THE MCINTOSH C 28 SOLID STATE STEREO PREAMPLIFIER

Reading Time: 37 Minutes

Price $1.25
Your MC 28 Stereo Preamplifier will give you many years of pleasant and satisfactory performance. If you have any questions, please contact:

CONTENTS

Service Contract. 1

CUSTOMER SERVICE

Mclntosh Laboratory Inc. 2 Chambers Street Binghamton, New York 13903 Phone: 607-723-3512
Installation. 2, 3 How to Connect. 4, 5, 6, 7 Adjusting The Top Panel Controls. 8 Using The Front Panel Controls. 9, 10 Using the Pushbuttons. 11 Balancing Your Stereo. 12, 13 Listening To Your Stereo. 13 Performance Limits and Ratings. 14, 15 Performance Charts. 16 Technical Description. 18 Block Diagram. 20
WARNING: TO PREVENT FIRE OR SHOCK HAZARD, DO NOT EXPOSE THIS UNIT TO RAIN OR MOISTURE. 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. The terms of the contract are: or mishandling is not covered by the SERVICE CONTRACT. 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. 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. 6. Your completely filled in application for a SERVICE CONTRACT must be postmarked within 30 days of the date of purchase of the instrument. 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.
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. 2. Any Mclntosh authorized service agency will repair all Mclntosh instruments at normal service rates. To receive the free service under the terms of the SERVICE CONTRACT, the SERVICE CONTRACT CERTIFICATE must accompany the instrument when taken to the service agency. 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
Copyright (c) 1970 By Mclntosh Laboratory Inc.

How To Connect

CONNECTING A RECORD PLAYER TO PHONO 1 Connect the cable from the "left" channel of the record player into the "L" PHONO 1 input jack. Connect the cable from the "right" channel of the record player into the "R" PHONO 1 jack. PHONO 2 is provided for the use of a second record player. Connect the cable from the "left" channel of the record player into the "L" PHONO 2 input jack. Connect the cable from the "right" channel of the record player into the "R" PHONO 2 input jack. CONNECTING A MICROPHONE Connect the cable from the "left" microphone to the "L" MIC input jack. Connect the cable from the "right" microphone to the "R" MIC input jack. CONNECTING A TAPE DECK FOR PLAYBACK Connect the cable from the "left" tape recorder head on the tape deck (one without its own electronics) to the "L" TAPE HEAD input. Connect the cable from the "right" tape recorder head to the "R" TAPE HEAD input. CONNECTING A STEREO TUNER Connect the cable from the "left" channel tuner output to the "L" tuner input jack. Connect the cable from the "right" channel tuner output to the "R" TUNER jack.

AUX Any high level program source such as another tuner or a TV set can be connected to the input jacks marked "AUX."
CONNECTING A TAPE RECORDER To Record: Connect a cable from the "L" TAPE OUTPUT jack marked TAPE 1 to the "left" high level input tape recorder. Connect a cable from the "R" TAPE OUTPUT jack marked TAPE 1 to the "right" high level input of the tape recorder. Connect a second tape recorder in the same fashion to the TAPE 2 outputs. To Playback Monitor: Connect the cable from the "left" channel output of a tape recorder to the high level inputs. "L" TAPE 1. Connect the cable from the "right" channel output of a tape recorder to the high level input. "R" TAPE. Connect a second tape recorder in the same fashion to the TAPE 2 input jacks.
CONNECTING THE C 28 TO POWER AMPLIFIERS Connect the MAIN output jacks to the input of a stereo power amplifier. The "L" jack is connected to the "left" amplifier input jack. The "R" jack is connected to the "right" amplifier input jack. The output impedance at the MAIN outlet is 100 ohms. Longer cables than are supplied can be connected between the C 28 and the amplifiers. The length of the cable is limited by the capacity of the cable. The total capacity must not exceed 1000 pF. For instance: cables with a capacity of 25 pF per foot may be 40 feet long. 13.5 pF per foot cable may be 75 feet long. The input impedance of the amplifiers should be 47,000 ohms or greater. CTR OUTPUT Use the CTR output to feed left plus right signal to a separate power amplifier for monophonic background music or for a center channel speaker. SPEAKER CONTROL RELAY To control main and remote loudspeakers from the front panel of the C 28 an accessory Mclntosh SCR control is needed. Plug the cable from the SCR control in the SPEAKER CONTROL RELAY receptacle. The speakers are then connected to the SCR con-
trol. The AC outlets on the SCR have a total capacity of 2400 watts. AC OUTLETS There are 4 black AC outlets, 2 green AC outlets, and one red AC outlet. The power to the black AC outlets is controlled by the front panel switch. Use these outlets for a tuner, tape recorder, etc. The green outlets are controlled by the top panel switch marked "Power Amplifier." The total capacity of all AC power outlets is 600 watts. To prevent burnout, use the AC outlets on the CR for power requirements exceeding 600 watts. The red receptacle is on at all times. Use the red outlet for a turntable or record changer. The turntable is protected by this arrangement. It is necessary to turn off the turntable or record changer with its own AC switch. 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 28.

Adjusting The Top Panel Controls
You will enjoy the best in stereo performance more when the stereo system is properly balanced. For proper balance each channel must be equal in loudness and similar in frequency response. Use the top panel LEVEL controls to balance system loudness and the top panel BASS TRIM controls to balance for frequency response differences at low frequencies. Do not use the front panel BALANCE control to correct for system unbalance. The BALANCE control is used to adjust for any unbalance in the source material, the record, etc. Before attempting to balance the output of the C 28 make certain the front panel controls are set properly. Turn the VOLUME control to the OFF (totally counter-clockwise) position. Set the MODE SELECTOR to STEREO 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 and LF pushbuttons should be in the OUT position and the COMPensation control in the FLAT position. Turn the INPUT SELECTOR to TUNER. Depress the PANLOC buttons and pull the preamplifier out to the adjust position. The controls on the top panel are now easily adjusted. On the top panel turn the BASS TRIM controls counter-clockwise. Turn all the level controls to the clockwise position. Turn the POWER AMPLIFIER switch on. With the tuner turned on, turn up the VOLUME control on the front panel until a comfortable room loudness is reached. Then switch the INPUT SELECTOR to PHONO 1, the MODE SELECTOR to L TO L & R, use a monophonic record and turn down the top panel LEFT PHONO 1 LEVEL control to match the loudness of the tuner. Repeat the procedure with the RIGHT PHONO 1 LEVEL control. When the channels are equally loud the system is balanced for loudness. Repeat the same steps for PHONO 2. Bass Trim A control has been provided in each channel that adjusts the bass loudness. These controls are used to compensate for the differences in loudspeaker response at low frequencies or for the room in which they are used. They are variable controls that provide up to 6 dB of boost below 100 Hz. With the control in the counter-clockwise position the response is flat. Clockwise rotation increases the bass loudness. Adjust one channel at a time.

Headphone Level

A 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 adjust for comfortable headphone listening first adjust the VOLUME control to the front panel to normal room loudness. Then, while wearing the headphones, adjust the HEADPHONE LEVEL control to the desired loudness level.

Output Level

A control has been provided in each channel that adjusts the output of the preamplifier. Use these controls to compensate for minor differences in loudspeaker efficiency or amplifier gain. These controls adjust the level to the MAIN OUTPUTS only. With the MODE SELECTOR in the MONO (L + R) position set the BALANCE control to 12 o'clock. Adjust the top panel OUTPUT LEVEL controls until the loudness from each loudspeaker is equal.

Center Channel Level

A control has been provided that adjusts the combined left plus right program level to the CTR output jacks.

