Using the C11 with a Stereo Tuner 13

Using the C11 with a Stereo Tape Machine_ 13

Using the C11 with Tape Deck 13
Using the C11 with Microphones for Stereo. 13

Listening to Monophonic Records 13

GUARANTEE 16

C11

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 one­thousandth 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 pre­serve 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

TECHNICAL DESCRIPTION

in environment. Also, people listening to the
music have varying ideas of correct tone bal­ance. 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 re­cording process.

Fourth, with programs originating from
several sources such as tuners, records, tape
machines, microphones, etc., a control cen­ter is needed to select and switch these
sources separately or in combination.

All of these jobs are performed with ex­cellence by the C11 and yet this instrument
is simple to operate, easy to mount, and is
the finest in appearance.

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 feed­back type circuits and operate in connection

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 asso­ciated with this section. Output level set con­trols are located at the input of the cathode
follower to allow simple balance of the entire
amplifying and speaker system. These con­trols 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 con­veniently be installed in furniture cabinets,
custom built installations, or professional

relay racks. The tubes and the electrical con­nections are conveniently located on the
back panel of the C11 for ready access.

1

MECHANICAL SPECIFICATIONS

Dimensions

Chassis: 14½ inches wide; 4¾ inches high;

12 inches deep including connectors.

Front Panel: 15¾ inches wide; 51/8 inches

high

Front Panel Mounting Space Required: 163/

8

inches wide; 5¼ inches high

ELECTRICAL SPECIFICATIONS

Power Requirements

117 volts, ac, 50/60 cycles, 30 watts

Input Sensitivity and Input Impedance

Auxiliary: 0.25 volt; 250,000 ohms
Tape: 0.25 volt; 250,000 ohms
Tuner 1: 0.25 volt; 250,000 ohms
Tuner 2: 0.25 volt; 250,000 ohms

Phono 1: 2 millivolts; 47,000 ohms
Phono 2: Same as phono 1
Tape Head: 2 millivolts; 1 megohm
Tape Compare (Monitor): 0.25 volt; 250,000

ohms

Microphone: 2.5 millivolts; 1 megohm

Frequency Response

± 0.5 db; 20 to 20,000 cycles

Distortion

Less than 0.2% at rated output, 20 to 20,000

cycles

Weight

Chassis: 15 pounds
Shipping Weight: 25 pounds

Finish

Anodized gold and black (front panel)

Main Output

2.5 volts with rated input
2 output jacks in parallel for each channel

Tape Output

0.25 volt with rated input
1 output jack for each channel

Left Plus Right Output

1 volt from generator impedance of 25,000

ohms

Voltage Amplification

Low-level inputs to Main Output: 1,000 to 1

(60db) at 1000 cycles

Low-level inputs to Tape Output: 100 to 1

(40 db) at 1000 cycles

High-level inputs to Main Output: 10 to 1

(20 db)

High-level inputs to TapeOutput: 1 to 1 (0 db)

Tape Compare (Monitor) input to

Main Output: 10 to 1 (20 db)

Hum and Noise

High-level inputs: 85 db below rated output
Low-level inputs: less than 2 microvolts at

input terminals

FRONT PANEL FACILITIES

Figure 1. C11 Front Panel

2

A-C Auxiliary Outlets

1 unswitched for tape machine or turntable,

colored Red

4 switched, colored Black

INPUT SELECTOR

INPUT SELECTOR

TUNER 2

TUNER 1

TAPE

AUX

PHONO 1

PHONO 2

MIC
TAPE HD

Select any one of eight program sources

with this switch:

1. AUX: any auxiliary service requiring flat
amplification, such as a television set, is
connected to the C11 through this posi­tion.

2. TAPE: any self-contained tape machine
(tape machine having its own playback
preamplifier) is connected to the C11

through this position.

3. TUNER 1: AM and FM outputs from a

stereo tuner or MPX FM program are con-

nected to the C11 through this position.

