McIntosh MR-77 Brochure

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!

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.

1 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

2 LINEAR PHASE BRIDGE DISCRIMINATOR

The linear phase filter would be useless if it had to work into an

ordinary 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.

"What does this mean to
investment in research, an

continuous testing; throug
urement can we promise
life, performance, highest
Mclntosh offers you a F

TRACT. During the first

dime for service. Mclntosh

guarantees labor. It costs

of a Mclntosh, the conserv

ticated appearance make
greater value when you a
to Mclntosh now.