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.

VOLUME

VOLUME

This continuously variable control regu-

lates the volume for both channels.

OUTPUT LEVEL CONTROLS

Under the panel end caps are the thumb
wheel OUTPUT LEVEL CONTROLS. The L
OUTPUT is on the left-hand side. The R
OUTPUT is on the right-hand side.

BACK PANEL FACILITIES

Figure 2. C11 Back Panel

AC OUTLETS

There are five AC outlets on the left-hand

side of the rear panel. (See Figure 2.) These
outlets have a maximum rating of 660 watt
total. The four black outlets are controlled by
the POWER ON-OFF switch on the front

panel. The red outlet is used for powering a
turntable or record changer. This outlet is

not switched so that the turntable power will

not be turned off while the turntable idler
wheel is engaged. With this arrangement it is

necessary to turn off the turntable with its
own control switch so that the turntable drive

system will not be damaged.

PANEL LIGHT

The PANEL LIGHT switch, located in the

lower left-hand corner of the back panel,

provides a choice of bright or dim front panel

lighting.

OUTPUT CONNECTIONS

The MAIN output connects to power am-

plifiers (Figure 2); the TAPE output connects

to a tape recorder.

The MAIN and TAPE output jacks are fed
from cathode followers. The input impedance
of devices connected to these outputs should
be 50,000 ohms or greater. The capacitive

reactance of connecting audio cables should
not be less than 8,000 ohms at 20,000

cycles. Longer cables than are normally sup-

plied can be connected between the C11

and the amplifiers or loudspeakers. The

length of the cable is limited by the capacity

of the cable per foot. The total capacity must

not exceed 1000 mmf. For instance; cables
with a capacity of 25 mmf per foot may be
40 feet long; 13.5 mmf per foot cable may be

75 feet long.

5

HIGH LEVEL INPUTS

These receptacles accept high-level pro­gram source connections as follows:
TAPE MONITOR (COMPARE) . . . accepts a

signal from a tape recorder with a monitor
head and preamplifier.

AUX . . . accepts any auxiliary service re-

quiring flat frequency response, such as a
T.V. set, tuner, tape recorder with its own
playback preamplifier, etc.

TAPE . . . accepts connection from a tape

machine with its own playback preamplifier.

TUNER 1 & TUNER 2 . . . accept AM and FM

outputs from a stereo tuner or a pair of
stereo tuners.

LOW LEVEL INPUTS

These receptacles accept low-level pro-

gram source connections as follows:

PHONO 1 & 2 . . . accepts connection for

normal stereo and normal monophonic
operation.

MIC . . . accepts connection from stereo

microphones.

TAPE HEAD . . . accepts connection from a

tape deck that does not contain its own

playback preamplifier.

TAPE EQUALIZATION

On the back panel there are two tape
equalizing controls. These controls should be
set to NAB for normal 7.5 inch tape speed
machines. Turning the TAPE EQUALIZATION
controls clockwise increases the treble re­sponse, turning it counterclockwise de­creases the treble response. Use the controls
to compensate for 3% tape speed for indi­vidual tape head characteristics.

LOUDSPEAKER PHASING CONNECTIONS

Two pairs of screw terminals are located
on the lower left section of the C11 back

panel. The speaker leads from the "left"

power amplifier should be connected to the
screw terminals marked FROM AMPLIFIER.
The pair of terminals marked TO SPEAKER
should be connected to the "left" loud­speaker.

These connections allow the front panel
PHASE switch to reverse the phase on the
left loudspeaker. This arrangement is con-

venient when setting up a stereo system.

The C11 can be installed in conventional
furniture cabinets, custom built installations
or professional relay racks. If the unit is to
be placed on a shelf or table-top, it is recom-

mended that it be housed in a Mcintosh L66
cabinet. Install the C11 from the front of the
cabinet, not from the rear.

To support the weight of the C11, the
wood panel used to mount it, should be at
least ¼ inch thick. If the front panel of a cabi-

net is made of wood, a shelf may be needed

to support the rear of the chassis to prevent

warping. When the C11 is mounted on a

metal rack panel, a shelf is not needed.

The C11 installation should allow 12
inches behind the front panel so that there
is at least 1½ inches for connectors. The de-

sirable width and height are 16½ inches and
5½ inches, respectively, so that sufficient
space is allowed for the circulation of air.
These are inside dimensions. The front panel

mounting space width and height are 163/

8

inches and 53/8 inches, respectively.

