McIntosh | C32 | THE MclNTOSH C32 SOLID STATE STEREO PREAMPLIFIER

THE MclNTOSH C32 SOLID STATE STEREO PREAMPLIFIER
Reading Time: 44 Minutes
Price $1.25
WARNING: TO PREVENT FIRE OR SHOCK
HAZARD, DO NOT EXPOSE THIS UNIT TO
RAIN OR MOISTURE.
The Mclntosh you have purchased has a serial number located on
the rear panel of the chassis.
Record that serial number here
for future references. The model and serial number are important
to you for any future service.
Your C 32 Stereo Preamplifier will
give you many years of pleasant and
satisfactory performance. If you
have any questions, please contact:
Contents
CUSTOMER SERVICE
INTRODUCTION
HOW TO INSTALL
HOW TO CONNECT
USING THE FRONT PANEL CONTROLS
USING THE PUSHBUTTONS
BALANCING YOUR STEREO
LISTENING TO YOUR STEREO
PERFORMANCE LIMITS AND RATINGS
PERFORMANCE CHARTS
TECHNICAL DESCRIPTION
BLOCK DIAGRAM
Mclntosh Laboratory Inc.
2 Chambers Street
Binghamton, New York 13903
Phone: 607-723-3512
Take Advantage of 3 years
of FREE Service...
Fill in the Application NOW.
THREE YEAR SERVICE CONTRACT
An application for a FREE THREE YEAR SERVICE CONTRACT is included with this manual.
mishandling is not covered by the SERVICE
CONTRACT.
The terms of the contract are:
4. The SERVICE CONTRACT is issued to you as
the original purchaser. To protect you from
misrepresentation this contract cannot be
transferred to a second owner.
1. Mclntosh will provide all parts, materials and
labor needed to return the measured performance of the instrument to the original performance limits free of any charge. The
SERVICE CONTRACT does not cover any
shipping costs to and from the authorized
service agency or the factory.
5. For your protection Mclntosh selects only
dealers who have technical competence to
guide purchasers fairly, and provide service
when necessary. To receive the SERVICE
CONTRACT your purchase must be made
from a Mclntosh franchised dealer.
2. Any Mclntosh authorized service agency
will repair Mclntosh instruments at normal
service rates. To receive the free service
under the terms of the SERVICE CONTRACT,
6. Your completely filled in application for a
SERVICE CONTRACT must be postmarked
within 30 days of the date of purchase of the
instrument.
the SERVICE CONTRACT CERTIFICATE must
accompany the instrument when taken to
the service agency.
7. To receive the SERVICE CONTRACT all information on the application must be filled
in. The SERVICE CONTRACT will be issued
when the completely filled in application is
received at Mclntosh Laboratory Incorporated
in Binghamton, New York.
3- Always have service done by a Mclntosh
authorized service agency. If the instrument
is modified or damaged, as a result of unauthorized repair the SERVICE CONTRACT
will be cancelled. Damage by improper use or
Copyright
©
1977 by Mclntosh Laboratory Inc.
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Introduction
How to install
The Mclntosh C 32 preamplifier provides the most comprehensive range of functions and control options. Many
of these are new in a preamplifier. The C 32 can only
serve you best when you understand what its functions
are and what it is designed to do. Spend some time with
this manual and get to know how this preamplifier works.
The PANLOC system of installing equipment conveniently and securely is a direct result of Mclntosh research.
By depressing the two PANLOC buttons on the front panel
of the C 32, the instrument either can be locked firmly in
place or unlocked so that the chassis can be slid forward,
giving you easy access to the top and rear panels.
The C 32 is a "dual" stereo preamplifier with a built-in
MONITOR POWER AMPLIFIER. There are two totally independent left and right stereo program lines running
through the preamplifier. One program line is the LISTEN
program line, the other is the RECORD program line. Each
program line can select its own program source from any
connected input signal—i.e. PHONO, TUNER, AUX, or
TAPES 1, 2 or 3 without interference with the other program line.
The trouble-free life of an electronic instrument is
greatly extended by providing sufficient ventilation to
prevent the buildup of high internal temperatures that
cause deterioration. Allow enough clearance so that cool
air can enter at the bottom of the cabinet and be vented
from the top. With adequate ventilation the instrument
can be mounted in any position. The recommended minimum space for installation is 15 inches (38.1 cm) deep,
17 inches (43.2 cm) wide, and 6 inches (15.2 cm) high.
The output of the LISTEN program line is affected by
all the front panel controls (except the RECORD switch)
and is fed to the OUTPUT MAIN and/or OUTPUT 1 and 2
jacks as selected by front panel pushbuttons. The output
of the RECORD program line is not affected by front panel
controls (except the RECORD switch) and is fed to all
OUTPUT RECORD jacks.