Power Amplifier On/Off

A switch has been provided that will control the AC power to the green POWER AMPLIFIER receptacles independently of the C 28 front panel control. Use this switch to turn off the amplifier when listening to the headphones, etc. IMPORTANT: TO HEAR THE PROGRAM FROM THE LOUDSPEAKERS THIS SWITCH MUST BE IN THE ON POSITION.
Using The Front Panel Controls
In the upper left of the front panel is a concentric control. The large outer knob is the BALANCE control. The small center knob is the COMPENSATION control. BALANCE The BALANCE control adjusts for unequal loudness in either the left or right channels. The loudness of the channels can be varied relative to each other without affecting their combined loudness. 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. COMPENSATION The COMPENSATION control is a three position switch. Pres: In the left of center position the response of the C28 is shaped to emphasize the upper midfrequencies. Flat: In the center position the response of the C 28 is unmodified. Loud: The LOUDness control automatically provides the correct amount of bass required to compensate for the change in response of the human ear at low loudness levels. When the volume is reduced, the music will seem to lose much of its bass and some of its treble. This effect is due to the sensitivity characteristic of human hearing. The response of the human ear to bass and treble pitch decreases more rapidly than its response to pitch centered in the mid-tonal range. The LOUDness switch converts the volume control to a loudness compensated control. Use LOUDness to listen at low volume and still hear full-frequency range. Tuner: Connects the output from any AM, FM or MPX FM tuner to the high level input stage. In the TUNER position the C 28 has flat amplification. There is 20 dB of gain to the MAIN outputs, 0 dB to the TAPE outputs and 17.5 dB to the LINE outputs. The input impedance is 250,000 ohms. Phono 1: Connects the output of any magnetic phono cartridge to the low level input stage. The response has been shaped to compensate for the characteristics of the magnetic phono cartridge. The gain at 1,000 Hz is 62 dB to the MAIN outputs, 42 dB to the TAPE outputs and 59.5 dB to the LINE outputs. The input impedance is 47,000 ohms. Phono 2: Same as PHONO 1. Mic: Connects the output of any high impedance microphone to the low level input stage. In the MIC position the C 28 has flat amplification. The gain is 60 dB to the MAIN outputs, 40 dB to the TAPE outputs and 57.5 dB to the LINE outputs. The input impedance is 500,000 ohms. Tape Hd: Connects the output of any tape head (a tape deck without its own electronics) to the low level input stages. The response has been shaped to compensate for the characteristics of the tape head. The gain at 500 Hz is 64 dB to the MAIN outputs, 44 dB to the TAPE outputs and 61.5 dB to the LINE outputs. The input impedance is 500,000 ohms. MODE SELECTOR Connects the program to the loudspeaker in the following seven ways: L to L & R: Connects the "left" input to both loudspeakers. R to L & R: Connects the "right" input to both loudspeakers. Stereo Rev: Connects the "left" input to the "right" loudspeaker and the "right" input to the "left" loudspeaker. Stereo: Connects the "left" input to the "left" loudspeaker and the "right" input to the "right" loudspeaker. Mono (L + R): adds the "left" input and the "right" input and then connects the L + R program to both amplifiers and 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.

INPUT SELECTOR

Aux: Connects the output from any high level program source requiring flat amplification to the high level input stage. Such a source could be a television set. In the AUX position the gain is 20 dB to the MAIN outputs, 0 dB to the TAPE outputs, and 17.5 dB to the LINE outputs. The input impedance is 250,000 ohms.
VOLUME ON/OFF Turning the VOLUME totally counter-clockwise turns the C28 OFF. The VOLUME control regulates the loudness in both channels. The VOLUME control has been precision tracked throughout the listening range (0 to -65 dB) for accurate stereo balance.

TREBLE

Left: Adjusts 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 about 4 dB. Right: Has the same effect on the sound from the right loudspeaker.

PANLOC

The C 28 has separate 11 position tone control switches in each channel for bass and treble. Left: Adjusts the bass loudness from the left loudspeaker. Clockwise rotation increases the bass loudness while counter-clockwise rotation decreases the bass loudness. Each step of the tone control adjusts the bass loudness 4 dB. Right: Has the same effect on the sound from the right loudspeaker.
Mclntosh developed PANLOC mounting brings professional installation technique to stereo. Depressing the PANLOC button fas with a ball point pen) 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.

Using The Pushbuttons

The C 28 is designed to be used with one, two or three tape recorders, for exampletape playback from a tape deck (one without its own electronics) and, in addition, two complete tape recorders. The front panel pushbuttons control the latter. The pushbuttons permit normal playback of either recorder, monitor of either recorder as recordings are being made, or copying tapes from one recorder to another while listening to a separate program. TAPE 1 PUSHBUTTON OUT. The program source is fed to the power amplifiers and heard through the loudspeakers. IN. The program source becomes the recorded tape on the tape recorder connected to TAPE INPUT 1. The recorded program from tape recorder 1 is fed to the power amplifiers and heard from the loudspeakers. With the pushbuttons in the monitor position a rectangle is lighted in RED above the pushbutton. When the RED light is on only the tape can be heard. To listen to other sources the pushbutton must be out and the light off. TAPE 2 The second complete tape recorder can be operated in the same fashion. TAPE 2 pushbutton also controls the program from a tape recorder plugged into the front panel jacks marked TAPE INPUT and TAPE OUTPUT. When a tape recorder is plugged into the front panel jacks all the facilities for TAPE 2 are automatically switched to the front panel packs. A tape recorder plugged into the TAPE 2 INPUTS and OUTPUTS on the back panel is automatically disconnected. Use the front panel pushbutton TAPE 2 to record on or playback from a tape recorder plugged into the front panel jacks.

TAPE COPY 1->2

TAPE COPY 2->1 This pushbutton, when pushed IN, connects the TAPE 2 OUTPUT jacks to the TAPE 1 INPUT jacks without affecting the program heard from the speakers. In this position a copy of the program on tape recorder 2 can be made on tape recorder 1. With the pushbutton in the IN position a rectangle is lighted in ORANGE above the pushbutton. To monitor the tape copy procedures use the TAPE 2 MONITOR pushbutton. LF (LOW FREQUENCY FILTER) Use the LF filter switch to reduce objectionable low-frequency noise created by a turntable or record changer or acoustically coupled feedback. OUT. filter disconnected. IN. low-frequency rumble and noise below 50 Hz are reduced when the switch is pushed to the IN position. With the LF pushbutton in the IN position a rectangle is lighted in GREEN above the pushbutton. When the GREEN light is on the low frequency filter is in operation. HF (HIGH FREQUENCY FILTER) Use the HF filter switch to reduce objectionable high-frequency noise such as record scratch. OUT. filter disconnect IN. rolls OFF response sharply above 7000 Hz With the HF pushbutton in the IN position a rectangle is lighted in GREEN above the pushbutton. When the GREEN light is on the high frequency filter is in operation. SPEAKER PUSHBUTTONS Speakers can be turned on and off when properly connected with the accessory Mclntosh SCR control. (See diagram Pg. 7) If the program is to be heard from the main speakers only, the REMOTE pushbutton is pushed IN. This turns off the remote speakers and lights a rectangle in BLUE above the pushbutton. The BLUE light indicates that the remote speakers are off and no program can be heard from them. If the program is to be heard from the remote speakers only the MAIN pushbutton is pushed IN. This turns off the main speakers and lights a rec-
This pushbutton, when pushed IN, connects the TAPE 1 OUTPUT jacks to the TAPE 2 INPUT jacks 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. With the pushbutton IN a rectangle is lighted in ORANGE above the pushbutton. To monitor the tape copy procedures use the TAPE 1 MONITOR pushbutton.

tangle in BLUE above the pushbutton. The BLUE light indicates that the main speakers are off and no program can be heard from them. To hear program from both main and remote speakers, both the MAIN and REMOTE pushbuttons must be out and the BLUE lights must be off. FRONT PANEL JACKS TAPE INPUT - TAPE OUTPUT When a tape recorder is plugged into the front panel jacks all the facilities for TAPE 2 are automatically switched to the front panel jacks. A tape recorder plugged into the TAPE 2 INPUTS and OUTPUTS on the back panel is automatically disconnected. Use the front panel pushbutton TAPE 2 to record or playback from a tape recorder plugged into the front panel jacks. HEADPHONES The front panel HEADPHONE jack has been designed to feed low impedance dynamic headphones. Electrostatic headphones generally require higher power than dynamic headphones. They must be connected to the output connectors on the power amplifier. Plug headphones into the front panel HEADPHONE jack. Adjust the front panel VOLUME control for comfortable headphone listening. (See Pg. 8} An amplifier in the C 28 provides the power that feeds both the HEADPHONE jack on the front panel and the LINE OUTPUT jacks on the rear panel. If you choose to listen to headphones only it is not necessary to operate the power amplifiers that feed the loudspeakers.
To turn the power amplifiers off use the switch on the top panel of the C 28 marked POWER AMPLIFIER. This switch controls the AC to the green POWER AMP receptacles on the back panel. With this switch in the OFF position nothing will be heard from the speakers.

