THE MclNTOSH MX113 FM/FM STEREO-AM TUNER

THE MclNTOSH MX113 FM/FM STEREO-AM TUNER
THE MclNTOSH MX113 FM/FM STEREO-AM TUNER-PREAMPLIFIER
Reading Time: 45 Minutes
Price $1.25
Your MX 113 AM-FM/FM stereo tuner
and stereo preamplifier will give you
many years of pleasant and satisfactory
performance. If you have any questions
please contact—
CONTENTS
Service Contract
CUSTOMER SERVICE
Mclntosh Laboratory Inc.
2 Chambers Street
Binghamton, New York 13903
Phone: 607-723-3512
WARNING: TO PREVENT FIRE OR
SHOCK HAZARD, DO NOT EXPOSE
THIS UNIT TO RAIN OR MOISTURE.
1
Installation
2, 3
How to Connect
4, 5
What the Controls Do
And How to Use Them
6, 7
Using the Pushbuttons
7
Balancing Your Stereo
8
Listening to Your Stereo
9
Performance Limits and
Ratings
Take Advantage of 3 years
of FREE Service ...
Fill in the Application NOW.
12, 13, 14
Technical Description
15, 16, 17
Block Diagrams
Station Log
THREE YEAR SERVICE CONTRACT
An application for a FREE THREE YEAR SERVICE CONTRACT is included with this manual.
The terms of the contract are:
or mishandling is not covered by the SERVICE CONTRACT.
4. The SERVICE CONTRACT is issued to you as
the original purchaser. To protect you from
misrepresentation this contract cannot be
transferred to a second owner.
1. Mclntosh will provide all parts, materials and
labor needed to return the measured performance of the instrument to the original performance limits free of any charge. The
SERVICE CONTRACT does not cover any shipping costs to and from the authorized service
agency or the factory.
5. For your protection Mclntosh selects only
dealers who have technical competence to
guide purchasers fairly, and provide service
when necessary. To receive the SERVICE
CONTRACT your purchase must be made
from a Mclntosh franchised dealer.
2. Any Mclntosh authorized service agency will
repair all Mclntosh instruments at normal
service rates. To receive the free service under
the terms of the SERVICE CONTRACT, the
SERVICE CONTRACT CERTIFICATE must accompany the instrument when taken to the
service agency.
6. Your completely filled in application for a
SERVICE CONTRACT must be postmarked
within 30 days of the date of purchase of
the instrument.
7. To receive the SERVICE CONTRACT all information on the application must be filled
in. The SERVICE CONTRACT will be issued
when the completely filled in application
is received at Mclntosh Laboratory Incorporated in Binghamton, New York.
3. Always have service done by a Mclntosh
authorized service agency. If the instrument
is modified or damaged, as a result of unauthorized repair the SERVICE CONTRACT
will be cancelled. Damage by improper use
1
Copyright © 1971 by Mclntosh Laboratory Inc.
10, 11
Performance Charts
18, 19
20
If the cutout is to be located from the front of the panel,
begin at 2. If the cutout is to be located from the rear of the
panel, begin here.
1. On the back of the cabinet panel, scribe a vertical centerline through the exact center of the area in which the
cutout is to be made.
Place the template against the back of the panel and
match the template centerline with the centerline on
the cabinet panel.
Make sure that there is at least ¼ inch clearance between the bottom of the dashed line of the cutout area
on the template and any shelf or brace below the proposed cutout.
Mark the two locating holes ("C" holes on the mounting
template).
Adequate ventilation extends the trouble-free life of
electronic instruments. It is generally found that each 10°
centigrade (18° F) rise in temperature reduces the life of
electrical insulation by one half. Adequate ventilation is an
inexpensive and effective means of preventing insulation
breakdown that results from unnecessarily high operating
temperatures. The direct benefit of adequate ventilation
is longer, trouble-free life.
Drill the two locating holes. Be certain the drill is perpendicular to the panel.
Now position the template on the front of the panel by
aligning the "C" locating holes on the template with the
drill holes.
2. If the cutout is to be located from the front of the panel:
Allow at least 15 inches deep x 17½ inches wide x 6
inches high for mounting the MX 113. Always allow for air
flow by either ventilation holes or space next to the bottom
of the instrument and a means for warm air to escape at
the top.
With the template in place against the cabinet panel,
mark the "A" and "B" drill holes and the four small
holes that identify the corners of the cutout. Join the
corner marks with a pencil. The edge of the template
can be used as a straight edge.
With adequate ventilation, the MX 113 can be mounted
in any position.