To install the instrument in a Mclntosh cabinet, follow
the instructions that are enclosed with the cabinet. For
any other type of installation:
1. Unpack from Carton
Remove the instrument PANLOC brackets, hardware
package, and mounting template from the carton. Remove the C 32 from its plastic bag and place it upside
down on the shipping pallet; unscrew the four plastic
feet from the bottom of the chassis.
The MONITOR AMPLIFIER program may be selected
from either the LISTEN or RECORD program lines. Separate GAIN controls for LEFT AND RIGHT MONITOR AMPLIFIER are located on the top panel. The signal selected
for the MONITOR AMPLIFIER is fed to the front panel
HEADPHONE jacks and the rear panel OUTPUT LINE and
MONITOR OUTPUT connectors.
2. Mark for Position
Place the mounting template in position to cover the
area of the cabinet panel where the instrument is to be
installed, and tape it in place. The broken lines that
represent the outline of the rectangular cutout also
represent the outside dimensions of the chassis. Make
sure these lines clear shelves, partitions, or any equipment. With the template in place, first mark the six A
and B holes and the four small holes that locate the
corners of the cutout. Then, join the four corner markings with pencil lines, using the edge of the template
as a straightedge.
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3. Drill Holes
Using a drill with a 3/16 inch bit held perpendicular to
the panel, drill the six A and B holes. Then, using a drill
bit slightly wider than the tip of your saw blade, drill
one hole at each of two diagonally opposite corners. The
holes should barely touch the inside edge of the pencilled
outline. Before taking the next step, make sure that
the six A and B holes have been drilled.
7. Install Instrument
Guide the AC power cord through the panel opening to
the back of the cabinet; then, slide the instrument into
the opening carefully so that the rails on the bottom of
each side of the chassis engage the tracks on the mounting brackets. Continue to slide the instrument into the
cabinet until it is stopped by the adjust position latches.
Press the latches inward, this permits the instrument to
slide into the cabinet until its front panel is flush with
the cabinet panel. Depress the PANLOC buttons at the
lower left and right corners of the instrument panel to
lock the unit firmly in the cabinet. Depressing the
PANLOC buttons again will unlock the instrument so
that it can be slid forward to the adjust position;
pressing inward on the adjust position latches permits
removal from the cabinet
4. Saw Panel Cutout
Sawing carefully on the inside of the pencilled lines,
first make the two long cuts and then the two short.
After the rectangular opening has been cut out, use a
file to square the corners and smooth any irregularities
in the cut edges.
5. Install Mounting Strips
In the hardware package you will find two mounting
strips and two sets of machine screws. For panels that
are less than ½ inch thick, use the ¾ inch screws; for
panels that are more than ½ inch thick, use the 1¼ inch
screws.
Starting at the right-hand side of the panel, insert a
screw of the proper length into the center hole in the
panel, marked B on the template. On the back of the
panel, align a mounting strip with the holes in the panel
and tighten the screw until the screwhead is pulled
slightly into the wood.
Repeat this procedure to attach the mounting strip
to the left side of the panel.
6. Attach PANLOC Brackets
Using two screws of the proper length in the A holes on
each side, attach the PANLOC brackets to the cabinet
panel; the short flange is mounted against the front
(face) of the cabinet panel. The screws pass through the
PANLOC bracket flange, the cabinet panel, and then
through the mounting strips previously mounted.
3
How to Connect
left high level input of the tape recorder.
Connect a cable from the OUTPUT R TAPE 1 jack to the
right high level input of the tape recorder
Connect second and third tape recorders in the same
fashion to the TAPE 2 and TAPE 3 outputs.
CONNECTING A TURNTABLE TO PHONO 1
Connect the cable from the "left" channel of the turntable into the INPUT L PHONO 1 jack.
Connect the cable from the "right" channel of the turntable into the INPUT R PHONO 1 jack.
To Playback/Monitor:
Connect the cable from the left channel output of a tape
recorder to the INPUT L TAPE 1.
Connect the cable from the right channel output of a tape
recorder to the INPUT R TAPE 1.
Connect second and third tape recorders in the same
fashion to the TAPE 2 and TAPE 3 INOUT jacks.
PHONO 2 is provided for the use of a second turntable.
Connect the cable from the "left" channel of the turntable into the INPUT L PHONO 2 jack.
Connect the cable from the "right" channel of the turntable into the INPUT R PHONO 2 jack.
TAPE RECORDER FRONT PANEL CONNECTION
Inputs and outputs for TAPE 3 are available at the TAPE 3
IN-OUT jacks on the front panel just left of the pushbuttons.