Positions "A" to "C" show the location of the
vertical center line, the use of the measuring
tool (mounting strip) to locate the horizontal
center line, and how to measure off the two
points to the right and left of the vertical
center line.

6

Figure 3. Cutout Measurements

MAKING THE FRONT PANEL CUTOUT

The panel is cut out using the "FRONT

PANEL CUTOUT TEMPLATE." To position
the template on the front of the panel, make
two locating holes from the back (inside) of
the panel using one of the mounting strips

(½ inch by 3½ inches) as a measuring tool.

Proceed as follows:

Scribe a vertical center line through the
exact center of the proposed cutout area
from the top of the panel to the top surface
of the shelf as illustrated in "A," Figure 3.

Using one of the mounting strips as a meas­uring tool, draw a horizontal line 3½ inches

above the shelf. (See "B," Figure 3.) Place a

mounting strip along the horizontal line to the
left of the vertical center line and mark a
point 3½ inches left from the vertical center

line. Repeat this procedure and mark a point
3½ inches to the right of the vertical center
line. These points should now be 3½ inches

up from the top of the shelf and 7 inches

apart, one 3½ inches to the left and one
3½ inches to the right of the vertical center

line. (See "C," Figure 3.) Drill a 3/16 inch hole

at each point. Hold the drill perpendicular to
the front panel so that the hole will be located

accurately on the front of the panel.

Position the template on the front of the
panel using the two locating holes to line it
up correctly. Scribe the rectangular opening

on the front panel and mark the position of
the six mounting holes. Drill the six 3/16 inch

mounting holes before cutting the panel

opening. Then cut out the opening. It is im-

portant that the cutout be just with in the lines.

inch or 3/8 inch shelf.) Remove the four plastic

feet from the bottom of the C11.

In the mounting hardware package are

four 6-32 flathead screws and eight 6-32

roundhead screws. Two of the flathead
screws of the proper length are used to at-

tach the mounting strips to the cabinet. Four

of the roundhead screws of the proper length
are used to attach the C11 to the cabinet and
mounting strips. The 6-32 x ½ inch screws
are to be used with panels ½ inch to 1 inch
in thickness.

Select the proper length 6-32 flathead

screws and use them to install the two mount-

ing strips behind the front panel. Be sure
that the edge of the strip with the clips is
toward the panel opening. Line up the mount­ing strips on each side of the front panel
cutout so the three holes in the strip are in

line with the three holes in the panel. (See

Figure 4.) Install the proper length flathead

screws in the center hole of each strip. Drive
them in so the flatheads are flush with the

panel; if necessary, countersink the two
center holes.

SHELF MOUNTING

If the installation requires a shelf, proceed
as follows: Locate the center of the shelf and
scribe a line from front to back. The "SHELF
CUTOUT PLATE" is marked for panel thick-

nesses from ¼ inch to 1 inch. Fold the tem­plate on the line that corresponds to the

thickness of the panel. Place it on the shelf

so that it butts against the inside of the panel.
Match the center line mark on the template
to the scribed center line on the shelf. Mark
the position of the four drill holes. Drill the
four ¼ inch holes.

INSTALLING THE C11

Remove the four screws holding the C11
to the shipping pallet. (Save these screws,
you will need them if your cabinet has a ¼

Figure 4. Securing the Mounting Strip to the Front Panel

Carefully insert the C11 through the front
of the panel opening so that it rests on the
shelf. Insert the proper length 6-32 round­head screws into the four holes in the mount­ing flanges on each end of the tuner front
panel. Drive them in, but do not tighten.

If the cabinet is fixed and will not be
moved about, it is not necessary to secure
the C11 chassis to the shelf. If the cabinet is
to be moved about, it is recommended that
the C11 chassis be secured to the shelf. The

four 10-32 x ½ inch screws used in shipping

are supplied for use if the shelf is under 3/

8

inch. Use the 10-32 x ¾ inch screws if this
shelf is V2 inch or 5/8 inch thick and the 10-32

x 1 inch screws if the shelf is ¾ inch or 7/

8

7

inch thick. Secure the chassis with the proper
length 10-32 machine screws, inserting them
from beneath the shelf. Do not tighten the

10-32 screws until you have tightened the

front panel screws.