Balancing your Stereo

The performance and enjoyment of a stereo system is greatly increased when the sound is properly balanced. The balance of the stereo system is affected by many things including room acoustics, furniture placement, room shape, small differences in loudspeakers, etc. Factors that affect proper stereo balance are correct phase for both channels and equal program loudness. TO BALANCE LOUDNESS 1. Set the MODE to MONO. 2. Play a familiar recording. 3. Turn the BALANCE control to the 12 o'clock position. 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.

Listening to your Stereo

LISTENING TO STEREO RECORDS Turn the INPUT SELECTOR to PHONO 1, or PHONO 2, whichever is connected to the record player you wish to hear. Set the MODE SELECTOR to STEREO. Adjust the VOLUME control to the desired volume. LISTENING TO MONOPHONIC RECORDS Turn the INPUT SELECTOR to PHONO 1, or PHONO 2, whichever is connected to the record player you wish to hear. Turn the MODE SELECTOR to MONO. Adjust the VOLUME control to the desired volume. LISTENING TO A TUNER Turn the INPUT SELECTOR to TUNER. Adjust the volume to a comfortable level. LISTENING TO A TAPE RECORDER Two tape recorders can be used with the C 28. Connect a three head tape recorder to TAPE 1 inputs. Connect a second three head tape recorder to TAPE 2. Recording and monitoring can be done using either tape recorders. Press the TAPE 1 or TAPE 2 pushbutton IN, which ever is connected to the tape recorder you wish to hear. Turn the MODE SELECTOR switch to STEREO or MONO, depending on the program on the tape. Adjust the VOLUME control to the desired volume. To monitor while recording your tape recorder must have separate record and playback heads and separate electronics. The pushbutton switch lets you monitor the quality of tape recordings made during the recording process. When the TAPE pushbutton is in the IN position it will play the sound from the tape as it passes the playback head, a moment after it is recorded. The recording process continues as usual. When the switch is in the OUT position program that is being recorded is heard. HOW TO COPY TAPE Put the tape to be copied on the recorder connected to TAPE 1 input. Press in the TAPE COPY 1->2 pushbutton. The signal available at the OUTPUT TAPE 2 jacks is the playback of TAPE 1. Record on the recorder connected to OUTPUT TAPE 2. The recording can be monitored by press13
ing in the TAPE 2 pushbutton. Instantaneous comparison on the recorded program with the original can be heard. LISTENING TO TAPE DECKS To listen to tape from a tape deck, proceed as follows: Turn the INPUT SELECTOR to TAPE HEAD. Turn the MODE SELECTOR to MONO (L + R) or STEREO, depending on the program on the tape. Adjust the VOLUME control to the desired volume. USING MICROPHONES Microphones in stereo may be used with the C28. The two MIC channels amplify microphone signals. They have a sensitivity of 2.5 millivolts and an input impedance of 0.5 megohm. For lower output microphones input transformers should be used to raise the voltage output to the 2.5 millivolt range.

Performance Limits and Ratings
Performance Limits are the maximum deviation from perfection permitted for a Mclntosh instrument. We promise you that your C 28 must be capable of performance at or exceeding these limits or you get your money back. Mclntosh is the only manufacturer that makes this guarantee.
to Tape Output 40 dB to Headphone/Line Output Tape Head at 500 Hz to Main Output 64 dB to Tape Output 44 dB to Headphone/Line Output
TRANSISTOR COMPLEMENT 26 silicon-planar transistors, 4 silicon diodes, 2 silicon bridge rectifiers POWER REQUIREMENT 120 volts, 50/60 Hz, 45 watts 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 COMPENSATION SWITCH Three position switch for Flat, Loudness, or Presence. Loudness position boosts low frequencies for low level listening. Presence position boosts mid frequencies 4 dB to increase "presence" effect. This control operates as a function of volume control position so full compensation is obtained at lower volume levels and flat response is obtained at full volume. BALANCE CONTROL Natural balance at center position, attenuation of left or right channel by rotating control VOLUME CONTROL Precision "tracked" at all listening levels. (0 to -65 dB). Does not change stereo balance as loudness is changed. The power ON/OFF switch is coupled with this control. INPUT SELECTOR Six positions: Auxiliary, Tuner, Phono 1, Phono 2, Microphone, and Tape Head MODE SELECTOR Seven positions: Left channel only to both speakers, Right channel only to both speakers. Stereo Reverse, Stereo, Mono, L + R to left speaker only, and L - R to right speaker only TAPE MONITOR SWITCHES Two push button switches. Either of two tape recorders can be monitored by selecting the TAPE 1 push button or TAPE 2 push button. They are mechanically interlocked to accept only one pushbutton at the IN position at one time. TAPE COPY SWITCH Two push button switches. Either of two tape recorders can be connected to copy from tape ma-
FREQUENCY RESPONSE +0 -0.5 dB 20 Hz to 20,000 Hz DISTORTION 0.1% at rated output level, 20 Hz to 20,000 Hz INPUT SENSITIVITY AND IMPEDANCE Auxiliary, Tuner, Tape 1, Tape 2, 0.25 volts at 250,000 ohms. Phono 1 and Phono 2, 2 millivolts at 47,000 ohms (1,000 Hz). Microphone, 2.5 millivolts at 500,000 ohms Tape Head, 2 millivolts at 500,000 ohms (500 Hz) HUM AND NOISE Auxiliary, Tuner, Tape 1, Tape 2, 90 dB below rated output Phono 1, Phone 2 and Tape Head, 78 dB below 10 millivolts input, equivalent to less than 1.2 microvolts at the input terminals Microphone, 1.5 microvolts at the input terminals OUTPUT LEVEL AND IMPEDANCE Main Output 2.5 volts with rated input, less than 100 ohms source impedance, to operate into 47,000 ohms or greater Tape Output 0.25 volts with rated input, less than 150 ohms source impedance, to operate into 47,000 ohms or greater Headphone/Line Output 0.75 volts into 8 ohm load or 2.5 volts into 600 ohm line, 0.2 ohm source impedance, level controls provided Center Channel Output 1.25 volts with rated input to both channels, to operate into 47,000 ohms or greater, level control provided VOLTAGE AMPLIFICATION IN DECIBELS Auxiliary, Tuner, Tape 1 and Tape 2 to Main Output 20 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

chine 1 to tape machine 2 or vice versa. They are mechanically interlocked to accept only one pushbutton at the IN position at one time. LF FILTER SWITCH (Rumble Filter) Flat or roll-off 12 dB per octave below 50 Hz, down to 18 dB at 20 Hz HF FILTER SWITCH (Scratch Filter) Flat or roll-off 12 dB per octave above 7000 Hz, down to 18 dB at 20,000 Hz SPEAKER SWITCHES (Operates with accessory speaker control relay) Main: Switch the MAIN loudspeaker system ON or OFF without affecting the performance of REMOTE speakers. Remote: Switch the REMOTE loudspeaker system ON or OFF without affecting the performance of MAIN speakers.
fier receptacles. Allows the power amplifiers to be turned off when not needed for headphone listening, etc. 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 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: 25 pounds (11.34 kg) net, 37 pounds (16.78 kg) in shipping carton

