Engineering
direction dictated a tuner design governed by insistence on great flexibility
and ease of use. This had to be done while designing an RF section with great
sensitivity and the world's best selectivity in keeping with the needs of low
distortion.
These values were
achieved and they retain the Mclntosh reputation of outstanding performance,
long life and reliability.
Tuning in a station
on the MR 80 is achieved electronically.
This assures long
term trouble free operation.
You can tune a
station on the MR 80 four different ways.
1. Manual tuning by
rotating the main tuning knob.
2. Auto Scan
automatically searches for the next available station up or down in frequency.
3. Presets - allows
you to select your four most listened to stations that can be tuned at the
touch of your finger tip.
4. Remote Scanning
will allow the MR 80 to be tuned to a station from a remote location.
Two separate antenna
systems can be connected to the MR 80.
1) An outdoor or
indoor FM antenna, or 2) a cable input from your local cable company. The
antenna selection is controlled by an electronic switching device containing
more than 75 dB of isolation and no signal loss as might normally be found in
external mechanical switch.
Indicator Lights
Three indicator
lights are provided. The uppermost STEREO indicates when a stereo broadcast is
being received. The second, LOCK, indicates when the tuner is locked to the
station. The third indicator light, FILTER, indicates when the stereo noise
filter is in operation.
Preset
These touch pads
select one of the four preset stations. Just touch to operate. A small
rectangle will light above the pad indicating which preset has been selected.
Frequency Display
Digital
The Frequency
Display indicates the received frequency to the nearest 100 kHz.
Signal Column
A column of LED
lamps respond to the signal strength of the station being received. The
stronger the signal the higher the column reaches.
Auto Scan
AUTO SCAN is
provided by two touch pads. These two touch pads start the tuner searching for
a new station. It will scan until it stops at a station or reaches the end of
the band. At the band end the tuner will reverse its scan direction.
Manual Tuning
When the MR 80 is
turned on the circuitry automatically selects the manual or knob tuning control
mode.
Selectivity Switch
Two degrees of IF
selectivity are selectable by the SELECTIVITY switch. The NARROW or normal
position provides adequate selectivity for stereo reception even under severe
receiving conditions. Setting the SELECTIVITY switch to SUPER NARROW adds an
additional 4-pole 4-zero quartz crystal filter. Use the SUPER NARROW position
to receive stations from distant cities which are on channels adjacent to local
stations.
Filter Switch
The MR 80 FILTER
switch provides automatic stereo noise reduction on weak stereo stations.
Mode Switch
A two position MODE
switch is provided so that you may select either automatic stereo or mono
reception.
Headphone Jack
A HEADPHONE jack is
provided to drive low impedance dynamic headphones from an internal power
amplifier.
Scan Control
The SCAN control
adjusts the speed at which the tuner searches for the next station.
Muting Control
MUTING suppresses
the background noise and hiss normally heard between stations.
Volume Control
The VOLUME control
has been precision tracked throughout the listening range (0 to - 65 dB) for
accurate stereo balance.
The MR 80 uses
electronic varactor tuning instead of the more conventional mechanically gauged
variable tuning capacitors. Variable tuning capacitors can with age collect
dust and dirt, reducing their performance. Mclntosh uses double varactor diodes
to provide the necessary tracking between the different tuned RF stages. When a
weak distant station is adjacent to a strong local station the Preselector
circuit will switch in an additional tuned circuit providing an extra degree of
selectivity reducing the interference from the adjacent strong station.
After the RF
amplifier two paralled tuned circuits are used to provide the proper load
impedance for the bipolar transistor. These two tuned circuits greatly improve
the image rejection and overload performance of the tuner, as well as
increasing the RF selectivity.
An innovative new
lock circuit was developed for use in the MR 80. This new circuit allows
correct tuning without the use of a center tune meter. The MR 80 will be
correctly tuned even if the station of the cable company is not on its correct
frequency. This is done by the use of two operational amplifiers. The lock
circuit will track a station even if it drifts 1 MHZ.
The mixer is a
balanced matched dual J-FET and bipolar transistor circuit. A low loss toroidal
phase splitting transformer is used as an impedance matching network in the
gate circuit of the mixer eliminating even order spurious responses. The MR 80
has the narrowest IF bandwidth ever used in a stereo tuner. It is the correct
width to let just one FM station through. The excellent selectivity of the MR
80 (210 kHz wide at 60 dB down) permits tuning to stations that are impossible
to receive on ordinary tuners.