IMPORTANT:

USE OF THE WRONG LENGTH 10-32
SCREWS MAY CAUSE ELECTRICAL
SHORTING IN THE CIRCUIT.

Attach the two metal panel end caps

(packed with mounting hardware) on each
end of the panel by sliding onto the pins.
(See Figure 5.) The end caps are held by
spring tension and can easily be removed if

the chassis is to be taken out of the cabinet.

END CAP

PUSH ON

Figure 5. Fitting of Panel End Caps to Panel

MOUNTING IN THE L66 CABINET

The Mcintosh L66 cabinet is supplied

with complete instructions and all necessary

hardware for installing the C11. The dimen-

CONNECTING

A-C CONNECTIONS

There are five a-c receptacles on the rear

panel. (See Figure 6.) These receptacles
have a maximum rating of 660-watt total. The
four black receptacles are controlled by the

POWER ON-OFF switch on the front panel.
The red receptacle is not switched. The red

receptacle is used for powering a turntable

sions of the L66 are 169/16 inches wide by
611/16 inches high, including mounting feet,
by 13¾ inches deep, including the front
panel and control knobs.

or record changer. The receptacle is not
switched so that the turntable power will not

be turned off while the turntable idler wheel

is engaged. The turntable is protected by
this arrangement because it is necessary to
turn off the turntable with its own control
switch so that no damage will result to the
drive system.

8

Figure 6. A-C Connections

The C11 provides eight separate program monitor.
inputs controlled by the INPUT SELECTOR The input program connection should be
switch and one input for tape comparison or made in accordance with Tables 1 and 2.

Figure 7. C11 Input Connections (Back Panel)

CONNECTION

TAPE MONITOR

(COMPARE)

AUX

TAPE

TUNER 1 &

TUNER 2

CONNECTION

PHONO 1 & 2

MAGNETIC

TAPE HEAD 1 &2

2-10 MV

FUNCTION

The tape monitor input accepts a signal from a tape

recorder with a monitor head and preamplifier.

The auxiliary input accepts any auxiliary service requiring

flat frequency response, such as a T.V. set, tuner, tape
recorder with its own playback preamplifier, etc.

The tape input operates with tape machines containing

their own playback preamplifier.

The tuner inputs accept AM and FM outputs from a stereo

tuner or a pair of stereo tuners or the multiplex output
of an adapter or multiplex tuner.

FUNCTION

These jacks are to be used with magnetic cartridges.

These jacks are to be used with a tape deck that does not

contain its own playback preamplifier.

INPUT

SENSITIVITY

0.25 V

0.25 V

0.25 V

0.25 V

INPUT

SENSITIVITY

2 MV

2 MV

INPUT

IMPEDANCE

250K

250K

250K

250K

INPUT

IMPEDANCE

47 K

1 megohm

If a phono cartridge requires less than
47,000 ohms load impedance, a resistor can
be added across the terminals of the car-

Desired Impedance

47,000 ohms (47K)
37,000 ohms (37K)

27,000 ohms (27K)

15,000 ohms (15K)

6,800 ohms (6.8K)

tridge to achieve the correct termination.
The following chart may be used as a guide:

Resistor Across Input
No Resistor

180,000 ohms (180K)

62,000 ohms (62K)
22,000 ohms (22K)

8,200 ohms (8.2K)

9

Figure 8. Turntables Feeding Low Level Input

OUTPUT CONNECTIONS

Two sets of outputs, located in the upper

left-hand corner of the back panel, are pro-

vided. (See Figure 2.)

The MAIN output connects to power am­plifiers (Figure 9) and the TAPE output to
feed a tape recorder.

The MAIN and TAPE output jacks are fed
from cathode followers. The input impedance
of devices connected to these outputs should

be 50,000 ohms or greater, and the capaci­tive reactance of audio cables connecting
these devices should not be less than 8,000
ohms at 20,000 cycles. This is the reactance
of a capacity of 1,000 mmf. Audio cable

having a capacity of 25 mmf per foot may be

40 feet long; 13.5 mmf per foot cable may be
75 feet long.

The tape output is affected only by the
INPUT SELECTOR in the AUX, TAPE, TUNER
1, TUNER, or MIC positions.

When the INPUT SELECTOR is turned to
PHONO 1 or PHONO 2 inputs then the record
compensator is included. When the INPUT
SELECTOR is turned to TAPE HD then the
record compensator switch should be set at
RIAA.

