McIntosh C29 Stereo Preamplifier Owner’s Manual
- June 5, 2024
- McIntosh
Table of Contents
Owner’s Manual
THE C 29 SOLID-STATE STEREO PREAMPLIFIER
Reading Time:38 Minutes
Price: S2.00
Your C 29 Preamplifier will give you many years of pleasant and satisfactory
performance. If you have any questions, please contact:
CUSTOMER SERVICE
McIntosh Laboratory Inc. 2 Chambers Street Binghamton, New York 13903.9990
Phone: 607-723-3512
Take Advantage of 3 years of Contract Service … Fill in the Application NOW
McINTOSH THREE YEAR SERVICE CONTRACT
An application for a THREE-YEAR SERVICE CONTRACT is included with this manual.
The terms of the contract are:
- McIntosh will provide all parts, materials, and labor needed to return the measured performance of the instrument to the original performance limits. The SERVICE CONTRACT does not cover any shipping costs to and from the authorized service agency or the factory.
- Any McIntosh authorized service agency will repair McIntosh instruments at normal service rates. To receive service under the terms of the SERVICE CON-TRACT, the SERVICE CONTRACT CERTIFICATE must be presented when the instrument is taken to the service agency.
- Always have service done by a McIntosh authorized service agency. If the instrument is modified or damaged, as a result of unauthorized repair the SERVICE CONTRACT will be canceled. Damage by improper use or mishandling is not covered by the SERVICE CONTRACT.
- 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.
- To receive the SERVICE CONTRACT your purchase must be made from a McIntosh franchised dealer.
- Your completely filled-in application for a SERVICE CONTRACT must be postmarked within 30 days of the date of purchase of the instrument.
- 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 McIntosh Laboratory Inc. in Binghamton, New York
The PANLOC system of installing equipment conveniently and securely is a
product of McIntosh’s research. By depressing the two PANLOC buttons on the
front panel, the instrument slide can be locked firmly in place or it can be
unlocked so that the chassis can slide forward, giving you easy access to the
top and rear panels.
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.
To install the instrument in a McIntosh cabinet, follow the instructions that
are enclosed with the cabinet. For any other type of installation follow these
instructions:
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Open the carton and remove the PANLOC brackets, hardware package, and mounting template from the carton. Remove the C 29 from its plastic bag and place it upside down on the shipping pallet; unscrew the four plastic feet from the bottom of the chassis.
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Mark the cabinet panel. Place the mounting template in the position on 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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Drill Holes Use a drill with a 3/16 inch bit held perpendicular to the panel and 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 penciled outline. Before taking the next step, make sure that the six A and B holes have been drilled.
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Saw the Panel Cutout Saw carefully on the inside of the penciled lines. First, make the two long cuts and then the two short cuts. After the rectangular opening has been cut out
using a file to square the corners and smooth any irregularities in the cut edges. -
Install the Mounting Strips
In the hardware package, you will find two mounting strips and two sets of machine screws. For panels that are less than 1/2 inch thick, use the 3/4 inch screws; for panels that are more than 1/2 inch thick, use the 1-1/4 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 strap with the holes in the panel and tighten the screw until the screwhead is .pulled into the wood.
Repeat this procedure to attach the mounting strip to the left side of the panel. -
Attach the 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. -
Install the 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 adjusted position latches. Press the latches in-ward, 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 slide forward to the adjust position; if you press inward on the adjust position latches then you can remove the instrument from the cabinet
How to connect
Rear panel input jacks are provided for 2 stereo high-level sources (AUX 1 and
AUX 2), a stereo tuner (TUNER), 2 stereo turntables (PH 1 and PH 2), stereo
high impedance microphones (MIC), and 2 stereo tape recorders (TAPE 1 and TAPE
2).
Rear panel output jacks are provided to feed 2 stereo tape recorders (TAPE 1
and TAPE 2), a stereo 600-ohm unbalanced line (LINE), and 2 stereo 2.5-volt
outputs (MAIN). Front panel jacks provide input and output facilities for a
tape recorder using the circuits of the rear panel TAPE 2 connections. Two
headphone jacks are provided which are fed by a stereo amplifier in the C 29.
