McIntosh MR 78 Brochure

Page 1

The McIntosh MR 78 FM/FM stereo tuner breaks
McIntosh performance records. McIntosh tuners have
exceeded the performance capabilities of all other
tuners available today. Yet with the MR 78, an out-
standing improvement has been achieved. It has the
lowest distortion and greatest selectivity character-
istics ever combined in a tuner. It is the culmination of
eight man years of serious development work.

This beautifully styled unit has so many superlative
performance characteristics that only some of the
major ones can be mentioned:

0 Multiple selectivity, normal, narrow and super narrow,
switchable from the front panel. An elegant solution to a
tough problem. Switching is done by means of diodes
using DC" switching; an ideal way to handle a difficult
RF problem. A two position RF selectivity diode switch-
ing circuit for low and high gain antennas adds a useful
parameter that is unique.

0 Linear Phase (constant delay) IF amplifier for low dis-
tortion at even high selectivity and low distortion. (Pat:
ented). Two eight-pole filters are selectable as well as a
four pole multi element crystal in the super narrow
position.

I A phase linear bridge discriminator provides distortion-
less conversion from FM to audio and exhibits a capture
ratio close to 0 dB. No active elements are used providing
a driftless ideal detector.

- 5 element tuning condenser improves R.F. front end be-
havior; more tuned circuits for better selectivity. Silver
plated chassis and R.F. coils for better shielding lower
losses and higher Q circuits.

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THE ULTIMATE FM TUNER

0 Highest spurious rejection 100 dB (lHF) and highest im-
age rejection 100 dB (88 to 108 MHZ). This means you
receive the stations at only the right place on the dial.
You dont receive the same stations or some mixture as
you tune across the dial.

0 Ultra Sonic muting provides smooth inter channel FM
noise suppression.

- McIntosh developed a special detecting circuit used in
the multiplex section. An 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 re-
covered information with the L - R carrier signal. This
yields the left and right program output with maximum
separation.

0 Uses a balanced mixer and coupling transformer circuit
for low intermodulation effects.

0 See the performance limits on the back page for many
other outstanding characteristics of this remarkable unit.

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THE FINEST TUNER IN THE WORLD TODAY. |

THE HEMAHKABLE MIT 78 TlIHEH

ANTENNA MATCHING

The MR 78 has an antenna matching circuit in the RF input. In
fringe areas a broad low-loss RF circuit provides maximum sensi-
tivity for a low-gain antenna. In metropolitan areas crowded with
many strong signals a sharp RF input circuitgreatly reduces spu-
rious responses and achieves maximum sensitivity when connected
to a high-gain antenna.

The RF bandpass of the antenna matching circuit can be modi-
fied by switching a resonator in or out of the circuit. Broad band-
pass is obtained by setting the ANTENNA MATCHING switch to
the LOW GAIN ANTENNA position.

Sharp bandpass is
obtained by settingthe
ANTENNA MATCHING
switch to the HIGH
GAIN ANTENNA posi-
tion. The RF input cir-
cuit becomes a double
tuned filter with high
Q in both resonators,
which provides sharp
bandpass. The oscillo-
graph photo shows the
two bandpass curves
of the RFinput circuit.

FRONT END

FM signals enter the tuner through the antenna terminals. A
coaxial cable conducts the signal to the RF amplifier. In the ampli-
fier the stations are separated, amplified, and converted to a com-
mon 10.7 MHz IF frequency. Instead of usinga conventional, easily
overloaded transistor or FET as a straight RF amplifier, the MR 78
uses a rugged Junction Field Effect Transistor as an impedance
converter to drive a 5-watt power transistor. This combination (a
cascade circuit) makes the RF amplifier virtually impossible to
overload or cross-modulate. As an example, if you are tuned to a 3
microvolt signal at 96.3 MHz, the MR 78 will reject signals else-
where on the dial which are at least, 4,000,000 times stronger.
Thus, a 12 volt signal received at 104.3 MHz would not bother
the signal at 96.3 MHz. When tuned to 104.3 MHz, the tuner will
not overload. Every MR 78 tuner must pass the 12 volt overload
test.

Completing the MR 78 front end is the oscillator. It uses a
high-Q ceramic form tank coil. The oscillator is free from spurious
radiations, and operates at high efficiency. Due to its high stabil-
ity, AFC and its attendant limitations are avoided.

Another new design in the MR 78 front end is the integrated cir-
cuit balanced mixer. This mixer is practically impossible to over-
load. Oscillator pulling, cross modulation, and other types of dis-
tortion so common in ordinary transistor or FET mixers is mini-
mized. A balanced bifilar transformer couples the 10.7 MHz output
to the IF amplifier.

NEW THREE POSITION SELECTIVITY

The MR 78 has excellent selectivity. The bandwidth (210 kHz
wide at 60 dB down) permits tuning in 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 number of stations crowding the
FM band requires a tuner with
variable selectivity.

Variable selectivity allows stereo
reception even under severe re-
ceiving conditions. In the NOR-
MAL position, a very low distor-
tion 8-pole linear phase filter is w. _ W
used in the IF circuit for listening "0"
to local broadcasts. ~

The NARROW position adds a
sharp 8-pole filter to the NOR-
MAL IF filter to yield a low distor-
tion (less than 0.2%), highly selec-

SELHTIVITV

F M DETECTOR DISCRIM INATOR