This allows rapid, temporary connections to TAPE 3 position
without getting at the rear panel, A metal shielded V
stereo phone plug is used for best shielding—similar to
the plugs used on low impedance headphones. Connections
follow the industry standards and are tip: left signal, ring:
right signal, and, sleeve: common ground
On the rear panel are two green AC power outlets and
a slide switch marked AUTO/MANUAL. Plug the AC power
cables from the turntable into the green TURNTABLE
POWER outlets on the rear panel. When the switch is in
the AUTO position, power to the black AC power outlets, can be controlled by the front panel POWER switch
or by the current drawn by a turntable plugged into
the green TURNTABLE POWER outlets. The current sensing green AC power outlets will control the AC power
to the entire system from the AC power on/off switch on
the turntable. When the turntable is turned off with its
own AC power switch, no current is drawn which causes
the current sensing relays in the C 32 to turn oft all AC
power to the system. With the AUTO/MANUAL switch in the
MANUAL position, AC power to the system will be controlled
by the front panel POWER pushbutton only.
Some turntables have electronic circuits that d r a w current
all the time. To use these turntables the AUTO/MANUAL
switch must be in the MANUAL position.
The green AC power outlets are protected with a one
ampere fuse. Any increase in the value of this fuse will
affect the operation of the sensing circuit and can cause
severe damage.
Connecting a Tape Recorder to the Listen Program Line
Connect a cable from the OUTPUT 1 —LEFT jack to the
left high level input of the tape recorder
Connect a cable from the OUTPUT 1 —RIGHT jack to the
right high level input of the tape recorder.
Output signal will be ted to the tape recorder when the
front panel pushbutton OUTPUT 1 is pushed in.
CONNECTING THE C 32 TO POWER AMPLIFIERS
Connect the OUTPUT MAIN jacks to the input of a
stereo power amplifier. The Left MAIN jack is connected
to the left amplifier input jack. The Right MAIN jack is
connected to the right amplifier input jack.
GROUND CONNECTION
A single ground post is provided. Grounds for turntables,
record changers, tape decks, etc. should be connected to
this post. The left and right program cables and the ground
wire from that source should be wound or twisted together.
To avoid hum, make sure the ground wire does not make
any connections to the shields of the left and right program
cables between the program source and the C 32.
Two additional stereo power amplifiers may be connected in the same fashion to the OUTPUT 1 and OUTPUT 2
jacks. Audio output signal is supplied to these jacks only
when front panel pushbutton SPEAKER/OUTPUT 1 and 2
pushbuttons are pressed IN. The input impedance of the
amplifiers used should be 5,000 ohms or greater.
SPEAKER CONTROL RELAY
To control loudspeakers by use of SPEAKER/OUTPUT 1
and 2 pushbuttons on the front panel an accessory Mclntosh
SCR (SPEAKER CONTROL RELAY) is needed. Plug the special
cable from the SCR control into the SPEAKER CONTROL
RELAY receptacle. The speakers are then connected to the
SCR control.
CONNECTING A STEREO TUNER
Connect the cable from the "left" channel tuner output
to the INPUT L TUNER jack.
Connect the cable from the "right" channel tuner output
to the INPUT R TUNER jack.
AUX—Any high level program source such as a tuner,
a TV set or a tape recorder can be connected to the INPUT
AUX jacks.
The SCR has two AC power outlets that provide additional capacity of 2400 watts. Use these outlets to supply
AC power to amplifiers or other components to be controlled by the ON OFF cycle of the C 32. Use the SCR
whenever the total load to be switched by the C 32 exceeds
its rating of 600 watts.
CONNECTING TAPE RECORDERS
To Record:
Connect a cable from the OUTPUT L TAPE 1 jack to the
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TAPE RECORDER 3
TAPE
RECORDER
2
TAPE
RECORDER
1
FM ANTENNA
TUNER
AC POWER
AC POWER TO
TAPE RECORDERS.
TUNERS, POWER
AMPLIFIERS.
TOTAL OF 600 WATTS.
FOR MORE AC POWER
USE THE SCR SPEAKER
CONTROL RELAY
T U R N T A B L E #2
AC
POWER
TURNTABLE #1
5
6
TO AC LINE
USE OF
PUSHBUTTONS
SPEAKER/OUTPUT
REMOTE
SPEAKERS
SPEAKER CONNECTIONS
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MAIN SPEAKERS
MONITOR AMPLIFIER SPEAKERS
Using the Front Panel Controls
Use the EQUALIZER FREQUENCY controls to modify the
sound and balance of material. Here are some suggestions
from which to start:
LISTEN and RECORD Input Selector Switches
The control at the left top of the front panel selects the
input for the LISTEN program line. The left bottom control
selects the input for the RECORD program line. Both operate in the same manner.
Problem
Bass too weak
Male vocalist needs reinforcing
Female reinforcing
Hum on program
Violins, trumpets dull
Drum "brushes" not audible
MODE SELECTOR
The MODE SELECTOR facilitates the accurate adjustment
of a stereo system for differences caused by room acoustics, loudspeaker placement and the other components
used in the system.
Equalizer Correction
Raise 30 and/or 150
Raise 150
Raise 500
Reduce 30 and LF FILTER
Raise 1500
Raise 10 K
To prevent interference from subsonic and supersonic
signals, the C 32 includes subsonic and supersonic filters
that attenuate signals below 20 Hz and above 20,000 Hz.