CONNECTING AUX 1 AND AUX 2
Connect the left channel cable from any high-level source (tuner. TV set, tape
recorder. etc.) to the INPUT AUX 1 left jack. Connect the right channel cable
to the INPUT AUX 1 Right jack. A second high-level source can be connected
similarly to INPUT AUX 2.
CONNECTING TURNTABLES
The C 29 has short plugs in the phono inputs. To prevent unwanted noise remove
the shorting plugs only from input jacks that are to be used. Connect the
cable from the left channel of the turntable into the INPUT PHono 1 left jack.
Connect the cable from the right channel of the turntable into the INPUT PHono
1 Right jack. For a second turntable, connect PHono 2 in the same way. after
removing the shorting plugs.
CONNECTING MICROPHONES
Connect the cables from high impedance microphones directly in the INPUT MIC
Left and Right jacks.
CONNECTING TAPE RECORDERS
To Record:
Connect a cable from the OUTPUT TAPE 1 Left jack to the left high-level input
of the tape recorder. Connect a cable from the OUTPUT TAPE 1 Right jack to the
right high-level input of the tape recorder. Connect a second recorder in the
same manner to the OUTPUT TAPE 2 jacks.
To Playback/Monitor: Connect a cable from the left channel output of a tape
recorder to the TAPE INPUT 1 Left jack. Connect a cable from the right channel
output of a tape recorder to the TAPE INPUT 1 Right jack. Connect a second
recorder in the same manner to the TAPE INPUT 2 jacks.
Front Panel Tape Recorder Jacks:
Tape recorder inputs and outputs are available at the TAPE IN-OUT jacks on the
front panel just to the left of the TAPE MONITOR pushbuttons. These jacks make
connections to TAPE 2 facilities without having to go to the rear panel. A
metal shielded 1/4 inch stereo phone plug is used. Connections are tip: left
signal. ring: right signal, and sleeve: common ground
When a tape recorder is plugged into the front jacks all the facilities
normally associated with TAPE 2 on the rear panel are automatically
transferred to the front panel jacks.
CONNECTING TO POWER AMPLIFIERS
Connect the jacks labeled “OUTPUTS MAIN” 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.
Cables are supplied to interconnect the C 29 to the power amplifier. Longer
cables can be used if needed. The length of the cable is limited by the
capacitance of the cable. The total cable capacitance must not exceed 1,000
pF. For instance: cables with a capacity of 25 pF per foot maybe 40 feet long.
13.5 pF per foot cable maybe 75 feet long. The input impedance of the
amplifiers should be 10k ohms or greater.
The second pair of MAIN OUTPUT jacks have been supplied to feed a second power
amplifier. In the event, it is desired to tape-record after the tone, filter,
and volume control the second set of OUTPUT MAIN jacks can be connected to the
tape recorder input. The controls are then all available to control the signal
before recording. Remember, any change in the setting of the controls will
change the program to the tape recorder. Since the recording signal available
at the OUTPUT MAIN is much higher than the output available from the OUTPUT
TAPE 1 or TAPE 2 jacks, it will be easy to overload the tape recorder input.
In this mode of operation, it will not be possible to monitor from the tape
recorder via the TAPE MONITOR pushbuttons while feeding the recorder from the
OUTPUT MAIN jacks. Depressing the TAPE MONITOR pushbutton will disconnect the
program source and may cause feedback oscillation.
SPEAKER CONTROL RELAY
To control loudspeakers by use of SPEAKERS 1 and 2 pushbuttons on the front
panel and accessory McIntosh SPEAKER CONTROL RELAY is needed. Plug the special
cable from the SPEAKER CONTROL RELAY into the C 29 back panel SPEAKER CONTROL
RELAY receptacle. In addition to loudspeaker connections and switching, the
SPEAKER CONTROL RELAY has two AC power outlets that provide an additional
capacity of 2400 watts. Use these outlets to supply AC power to amplifiers or
other components whenever the total load to be switched by the C 29 exceeds
its rating of 600 watts.