To prepare the MX 113 for installation remove the protective covering. Turn the MX 113 upside down so that it
rests on its top on the shipping pallet. Remove the four
plastic feet fastened to the bottom of the chassis.
Next, place the mounting brackets, the parts bag and the
mounting template at hand.
The PANLOC professional mounting design eliminates
the need for any shelf or bracket to support the MX 113. It
is completely supported by its own mounting brackets.
The design of the mounting template allows you to position or locate the cutout from the front or rear of the panel
to which the instrument is to be mounted. Position the plastic mounting template over the area of the panel to be cut
out for installation.
2
IMPORTANT: DRILL THE 6 HOLES BEFORE MAKING
THE CUTOUT.
Accurately drill the three holes on each side of the cutout area with a 3/16 inch drill.
With the saw on the INSIDE OF THE PENCIL LINES
carefully cut out the rectangular opening.
Secure the mounting strips to the rear of the cabinet
panel using two screws from the hardware package.
Insert the screws in the center holes of cabinet panel
("B" holes on the template) and tighten. The screw head
should pull into the wood slightly. (Use two ¾ inch long
screws for panels under ½ inch, or two 1¼ inch long
screws for panels ½ inch thick and larger.)
Attach the mounting brackets to the cabinet panel using
four screws.
Place the template over the mounting screws. The
mounting screws should be centered in the "A" and "B"
holes on the template. The sides of the mounting brackets
should match the vertical dash lines on the template. If
necessary, loosen the screws and push the brackets into
alignment and retighten.
Insert the power cord through the opening. Carefully
slide the MX 113 into the opening so the rails on the bottom of the equipment slide in the track of the mounting
brackets. Slide the instrument in until it stops at the adjust
position latches. Press the latches in and continue to slide
the instrument in until the front panel is against the
cabinet panel. At the bottom corners of the front panel are
the PANLOC buttons. Depressing the PANLOC buttons
will lock the instrument firmly in the installation. Depressing the PANLOC buttons a second time will release the
instrument. You can then slide the instrument forward to
the inspection-adjustment position. Depressing the inspection-adjustment position latches will allow the instrument
to slide completely out of the installation.
With the MX 113 one of three antenna systems can be
used: (1) the indoor dipole supplied with the MX 113,
(2) an outdoor FM antenna, or (3) an all channel (UHF-VHFFM) antenna. In fringe areas best results will probably be
obtained with the use of an outdoor FM antenna. In many
areas the indoor dipole may be satisfactory.
How to Connect
CONNECTING A RECORD PLAYER TO PHONO 1
Connect the cable from the left channel of the record
player into the L PHONO 1 input jack.
CONNECTING AN INDOOR DIPOLE ANTENNA
Connect the cable from the right channel of the record
player into the R PHONO 1 input jack.
The flexible folded dipole antenna (300 ohm) supplied
with the MX 113 is for indoor use in urban or high strength
signal areas.
PHONO 2 is provided for the use of a second record
player.
Connect the two leads from the dipole to the terminals
marked FM ANT (red). The flexibility of the thin flat wire
assembly permits it to be placed under a rug, tacked behind
the stereo . . . or, placed in any other convenient location.
In some cases, it may be necessary to "position" the antenna for best signal reception. This should be done before
it is permanently located or tacked down. Keep the antenna
away from metal objects. Do not attach to a metal surface.
Connect the cable from the left channel of the record
player into the L PHONO 2 input jack.
Connect the cable from the right channel of the record
player into the R PHONO 2 input jack.
AUX
Any high level program source such as another tuner or
a TV set can be connected to the input jacks marked AUX.
CONNECTING AN OUTDOOR FM ANTENNA
CONNECTING A TAPE RECORDER
An outdoor antenna is recommended for optimum performance in all areas. In fringe (outlying) areas, best results
will be obtained with a highly directional FM antenna used
in conjunction with a rotator. Rotate the antenna until the
best reception is obtained. Connect the 300 ohm antenna to
the terminals marked FM ANT (red).
To Record
Connect a cable from the L TAPE OUTPUT jack to the
left high level input of a tape recorder.
Connect a cable from the R TAPE OUTPUT jack to the
right high level input of the tape recorder.
CONNECTING A 75 OHM COAXIAL ANTENNA
To Playback/Monitor
An unbalanced 75 ohm antenna can be connected to the
MX 113 with coaxial cable. Connect the center conductor
to the right FM ANT (red) connector. The shield is connected
to the GND (black) connector.
Connect the cable from the left channel output of a tape
recorder to the high level inputs . . . L TAPE.
Connect the cable from the right channel output of a
tape recorder to the high level inputs. . . R TAPE.