They are bypassed when the EQ OUT pushbutton is pressed
IN which extends the frequency response to 10 Hz to
100,000 Hz.
The MODE SELECTOR switch affects the program on
the LISTEN program line only and connects the program
to the loudspeaker in seven ways:
L to L and R: Connects the left input to both loudspeakers.
R to L and R: Connects the right input to both loudspeakers.
STEREO: Connects the left input to the left loudspeaker
and the right input to the right loudspeaker.
BALANCE and LOUDNESS
The BALANCE and LOUDNESS controls are concentric.
The BALANCE control (large outer knob) adjusts for equal
volume of either the left or right channels. The volume of
the channels can be varied relative to each other without
affecting their combined volume.
MONO (L + R): Adds the left and right inputs together and
connects to both loudspeakers.
LEFT . . . turning the control to the left accents the left
channel by reducing the right channel output.
L + R to L: Connects the left plus right program to the
left loudspeaker only.
RIGHT . . . turning the control to the right accents the
right channel by reducing the left channel output.
STEREO REV: Connects the left input to the right loudspeaker and the right input to the left loudspeaker.
L - R to R: Connects the left plus right program to the
right loudspeaker only.
LOUDNESS
The LOUDNESS control (small center knob) increases
both bass and treble frequencies of both channels as it is
turned clockwise. Adjustment of the LOUDNESS control
allows life-like frequency balance when playing music
softly. Its contour is the same, regardless of the position
of the volume control. This contour is accurately modelled
after the family of "Equal Loudness" curves identified by
Fletcher and Munson.
EQUALIZER FREQUENCY Controls
Each of five EQUALIZER FREQUENCY controls raises or
lowers a band of frequencies centered on the frequency
marked above the control. Both left and right channels of
the LISTEN program line are affected. The center, or flat,
position of the control has a detent for easy reference.
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EXPANDER
The EXPANDER affects both channels of the LISTEN
program line only. The circuit enables you to correct for
the compression that is imposed on most of the program
material available—records, tapes and FM. Compression
is used for many practical reasons but limits the dynamic
range—and, therefore, the realism—of the music. Programs
vary in their need for expansion. Live recordings may not
need any at all. Rotation of the EXPANDER causes the
loudness of the program to be affected logarithmically.
The point at which operation of the expander starts is
selected by the rotary LEVEL MATCH control on the top
panel. The attack speed of the expander is set with the
SPEED switch on the top panel. Settings of FAST, NORM
and SLOW change the attack time of the expander.
As the EXPANDER control is rotated clockwise the circuit
acts in two ways:
1. Loudness is reduced for signals below a predetermined
set level. The farther below set level the program is, the
more the loudness is reduced.
2. Loudness is increased for signals above set level. The
greater the program is above set level, the more the
loudness is increased.
The amount of loudness expansion imposed on incoming
signals is determined by the position of the EXPANDER
control. Clockwise rotation increases the effect. As the
EXPANDER knob is rotated clockwise, undesirable noises
such as hum, scratch and hiss are reduced. The charts
show the action of the EXPANDER CIRCUIT. When rotated
fully counterclockwise, the front panel EXPANDER knob
activates a switch which completely by-passes all EXPANDER circuitry.
The LEVEL MATCH control on the top panel of the C 32
adjusts the set level. This is the point above and below
which expansion is introduced when the EXPANDER knob
is turned clockwise. Set the LEVEL MATCH controls for each
channel while listening to a program. Switch the EXPANDER
in and out. The average sound level of the system should be
the same with the EXPANDER knob in the desired position
of EXPANSION as it is in the bypass (OFF) position.
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MONITOR AMPLIFIER
Although its primary purpose is to drive the headphone
jacks, the MONITOR AMPLIFIER may additionally be used:
A. To reduce noise (hum, hiss or scratch)
1. Select the desired program source with LISTEN front
panel selector switch.
1. To listen, on speakers, to any of the inputs connected to
the C 32 without the use of a separate stereo power
amplifier. Stereo loudspeakers can be connected to the
rear panel 8 ohm terminals. The program source for the
MONITOR AMPLIFIER may be selected from either the
LISTEN program line or the RECORD program line by
means of the top panel INPUT switch. Beside the INPUT
switch are LEFT GAIN and RIGHT GAIN controls. They
control the volume of the respective channels of the
MONITOR AMPLIFIER.
2. Switch top panel SPEED control to NORM.
3. Increase VOLUME control during a quiet passage of
the program until noise is clearly audible.
4. Rotate EXPANDER control clockwise until the noise
is acceptably reduced.
5. Adjust the LEVEL MATCH controls.
B. To improve the "live" sound of recorded or transmitted
program material:
2. To drive a 600 ohm unbalanced line connected to
OUTPUT LINE jacks.