After the mixer the
signal is electronically switched to go either directly to the IF amplifier or
to go through a quartz crystal filter. The SUPER NARROW selectivity position
adds a 4 pole - 4 zero crystal filter to the other 5 IF filters. SUPER NARROW permits
receiving stations never heard before with most other FM tuners. The 5 stages
of IF amplification provide the necessary gain to reduce noise in the signal
and interference from other stations. The 5 IF stages use piezoelectric fixed
frequency filters in place of normal tuned circuits so the IF stages will
always stay in alignment, even with age. The signal strength indicator column
is summed off of all 5 IF stages instead of just 1 so it is looking at the
signal strength throughout the entire IF system.
Following the
selectivity section of the IF amplifier is the LIMITER. A total gain of 80 dB
is used in this circuit. The use of very high gain in the limiter circuit
produces hard limiting with very good impulse noise rejection. Limiter
bandwidth is greater than 50 MHz, producing excellent detector capture
characteristics. A broadband Foster-Seeley discriminator is used as the
detector. This detector coupled with the broadband limiter produces
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
adjacent 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.
In the PLL the
internal oscillator operates at 228kHz, locked onto the 19kHz pilot tone. The
228kHz, feeds a 3 stage Johnson counter via a binary divider to generate a
series of square waves. Suitably connected NAND gates and exclusive OR gates
produce the tri-level drive waveform for the various demodulators in the
circuit. The usual square waveforms have been replaced in the PLL and decoder
sections by tri-level waveforms. These tri-level forms contain no harmonics
which are multiples of 2 or 3. This eliminates frequency translation and
detection of interference from the side-bands of adjacent stations since the
third harmonic of the sub-carrier (114kHz) is excluded. It also eliminates
interference from SCA broadcasts since the third harmonic of the pilot tone
(57kHz) is excluded.
Unwanted spurious
audible components and phase jitter in the PLL are Inherently eliminated by
this technique.
Additional
advantages of the phase locked loop stereo demodulation are the elimination of
inductors to minimize drift, integral lamp driving capability to indicate the
presence of the 19kHz pilot carrier, excellent channel separation over the
entire audio frequency range, extremely low distortion, low output 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. The 25ms position is
for use with an external noise reduction adapter.
An electronic blend
filter circuit, implemented with two J-FETs of a quad J-FET package, is used to
reduce out of phase noise when in the stereo mode and tuned to a weak station.
This filter is actually a twin-T bandpass that blends the high and low frequencies,
leaving separation unaffected at midfrequencies. This results in a greatly
improved stereo image when the filter is required.
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. The - 15, - 5.2, 5, 15 and 30v use integrated circuit 3
terminal regulators, while the 3ma current source is made with discrete
transistors because of the high voltage on the input terminal. The remaining
voltages are used for the headphone amplifier and the touch control reference
signal driver.
Mclntosh,
recognizing the need for improved reliability, has designed a new circuit to
drive incandecent lamps. This new circuit prevents the filaments from failing
due to notching when operated on direct current. This failure mode can reduce
lamp life from one half to one tenth of the data sheet value. In the MR 80 the
three lamps that are used for STEREO, LOCK and FILTER indicators are operated
on AC at lower than rated voltage to extend the useful life to well in excess
of 15 years. Only Mclntosh brings you this feature.
Specifications
TUNING: 88 to 108 MHz
ANTENNA
INPUTS: One 300 Ω balanced and two 75 Ω 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 frequencies 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:
Adjacent channel : 8
dB (Narrow); 60 dB (Super Narrow)
Alternate channel :
90 dB (Narrow); 110 dB (Super Narrow)
SPURIOUS
REJECTION: 110 dB
TUNER IM (RF): -23 dBm 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 Ω
FIXED
: 1V into 47k Ω
GENERAL INFORMATION
POWER
REQUIREMENTS: 120 volts, 50/60 Hz.
POWER
Consumptions: 25 watts
SEMICONDUCTOR
COMPLEMENT:
57 Transistors, 68
Integrated Circuits, 81 Diodes, 4 LED Displays, 18 LED's, 7 Neon Lamps
DIMENSIONS
Front panel
measures: 406 mm (16") wide by 138 mm (5-7/16") high.
Chassis measures:
375 mm (14-3/4") wide by 122 mm (4-13/16") high by 330mm (13")
deep , including connectors.
Knob clearance
required is 32 mm (1-1/4") 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: 12,2 kg (27 pounds) net, 17,7 kg (39 pounds) in shipping carton