CONNECTING AC POWER
The preamplifier AC power cord is plugged into a 120 volt 60 Hz wall outlet.
There are two types of AC power outlets on the back panel: four black and two
green.
The green AC power outlets are on at all times. Plug the AC power cables from
the turntable into the green TURNTABLE power outlets on the rear panel. The
black outlets are switched on and off when the preamplifier is turned on or
off. These are intended for power amplifiers, equalizers, and other
accessories with up to 600 watts total capacity. The POWER ON pushbutton
shares AC power control with the AC power switch on a turntable, through a
current detecting switch circuit. On the rear panel, the TURNTABLE AUTO/MANUAL
switch selects the mode of operation. When the switch is in the AUTO position
and a turntable is plugged into one of the green AC power outlets, the AC
power to the preamplifier and to the black AC power outlets can be controlled
by the turntable on/off switch. When AC power to the turntable is turned on,
automatically the preamplifier and the switched black AC power outlets are
turned on. The system will remain on until the turntable is turned off. The
POWER ON pushbutton controls the AC power for any source other than the
turntable.
In the MANUAL position, only the POWER ON pushbutton will turn AC power on or
off.
Some turntables have electronic circuits that draw current all the time. To
use these turntables the AUTO/MANUAL switch must be in the MANUAL position.
With the AUTO/MANUAL switch in the MANUAL position, AC power to the system
will be controlled by the front panel POWER pushbutton only.
The green AC power outlets are protected with a one-ampere fuse. Any increase
in the value of this fuse will affect the protection of the sensing circuit
and can cause damage.
CONNECTING PROGRAM SOURCE GROUNDS
A single GROUND post is provided to which grounds for turntables, record
changers, tape decks, etc. are connected. To prevent hum pickup, the left and
right program cables and the ground wire from that source should be wound or
twisted together. Make sure the ground wire does not make any connection to
the shields of the left and right program cables between the source and the
input of the preamplifier.
FUSES
A 1.0 AMP fuse protects the preamplifier circuits. The fuse does not protect
additional equipment connected to the back panel AC outlets. The green AC
power outlets are protected with a one-ampere fuse. Any increase in the value
of this fuse will affect the protection of the sensing circuit and can cause
damage.
The Front Panel Controls and How to Use Them
BALANCE and LOUDness
The BALANCE and LOUDness controls are concentric. The BAL-ANCE control (large
outer knob) adjusts for an equal volume of either the left or right channels.
The volume of the channels can be varied relative to each. left … turning the
control to the left accents the left channel by reducing the right channel
output. right . . . turning the control to the right accents the right channel
by reducing the left channel output.
LOUDness
Use the LOUDness control for full frequency range listening at even the
softest listening levels. The LOUDness control (the small center knob of the
concentric control) provides a low-frequency boost to compensate for a hearing
characteristic of the human ear at low listening levels. The ear becomes less
sensitive to low frequencies as volume is reduced. Increased loudness
compensation is therefore desirable at lower listening levels. The loudness
control boosts the low frequencies so that the ear hears approximately the
same musical balance as it would at higher listening levels.
FLAT: (Maximum counterclockwise rotation) Full volume with flat frequency
response. The loudness compensation is inoperative in this position.
Turning the control clockwise toward MAX reduces the listening volume, and
automatically increases the compensation by boosting bass.
INPUT SELECTOR
The six-position INPUT SELECTOR controls the input program. When the INPUT
SELECTOR is turned to
AUX 1: the output from any high-level program source requiring flat
amplification is connected to the high-level input stage. Such a source could
be another tape recorder or a television set. AUX 2: same as AUX 1
TUNER :
the output from any AM, FM, or MPX FM tuner is connected to the high-level
input stage. In the TUNER position, the C 29 has flat amplification.