On the back panel there are two TAPE
EQUALIZATION controls. These controls
should be set to NAB for normal 7.5 inch tape
speed machines. Turning the TAPE EQUAL-

IZATION controls clockwise increases the

10

Figure 9. MAIN Output Connected to Power Amplifiers

treble response, turning it counterclockwise
decreases the treble response. Use the con­trols to compensate for 3% tape speed for

individual tape head characteristics.

A left plus right output jack is next to the
MAIN output. It is marked L+R. A mono­phonic signal can be distributed to other
rooms by connecting a third power amplifier
to the jack marked L+R. This amplifier is
used to drive the monophonic loudspeakers.
The cable connecting to this output should
not have a capacity of more than 200 mmf.

The input impedance of the power amplifier

connecting to this output should not be less

than 150,000 ohms (150K). The generator

impedance at this output is approximately

25,000 ohms (25K).

LOUDSPEAKER PHASING CONNECTIONS

Two pairs of screw terminals are located

on the lower left section of the C11 back

panel. The speaker leads from the "left"

power amplifier should be connected to the
screw terminals marked FROM AMPLIFIER.
The pair of terminals marked TO SPEAKER

should be connected to the "left" loud-

speaker.

These connections allow the front panel

PHASE switch to reverse the phase on the

left loudspeaker. This arrangement is con-

venient when setting up a stereo system.

GROUND CONNECTION

A single ground post is provided. The
chassis ground from turntable, record chang­ers (motors used with each), tape decks, etc.,
should be returned to this post. Do not dupli-

cate this ground circuit. Hum is likely to be
heard in the system if duplicate ground re-

turns are used.

The left and right program cables from
each source should be twisted together and
the ground wire from each source can be
wound or twisted in with these cables. To
avoid hum, make sure the ground wire does

not make any connections to shields of the
left and right channel cables except for the

connection provided with the C11 ground

post.

OPERATING INSTRUCTIONS

BALANCING A STEREO SYSTEM

The ultimate in stereo performance and
listening enjoyment is obtained through the
proper balancing of the stereo system. A
properly balanced stereo system must be in
phase. Each channel must be equal in loud­ness and similar in frequency response.

Do not use the C11 BALANCE control for
this procedure. The C11 BALANCE control
is used to adjust for any unbalance in the
source material, the phono cartridge, and
tape machine.

Before attempting the balancing of the
C11 make sure the controls on the amplifiers
are set properly. On the MC240 and MC275

turn the control marked BALANCE to its

center position. On the MC225 set the input
level controls for each channel to the black
dot above the control.

To properly balance the C11, proceed as
follows: A familiar recording, either stereo­phonic or monophonic, should be used in
balancing the C11.

1. Turn the INPUT SELECTOR to the posi-

tion corresponding to the program selected.

2. Turn the BASS CONTROLS and TREBLE

CONTROLS to their 0 positions.

3. Turn the MODE SELECTOR to the L+R

TO L position.

4. Place the COMPENSATOR switch in the

RIAA position.

5. Place the TAPE switch in the NORMAL

position.

6. Place the PHASE switch in the NORMAL

position.

7. Place the POWER switch in the ON

position.

8. Place the RUMBLE switch in the FLAT

position.

9. Place the H.F. cutoff filter switch in the

FLAT position.

10. Place the LOUDNESS switch in the

NORMAL position.

11. Turn the BALANCE control to the 0

position.

12. While the program is playing, alternate

the MODE SELECTOR between the L+R TO

L position and the L+R TO R position. Adjust

the thumb wheel level controls under the

end caps until the loudspeakers are of equal
loudness.

When the proper balancing of the Mcin­tosh C11 is accomplished, the stereo system
will remain balanced throughout all modes
of operation.

11

ADJUSTING PHASE

1. Place the COMPENSATOR switch in the

RIAA position.

2. Set the MODE SELECTOR to STEREO.

3. Turn the BASS CONTROLS and TREBLE

CONTROLS to 0.

Stand approximately 10 feet in front of
and midway between the loudspeakers. The
source of sound should appear to be directly

in front of you. Alternate the PHASE switch
between NORMAL and REVERSE. If the

sound is not directly in front of you in the

NORMAL position, reverse the leads to one

loudspeaker. The PHASE control is used to
correct phase in the source material when­ever necessary.

records always require an adjustment of the
BALANCE control to one side of the center,

the condition indicates an unbalanced stereo

cartridge. While this is no great disadvantage
as such, you can correct for it by offsetting
one of the power amplifier input gain settings.

