Specifications

phone jack. A turn-on delay circuit using a light-
emitting diode/light dependent resistor network that
transmits no signal for two seconds after power is
applied also operates to turn off signals almost in-
stantly when power is turned off. This arrangement
serves to keep turn-on and turn-offs of the tuner-pre-
amplifier transient-free.
The power transformer of the MX 1 1 7 is triple
shielded (copper strap, silicon steel strap and steel
outer shell) for minimum hum and radiation. A full
wave bridge rectifier with 3300 mfd filter capacitors
provide the DC voltages which are applied to posi-
tive and negative supply regulators. IC regulators
supply the dual-polarity 18 volts of DC needed for
the low-level amplifier stages.
Fig. 4—Mono and stereo quieting
and distortion characteristics, FM section.
FM Performance Measurements
Figure 4 is a multiple plot of mono and stereo
quieting characteristics and mono and stereo total
harmonic distortion characteristics (at 1 kHz) of the
FM tuner section of the MX 1 1 7. Usable sensitivity
in mono measured 10.8 dBf (1.9 uV, 300 ohms) or a
bit better than claimed, while in stereo, usable sensi-
tivity was determined by the stereo switching thres-
hold, which occurred at 1 5 dBf (3.1 uV). The more
important 50 dB quieting point was reached in mono
at a very low signal strength of only 1 2 dBf (2.2 uV),
while in the stereo mode, that degree of quieting
was reached at a signal input level of only 27.5 dBf
(13.0 uV), about as low as we have measured for
any stereo FM tuner. Mclntosh, as usual, seems to
insist upon publishing ultra-conservative specifica-
tion. In the case of the MX 1 1 7 they claimed only a
minimum of 70 dB of signal-to-noise in mono and
stereo FM. In fact, our sample measured S/N of 83
dB in mono! Even in the stereo mode, where S/N is
generally poorer, we still obtained a reading of 78 dB
for an input of 65 dBf (approximately 1 000 uV) and,
with somewhat stronger signals, the S/N improved
even further to 80 dB.
Fig. 5 —Harmonic distortion vs. frequency,
Mclntosh MX 1 1 7 Tuner-Preamp (FM tuner section)
Distortion, too, was considerable better than
claimed by Mclntosh. Under strong-signal conditions
(standard test conditions at 65 dBf), harmonic dis-
tortion for a 1 kHz signal at 100% modualation mea-
sured 0.086% in mono and almost as low, 0.10% in
stereo. Nor was this low level of distortion limited to
mid-frequencies as can be seen by examining Fig. 5,
which plots distortion as a function of modulating
frequencies.
Fig. 6 —Frequency response (upper trace) and stereo
separation, Mclntosh MX 117 Tuner-Preamp
Figure 6 is a 'scope photo of a spectrum analyzer
multiple sweep in which the upper trace represents
output from the left channel main output with a Left-
only signal modulating our FM generator and sweep-
ing from 20 Hz to 20 kHz. The lower trace was ob-
tained by subsequently measuring the output of the
Right channel under the same modulation condi-
tions, and is therefore a measure of stereo separa-
tion versus frequency. The vertical scale is 1 0 dB per
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