PHono 1: the output of a magnetic phono cartridge plugged into PHono 1 is
connected to the low-level amplifying stages. The response of these stages has
been shaped to precisely conform to revised RIAA standards.
PHono 2: Same as PHono 1
MIC: the output of any high impedance microphone is connected to the low-level
input stage. In the MIC position, the C 29 has flat amplification.
MODE SELECTOR
The MODE SELECTOR facilitates the accurate adjustment of a stereo system for
some differences caused by room acoustics, loudspeaker placement, and the
other components used in the system. The MODE SELECTOR switch connects the
program to the loudspeaker in seven ways:
L to L and R: Connects the left program to both loudspeakers.
R to L and R: Connects the right program to both loudspeakers.
STEREO REV: Connects the left program to the right loudspeaker and the right
program to the left loudspeaker.
STEREO: Connects the left program to the left loudspeaker and the right
program to the right loudspeaker.
MONO (L + R): Adds the left and right programs together and connects to both
loudspeakers.
L + R to L: Connects the left plus right program to the left loudspeaker only.
L + R to R: Connects the left plus right program to the right loudspeaker
only.
VOLUME CONTROL
The VOLUME control is a precision step control manufactured for McIntosh
Laboratory. It has 32 steps with a 70 dB range, plus volume off. Left and
right channel tracking are within 1 dB. This extreme accuracy is obtained
through special electronically controlled resistance element trimming.
BASS
Concentric, 11 positions, tone control switches adjust the bass. The outer
knob adjusts the right channel bass response. The inner knob adjusts the left
channel bass response. Left: Adjust the bass loudness from the left
loudspeaker. Clockwise rotation increases the bass loudness while
counterclockwise rotation decreases the bass loudness. Each step of the tone
control adjusts the bass loudness by about 4 dB. Right: Has the same effect on
the sound from the right loudspeaker.
TREBLE
Concentric, 11 positions, tone control switches ad-just the treble. The outer
knob adjusts the right 
channel treble response. The inner knob adjusts the left channel treble response. Left: Adjust the treble loudness from the left loudspeaker. Clockwise rotation increases the treble loudness while counterclockwise rotation decreases the treble loudness. Each step of the tone control adjusts the treble loudness by about 4 dB. Right: Has the same effect on the sound from the right loudspeaker.
TAPE PUSHBUTTONS
IMPORTANT: When the C 29 is operated with either MONITOR pushbutton at the
In position, the pro-gram heard will be that from the tape recorders only.
Signals from any other source will not be heard from the loudspeakers. To hear
any other source, make sure the MONITOR pushbuttons are OUT.
The MONITOR switches are mechanically interlocked to prevent simultaneous
monitoring from two tape recorders. If one button is in position, it must be
pushed again to release it to the out position before the other button can be
pushed.
The C 29 is designed so it may be used with two tape recorders. The four left
pushbuttons control the signal output of these recorders. They permit
recordings to be monitored as they are being recorded, or copying of tapes
from one recorder to another while listening to a separate program or the
playback of either recorder.
MONITOR TAPE 1 pushbutton out: The program source as selected by the INPUT
SELECTOR is fed to the power amplifiers and heard through the loudspeakers;
the pushbutton in Signal from a tape recorder plugged into INPUTS TAPE 1 is
fed to the power amplifiers and heard through the loudspeakers.
MONITOR TAPE 2 pushbutton: Functions similarly to monitor Tape 1. It also
controls the program from a tape recorder plugged into the front panel TAPE IN
and OUT jacks. When a tape recorder is plugged into the front jacks all the
facilities normally fed to TAPE 2 on the rear panel are automatically
transferred to the front panel. The tape recorder plugged into the TAPE 2 IN
and OUT jacks on the rear panel is automatically disconnected.