FRONT PANEL TAPE JACKS

Allows connection to input and output of a tape recorder from the front panel of the C 28. Inserting plugs into their jacks disconnects the TAPE 2 circuits from the rear panel of the C 28 and uses the TAPE 2 facilities for the front panel jacks. HEADPHONE JACK For listening with either low or high impedance dynamic stereo headphones. Power to this jack is supplied by an amplifier provided in the C 28. Headphone listening can be accomplished without the use of an external power amplifier. SECONDARY CONTROLS The following controls are located behind the front panel on top of the C 28 chassis. These controls are readily accessible by depressing the PANLOC buttons and sliding the C 28 forward from the mounting panel. LOW FREQUENCY TRIM CONTROLS Permits the increase in output of frequencies below 100 Hz of up to 6 dB to compensate for unequal speaker response or the unequal influence of room acoustics. PHONO 1 AND PHONO 2 LEVEL CONTROLS Permits variations in the phono input sensitivity of up to 10 dB. Provides for optimum signal to noise ratio and proper balance of the channels of the phono cartridge. OUTPUT LEVEL CONTROLS Permits the balance of the entire system to be conveniently preset. HEADPHONE LEVEL CONTROLS Adjusts the level and balance of the headphone/ line output. POWER AMPLIFIER ON-OFF SWITCH Controls power to the green 120 volt Power Ampli15

Performance Charts

Technical Description
Basically, each channel of your C 28 consists of four main parts: low level amplifier, high level amplifier, active filters and headphone amplifier. Common regulated power supplies furnish power to both channels.

LOW LEVEL AMPLIFIER

Each channel of the low level amplifier is a four transistor differential amplifier input circuit. Precise equalization is maintained by the use of negative feedback and appropriate components specially designed for low noise. Particular attention has been exercised in the use of transistors having exceptional low noise characteristics. The differential amplifier stage is the basis for the high open-loop gain of this portion of the circuit. With a higher open-loop gain there is ample negative feedback available under all equalization conditions to ensure an extremely low level of harmonic distortion. Because equalization has been designed for minimum error the response from both tape and records is accurate. One of the important features of this section is the use of set level potentiometers in the phono circuit. The gam of the phono preamplifier stages can be adjusted from 32 dB to 42 dB to correspond to the sensitivity of your phono cartridge. The phono set level controls in your C 28 are designed into the negative feedback loop. They are not potentiometers at the input or output of the low level amplifier. This important design consideration allows the gam to be reduced from 42 dB to 32 dB without adversely affecting the noise level. Because the control is in the feedback loop the level of noise and distortion is reduced 10 dB but the maximum input voltage that this section can handle is increased by 10 dB. With 42 dB of gain in the phono section the maximum input voltage that the low level amplifier can accept without overloading is 150 mV at 1000 Hz. When the gam is reduced to 32 dB this section can accept over 0.5 volt without overloading at 1000 Hz.
HIGH LEVEL AMPLIFIER The linear high level amplifier has a gain of 20 dB. The same careful design considerations apply with respect to noise and the reduction in non-linear distortion. Each channel of the high level amplifier consists of 3 transistors selected for low noise characteristics. In the feedback loop, two 11 position switches 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. At the input of the high level amplifier are the bass trim control and the switch which selects loudness or presence compensation. FILTER AMPLIFIER The filter amplifier serves three functions: (1) a high frequency filter, (2) a low freqency filter, and (3) a 20.000 Hz low pass filter. Each channel of the filter amplifier has two transistors connected in compound emitter follower configuration. The resistive and capacative elements form a 12 dB per octave active RC filter. The high frequency filter is a 7000 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 Hz. A 20,000 Hz active, low pass, filter is connected at all times to reduce wideband noise yet maintaining flat frequency response up to 20,000 Hz. The non-linear distortion of these active filters is very low even at cut off frequency. This is not the case in passive f i l t e r s where a very low impedance at the cut off frequency is presented to the driving source. This low impedance will cause high nonlinear distortion at and near the cut o f f frequency. The design of the C 28 eliminates this problem. HEADPHONE AMPLIFIER The headphone amplifier is capable of producing 0.75 volts of output into 8 ohm headphones with less than 0.1% harmonic distortion. This is adequate power to drive any dynamic type headphone. The maximum output of the headphone amplifier is 2.5 volts into 50 ohms or greater at the LINE OUTPUT terminals on the rear panel. The internal impedance of the headphone amplifier is less than 0.2 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.

POWER SUPPLY The power supply consists of a low impedance 75 volt power supply and a 14 volt power supply for the headphone amplifier. The 75 volt supply is stabilized by a series regulator transistor and a zener diode. An accessory filter chain and voltage dividing network provides 18 volts to the low level circuits. The headphone amplifier is powered by a separate 14 volt supply which uses a transistor as an effective ripple filter. A principle design consideration was exceptionally low hum level. First the power transformer of the C 28 uses a magnetic core with very low flux density. Double shielding has been accomplished by surrounding the transformer f i r s t with strips of copper, and then with strips of treated soft iron. The shielded transformer is potted in a heavy gauge soft steel can. To prevent unbalance of the magnetic flux of the transformer, the secondary voltage is rectified by silicon diodes in a bridge configuration.

Block Diagram

MCINTOSH LABORATORY INC. 2 CHAMBERS ST., BINGHAMTON, N. Y. 13903

607-723-3512

Design subject to change without notice. Printed in U.S.A.

038-343

Use and hear AM as never before. The MAC 1900 has a high quality loopstick AM antenna. It can be rotated for maximum performance, optimum signal reception and minimum interference. Each MAC 1900 loopstick is tuned for optimum performance. Custom matching maximizes performance. You can mount the receiver in any position without the sacrifice of sensitivity.
PREAMPLIFIER The preamplifier is an outstanding example of what the electronic designers have done to provide for highest quality with great flexibility in a space limited housing. It has unusually low noise and low distortion. For instance, you can play, record, and monitor on two tape recorders.

POWER AMPLIFIER

There's more real power and more protection. The power transistors are mounted on oversized black anodized heat sinks. Under normal operation the transistors will operate at low temperature. The power transistors used in the output circuits are selected for their high power dissipation capability, wide frequency response and large "safe operating area."
The low distortion and stability of the MAC 1900 power amplifier circuit allows it to be used with any dynamic or electrostatic speaker system. McIntosh output circuit with instantaneous current limiting totally protects you. This reserve power and complete protection allows safe operation with as many as three pairs of speakers, individually or all together! You have front panel switching for three stereo loudspeaker systems of any type!

RECEIVER IS THE

you get more value you get more protection from service costs you get more electronic protection you get more real power you get more useful flexibility you get more results from new technology you get more pure pleasure
AM-FM/FM STEREO R E C E I V E R Shown in walnut veneer cabinet
TWO YEAR S E R V I C E CONTRACT
To make the value even greater, buy a McIntosh Audio product and get a free 2 YEAR SERVICE CONTRACT! An outstanding feature of the McIntosh Service Contract is the protection you get. Normal wear and tear as well as any manufacturing defect costs you nothing.
Read about the Guaranteed Performance of the

MAC 1900

PREAMPLIFIER AND POWER AMPLIFIER

4 ohms, 8 ohms, or 16 ohms

RATED POWER BAND:

20 Hz to 20,000 Hz
TOTAL HARMONIC DISTORTION:
0.2% maximum harmonic distortion at any power level from 250 milliwatts to rated power per channel from 20 Hz to 20,000 Hz, both channels operating
INTERMODULATION DISTORTION: 0.2% if instantaneous peak power output is t w i c e rated continuous average power or less per channel with both channels operating for any combination of frequencies 20 Hz to 20,000 Hz FREQUENCY RESPONSE: (at one watt Output) 20 Hz to , 0 Hz +0.5 -0.5 dB NOISE AND HUM: Power Amplifier: 95 dB below rated output Tape Input: 90 dB below rated output Phono Input: 76 dB below 10 rnV input DAMPING FACTOR:
56 at 8 ohms output 112 at 16 ohrns output
INPUT SENSITIVITY AND IMPEDANCE: Power Amplifier: 2.5 volts, 0 , 0 ohms
Phono 1 and Phono 2 : 2.0 mV, 47,000 ohms
Tape 1 and Tape 2: 0 mV, 0 , 0 ohms TAPE OUTPUT: Tuner: 1.0 volt at 100% modulation (FM) Tape: 250 mV with rated input at 500 Hz Phono: 1.2 volts with mV input at Hz BASS CONTROLS: 16 dB at , 0 Hz TREBLE CONTROLS: 16 dB at , 0 Hz L.F. FILTER: Active filter, dB per octave roll off below 50 Hz, down 18 dB