When switching from STEREO to STEREO

REV you will now experience a change in

volume as a result of this correction.

If the stereo sound seems to come from
either side of the room instead of being dis­tributed between the loudspeakers, adjust

the PHASE control to 180°. This listening

effect is due to reproducing sound that is out
of phase from one channel to the other. You
will find some records differ from others in
this respect and that some tapes differ from

records.

LISTENING TO A STEREO RECORD

Upon completion of the connecting and
balancing instructions, the C11 is ready for
use. To listen to stereo records, proceed as

follows:

1. Set the MODE SELECTOR to STEREO.

2. Set the PHASE switch to NORMAL.

3. Set the H.F. cutoff filter to FLAT.

4. Set the LOUDNESS control to NORMAL.

5. Rotate the INPUT SELECTOR to PHONO

1 or PHONO 2 whichever is connected to the

cartridge you wish to hear.

6. Set the COMPENSATOR control to

RIAA.

7. Set the BASS CONTROLS and TREBLE

CONTROLS to 0.

8. Place the RUMBLE control in the FLAT

position.

9. Place the TAPE control in the NORMAL

position.

10. Adjust the VOLUME control to the de-

sired volume.

ADJUSTING BALANCE CONTROL AFTER

THE SYSTEM HAS BEEN BALANCED

If after balancing your system as outlined

in this manual you then find that nearly all

ADJUSTING FOR SPECIAL EFFECTS

H.F. Cutoff Filter. If you wish to reproduce

old, badly worn records, you can minimize
the surface noise by switching the H.F. cutoff
filter to the FILTER position. (See section
entitled "Front Panel Facilities.")

Rumble Filter. If you are using a turntable

or changer which has low-frequency rumble

noise, you may reduce it by pushing the

RUMBLE filter switch to the FILTER position.

Bass Controls and Treble Controls. The
tone balance which you hear when listening
to an orchestra is affected by the conductor's

instructions to his musicians, the acoustical
environment in which you are listening, and

your own subjective hearing interpretation.

Tone balance will even depend on the room
or hall where you listen to the music. Con­sidering these conditions, it is easy to see
why tone balance controls play a major role

in correcting for the following factors:

1. Each person's subjective idea of tone

balance.

2. Loudspeaker frequency response char-

acteristics.

3. Loudspeaker placement in the listen-

ing room.

12

4. The conductor's idea of tone balance

at the time the recording was made.

5. The microphone frequency response

characteristics.

6. The recording process influences.

These factors can be considered as en­vironmental influences. The BASS CON­TROLS and TREBLE CONTROLS are designed

to provide a degree of compensation for
effects of environment. Listen to your system
with each control set to zero. If you wish to

reduce treble in relation to bass, rotate the
TREBLE CONTROLS counterclockwise until
the tone balance sounds correct to you.
These controls will modify tone balance with-

out introducing any undesirable effects. Do

not be surprised if you find your preference

in tone changing from time to time.

Compensator. The COMPENSATOR con-

trol is used to correct for the necessary pro­gram equalization which the recording proc-

ess introduces. Recording requires a change

in the distribution of intensity with frequency.
Without compensation a magnetic cartridge
would sound deficient in the bass range and
overly bright or shrill in the treble range.

Loudness. Due to a selective shift in sensi-

tivity of human hearing, music reproduced at

very low volume loses its bass and treble.

The LOUDNESS switch on the C11 changes
the VOLUME control to a loudness control to
correct for this effect. When you wish to listen
to music at a greatly reduced loudness level
and yet hear bass and treble, set the LOUD-

NESS switch to the COMPENSATED position.

USING THE C11 WITH A STEREO TUNER

1. Turn the INPUT SELECTOR to the posi-

tion corresponding to the program selected.

2. Turn the BASS CONTROLS and TREBLE

CONTROLS to their 0 positions.

3. Turn the MODE SELECTOR to STEREO,

4. Place the TAPE switch in the NORMAL

position.

5. Place the PHASE switch in the NORMAL

position.

6. Place the POWER switch in the ON

position.

7. Place the RUMBLE switch in the FLAT

position.

8. Place the H.F. cutoff filter switch in the

FLAT position.

9. Place the LOUDNESS switch in the

NORMAL position.