TAPE COPY T1 — T2 pushbutton in: connects the output from tape recorder 1 to
the input of tape recorder 2 without affecting the program being heard from
the speakers. In this position, a copy of the program on tape recorder 1 can
be made on tape recorder 2. To monitor the original use of MONITOR
TAPE 1 pushbutton and to monitor the copy use MONITOR TAPE 2 pushbutton. TAPE
COPY T2 — T1 pushbutton in: connects the output from tape recorder 2 to the
input of tape recorder 1 without affecting the program being heard from the
speakers. In this position, A copy of the tape program on recorder 2 can be
made on recorder 1. To monitor the original use of the MONITOR TAPE 2
pushbutton and to monitor the copy use MONITOR TAPE 1 pushbutton.
LF-HF FILTERS
Use the LF-HF FILTERS pushbutton to reduce objectionable low and high-
frequency noises (below 50 Hz and above 7 kHz). With the pushbutton in, noise
is reduced; out: filters are disconnected.
SPEAKER 1 and 2
Speakers can be turned on and off when properly connected with the accessory
McIntosh SPEAKER CONTROL RELAY. The SPEAKER 1 and 2 pushbuttons control the
operation of a SPEAKER CONTROL RELAY when it is plugged into the C 29 rear
SPEAKER CONTROL RELAY socket. The SPEAKER CONTROL RELAY controls the audio to
two pairs of stereo loudspeakers. The AC power to two AC receptacles on the
SPEAKER CONTROL RELAY is controlled by the ON-OFF cycle of the C 29. The total
capacity of the SPEAKER CONTROL RELAY AC power receptacles is 2400 watts.
POWER ON
The POWER ON pushbutton shares AC power control, through a current detecting
switch circuit, with the AC power switch on a turntable. On the rear panel,
the TURNTABLE AUTO/MANUAL switch selects the mode of operation. When the
switch is in the AUTO position and a turntable is plugged into one of the
green AC power outlets, the AC power to the preamp and to the black AC power
outlets can be controlled by the turntable on/off switch. When AC power to the
turntable is turned on, automatically the preamplifier and the SWITCHED black
AC power outlets are turned on. The system will remain on until the turntable
Is turned off. The POWER ON pushbutton switch parallels the automatic
turntable power control feature.
The POWER ON pushbutton is used to turn on and off power when the turntable is
not used. The POWER ON pushbutton must be out or off for the turntable to
control the AC power. In the MANUAL position, only the POWER ON pushbutton
will turn the preamplifier and black outlet AC power on and off.
TAPE RECORDER FRONT PANEL CONNECTION
Input and output facilities are available at the TAPE IN-OUT jacks on the
front panel. These front panel jacks make connections without having to get at
the rear panel. When using the front panel jacks, the rear panel TAPE 2
facilities are disconnected automatically. A metal shielded 114-inch stereo
phono plug is used for best shielding. Connections follow the industry
standards and are tip: left signal, ring: right signal, and, sleeve: common
ground.
HEADPHONES
The front panel HEADPHONE jack has been designed to feed low impedance dynamic
headphones. Electrostatic headphones generally require higher power than
dynamic headphones and are connected to the output terminals on the power
amplifier.
Plug headphones into the front panel HEAD-PHONE jack. Adjust the front panel
VOLUME control for comfortable headphone listening. Additional top Panel
HEADPHONE LEVEL controls also adjust the loudness of the program when using
headphones. See the section below for top-panel controls.
An amplifier in the C 29 provides the power that feeds both the HEADPHONE
jacks on the front panel and the LINE OUTPUT jacks on the rear panel.
PADLOCK
McIntosh developed PANLOC mounting and brings professional installation
techniques to stereo. Depressing the PANLOC button will release the
instrument. It can then be pulled toward you to the “adjustment” position. In
this position, the top panel controls can be adjusted
Top Panel Controls
To gain access to the top panel controls depress the PANLOC buttons and pull
the preamplifier out to the adjusted position. The controls are now easily
operated. HEADPHONE & LINE OUTPUT
Control has been provided in each channel to adjust the loudness of the
program when using headphones. The controls adjust the output in each channel
to the HEADPHONE jack only and do not affect the program loudness from the
loudspeakers. To ad-just for comfortable headphone listening first adjust the
VOLUME control to normal room loudness. Then, while wearing the headphones,
adjust the HEADPHONE LEVEL controls to the desired loudness level.
