Specifications

Rear Panel Controls
Stereo pairs of input jacks and a chassis ground
terminal are located at the extreme right of the rear
panel of the MX 1 1 7. Inboard of these are two pairs
of "Main" output jacks, line out jacks (designed to
operate into 600-ohm loads), the tape-out jacks (for
connection to up to two tape decks) and vertical and
horizontal oscilloscope output jacks which may be
connected to Mclntosh's "Maximum Performance
Indicator" or to any oscilloscope for observation of
multipath phenomena during orientation and optimi-
zation of an FM antenna. A pivotable AM loopstick
ferrite antenna is located at mid-panel, and next to it
is an FM preselector switch which introduces addi-
tional tuned-circuit filtering for additional RF selec-
tivity in the event of strong-signal overload condi-
tions. Normally, this switch is left in the "out" posi-
tion.
Fig. 2 —Rear panel view of
Mclntosh MX 1 1 7 Tuner-Preamplifier
External AM, ground, and 300-ohm FM antenna
connection terminals of the "push to insert wire"
spring-loaded type are at the upper right of the rear
panel, while alongside is a standard coxial connector
for use with 75-ohm transmission lines. Three swit-
ched and two unswitched convenience AC outlets
complete the rear panel layout. Up to 600 watts of
power can be drawn from all of these AC recep-
tacles, combined.
Circuit Highlights
The FM front end employs five sections of an
8-section variable capacitor (four, when the prese-
lector switch is in the "out" position). As with most
of the switch functions of the MX 117, even the pre-
selector switching is accomplished electronically,
with a DC voltage controlling PIN semiconductors
diodes which do the actual switching. Front panel
selector switching, for example, simply switches
control voltages which turn FET analog switches on
or off. Since the actual switches are located near the
input jacks, pickup noise and high-frequency losses
are minimized compared with conventional mechani-
cal switching arrangements.
A double-tuned MOS-FET RF Amplifier and a bal-
anced MOS-FET mixer are used in the FM front end.
A MOS-FET buffer amplifier is used between the
local oscillator and the mixer. The oscillator is fine
tuned by a varactor dioide operated by a correction
voltage which is derived from a patented Mclntosh
circuit call Automatic Frequency Lock (AFL) which
turns on a "lock" voltage when perfectly centered
tuning has been reached.
The FM I-F section uses five integrated circuit am-
plifiers and four piezo-electric filters, for a total gain
of 1 40 dB. A full Foster-Seeley discriminator (as op-
posed to the more common Ratio Detector) discri-
minator completes the I-F system. The composite
demodulated signal feeds the stereo FM multiplex
section, the heart of which is a new type of phase-
locked-loop stereo decoder IC. This IC incorporates
an automatic variable separation control (to reduce
background noise during weak-signal stereo recep-
tion), and tri-level digital waveform generation which
eliminates interference from SCA signals and from
the sideband of adjacent channel FM signals. 1 9 kHz
and 38 kHz carrier suppression circuits are used to
attenuate any residual carrier components following
multiplex decoding. The FM muting circuit employed
in the MX 117 operates by detecting ultrasonic
noise and by sensing correct center-tuning of the
detector circuit. Muting of the audio signal is done
with a positive acting FET switching circuit.
The AM tuner section employs a three-section tun-
ing capacitor and a special AM-RF amplifier which
maintains constant selectivity, constant sensitivity
and high image rejection across the entire AM band.
An autodyne circuit is used for the AM mixer and
two double-tuned transformers are used in the AM-
IF section. A 10 kHz "whistle filter" is included in
the AM tuner section, as is a two-section AVC filter
for lower distortion at bass frequencies.
The phono preamplifier-equalizer section uses an
IC operational amplifier whose differential input
stage has been optimized for low noise and low dis-
tortion. The feedback network which also provides
RIAA equalization employs 1 % metal film resistors
and 5% polyfilm capacitors. The gain of this preamp
section is just over 41 dB. As for the unusual
loudness control arrangement referred to earlier, it
uses the same sort of IC operational amp used in the
phono preamp stages. Two feedback loops are
employed: one flat, the other conforming to the
Fletcher-Munson equal loudness contours. A potent-
iometer (the front panel "LOUDNESS" control) plac-
ed between these loops makes it possible to select
any curve from flat response to full loudness com-
pensation. Once the contour is set by the user, it re-
mains fixed and independent of the position of the
master volume control. The equalizer-amplifier also
uses a low-noise operational amplifier. Three other
op-amps are arranged in the circuit equivalents of
three tuned circuits; each resonant at one of the
three equalizer center frequencies.
The output amplifier of the MX 1 1 7 is a push-pull
complementary class AB circuit which uses a signal-
inverting differential stage at its input. The amplifier
drives the main and line outputs as well as the head-
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