USING THE C11 WITH A STEREO TAPE

MACHINE

A stereo tape machine with its own play-

back preamplifiers should be plugged into

the TAPE INPUTS—not the TAPE HEAD in-

puts. The information on adjusting the C11
for listening to a stereo tuner will also apply

when listening to a tape machine.

USING THE C11 WITH TAPE DECKS

1. Turn the INPUT SELECTOR to the posi-

tion corresponding to the program selected.

2. Turn the BASS CONTROLS and TREBLE

CONTROLS to their 0 positions.

3. Turn the MODE SELECTOR to STEREO,

4. Place the TAPE switch in the NORMAL

position.

5. Place the PHASE switch in the NORMAL

position.

6. Place the POWER switch in the ON

position.

7. Place the RUMBLE switch in the FLAT

position.

8. Place the H.F. cutoff filter switch in the

FLAT position.

9. Place the LOUDNESS switch in the

NORMAL position.

USING THE C11 WITH MICROPHONES

FOR STEREO

Microphones in stereo may be used with
the C11. The two MIC channels amplify mi­crophone signals. They have a sensitivity of
2 millivolts and an input impedance of 1
megohm. For lower output microphones in-

put transformers should be used to raise the

voltage output to the 2 millivolt range.

When the INPUT SELECTOR is turned to

the MIC position, the COMPENSATOR con-

trol does not operate. All the other controls

operate and may be used the same as for
any other program source.

LISTENING TO MONOPHONIC RECORDS

If you wish to listen to monophonic rec­ords, switch the INPUT SELECTOR to PHONO

1 or PHONO 2. Turn the MODE SELECTOR to

the L TO L+R or R TO L+R position. L TO

L+R position connects the left input to both
loudspeakers. R TO L+R position connects

the right input to both loudspeakers.

13

EQUALIZATION CURVES

25

20

15

10

5

0

-5

RESPONSE IN DB

-10

-15

-20

-25

20 100

BASS AND TREBLE CONTROLS

20

15

10

5

0

-5

-10

RESPONSE IN DB

-15

-20

1KC

FREQUENCY

Figure 10. Equalization curves.

IOKC

20

KC

14

20

100

FREQUENCY

Figure 11. Bass and treble controls.

1KC

10 KC

20

KC

RESPONSE IN DB

RUMBLE AND HIGH FREQUENCY FILTERS

0

-5

-10

-15

-20

-25

-30

20

LOUDNESS CONTROL

20

15

10

5

0

-5

RESPONSE IN DB

-10

-15

100

FREQUENCY

1

KC

Figure 12. Rumble filter and high frequency filter.

10 KC

20 KC

-20

20 100 1KC 10KC

FREQUENCY

Figure 13. Loudness control.

20 KC

15

Your C11 will give you many years of pleasant and satisfactory
performance. If you have any questions concerning the oper­ation or maintenance of this preamplifier please contact:

Customer Service

Mcintosh Laboratory Inc.

2 Chambers Street

Binghamton, New York
Our telephone number is 723-5491.
The direct dial area code is 607.

GUARANTEE

Mcintosh Laboratory Incorporated guar­antees this equipment to perform as adver­tised. We also guarantee the mechanical and

electrical workmanship and components of

this equipment to be free of defects for a

3-YEAR FACTORY SERVICE CONTRACT

An application for a FREE 3-YEAR FAC­TORY SERVICE CONTRACT is included in the
pocket in the back cover of this manual. The

FREE 3-YEAR FACTORY SERVICE CONTRACT

will be issued by Mcintosh Laboratory upon

receipt of the completely filled out applica-

tion form. The term of this contract is de-

In Canada: manufactured under license by:

McCurdy Radio Industries, Ltd.
22 Front Street West
Toronto, Canada

period of 90 days from date of purchase.

This guarantee does not extend to compo-

nents damaged by improper use nor does it
extend to transportation to and from the

factory.

fined in the 3-year factory service contract.

If the application is not mailed to Mcintosh

Laboratory, only the services offered under
the standard 90-day guarantee will apply on
this equipment. TAKE ADVANTAGE OF 3

YEARS OF FREE FACTORY SERVICE BY

FILLING IN THE APPLICATION NOW.

16

Design subject to change without notice.

LABORATORY INC.

2 CHAMBERS STREET, BINGHAMTON, N. Y.

Made in U.S.A .

Phone-Area Code 607-723-5491

Printed in U.S.A.