1. Select LISTEN input.
3. The extensive flexibility of the C 32 permits many other
possible uses of the MONITOR AMPLIFIER such as
adding a reverberation device, time delay or "ambience"
accessory unit, discrete 4-channel, etc.
2. Switch top panel SPEED control to NORM.
3. Increase VOLUME to satisfactory level.
4. Rotate the EXPANDER control clockwise until the
dynamic range of the music, the ratio of loud to soft
is correct for you.
5. Adjust the LEVEL MATCH controls as described previously.
By using the EXPANDER controls in conjunction with the
EQUALIZER FREQUENCY controls, the C 32 may be used
to de-emphasize and decompress disc and tape program
material.
HEADPHONE Jacks
The stereo HEADPHONE jacks are driven by the built-in
MONITOR AMPLIFIER. Either LISTEN or RECORD programs
can be heard depending on the position of the INPUT
switch on the MONITOR AMPLIFIER located on the top
panel. The LEFT and RIGHT GAIN controls regulate headphone volume:
A. In conjunction with the main front panel VOLUME control if the top panel INPUT switch is in LISTEN position,
B. Exclusively if the INPUT switch is in RECORD position.
The upper HEADPHONE jack is used to feed electrostatic
headphones. It is fed directly by the MONITOR AMPLIFIER.
Electrostatic headphones require more power than dynamic
type headphones as a rule. The lower headphone jack is
used to feed low impedance dynamic headphones. It is
fed by the MONITOR AMPLIFIER through a matching network.
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Using the Pushbuttons
PHONO 1-2
The PHONO 1-2 pushbutton selects from either PHONO 1
or PHONO 2 inputs. When the button is out—the indicator
above the 1 will light and the PHONO 1 signals will be
connected to the LISTEN and RECORD switches. When the
pushbutton is in, the indicator above the 2 will light and
the PHONO 2 inputs will be connected to the LISTEN and
RECORD switches.
HF FILTER
The HF FILTER affects only the LISTEN program line.
With the HF FILTER IN all frequencies above 7,000 Hz are
attenuated at the rate of 12 dB per octave. Use it to reduce
undesirable high frequency noise such as record surface
noise or tape hiss.
SPEAKER/OUTPUT 1 and 2
The SPEAKER/OUTPUT 1 and 2 pushbuttons operate
only on the LISTEN program line. Each serve dual purposes.
RECORD MONITOR
When pressed IN, the RECORD MONITOR pushbutton
switches the LISTEN input to the output of the RECORD
program line. In the IN position the program heard on the
LISTEN program line is the program on the RECORD program line.
When pressed IN, they
A. Connect the LISTEN program to the OUTPUT 1 and 2
jacks on the rear panel. Sound can thus be switched on
and off in areas served by additional amplifiers connected to these jacks. Typical uses would be the switching of music to selected living areas, a swimming pool
or an outdoor recreation area.
EQ OUT
The EQ OUT pushbutton operates to bypass the program
equalizers, the LF and HF filters and the subsonic and
supersonic filters on the LISTEN program line. With the
EQ OUT pushbutton pressed IN, the total bandwidth of
the C 32 is 10 to 100,000 Hz. The indicator light above
the EQ OUT pushbutton is illuminated when the pushbutton
is pressed IN indicating that the EQUALIZER FREQUENCY
and the HF and LF FILTERS are removed from the circuit.
B. Control the operation of a SCR relay when it is plugged
into the rear panel SPEAKER CONTROL RELAY socket.
The SCR controls the audio to two pairs of stereo loudspeakers. The AC power to two AC receptacles on the SCR
is controlled by the ON-OFF cycle of the C 32. The total
AC power capacity of the receptacles is 2400 watts.
POWER
The POWER switch energizes the C 32 circuits and supplies AC power to the black rear panel AC power outlets.
The black AC power outlets are not fused.
LF FILTER
The LF FILTER affects only the LISTEN program line
when pressed in. With the LF FILTER IN all frequencies
below 50 Hz are attenuated at the rate of 12 dB per octave.
Use it to reduce undesirable low frequency noise such as
rumble or acoustic feedback.
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Balancing Your Stereo
3. Turn the BALANCE control to the 12 o'clock position.
The performance and enjoyment of a stereo system is
greatly increased when the sound is properly balanced.
Balance is affected by many things including room acoustics, furniture placement, room shape, small differences in
loudspeakers, etc. The input gain controls on your stereo
power amplifier should be used to balance the system.
The BALANCE control on the C 32 should be used to adjust
for imbalance in program material.
4. While the program is playing, stand between the two
loudspeakers. Listen for a difference in loudness between speakers. Balance the system by adjusting the
controls on the power amplifiers. Next, set the MODE
selector to STEREO. If there is then a difference in
loudness turn the BALANCE control toward the speaker
that is not as loud. Adjust the BALANCE control until
the sound is equally loud from both speakers.
