Specifications

as the detector coupled with a broadband limiter to
produce unmeasurable noise and distortion.
The heart of the multiplex section is a new third
generation phase locked loop (PLL) stereo decoder
integrated circuit (IC). This PLL IC incorporates two
special systems, an automatic variable separation
control circuit to reduce background noise when
receiving weak stereo stations, and tri-level digital
waveform generation which eliminates interference
from SCA signals and from the sidebands of adja-
cent channel FM signals.
The variable separation control is operated from
the IF amplifier's signal strength detector. A smooth
transition is provided from mono to stereo or from
stereo to mono at weak signal levels to provide the
optimum signal to noise ratio and best stereo
separation for the prevailing signal conditions. The
circuit operates only during stereo reception. It
switches automatically to monophonic if the 19 kHz
pilot tone is absent.
Additional advantages of the phase locked loop
stereo demodulation are the elimination of induc-
tors to minimize drift, integral lamp driving capabili-
ty to indicate the presence of the 19kHz pilot carrier,
excellent channel separation over the entire audio
frequency range, extremely low distortion, low out-
put impedance, and transient-free mono/stereo switching.
Following the MPX decoder is the three position
de-emphasis switch. The three different positions
allow the MR 80 to be used in North America with
standard 75ms de-emphasis and in Western Europe
and the Far East with 50ms de-emphasis. A 25ms posi-
tion is provided for use with an external noise reduc-
tion devices.
An electronic blend filter circuit, using two J-FETs
of a quad J-FET package, reduces out of phase noise
when in the stereo mode and when tuned to a weak
station. The filter is a twin-T bandpass that blends
the high and low frequencies, leaving separation
unaffected at mid-frequencies. This results in a
greatly improved stereo image when the filter is re-
quired.
Special design attention has been given to the
power supply section. Nine separate power circuits
are used. Six of these are regulated to prevent loss
of performance during a brown out.
PERFORMANCE LIMITS and RATINGS
TUNING:
88 to 108 MHz
ANTENNA INPUTS:
One 300W balanced or two 75W unbalanced.
INTERMEDIATE FREQUENCY:
10.7 MHz
SENSITIVITY:
9.3 dBf (1.6mV) for 35 dB of quieting
14.7 dBf (3mV) for 50 dB of quieting
13.2 dBf (2.5mV) for 3% total noise and harmonic
distortion
SIGNAL TO NOISE RATIO:
75 dB below 100% modulation
HARMONIC DISTORTION:
0.2% 20 Hz to 15 kHz, mono or stereo
Typically, 0.08% at 1000 Hz
INTERMODULATION DISTORTION:
0.15% mono or stereo for any combination of fre-
quencies from 20 Hz to 15,000 Hz with peak
modulation equal to 100% or less. Typically 0.1 %
FREQUENCY RESPONSE:
Mono and Stereo ± 1 dB 20 Hz to 15 kHz with 75,
50 or 25mS de-emphasis
CAPTURE RATIO:
1.5 dB
SELECTIVITY:
Narrow
8 dB
90 dB
Super Narrow
60 dB
110 dB
Adjacent channel
Alternate channel
SPURIOUS REJECTION:
110 dB
TUNER IM (RF):
-23dBm for 2 signals 1 MHz apart
TUNER INTERCEPT POINT:
-10 dBm 75W
IMAGE REJECTION:
90 dB
MAXIMUM SIGNAL INPUT:
8 volts across 75W (1W) antenna terminal will not
increase harmonic or intermodulation distortion.
AUDIO HUM:
75 dB down from 100% modulation
MUTING:
70 dB noise reduction between stations
MUTING THRESHOLD:
2mV to 1000mV
SCA REJECTION:
60 dB minimum
STEREO SEPARATION:
50 dB to 1000 Hz
STEREO FILTER:
10 dB noise reduction
AUDIO OUTPUT:
Variable: 2.5V into 47k
Fixed: 1V into 47k
GENERAL INFORMATION
POWER REQUIREMENTS:
120 volts 50/60 Hz. 25 watts
SEMICONDUCTOR COMPLEMENT:
57 Transistors, 68 Integrated Circuits, 81 Diodes,
4 LED Displays, 18 LED's, 7 Neon Lamps
MECHANICAL INFORMATION
SIZE:
Front panel measures 16 inches wide (40.6 cm) by
5 7/16 inches high (13.8 cm). Chassis measures 14
3/4 inches wide (37.5 cm) by 4 13/16 inches high
(12.2 cm) by 13 inches deep (33 cm), including con-
nectors. Knob clearance required is 1 1/4 inches
(3.2 cm) in front of mounting panel.
FINISH:
Front panel is anodized gold and black with
special gold/teal nomenclature illumination.
Chassis is black.
MOUNTING:
Mclntosh developed professional PANLOC.
WEIGHT:
27 pounds (12.2 kg) net, 39 pounds (17.7 kg) in
shipping carton.
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