McIntosh MR 77

 Mclntosh research is a continuous program of exploration for new technology that permits performance improvement and greater value for you. This intensive research program developed the new technology necessary for the realization of these two new design concepts for the MR 77.

NEW DESIGN CONCEPTS, MODERN HIGH SPEED COMPUTERS, LATEST TEST EQUIPMENT,

And, thorough, uninhibited research has developed the new technology necessary for the first Truly Low Distortion FM Tuner …  the MCINTOSH MR 77!

 THE LINEAR PHASE IF FILTER

Even since the beginning of FM, research engineers have realized that constant delay, or linear phase, IF filters were necessary for low distortion reception. Crude approximations to constant delay have always been used in FM tuners — with disappointing results.

So-Called "Butterworth" or "Legandre" filters offer only a fair compromise with respect to delay error. Crystal and ceramic filters, usually based on the "Chebychev" model, work fairly well and give good selectivity, but none of these are constant delay (linear-phase) filters. Commercial tuners using these filters can show 5% stereo IM distortion at 100% modulation, and have delay errors up to 100%. In sharp contrast, the linear phase filter allows a tuner to show only .1% IM distortion at 100% modulation and has a delay error of only 1.2% in the useful bandpass. In its useful bandpass, it is a true mathematical approximation to linear-phase — the world's finest selective, linear-phase, minimum-phase shift filter.

A FORTRAN computer program using an algorithm that took six years to develop was used in its design. The mathematical complexity of the filter design procedure is almost beyond belief. Using a process called "numerical integration in the complex S-plane," a high speed IBM 1130 computer spent eighteen minutes on the design of the MR 77 IF filter. A human engineer, working twenty-four hours a day and seven days a week, would have taken 300 years to finish this work . . . assuming he made no mistakesl

 LINEAR PHASE BRIDGE DISCRIMINATOR

The linear phase filter would be useless if it had to work into anordinary FM detector. Thus a new detector with suitably low distortion had to be developed. A search of the available literature revealed a little-known bridge circuit with a theoretical distortion of zero! However, designing a practical working circuit for a commercially feasible stereo tuner took some doing. A U. S. patent is pending on this circuit.

Distortion performance of the bridge detector is close to the theoretical zero. In addition to its excellent distortion performance, the bridge detector also exhibits capture ratio close to 0 dB. The linear-phase bridge discriminator uses a balanced transmission line bridge in conjunction with a differential voltage-doubling rectifier to achieve 99.9% accuracy demodulation of FM signals. The only adjustments in the MR 77 detector are two simple variable resistors. These resistors center the tuning meter and set the transistor bias. Complex tuning for minimum distortion is not needed.

 YOU ARE PROTECTED WHEN YOU BUY MCINTOSH

Every Mclntosh instrument — every one — is tested to be equal to or better than the performance limits advertised. When a performance limit of 0.2% harmonic distortion is established for an instrument, Mclntosh means that every, each, all of the instruments manufactured must be capable of performance to that limit — or better — or your full purchase price is refunded.

One of the reasons Mclntosh can make this promise is that we 100% test each of the instruments for maximum performance. We are not content knowing that 10% of our instruments are tested and meet the performance requirements established by our engineering group. We must know that all of the instruments meet the requirements. This vigorous pursuit of excellence takes time. At Mclntosh more time means more care, more protection for you. There's no production rush at Mclntosh.

 Specifications

USABLE SENSITIVITY:

2 microvolts for 35 dB of quieting;

2.5 microvolts at 100% modulation (±75 kHz deviation) for 3% totalnoise and harmonic distortion

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. Typically 0.1%

AUDIO FREQUENCY RESPONSE:  ±1 dB 20 Hz to 15,000 Hz with standard deemphasis, (75 μS) 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; 88 to 108 MHz (IHF)

SELECTIVITY:

Adjacent channel 6 dB IHF, carrier 47 dB down

Alternate channel 50 dB IHF, carrier 90 dB down

STEREO SEPARATION:  40 dB at 1,000 Hz

STEREO FILTER:

10 dB noise reduction in position 1

20 dB noise reduction in position 2

SCA FILTER:  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 microvolt

Position 2 :  20 microvolt

ANTENNA INPUTS:  300 ohms balanced; 75 ohms unbalanced

MAXIMUM SIGNAL INPUT:  12 RF 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 linear phase filter;  2 IC's;  1 J-FET, and push-pull overlay power transistor stage driving a linear phase bridge discriminator

STEREO INDICATOR:  Front panel stereo light activated by 19,000 Hz only

AUTOMATIC MONO-STEREO SWITCH:  Mclntosh developed; all electronic automatic mono-stereo switching circuit

SEMICONDUCTOR COMPLEMENT:  21 Transistors; 4 Integrated Circuits; 1 Indicator Tube

POWER REQUIREMENT:  120 - 240 volts,  50/60 Hz, 35 watts

FRONT PANEL:  16" wide (406 mm) by 5-7/16" high (138 mm)

CHASSIS:  15" wide (381 mm) by 13" deep (330 mm) including PANLOC shelf and back panel connectors.

Knob clearance: 1½ " (381 mm) in front of mounting panel

FINISH:  Front Panel: Anodized gold and black with special gold/teal nomenclature illumination. Chassis Chrome and black

MOUNTING:  Mclntosh developed professional PANLOC

WEIGHT:

27 pounds (12.25 kg) net

39 pounds (17.69 kg) in shipping carton