1. Set the MODE to MONO.
2. Play a familiar recording.
Listening to Your Stereo
it is fed to the tape recorder, or, in the case of tape recorders
having separate playback heads and associated preamplifiers, directly oft the tape. To monitor the program being
ted to the tape recorder, press the RECORD MONITOR
pushbutton IN, To monitor from the playback head of the
tape recorder as the program is being recorded turn the
LISTEN switch to TAPE 1. 2 or 3.
LISTENING TO STEREO RECORDS
Turn the LISTEN selector to PHONO 1, or PHONO 2,
whichever is connected to the turntable you wish to hear.
Set the MODE SELECTOR to STEREO.
Adjust the VOLUME control to the desired volume.
LISTENING TO MONOPHONIC RECORDS
Turn the LISTEN selector to PHONO 1 or PHONO 2,
whichever is connected to the turntable you wish to hear.
USING THE LISTEN CONTROLS FOR TAPE RECORDING
To modify a program before recording, the OUTPUT 1
or 2 outputs on the program line may be fed to a tape recorder. For connection instructions, see page 4 under "How
to Connect."
Turn the MODE SELECTOR to MONO
Adjust the VOLUME control to the desired volume,
The controls in the LISTEN program line are all available
to alter the signal before recording Note that once recording has started, the controls will change the program
to the tape recorder. Since the available signal output
from the OUTPUT 1 or OUTPUT 2 is much higher than the
output available from the OUTPUT TAPE 1, TAPE 2, or
TAPE 3 jacks, be sure the signal does not overload the tape
recorder input,
LISTENING TO A TUNER
Turn the LISTEN selector to TUNER
Adjust the volume to a comfortable level.
LISTENING TO A TAPE RECORDER
Three tape recorders can be used with the C 32.
Turn the LISTEN selector to TAPE 1, 2 or 3 whichever is
connected to the tape recorder you wish to hear.
HOW TO COPY TAPE
The tape to be copied is ted to INPUT TAPE 1 Set the
RECORD selector to TAPE 1. The signal available at the
OUTPUT TAPE 2 and 3 jacks is the playback of TAPE 1
Recording is done on either recorder 2 or 3, or both and
can be monitored on the LISTEN program line by selecting
the appropriate TAPE position of the LISTEN knob.
Turn the MODE SELECTOR to STEREO or MONO, depending on the program on the tape
Adjust the VOLUME control to the desired volume.
TAPE MONITORING
A program being recorded may be monitored either as
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Performance Limits and Ratings
Performance Limits die the maximum deviation from
perfection permitted for a Mclntosh instrument. We promise
you that your C 32 must be capable of performance at or
exceeding these limits or you get your money back.
HF FILTER
Flat or roll-off at 12 dB per octave above 7000 Hz
FREQUENCY RESPONSE
+0 -0.5 dB 20 Hz to 20,000 Hz
(with equalizer out: +0 -1 dB from 10 Hz to 100,000 Hz)
VOLTAGE AMPLIFICATION in Decibels
(all equalizers and filters flat)
DISTORTION
.05% maximum, at rated output level, 20 Hz to 20,000 Hz
Input
Auxiliary, Tuner
Tape 1, 2 or 3
Phono 1
Phono 2
INPUT S E N S I T I V I T Y AND IMPEDANCE
PHONO 1 and 2 2 millivolts at 47,000 ohms 65 pF,
AUXiltary, TUNER TAPE 1, 2 and 3: 250 millivolts at
50,000 ohms
Main
20 dB
Tape
1,2,3
0dB
Monitor
Amp
20 dB
62 dB
42 dB
62 dB
SEMICONDUCTOR C O M P L E M E N T
67 Transistors
35 Integrated Circuits
62 Diodes
2 Field Effect Transistors
1 Silicon Controlled Rectifier (SCR)
HUM AND NOISE
AUXiliary, TUNER, TAPE 1, 2 and 3. IHF 100 dB unweighted--90 dB
PHONO 1 and 2 IHF 90 dB, unweighted 80 dB below 10
millivolt input or equivalent to less than 1 microvolt at the
input terminals
AC POWER OUTLETS
2 automatic current sensing (green)
4 switched (black)
OUTPUT LEVEL A N D I M P E D A N C E
MAIN Output 2.5 volts with rated input, 220 ohms source
impedance, to operate into 5,000 ohm or greater
TAPE Output 250 millivolts with rated input to operate
into 5,000 ohms or greater
POWER R E Q U I R E M E N T S
120 volts, 50/60 Hz, 25 to 85 w a t t s
MONITOR, HEADPHONE, LINE Output: 12
watts per channel, continuous, into 8 ohms
at 0,1% harmonic distortion 20 Hz to
20,000 Hz or 5 volts RMS into 600 ohm
line—level controls provided
MECHANICAL INFORMATION
SIZE: Front panel measures 16 inches wide (40,64 cm) by
5-7/16 inches deep (13.81 cm). Chassis measures 15
inches wide (38.1 cm) by 5 inches high (12.7 cm) by 13
inches deep (33.02 cm), including PANLOC shelf and back
panel connectors Knob clearance required is 1-1/2 inches
(3.81 cm) in front of the mounting panel.