4. TUNER 2: same as TUNER 1.

5. PHONO 1: connects the C11 for stereo

and monophonic operation for records.

6. PHONO 2: same as PHONO 1.

7. MIC: stereo microphones are connected

to the C11 through this position.

8. TAPE HD: a tape deck that does not con-

tain its own playback preamplifier is con-

nected to the C11 through this position.

MODE SELECTOR

MODE SELECTOR

STEREO REV

R TO L&R

L

TO L&R

STEREO

MONO (L+R)

L+R TO L

L+R TO R

Listen thru both loudspeakers to either
track of a stereo program source.
Turn the MODE SELECTOR to:

1. L TO L & R: connects the "left" input to
both loudspeakers.

2. R TO L & R: connects the "right" input to
both loudspeakers.

3. STEREO REV: connects the "left" input to
the "right" loudspeaker and the "right"
input to the "left" loudspeaker.

4. STEREO: connects the "left" input to the

"left" loudspeaker and the "right" input

to the "right" loudspeaker.

5. MONO (L+R): adds the "left" input and
the "right" input and then connects the

L+R program to both amplifiers and loud­speakers.

6. L+R TO L: connects the "left plus right"

programs to the "left" loudspeaker only.

7. L+R TO R: connects the "left plus right"
programs to the "right" loudspeaker only.

BASS CONTROLS

BASS CONTROLS

LEFT

0 0

RIGHT

The LEFT and RIGHT BASS CONTROLS

regulate bass loudness to the left and right
speakers, respectively. Clockwise rotation in­creases bass loudness; counterclockwise

rotation decreases bass loudness.

TREBLE CONTROLS

TREBLE CONTROLS

Use the MODE SELECTOR to:

Listen to normal stereo (4 following and

page 16).

Reverse the left and right arrangement of

musical instruments (3 following and page

12).
Balance the amplifiers and loudspeakers

in a stereo system (6 and 7 following and
page 11).

Listen to monphonic sound (1 and 2

following and page 13).

LEFT

0

RIGHT

0

The LEFT and RIGHT TREBLE CONTROLS
regulate treble loudness to the left and right
speakers, respectively. Clockwise rotation
increases treble loudness; counterclockwise
rotation decreases treble loudness.

3

BALANCE

BALANCE

RIGHT

LEFT

0

The C11 is balanced for unequal program

sources by this control.

LEFT . . . turning the control to the left ac-

cents the left channel by reducing the right
channel output.

RIGHT . . . turning the control to the right ac-

cents the right channel by reducing the

left channel output.

This two-positioned switch reverses the
phase in the left channel to correct for loud­speaker or program phasing.

POWER

POWER

ON

OFF

The C11 and the four black receptacles on

the back panel are turned on by this switch.

RUMBLE

COMPENSATOR

COMPENSATOR

RIAA

LP

This control corrects for program equali-

zation introduced by the recording process.

TAPE

TAPE

NORMAL

MONITOR

This control makes it possible to instan­taneously compare the recorded material
with the source signal. Tape jacks on the back

panel accept a signal from a tape recorder

with a monitor head and preamplifier.

NORMAL . . . the program source is fed

through the power amplifiers and the loud-

speakers.

MONITOR . . . the signal source becomes the

monitored program from the recorded tape
and is fed through the power amplifiers and
loudspeakers.

RUMBLE

FLAT

FILTER

Low-frequency rumble noise below 50cps
created by a turntable or record changer and
acoustically coupled feedback are reduced
when the RUMBLE filter button is pushed to
the FILTER position.

H.F.

H.F.

FLAT

FILTER

This switch minimizes surface noise when

reproducing old, badly worn recordings. Its
positions are:

FLAT . . . filter disconnected.
FILTER . . . rolls off response sharply at 5KC.

LOUDNESS

LOUDNESS

NORMAL

PHASE

4

PHASE

NORMAL

REVERSE

COMPENSATED

This switch converts the VOLUME control

to a loudness compensated control when in
the COMPENSATED position.