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
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