FINISH: Front panel is anodized gold and black with
special gold/teal nomenclature illumination. Chassis is
black
MOUNTING: Exclusive Mclntosh developed professional
PANLOC
WEIGHT, 26 pounds (11.79 kg) net, 36 pounds (16.33 kg)
in shipping carton
PROGRAM EQUALIZER
Five, 2 octave frequency bands, each band has 12 dB of
boost or cut at 30, 150, 500, 1500 and 10,000 Hz
LF FILTER
Flat or roll-oft at 12 dB per octave below 50 Hz
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Performance Charts
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Technical Description
The dual program line control begins at two stereo
selector switches feeding from a common group of input
sources (PHONO PREAMP, TUNER, AUX, TAPE 1, 2, or 3)
to two separate stereo high level amplifiers. One of these
is the LISTEN amplifier, the other is the RECORD amplifier.
The LISTEN amplifier provides signal processing by high
and low pass filters, five equalizers, loudness compensation
and a logarithmic expander. The other, the RECORD amplifier, feeds the selected signal to the tape record output
connections.
switches that are self cleaning and extremely reliable. They
switch small DC voltages which turn the FET Analog
switches on or off. The design eliminates degradation of
frequency response or noise pickup.
Mode Selection
The LISTEN signal, as it leave its input selector switch
is connected to the MODE SELECTOR switch. The configuration of this switch permits combining the L and R programs
and connecting to LEFT or RIGHT outputs. This procedure
reveals system imbalance of less than a decibel, thus providing the means for very precise system balancing. LEFT
input to both L and R outputs and RIGHT input to both
L and R outputs is also provided again affording the same
degree of precision in balancing input signals. The switch
also provides STEREO REVERSE and MONO positions.
A stereo monitor amplifier in the C 32 feeds HEADPHONE, MONITOR and LINE OUTPUT. The input to the
MONITOR AMPLIFIER can be selected from either LISTEN
or RECORD program lines.
Phono Preamplifier
Each phono preamplifier circuit uses four specially selected low noise transistors arranged in very low impedance
configuration. To achieve low noise a 68 ohm feedback
termination is used. As a consequence, the preamplifier
must be capable of operating as a power amplifier to drive
this low impedance with low distortion. The actual power
output capability of this stage is more than 100 milliwatts.
Precise Tracking Volume Control
The volume control is designed and manufactured for
Mclntosh Laboratory. It is a step attenuator which has left
to right tracking accuracy within 1 dB throughout its entire
range. Such extremely accurate matching is achieved
through electronically controlled laser trimming of the
resistance material deposited on pairs of printed circuits.
Since the switch commutator touches only contact pads
and not the actual resistance element, tracking accuracy
is not degraded with use as in ordinary volume controls.
The C 32 is engineered to follow the RIAA equalization
curve precisely. One percent resistors and five percent
capacitors are used to ensure exact equalization of the
playback signal to the RIAA curve.
Loudness Compensation
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 speaker efficiency, amplifier
Input Selector Switching
A l l input switching is done electronically, using Field
Effect Analog switches (FET). The mechanical LISTEN and
RECORD switches on the front panel are simple, single deck
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gain and differences in input level.
A switched bypass link provides a program path around
the expander, to maintain a constant signal level with the
expander in or out of the circuit. The gain of the amplifier
block incorporated in the link approximates the gain of
the expander circuit.
The C 32 uses active circuitry, electrically independent
of the volume control. Close conformity to Fletcher Munson
Equal Loudness Curves is attained regardless of volume
control position.
The Record Program Line
The C 32 is designed to permit simultaneous recording
on up to three tape recorders of any program input selected
on the RECORD switch regardless of what is being heard
on the LISTEN program line. The RECORD switch selects
its input from the same inputs, but entirely independently
from the LISTEN switch. As this selection is by means of
high impedance FET Analog switches, switching to or over
an input in use on the LISTEN program line does not cause
any audio interference.
Active Filter Circuitry
Loudness, equalizer, and band pass filters of the C 32
are all constructed with ion implanted junction field effect
operational amplifiers (popularly called "Op Amps").
These new devices amplify with a 6 dB better signal to
noise ratio than bipolar input op amps.
Program Equalizers
To adjust for program limitations and personal preferences the C 32 LISTEN program line has a five band boost/
cut program EQUALIZER based on resonant circuit operational amplifier. The preamplifier is flat when the EQUALIZER controls are at the 12 o'clock position. EQUALIZER
center frequencies of 30, 150, 500, 1500 and 10,000 Hz
were chosen to cover the audio spectrum in approximately
equal two octave bandwidths. Maximum boost and cut is
12 dB at band centers.