GENERAL

POWER REQUIREMENTS: 120 volts, / Hz, 40 w a t t s at zero signal output, 300 watts at rated output SEMICONDUCTOR COMPLEMENT: silicon field e f f e c t of bipolar transistors 3 integrated circuits 4 thyrisistors

H.F. FILTER:

Active filter, 12 dB per octave roll off above 7,000 Hz, down

13 dB at , 0 Hz

39 silicon rectifiers ana diodes MECHANICAL
SIZE: Front panel measures 16 inches wide ( 4 0. cm) by 5 - 1 / 2 inches high ( 1 3. cm). Chassis measures 15 inches wide ( 3 8. 1 cm) by 5-1/8 inches high (1 3.02 cm) by 15 inches deep (38.1 cm) including back panel connectors. Knob clearance required is 1 -1/2 inches ( 3. cm) in front of the mounting panel FINISH: Front panel is anodized gold w i t h black WEIGHT: 33 pounds (14.97 kg) net 46 pounds (20.87 kg) in shipping carton

SENSITIVITY: 75 mV (external ant.) SIGNAL TO NOISE RATIO: 45 dB minimum; 55 dB at 0 % modulation HARMONIC DISTORTION: Will not exceed 1% at 30% modulation ADJACENT CHANNEL S E L E C T I V I T Y : 30 dB minimum IMAGE REJECTION: 65 dB minimum, 540 kHz 1600 kHz
From the LOUDSPEAKER SCIENTISTS at

THE SOUND of REALITY

WHAT IS THE MEASURE OF A LOUDSPEAKER?
A loudspeaker is a "sound imaging" device much the same as a photograph is a "visual imaging" device. You measure the excellence of a photograph by judging the coincidence of the visual image with reality. You measure the excellence of a loudspeaker by judging the coincidence of the sound image with reality. After considering both the reality and the sound image you make the ultimate judgment based on what you hear. The most important thing a loudspeaker can do for you is to sound right the first time you listen to it, the next time you listen to it and every time you listen to it.
MAKING A REAL SOUND IMAGE
When you look in a perfectly flat mirror you will see an accurate image of y o u r s e l f. If the mirror is bent then the accuracy of the image is altered. Mirrors can have other accuracy problems. They can be tinted so that the color coincidence of the object and the image is altered. In addition, the image may correspond in shape and size for one color but be out of shape or size for another color. Optical and sound imaging devices have analogous problems. Considering these facts it is possible to state the concept of image fidelity: the image should coincide with the object in every detail. It should be no more nor no less. Applying the image fidelity concept to a sound system requires a statement like this: We should hear the original sound - nothing subtracted - nothing added! To the eternal credit of sound scientists and engineers most of the links in the sound imaging chain have reached a high level of perfection. The loudspeaker has been the last link in need of an advancement to fidelity.
THE MCINTOSH PROMISE OF PERFORMANCE
A McIntosh Loudspeaker is a promise of a new psychoacoustic experience the experience of reality in your listening room - - - the experience of listening to an almost perfect sound image. From many man years of research, McIntosh promises you nearly perfect sound images will occur in your listening room - - - whatever the room is like! (See page 18 for the McIntosh Environmental Equalizers.) They give you the flexibility to properly match McIntosh loudspeakers to your room. For the first time loudspeakers and electronics have been designed together to give you near perfection in reproduction in your listening room. To say it differently - - - if the actual live or real sound would please you in your listening room then the McIntosh loudspeaker in your listening room will equally please you.

C-26 PREAMPLIFIER

BASS: Separate 11 position rotary switches for each channel. 20 dB to +16 dB at 20 Hz. TREBLE; Separate 11 position rotary switches for each channel. -20 dB to +20 dB at 20,000 Hz. LOUDNESS: Flat response, or continuously variable loudness equalization as volume level is reduced. TAPE MONITOR: Two pushbutton switches. Either of 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. LF F I L T E R (Rumble F i l t e r ) : Flat or r o l l - o f f 6 dB per octave below 50 Hz, down 12 dB at 20 Hz. HF F I L T E R (Scratch F i l t e r ) : Flat or roll-off 6 dB per octave above 6,000 Hz, down 12 dB at 20,000 Hz. SPEAKER: Main - Switch the MAIN loudspeaker system ON or O F F without affecting the performance of R E M O T E speakers. Remote - Switch the R E M O T E loudspeaker system ON or OFF without affecting the performance of MAIN speakers. HEADPHONE JACK: For listening with low impedance dynamic stereo headphones. Power to this jack is supplied when the output of the amplifier is properly connected to the C 26. CENTER CHANNEL L E V E L : Top of chassis control to adjust the output level of the left plus right program material at the C E N T E R C H A N N E L output on the back panel. PHASE CONTROL: Electronically reverse phase in the left channel to correct "out of phase" program sources.
FREQUENCY RESPONSE: +0, -0.5 dB 20 Hz to 20,000 Hz. DISTORTION: Will not exceed 0.1% at any level up to 2.5 v o l t s output, 20 Hz to 20,000 Hz. INPUT SENSITIVITY AND IMPEDANCE: Auxiliary, Tuner, Tape 1, Tape 2, 0.25 volts at 250,000 ohms. Phono 1 and Phono 2, 2 millivolts at 47,000 ohms (1,000 H z ). HUM AND NOISE; Auxiliary, Tuner, Tape 1, and Tape 2, 85 dB below rated output. Phono 1, Phono 2, 74 dB below 10 millivolts input, equivalent to less than 2 microvolts at the input terminals. OUTPUT L E V E L AND IMPEDANCE: Main Output: 2,5 v o l t s with rated input, 200 ohms source impedance, to operate into 47,000 ohms or more. Tape Output: 0.25 v o l t s , 200 ohms source impedance, from low level inputs to operate into 47,000 ohms or more. Center Channel Output: (L + R) 2.5 v o l t s with rated input to both channels, 1,200 ohms source impedance, to operate into 47,000 ohms or more. A level control a d j u s t s the center channel output from +6 dB with respect to Main output. AMPLIFICATION IN D E C I B E L S : A u x i l i a r y , Tuner, Tape 1 and Tape 2 to Main Output 20 dB; to Tape Output 0 dB; Phono 1 and Phono 2 (at 1,000 Hz); to Main Output 62 dB; to Tape Output 42 dB. SEMICONDUCTOR: 18 silicon planar transistors, and 3 silicon diodes. POWER R E Q U I R E M E N T : 120 volts, 50/60 Hz, 15 watts. MECHANICAL S I Z E : Front panel: 16 inches wide (40.64 cm) by 5 - 7 / inches high (13.81 cm). Chassis: 15 inches wide (38,1 cm) by 5 inches high (12.7 cm) by 13 inches deep (33.02 cm) including PANLOC mounting brackets and back panel connectors. Knob clearance required as 1-1/2 inches (3.81 cm) in front of the mounting panel. FINISH: Front panel is anodized gold and black with special McIntosh gold/teal panel nomenclature illumination. CHASSIS: black. MOUNTING: McIntosh developed professional PANLOC. WEIGHT: 18 pounds (8.16 kg) net, 33 pounds (14.97 kg) in shipping carton.