MAIN OUTPUT LEVEL
Control has been provided in each channel that adjusts the output of the
preamplifier. Use these controls to compensate for minor differences in room
effects, loudspeaker efficiency, or amplifier gain.
Best stereo performance is achieved when the stereo system is properly
balanced. For proper balance, each channel must be equal in loudness. Use the
top panel level controls to balance system loudness.
This procedure reserves the BALANCE control to adjust for any unbalance in the
source material, the record, etc.
Before attempting to balance the system make certain the front panel controls
are set properly.
Set the MODE SELECTOR to MONO and the BALANCE control at the center or 12
o’clock position. Turn the tone controls to the center or 12 o’clock position.
The HF – LF pushbuttons should be in the OUT position.
With the tuner turned on, turn up the VOLUME control on the front panel until
a comfortable room loudness is reached. Adjust the top panel MAIN OUTPUT LEVEL
controls until the loudness from each loudspeaker is equal.
Specifications
PERFORMANCE LIMITS AND RATINGS
We promise you that the C 29 you buy, at the time of your purchase, is capable
of performing at or exceeding these limits or you get your money back.
McIntosh PERFORMANCE LIMITS are the maximum departure from performance
perfection permitted for a McIntosh instrument.
FREQUENCY RESPONSE
+0 —0.5 dB 20 Hz to 20,000 Hz
DISTORTION
.02% maximum at the rated output level, 20 Hz to 20,000 Hz
INPUT SENSITIVITY AND IMPEDANCE
AUXiliary, TUNER, TAPE 1, TAPE 2, 0.25 volts at 100,000 ohms; PHono 1 and
PHono 2, 2 millivolts (1,000 Hz) at 47,000 ohms and 65 pF; MICrophone, 2.5
millivolts at 10,000 ohms
HUM AND NOISE
AUXiliary, TUNER, TAPE 1, TAPE 2, IHFA 100 dB, unweighted 90 dB below rated
output; PHono 1, PHono 2 IHFA 90 dB, unweighted 80 dB below 10 millivolts
input, equivalent to less than 1.0 microvolt at the input terminals;
MICrophone, 1.5 microvolts at the input terminals.
OUTPUT LEVEL AND IMPEDANCE
MAIN: 2.5 volts with rated input, less than 100 ohms source impedance, to
operate into 10,000 ohms or greater
TAPE: 0.25 volts with rated input, less than 200 ohms source impedance,
to operate into 10,000 ohms or greater
HEADPHONE/LINE: 0.75 volts into 8-ohm load or 2.5 volts into 600-ohm line,
47-ohm source impedance, level controls provided
VOLTAGE AMPLIFICATION IN DECIBELS
AUXiliary, TUNER, TAPE 1, and TAPE 2
to MAIN Output20 dB
to TAPE Output 0 dB
to HEADPHONE/LINE Output 30 dB
PHono 1 and PHono 2 at 1 kHz
to MAIN Output 62 dB
to TAPE Output 42 dB
to HEADPHONE/LINE Output 72 dB
MICrophone
to MAIN Output 60 dB
to TAPE Output 40 dB
to HEADPHONE/LINE Output 70 dB
SEMICONDUCTOR COMPLEMENT
9 Integrated Circuits
2 Transistors
11 Silicon Diodes
8 Light Emitting Diodes (LED)
1 Silicon Controlled Rectifier (SCR)
1 Dual Light Dependent Resistor Network (LDR)
POWER REQUIREMENT
120 volts, 50/60 Hz, 45 watts
SIZE: Front Panel measures 16 inches wide (40.6 cm) by 5 7/16 inches high
(13.8 cm). Chassis measures 14 3/4 inches wide (37.5 cm) by 4 13/16 inches
high (12.2 cm) by 13 inches deep (30.0 cm), including PANLOC shelf and back
panel connectors. Knob clearance required is 1 1/4 inches (3.2 cm) in front of
the mounting panel.