Output from the RECORD switch is fed through tape
interlock switches to the three pairs of tape recorder output
jacks. In the event that one of the tape recorders is chosen
as an input signal to the RECORD program line, its associated tape interlock is opened to prevent feedback through
that tape recorder back into the C 32 input.
Monitor Amplifier/Headphone Circuits
HF and LF Filters
The HF and LF filters are selected by pushbutton switches
in a manner electrically similar to the program EQUALIZERS
and are pushbutton switch selected. The HF filter attenuates all frequencies above 5 kHz, reaching a rate of 12 dB
per octave, at 7 kHz (at which point attenuation is 3 dB
below the 5 kHz level). The LF filter attenuates all frequencies below 50 Hz, at a rate of 12 dB per octave.
The C 32 contains a stereo power amplifier which provides adequate power to drive electrostatic headphones.
The upper HEADPHONE output jack is connected directly
to this MONITOR AMPLIFIER output, making the full 12
watts per channel power available to drive those headphones which require it. The lower HEADPHONE jack is
fed through a network designed to match low impedance
dynamic headphones.
All program EQUALIZERS and HF/LF filters are bypassed
when the EQ OUT pushbutton switch is depressed. The
EQ OUT switch also removes subsonic and supersonic filters below 20 Hz and above 20,000 Hz, extending total
frequency response to 10 Hz to 100,000 Hz.
In addition, the MONITOR AMPLIFIER may be switched
to either program line, controlled and connected with
enough flexibility that several other uses for it are possible.
Some of these are:
1. As a preamplifier/power amplifier in a completely
separate stereo system.
The Expander
To overcome the compression imposed in radio broadcasting and recording, and to reduce hum, scratch and hiss,
the C 32 has a logarithmic program expander in the
LISTEN program line. Controls are provided to adjust the
operating point, attack time and expansion ratio.
2. To power rear channel speakers when used in a 4channel discreet system.
3. To operate speakers in another area.
4. To feed a 600 ohm line.
Signal from the equalizer circuit is applied to a voltage
controlled amplifier (VCA) which operates as a variable
gain block. Control voltages for this VCA are developed
from a sample taken from the output of the equalizer. The
electronic processing of this sample is detailed. It includes
band shaping, logarithmic amplification, full wave rectification, level setting, expansion ratio regulation, attack
timing, level setting and DC amplification. The resulting
voltage controls the gain of the VCA to cause logarithmic
gain reduction below set level and logarithmic expansion
above set level.
On the rear panel are two green AC power outlets and
a slide switch marked AUTO/MANUAL. Plug the AC power
cables from the turntable into the green TURNTABLE
POWER outlets on the rear panel. When the switch is in
the AUTO position, power to the black AC power outlets,
can be controlled by the front panel POWER switch or
by the current drawn by a turntable plugged into the
green TURNTABLE POWER outlets. The current sensing
green AC power outlets will control the AC power to the
entire system from the AC power on/off switch on the
turntable. When the turntable is turned off with its own
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AC power switch, no current is drawn which causes the
current sensing relays in the C 32 to turn off all AC power
to the system.
Special Output Switching
In addition to the OUTPUT MAIN jacks, two additional
pairs of output jacks, OUTPUT 1 and OUTPUT 2, are provided. These are individually switched from the front
panel pushbuttons SPEAKER/OUTPUT. The C 32 output
signal can be fed to two additional stereo power amplifiers
independent of the main system stereo amplifier. Alternatively, these outputs may be used to drive reverberation
devices, delay lines, etc. The SPEAKER/OUTPUT pushbutton
switches provide the voltage to control a SCR speaker control relay.
Power Supply
To minimize hum pickup—and thus improve signal to
noise ratio—the C 32 power transformer is triple shielded.
Shielding includes a copper strap, a silicon steel strap and
finally, a steel outer shell. The transformer output voltage
is fed to a full wave bridge with 5,000 microfarad filter
capacitors to provide the plus and minus 24 volts powering
the MONITOR AMPLIFIER. The plus and minus 18 volts
needed for low level and op amp stages is derived from the
24 volt supply and controlled with integrated circuit voltage regulators.
Turn on Delay
The C 32 has transient free turn on and turn off characteristics. A relay, time controlled by a transistor switch,
connects the output of the preamplifier to the output jacks.
The control to the transistor switch is derived from a long
time constant capacitor charging network that turns the
relay on approximately two seconds after the C 32 is
turned on. The same circuit has a short turn-off time constant which turns off the relay before the preamplifier's
main power supply has had a chance to discharge.
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Block Diagram
MclNTOSH LABORATORY INC.
2 CHAMBERS ST. BINGHAMTON, N. Y. 13903
607-723-3512
The continuous improvement of its products is the policy of
Mclntosh Laboratory Incorporated, who reserve the right to
improve design without notice.
Printed in U.S.A.
038-990
BE032003
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