Distortion performance of the bridge detector is pretty close to the theoretical zero. In addition to its excellent distortion performance, the bridge detector also exhibits capture ratio close to 0 dB. Tuned circuits are not used in the MR 78 detector. They are quite difficult to manufacture and align accurately, and ordinary tuned-circuit discriminators go out of adjustment. There has been much talk about "permanently aligned" IF filters, but much silence concerning the most important source of misalignment in these same tuners - the discriminator. The two simple variable resistor adjustments in the MR 78 detector merely center the tuning meter and set the transistor bias. Complex tuning for minimum distortion is not needed. NEW VARIABLE SELECTIVITY The MR 78 has excellent selectivity. The bandwidth (210 kHz wide at 60 dB down) permits tuning stations that are impossible on ordinary tuners. Even though the MR 78 has the narrowest IF bandwidth ever used in a stereo tuner, (it is the correct width to let just one FM station through) the great number of stations crowding the FM band requires a tuner with variable selectivity. Variable selectivity allows stereo reception even under severe receiving conditions. In the NORMAL position, a very low distortion 8-pole filter is used in the IF circuit for listening to local broadcasts. The NARROW position adds a sharp 8-pole filter to the NORMAL IF filter to yield a low distortion (less than 0.2%), highly selective 16-pole composite IF filter. In the NARROW position interference is reduced while receiving distant stations. SUPER-NARROW position adds a 4-pole 4-zero crystal filter to the two other IF filters. SUPER NARROW permits receiving distant stations which are on channels adjacent to local stations. With an adequate FM antenna there are usable signals never heard before with ordinary FM tuners.
Beautiful styling, extended control flexibility and meaningful illuminated operational indicators bring the McIntosh MR 78 to a new high level of professionalism.
PERFORMANCE GUARANTEE: Performance limits are the maximum deviation from perfection permitted for a McIntosh instrument. We promise you that the MR 78 you buy must be capable of performance at or exceeding these limits or you get your money back. McIntosh is the only manufacturer that makes this guarantee.
TUNING RANGE: 88 to 108 MHz. ANTENNA INPUTS: 300 ohms balanced; 75 ohms unbalanced. INTERMEDIATE FREQUENCY: 10.7 MHz. SENSITIVITY: 2 mV for 35 dB quieting; 2.5 mV at 100% modulation ( 75 kHz deviation) for 3% total noise and harmonic distortion. SIGNAL TO NOISE RATIO: 75 dB below 100% modulation. HARMONIC DISTORTION: 0.2% mono or stereo at 100% modulation, 20 Hz to 15,000 Hz. Typically, 0.05% at 1,000 Hz. DRIFT: 25,000 Hz for the first two minutes; thereafter 5,000 Hz at 25 C in 24 hours. FREQUENCY RESPONSE: Mono: 1 dB 20 Hz to 20,000 Hz with standard deemphasis, (75 mS); Stereo: 1 dB 20 Hz to 15,000 Hz with standard de-emphasis (75 mS). CAPTURE RATIO: 0.25 dB detector only; 2.5 dB complete tuner. SELECTIVITY: Switch Setting: NORMAL NARROW SUPER NARROW Adjacent Channel 7 dB 22 dB 55 dB Alternate Channel 55 dB > 90 dB >> 90 dB SPURIOUS REJECTION: 100dB IHF. IMAGE REJECTION: 100 dB at 88 to 108 MHz ( I H F ). INTERMODULATION DISTORTION: 0.2% mono or stereo for any combination of frequencies from 20 Hz to 15,000 Hz with peak modulation equal to 100% or less. Typically 0.1%.

MAXIMUM SIGNAL INPUT: 12 volts across 300 ohm antenna terminals will not increase harmonic or intermoduiation distortion. AUDIO HUM: 75 dB down from 100% modulation. MUTING: 70 dB noise reduction between stations. MUTING THRESHOLD (Typical): DISTANT position 5 mV; LOCAL position 20 mV SCA FILTER: 50 dB down from 67 kHz to 74 kHz; 275 dB per octave slope. STEREO SEPARATION: 40 dB at 1,000 Hz. STEREO FILTER (Typical): 10 dB noise reduction in Position 1. 20 dB noise reduction in Position 2. AUDIO OUTPUT: Front Panel Controlled: 2.5 volts into 47,000 ohms; Fixed Output: 2.5 volts into 47,000 ohms, 1.0 volts into 600 ohms. All tuner performance limits were measured with SELECTIVITY switch set at NORMAL, unless otherwise stated. GENERAL POWER REQUIREMENT: 120 volts, 50/60 Hz 35 watts. SEMICONDUCTOR COMPLEMENT: 3 JFET's, 2 MOSFET's, 17 Bipolar Transistors, 43 Diodes, 4 Integrated Circuits. MECHANICAL SIZE: Front panel: 16 inches wide (40.64 cm) by 5-7/16 inches high (13.81 cm); Chassis: 15 inches wide (38.1 cm) by 13 inches deep (33.02 cm), including PANLOC shelf and back panel connectors; Knob Clearance: 1-1/2 inches (3.81 cm) in front of mounting panel. FINISH: Front panel: Anodized gold and black with special gold/teal panel nomenclature illumination; Chassis: Chrome and black. MOUNTING: McIntosh developed professional PANLOC. WEIGHT: 27 pounds (12.25 kg) shipping carton. net, 39 pounds (17.69 kg) in
LOW DISTORTION AND HIGH PERFORMANCE FOR SUPERIOR FM

THE MR 77

USABLE SENSITIVITY:
2 mV for 35 dB of quieting, 2.5 microvolts typical. SIGNAL TO NOISE RATIO; 75 dB below 100% modulation HARMONIC DISTORTION: Will not exceed 0.2% mono or stereo at 100% modulation, 20 Hz to 15,000 Hz. INTERMODULATION DISTORTION: Will not exceed 0.2% mono or stereo for any combination of frequencies from 20 Hz to 15,000 Hz with peak modulation equal to 100% or less, 0.1% typical. AUDIO FREQUENCY RESPONSE: 1 dB 20 Hz to 15,000 Hz with standard de-emphasis, (75 m5) and 19,000 Hz pilot filter. CAPTURE RATIO: 0.25 dB detector only; 2.5 dB complete tuner at 100% modulation. SPURIOUS REJECTION: 100 dB. IMAGE REJECTION: 100 dB at 88 to 108 MHz ( 1 H F ). SELECTIVITY: Adjacent channel: 6 dB; Alternate channel: 50 dB. STEREO SEPARATION: 40 dB at 1,000 Hz. STEREO F I L T E R : 10 dB noise reduction in position 1; 20 dB noise reduction in position 2. SCA F I L T E R : 50 dB down from 67 kHz to 74 kHz; 275 dB per octave slope. DRIFT: 25,000 Hz in first two minutes; thereafter 5,000 Hz in normal temperatures. MUTING: 70 dB noise reduction between stations. MUTING THRESHOLD: Position 1, 5 mV. Position 2, 20 mV.

ANTENNA INPUTS:

MAXIMUM SIGNAL INPUT: 12 volts across 300 ohms antenna terminals will not increase harmonic or intermodulation distortion. AUDIO OUTPUT;
2.5 volts into 47,000 ohms; 1 volt into 600 ohms from fixed output.
IF SYSTEM: 8-Pole IF filter, 2 IC's 1 J-FET, and push-pull overlay power transistor stage driving a linear phase bridge discriminator. STEREO INDICATOR: Stereo light activated by 19,000 Hz only. AUTOMATIC MONO-STEREO SWITCH: McIntosh developed; all electronic automatic mono-stereo switching circuit. GENERAL SEMICONDUCTOR COMPLEMENT: 21 Transistors 4 Integrated Circuits 1 Indicator Tube. POWER REQUIREMENT: 120 volts, 50/60 Hz, 35 watts. MECHANICAL SIZE Front panel: 16 inches wide (40.64 cm) by 5-7/16 inches high (13.81 cm); Chassis: 15 inches wide (38.1 cm) by 13 inches deep (33.02 cm) including PANLOC shelf and back panel connectors. Knob Clearance: 1-1/2 inches (3.81 cm) in front of mounting panel. FINISH: Front panel: Anodized gold and black with special gold/ teal nomenclature illumination. Chassis: Chrome and black. MOUNTING: McIntosh developed professional PANLOC. WEIGHT: 27 pounds (12.25 kg) net, 39 pounds (17.69 kg) in shipping carton.
300 ohms balanced; 75 ohms unbalanced.
NEW ENGINEERING NEW PERFORMANCE THE MR 74 AM-FM/FM STEREO TUNER
Shown in walnut veneer cabinet A new addition to the front panel is the SELECT pushbutton. With it, control of the IF characteristics is brought to the front panel. It allows stereo reception even under severe receiving conditions. In the NORMAL position a very low distortion dual QUADTUNED IF filter is used. The dual QUAD-TUNED IF filter has unusual adjacent channel selectivity and low distortion. The QUADTUNED IF filter has equal time delay in its pass band region. All other IF filters have excessive delay distortion. The QUAD-TUNED IF filter has almost no delay distortion from antenna input to discriminator output! You get overall lower distortion performance. Activating the SELECTivity pushbutton routes the signal to two double-tuned transformers, a ceramic filter network, and a singlegate MOS-FET. The sides of the IF curve are compressed by this circuit narrowing the IF bandpass. In this mode of operation weak stations adjacent to strong stations can be tuned with surprising clarity. McIntosh has developed a special detecting circuit used in the multiplex section. A particular advantage of this circuit is the elimination of the critical adjustments necessary with commonly used matrixing circuits. The circuit detects the L - R sidebands, then automatically matrixes the recovered information with the L + R carrier signal. This yields the left and right program output with maximum separation. AM For greater spurious rejection the AM-RF amplifier circuit includes a three section variable tuning capacitor in the metal enclosed shielded RF module which also houses the FM-RF front end. The AM circuit has constant sensitivity, constant selectivity, high image rejection across the complete AM band. This circuit design achieves equal sensitivity even down at the low end of the band. Spurious, image, and intermediate frequency rejection are all superior. The McIntosh circuit is unique in a superheterodyne AM receiver. A high-quality loopstick antenna is provided. It can be rotated for maximum performance, optimum signal rejection or minimum interference. Each loopstick is individually tuned for optimum performance. After tuning the loopstick is then sealed. Custom matching of the loopstick to the AM-RF front end maximizes the performance of the loopstick antenna.

each side of the center frequency. The filters are permanently sealed and do not require adjusting. The IF cannot drift nor vibrate out of adjustment. The exceptionally high gain of the two integrated circuits assures "hard limiting" at very low levels of input signals. Each integrated circuit contains 16 transistors, 3 zener diodes, 5 diodes and 23 resistors, all on a single monolithic silicon chip. VARIABLE SELECTIVITY A new addition to the front panel is the SELECT pushbutton. With it, control of the IF characteristics is brought to the front panel. It allows stereo reception even under severe receiving conditions. In the NORMAL position a very low distortion dual QUADTUNED IF filter is used. It exhibits unusual excellent adjacent channel selectivity and low distortion. The QUAD-TUNED IF filter has equal time delay in its pass band region. All other IF filters have excessive distortion.
The QUAD-TUNED IF filter has almost no delay distortion from antenna input to discriminator output! You get overall lower distortion performance. Activating the SELECTivity pushbutton routes the signal to two double-tuned transformers, a ceramic filter network, a singlegate MOS-FET, and the dual QUAD-TUNED IF filters. The sides of the IF curve are compressed, narrowing the IF bandpass. In this mode weak stations adjacent to strong stations can be tuned with surprising clarity. McIntosh has developed a special detecting circuit used in the multiplex section. A particular advantage of This circuit is the elimination of the critical adjustments necessary with commonly used matrixing circuits. The circuit detects the L R sidebands, then automatically matrixes the recovered information with the L + R carrier signal. This yields the left and right program output with maximum separation.
MX 113 AM-FM/FM STEREO TUNER PREAMPLIFIER Shown in walnut veneer cabinet
AM-FM/FM STEREO For greater spurious rejection the AM-RF amplifier circuit includes a three section variable tuning capacitor in the metal enclosed shielded RF module which also houses the FM-RF front end. The AM circuit has constant sensitivity, constant selectivity, high image rejection across the complete AM band. This circuit design achieves equal sensitivity even down at the low end of the band. Spurious, image, and intermediate

frequency rejection are all superior. The McIntosh circuit is unique in a superheterodyne AM receiver. A high-qualtiy loopstick antenna is provided. It can be rotated for maximum performance, optimum signal reception or minimum interference. Each loopstick is individually Tuned for optimum performance. After tuning The loopstick is then sealed. Custom matching of the loopstick to the AM-RF front end maximizes the performance of the loopstick antenna.
RELIABILITY AND IDEAL FLEXIBILITY. STEREO CONTROL CENTER

TUNER PREAMPLIFIER

USABLE SENSITIVITY: 2.5 microvolts at 100% modulation ( 75 kHz deviation) for less than 3% total noise and harmonic distortion, SIGNAL TO NOISE RATIO: 70 dB at 100% modulation, HARMONIC DISTORTION: Mono: Will not exceed 0.3% at 100% modulation 75 kHz deviation. Stereo: Will not exceed 0.5% at 100% modulation 75 kHz deviation. FREQUENCY RESPONSE: 1 dB from 20 Hz to 15,000 Hz with standard de-emphasis (75mS) and 19,000 Hz pilot filter. CAPTURE RATIO: 1.5 dB SPURIOUS REJECTION: 90dB IMAGE REJECTION: 95 dB at 88 to 108 MHz (IHF) STEREO SEPARATION: Exceeds 35 dB at 1,000 Hz. SELECTIVITY: Switch Setting: OUT IN Adjacent Channel: 6dB 15dB Alternate Channel: 58 dB 88 dB TUNING INDICATOR: D'Arsonval movement meter with increased sensitivity. STEREO INDICATOR: Stereo light activated by 19,000 Hz pilot signal only.
BASE CONTROL: -18 dB to + 16 dB at 20 Hz. TREBLE CONTROL: 20 dB at 20,000 Hz. LF FILTER: Flat or roll off below 50 Hz, down 12 dB at 20 Hz. HF FILTER: Flat or roll off above 5,000 Hz, down 12 dB at 20,000 Hz. POWER REQUIREMENTS: 120 volts, 50/60 Hz, 30 watts TRANSISTOR COMPLEMENT: 2-JFET 3-MOSFET 30Silicon Planar 31-Diodes 2Integrated Circuits (each contains the equivalent of 16 transistors and 8 diodes).
FACILITIES AND FEATURES VOLUME CONTROL: Precision "tracked" at all listening
AM SENSITIVITY: 75 microvolts at 1,000 kHz (using external antenna input). SIGNAL TO NOISE RATIO: 45 dB HARMONIC DISTORTION: 1% at 30% modulation. FREQUENCY RESPONSE: Down 6dB at 3,500 Hz. SELECTIVITY: Switch Setting: OUT IN Adjacent Channel: 35 dB 45 dB IMAGE REJECTION: 65 dB; 540 kHz to 1600 kHz

PREAMPLIFIER

FREQUENCY RESPONSE: 0.5 dB, 20 to 20,000 Hz. DISTORTION: Will not exceed 0.1% at 2.5 volts output, 20 to 20,000 Hz. INPUT SENSITIVITY AND IMPEDANCE: Phono 1 and Phono 2: 2 millivolts for 2.5 volts output at 1,000 Hz, 47,000 ohms; Auxiliary and Tape: 0.25 volts for 2.5 volts output; 250,000 ohms. VOLTAGE AMPLIFICATION: Phono 1, Phono 2 to Main output 62 dB, to Tape output 42 dB. Auxiliary, Tape to Main output 20 dB to Tape output 0 dB. OUTPUT: Main: 2.5 volts with rated input. Up to 10 volts can be developed without increase in distortion. FM will produce 10 volts output at 100% modulation. Tape: 0.25 volts with rated input. Phono signal to 10 millivolts produces 1.2 volts output. FM will produce 1 volt output at 100% modulation. L + R 2 volts with rated input. HUM AND NOISE: Phono 1 and Phono 2: 72 dB below 10 millivolt input; equivalent to less than 3 microvolts at the input terminals. Aux-Tape: 85 dB below 2.5 volts output, unweighted.

levels. (0 to 65 dB). Does not change stereo balance as loudness is changed. The AC power ON/OFF switch is coupled with this control. BALANCE CONTROL: Natural balance at center position, attenuation of left or right channel by rotating control. LOUDNESS: Loudness compensated or flat responseLoudness position boosts low frequencies for low level listening. Operates as a function of volume control position. Full compensation is obtained at lower volume levels and flat response is obtained at full volume. SELECTIVITY: Increases the ability of the tuner to separate a weak (distant) station from a strong (local) station on adjacent channels. MODE: Selects either stereo or mono operation. PHASE CONTROL: Electronically reverses phase in the left channel to correct "out of phase" program sources. MUTING: Suppresses the background noise and hiss normally heard between FM stations. TAPE MONITOR: Pushbutton; compares recorded tape with program source while recording. MUTING ADJUST: Modifies the noise rejection threshold on FM. DIAL SCALE INTENSITY; Modifies the brightness of the illumination of the front panel.