FINISH: Front panel is anodized gold and black with special gold/teal
nomenclature illumination. The chassis is black.
MOUNTING: Exclusive McIntosh developed professional PANLOC
WEIGHT: 21 pounds (9.5 kg) net, 33 pounds (15 kg) in the shipping carton.
Facilities and Features
BASS CONTROLS
Separate 11-position rotary switches for each channel, + 20 dB to —20 dB at 20
Hz
TREBLE CONTROLS
Separate 11 position rotary switches for each channel, + 18 dB to — 18 dB at
20,000 Hz
BALANCE CONTROL
Natural balance at the center position, attenuation of the left or right
channel by rotating control
PRECISE TRACKING VOLUME CONTROL
A precision step volume control with a left to right, tacking accuracy within
1 dB through its entire range.
SIX SOURCE INPUT SELECTOR
AUXiliary 1 and 2, TUNER, PHono 1 and 2, MICrophone
MODE SELECTOR
Seven positions: Left channel only to both speakers, Right channel only to
both speakers, Stereo Reverse, Stereo, Mono, L + R to the left speaker only,
and L + R to the right speaker only
TAPE MONITOR SWITCHES
Two pushbutton switches. Either of the two tape recorders can be monitored by
selecting the TAPE 1 pushbutton or TAPE 2 pushbutton. They are mechanically
interlocked to accept only one pushbutton at the IN position at one time.
TAPE COPY SWITCH
Two pushbutton switches. Either of the two tape recorders can be connected to
copy from tape recorder 1 to tape recorder 2 or vice versa. They are
mechanically interlocked to accept only one pushbutton at the IN position at
one time.
LF • HF FILTERS
Reduce unwanted high-frequency noise (above 7 kHz) and low-frequency rumble
etc. (below 50 Hz) at 12 dB per octave rate.
FRONT PANEL TAPE JACK
Allows connection to input and output of a tape recorder from the front panel.
Inserting plugs into the front panel jacks disconnects the TAPE 2 circuits
from the rear panel and uses the TAPE 2 facilities for the front panel jacks.
HEADPHONE JACKS
For listening with either low or high-impedance dynamic stereo headphones.
Power to these jacks is
supplied by an amplifier in the C 29. Headphone listening can be accomplished
without the use of an external power amplifier.
SPEAKER SWITCHES
(Operates with accessory speaker control relay) Turn two sets of speakers on
or off when properly interconnected with the accessory SPEAKER CONTROL RELAY.
MAIN OUTPUT LEVEL CONTROLS
Permits the balance of the entire system to be conveniently preset.
HEADPHONE & LINE OUTPUT LEVEL CONTROLS
Adjusts the level and balance of the HEAD-PHONE/LINE output.
Technical Description
AUDIO SECTION
Each channel of the C 29 has four basic sections. They are phono amplifiers,
high-level amplifiers, filter amplifiers, and headphone amplifiers.
PHONO AMPLIFIER
The phono amplifier uses a high technology integrated circuit operational
amplifier. Its differential input stage has been optimized for low noise and
low distortion performance. Open-loop gain of this integrated circuit is
100,000. With the high open-loop gain, a large amount of negative feedback can
be used around the phono amplifier to further reduce noise and distortion. The
feedback network also pro-vides precision RIAA frequency compensation. The
network uses 1% metal film resistors and 5% poly film capacitors. To achieve
low noise performance it is essential that the feedback network be very low
impedance. As a consequence, the preamplifier must be capable of operating as
a power amplifier to drive this impedance. The actual power output capability
of this preamplifier stage is more than 100 milliwatts, a great margin beyond
that which is required. The input sensitivity of the phono amplifier is 2
millivolts. The gain of the amplifier is 42 dB at 1000 Hz. The phono amplifier
has a very wide dynamic range. At 1000 Hz the phono input circuit will accept
100 millivolts without overload, a voltage far greater than the output of any
current magnetic phono cartridge. Phono input overload, therefore, is
virtually impossible. A signal level of 10 millivolts at the phono input at
1000 Hz will produce 1.2 volts at the tape output. The tape output has a
source impedance of 200 ohms, designed to operate into a load impedance of
47,000 ohms or greater.
