McIntosh C-28

 McIntosh engineers could not be content with just another preamplifier. New concepts and new technology have produced a preamplifier that gives you the greatest flexibility ever. Look at the great number of ways you can enjoy the C 28 .......

Use 3 tape machines 2 with their own electronics and 1 tape playback deck with complete easy front panel switching Built-in Headphone Amplifier listen to your favorite music - - - privately.

Main and Remote Loudspeaker Switching turn the main speakers on or off without affecting the remote speakers and vice versa (operates with accessory relay).

New Low Noise Phono Input listen to your records with a new quietness.

Individual Channel Phono Level Controls match levels from different phono cartridges without degrading signal to noise ratio.

Individual Channel Output Level Controls perfect balance from your stereo always.

Individual Channel Tone Control Switches complete, repeatable flexibility.

NEW Compensation Control one position for loudness compensation, one position is flat and (NEW) a third position that adds presence compensation!

 NEW LOW NOISE PHONO CIRCUITS

New records and tapes with greatly increased dynamic range demanded new low noise circuits. McIntosh scientists developed a new DIFFERENTIAL INPUT CIRCUIT that reduced phono input noise levels from approximately 2.4 microvolts in an excellent preamplifier to a new level of only 1.2 microvolts! The differential input circuit has only been used in very sensitive professional test equipment and in medico-electronics. The preamplifier will not overload or change distortion for any phono input signal from 2 millivolts up to 500 millivolts. This represents a dynamic range of approximately 3000 to 1 on a voltage basis. This fantastic improvement necessitated extreme care in layout and manufacturing. The signal circuits need careful shielding and wiring with coaxial cable to prevent noise and crosstalk in the preamplifier from destroying the low noise of the input circuit.

 NEW TAPE FLEXIBILITY

With the C 28 you can copy from one tape recorder to another while listening to a completely different program! In addition, you can monitor the recording by simply pushing a button and an input circuit has been provided to accept the signal from a tape playback deck. You can use three tape machines with the C 28. There are front panel jacks that permit the use of the third tape recorder. When plugged into the front panel jacks the tape recorder connected to Tape Recorder 2 is automatically disconnected and the controls provided are used with the third tape recorder.

 NEW HEADPHONE AMPLIFIER

Use your headphones for private listening. Ample power has been provided to power todays high quality low impedance dynamic headphones, plus a separate power switch in the preamplifier turns the power amplifiers on or off. It is not necessary to operate the power amplifiers while listening to headphones.

FACILITIES AND FEATURES

BASS CONTROLS:

11 position rotary switch in each channel, ± 20 dB at 20 Hz.

TREBLE CONTROLS:

11 position rotary switch in each channel, ± 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.

VOLUME CONTROL:

AC power ON/OFF switch is coupled with this control.

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:

Either of two tape recorders can be monitored by use of either the TAPE 1 or TAPE 2 pushbutton.

TAPE COPY SWITCH:

Provides switching to copy from tape machine 1 to tape machine 2 or vice versa without affecting the program being heard.

LF FILTER SWITCH (Rumble Filter):

Flat or roll-off at 12 dB per octave below 50 Hz, down

18 dB at 20 Hz.

HF FILTER SWITCH (Scratch Filter):

Flat or roll-off at 12 dB per octave above 7,000 Hz, down 18 dB at 20,000 Hz.

SPEAKER SWITCHES (Operates with accessory relay):

Turn the main speakers on or off without affecting the remote speakers and vice versa.

HEADPHONE JACK:

Power to this jack is supplied by an amplifier provided in the C 28.

LOW FREQUENCY TRIM CONTROLS:

Use to compensate for unequal speaker response or the unequal influence of room acoustics.

PHONO 1 AND PHONO 2 LEVEL CONTROLS:

Provides for optimum signal to noise ratio and proper balance of the channels of the phono cartridge.

OUTPUT LEVEL CONTROLS:

Permits presetting the balance of the entire system.

HEADPHONE LEVEL CONTROLS:

Adjusts the output of the headphone/line amplifier output.

TRANSISTOR COMPLEMENT:

26 silicon-planar transistors, 4 silicon diodes, 2 silicon bridge rectifiers.

Specifications

FREQUENCY RESPONSE:  +0-0.5 dB 20 Hz to 20,000 Hz

DISTORTION:  Will not exceed 0.1% at rated output level, 20 Hz to 20,000 Hz.

INPUT SENSITIVITY AND IMPEDANCE: 

Aux, Tuner, Tape 1, Tape 2 : 0.25 volts / 250,000 ohms.

Phono 1 and Phono 2 : 2 millivolts / 47,000 ohms (1,000 Hz).

Microphone : 2.5 millivolts / 500,000 ohms.

Tape Head : 2 millivolts / 500,000 ohms (500 Hz).

HUM AND NOISE:

Aux, Tuner, Tape 1, Tape 2 : 90 dB below rated output.

Phono 1, Phono 2 and Tape Head : 78 dB below 10 millivolts input, equivalent to less than 1.2 microvolts at the input terminals. Microphone : equivalent to less than 1.5 microvolts at the input terminals.

OUTPUT LEVEL AND IMPEDANCE:

Main Output : 2.5 volts with rated input, 100 ohms source impedance, to operate into 47,000 ohms or more.

Tape Output : 0.25 volts, 150 ohms source impedance, from low level inputs, to operate into 47,000 ohms or more.

Headphone/Line Output : 0.75 volts into 8 ohm load or 2.5 volts into 600 ohm line, 0.2 ohm source impedance,

Center Channel Output : 1.25 volts with rated input to both channels, to operate into 47,000 ohms or greater.

AMPLIFICATION IN DECIBELS:

Aux, Tuner, Tape 1 and 2:

to Main Output : 20 dB;

to Tape Output : 0 dB;

to Headphone/Line Output : 17.5 dB.

Phono 1 and Phono 2 at 1,000 Hz:

to Main Output : 62 dB;

to Tape Output : 42 dB;

to Headphone/Line Output : 59.5 dB.

Microphone:

to Main Output : 60dB;

to Tape Output : 40 dB;

to Headphone/Line Output : 57.5 dB.

Tape Head at 500 Hz:

to Main Output : 64 dB;

to Tape Output : 44 dB:

to Headphone/Line Output : 61.5 dB.

POWER REQUIREMENT:  120 volts, 50/60 Hz, 45 watts.

DIMENSIONS:  Front panel measures 16 inches wide (40.64 cm) by 5-7/16 inches high (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 mounting brackets and back panel connectors. Knob clearance required is 1-1/2 inches (3.81 cm) in front of the mounting panel.

FINISH:  Front panel is anodized gold and black with special gold/ teal nomenclature illumination. Chassis is black.

MOUNTING:  Exclusive Mclntosh developed professional PANLOC.

WEIGHT:  25 pounds (11.34 kg) net, 37 pounds (16.78 kg) in shipping carton.