MECHANICAL

SIZE: Front panel: 16 inches wide (40.64 cm) by 5-7/16 inches high (13.81 cm); Chassis: 15 inches wide (38.1 cm) by 13 inches deep (33.02 cm), including PANLOC shelf and back panel connectors, Knob Clearance: 1-1/2 inches (3.81 cm) in front of mounting panel. FINISH: Front panel: Anodized gold and black with special gold/teal panel nomenclature illumination; Chassis: Chrome and black. MOUNTING: McIntosh developed professional PANLOC. WEIGHT: 26 pounds (11.79 kg) net, 38 pounds (17.24 kg) in shipping carton.
MA 6100.Here is performance once associated only with separate preamps and power amps
The MA d e l i v e r s M c I n t o s h performance and quality in a combination solid state preamplifier and solid state power amplifier. The stereo preamplifier has the lowest hum and noise of any c o m b i n a t i o n unit. The MA reproduces music accurately. There is no fuzziness. Here is the power you need to give you the sound of f i v e music in your home. The Silicon r e c t i f i e r s power supply h a s instant response to the amplifiers needs. Recovery f r o m the loudest musical passage is instantaneous. The music sounds alive and thrilling, not clouded by power supply under design. Aux, Tape, Tuner: 90 dB below rated output Phono Input, Tape Hd.: 76 dB below 10 mV input OUTPUT V O L T A G E : At TAPE output: Aux, Tape, Tuner: 0 mV with rated input Phono: 0 mV with rated input; 1.2 v o l t s with 1.0 mV input
Tape Hd: 0 mV at 0 Hz with rated input DAMPING F A C T O R : 50 at 3 ohms output 0 at 16 ohms output INPUT S E N S I T I V I T Y AND IMPEDANCE: Power Amplifier: 3 volts, 0 , 0 ohms Phono 1 and Phono 2: 2. 5 mV at Hz, , 0 ohms Tape Head: 3 mV, , 0 ohms Tape, A u x , and Tuner: 0 mV, 0 , 0 ohms BASS CONTROLS:

McIntosh amplifiers have been the "LABORATORY STANDARD" in vacuum electronics for 20 years. McIntosh audio scientists have generated solid state innovations that have continued the McIntosh reputation for "LABORATORY STANDARD". New levels of performance, even greater reliability, and highest quality have created levels of cleanness and beauty in music that until now have been clouded by lower performance standards.
You get FULL POWER AT ALL SPEAKER IMPEDANCES. Reliability and long trouble free life comes, in part, from McIntosh Sentry Monitoring Circuits. The SENTRY MONITORING CIRCUIT prevents failure of the power transistors due to excessive mismatch of the output. With the amplifier operating normally the SENTRY MONITORING CIRCUIT has no effect on the signals passing through the power amplifiers. If the power dissipation should rise above normal, the SENTRY MONITORING CIRCUIT restricts the drive voltage to the output transistors. The SENTRY MONITORING CIRCUIT acts instantaneously. You are assured of complete circuit reliability. McIntosh is the only amplifier with this degree of protection. To permit you to measure the performance, provide for correct system balance, and to obtain accurate power readings McIntosh has developed DYNAMIC PEAK LOCKING METERS. Ordinary meters lack the capability of indicating the short interval power in a sound wave. The mass of the meter movement is too great to respond to instantaneous changes in music program material. Superior McIntosh engineering has developed new circuits that permits the meters to respond to the short interval power in sound wave to an accuracy of 98% of the true value. Two new circuits were required to provide the accuracy. The first circuit is an accelerating circuit. It compensates for the inertia characteristics of the meter movement. The second circuit is a "time stretching" circuit. Short interval power fluctuation is so rapid that the eye might not perceive the instantaneous power reading. The "time stretching" circuit holds the meter needle at peak reading for a few milliseconds to permit the eye to perceive. The DYNAMIC PEAK LOCKING METERS represent another major engineering advancement by McIntosh audio scientists. And best of all - you are protected for THREE FULL YEARS from any service costs. With the purchase of a McIntosh you are offered a FREE THREE YEAR SERVICE CONTRACT. You can't pay us for the repair of a McIntosh for the first three years you own it! McIntosh is the best in PERFORMANCE, RELIABILITY, AND VALUE.

Stereo: 4 ohms, 8 ohms, or 16 ohms; separate terminals are provided for each output; Mono: 2 ohms, 4 ohms, or 8 ohms; separate terminals are provided for each output

RATED P O W E R BAND:

Stereo: 4 ohms, 8 ohms, or 16 ohms; separate terminals are provided for each output; Mono; 2 ohms, 4 ohms, or 8 ohms; separate terminals are provided for each output
Stereo: 0.25% maximum harmonic distortion at any power level from 250 milliwatts to 50 watts per channel from 20 Hz to 20,000 Hz, both channels operating Mono: 0.25% maximum harmonic distortion at any power level from 250 milliwatts to 100 watts from 20 Hz to 20,000 Hz
INTERMODULATION DISTORTION: Stereo: 0.25% if i n s t a n t a n e o u s peak power output is 100 w a t t s or less per channel with both c h a n n e l s o p e r a t i n g for any combination of f r e q u e n c i e s 20 Hz to , 0 Hz Mono: 0. % if instantaneous peak power output is 200 w a t t s or less for any combination of frequencies 20 Hz to , 0 Hz FREQUENCY RESPONSE: ( a t one watt o u t p u t ] 20 Hz to 20,000 Hz +0 - 0. dB NOISE AND HUM: 90 dB below rated output OUTPUT IMPEDANCE: STEREO 4, 8, and 16 ohms MONO 2, 4, and 8 ohrns OUTPUT VOLTAGES: v o l t s for d i s t r i b u t i o n lines DAMPING F A C T O R : 15 at 4 ohms output 38 at 8 ohms output 17 at 16 ohms output INPUT IMPEDANCE: 0 , 0 ohms INPUT S E N S I T I V I T Y : 0.5 volt. Level control provided for higher input voltage
Stereo: 0.25% maximum harmonic distortion at any power level from 250 milliwatts to 105 watts per channel from 20 Hz to 20,000 Hz, both channels operating
0.25% maximum harmonic distortion at any power level from 250 milliwatts to 210 watts from 20 Hz to 20,000 Hz
INTERMODULATION D I S T O R T I O N : Stereo: 0. % if instantaneous peak power output is 210 w a t t s or less per channel with both channels operating for any combination of frequencies 20 Hz to , 0 Hz Mono: 0. % if instantaneous peak power output is 420 w a t t s or less for any combination of f r e q u e n c i e s 20 Hz to , 0 Hz FREQUENCY RESPONSE: (at one watt output) 20 HZ to , 0 Hz +0 - 0. dB NOISE AND HUM: 90 dB or more below rated output OUTPUT IMPEDANCE: STEREO 4, 8, and 16 ohms MONO 2, 4, and 8 ohms OUTPUT VOLTAGES: 25 v o l t s for distribution lines DAMPING F A C T O R : 20 at 4 ohms output 14 at 8 ohms output 11 at 16 ohms output INPUT IMPEDANCE: 0 , 0 ohms INPUT S E N S I T I V I T Y : 0.5 volt. Level control provided for higher input v o l t a g e