HIGH-LEVEL AMPLIFIER
At the input to the high-level amplifier, the signal passes through the mode
switch, then through the volume control and the loudness control. The loudness
control is independent of the volume control permitting any amount of loudness
compensation to be introduced regardless of the position of the volume
control. The linear high-level amplifier has a gain of 20 dB. The same type of
integrated circuit operational amplifier as used in the phono amplifier is
used to minimize noise and distortion in the high-level amplifier. The
feedback loop around this amplifier uses frequency-selective bass and treble
networks with two 11-position switches which allow up to 20 dB of boost or cut
at 20 Hz and up to 18 dB of boost or cut at 20,000 Hz.
FILTER AMPLIFIER
The filter amplifier serves three functions: a high
frequency filter, a low-frequency filter, and a 20,000 Hz low pass filter.
Each channel of the filter amplifier again utilizes the same type of
operational amplifier as was used in the phono stage and high-level amplifier.
The resistive and capacitive elements form a 12 dB per octave active RC
filter. The high-frequency filter is a 7,000 Hz active low pass filter. The
low-frequency filter is a 50 Hz active high pass filter. The filter amplifier
also forms a 20,000 Hz active low pass filter to reduce noise outside the
useful sound spectrum while leaving the preamplifier response flat to 20,000
Hz. This low pass filter is connected at all times to reduce wideband noise
yet maintain a flat frequency response to 20,000 Hz. The non-linear distortion
of the active filter elements In the C 29 is very low even at the cutoff
frequency. This is not always the case with passive filters that present to
the driving source a very low impedance at the cutoff frequency.
HEADPHONE AMPLIFIER
The integrated circuit headphone amplifier is capable of driving two pairs of
dynamic headphones with less than .1% harmonic distortion. The maximum output
of the headphone amplifier is 2.5 volts into 50 ohms or greater. The internal
impedance of the headphone amplifier is 47 ohms. Long shielded cables can be
used without adversely affecting the frequency response. The headphone level
controls adjust the output level and balance of the headphone amplifier.
TURN ON DELAY
The C 29 has transient free turn-on and turn oft characteristics. A light-
dependent resistor, time con-trolled, connects the output of the preamplifier
to the output jacks. The control of the resistor is derived from a long time
constant that turns on approximately two seconds after the power switch. The
same circuit has a short turn-off time constant which turns off before the
preamplifier’s main power supply has a chance to discharge.
AUTO TURN ON
On the rear panel are two green AC power outlets and an AUTO/MANUAL slide
switch. Plug the AC power cables from the turntable into the green turn-table
power outlets on the rear panel. When the switch is in the AUTO position
current that is drawn by the turntable will be sensed and will cause a relay
to close. This relay controls the AC power to the C 29 and the black AC power
outlets. When the current drain ceases the preamplifier and the AC power
outlets will turn off. The complete system can be controlled from the
turntable off and on the switch.
Performance Charts
The front panel POWER ON pushbutton must be left in the off or out position
for this automatic control to operate. When the rear panel slide switch is in
the manual position, only the front panel pushbutton has control.
POWER SUPPLY
To minimize hum pickup and thus improve signal-to-noise ratio the C 29 power
transformer is triple shielded. Shielding includes a copper strap, a silicon
steel strap, and a steel outer shell. The transformer output voltage is fed to
a full-wave bridge rectifier with 3,000 microfarad filter capacitors to
provide the + 24 volts for powering the headphone amplifier and the plus
voltage regulator and —24 volts for the minus regulator. The ±18 volts needed
for low-level and operational amplifier stages is controlled with integrated
circuit voltage regulators.