CONNECTING AN AM ANTENNA
CONNECTING THE MX 113 TO POWER AMPLIFIERS
A high-quality loopstick antenna is provided. It can be
rotated through nearly 180° in all directions for maximum
performance, optimum signal reception or minimum interference. With this mobility you will not suffer loss of sensitivity regardless of the angle at which the instrument is
mounted. A back panel antenna jack is provided for connecting an external antenna if desired.
Connect the MAIN OUTPUT jacks to the input of a stereo
power amplifier. The L jack is connected to the left amplifier input jack. The R jack is connected to the right amplifier input jack.
The output source impedance at the MAIN OUTPUT is
200 ohms. Longer cables than supplied can be used between the MX 113 and the amplifier. The length of the
cable is limited by the capacity of the cable. The total
capacity must not exceed 1,000 pF. For instance: cables
with a capacity of 25 pF per foot may be 40 feet long.
13.5 pF per foot cable may be 75 feet long. The input
impedance of the amplifiers should be 47,000 ohms or
greater.
AC POWER OUTLETS
There are two black AC power outlets, and one red AC
power outlet. The AC power to the black outlets is controlled
by the front panel switch. Use these outlets for a power amplifier, or tape recorder, etc. The red receptable is on at all
times. Use the red outlet for a turntable or record changer.
The turntable is protected by this arrangement. It is necessary to turn off the turntable or record changer with its
own AC power switch.
L + R OUTPUT
Use the L + R OUTPUT to feed left plus right signal to a
separate power amplifier for monophonic background
music or for a center channel speaker.
GROUND CONNECTION
A single ground post is provided. Grounds for turntables,
record changers, tape decks, etc. should be connected to
this post. The left and right program cables and the ground
wire from that source should be loosely twisted together.
To avoid hum, make sure the ground wire does not make
any contact to the shields of the left and right program
cables between the program source and the MX 113.
CONNECTING AN FM ANTENNA
Satisfactory stereo where mono reception has been
satisfactory requires about ten times as much signal from
the antenna. Monophonic reception that is satisfactory
on an indoor antenna may require the use of an outdoor
antenna for stereo reception of equivalent quality.
4
TURNTABLE
TAPE RECORDER
FM A N T E N N A
AM A N T E N N A
TO 120V AC OUTLET
POWER
AMPLIFIER
RIGHT SPEAKER
LEFT SPEAKER
5
What the Controls Do and How to Use Them
TREBLE
INPUT SELECTOR
The TREBLE is a concentric control. The outer knob controls the high frequency response in the right channel. The
center knob controls the high frequency response in the
left channel. The two knobs are friction coupled. This permits them to be adjusted together or independently.
Clockwise rotation increases highs and counterclockwise
decreases highs. Turn the control to the center position for
flat response.
Select any one of five program sources:
AUX: Connects the output from any high level program
source requiring flat amplification to the high level
input stage. In the AUX position the gain is 20 dB to
the MAIN outputs and 0 dB to the TAPE outputs. The input impedance is 250,000 ohms.
TAPE: Connects the output from a complete tape recorder to the high level input stage of the MX 113. The
TAPE position has flat amplification. The gain is 20 dB
to the MAIN outputs. The gain is 0 dB to the TAPE
outputs.
BALANCE/LOUDNESS
The BALANCE/LOUDNESS is a concentric control. The
outer knob controls the balance between channels. The
center knob is a switch that adds loudness compensation
for low volume listening.
AM: Connects the AM tuner portion of the MX 113 to
the output jacks.
BALANCE
FM: Connects the FM tuner portion of the MX 113 to
the output jacks.
The BALANCE control adjusts for unequal volume in
either the left or right channels. The volume of each channel can be varied relative to the other without affecting
their combined loudness.
PHONO 1: Connects the output of any magnetic phono
cartridge to the low level input stage. The response of
the low level stages has been shaped to conform to
RIAA standards. The gam at 1000 Hz is 62 dB to the
MAIN outputs; 42 dB to the TAPE outputs. The input
impedance is 47,000 ohms.
LEFT . . . turning the control to the left accents the left
channel by reducing the right channel output
RIGHT . . . turning the control to right accents the right
channel by reducing the left channel output.
PHONO 2: Same as PHONO 1
BASS
LOUDNESS
The LOUDNESS control automatically provides the correct amount of bass required to compensate for the change
in response of the human ear at low-loudness levels.
The BASS is a concentric control. The outer knob controls
the low frequency response in the right channel. The center
knob controls the low frequency response in the left channel. The two knobs are friction coupled. This permits them
to be adjusted together or independently. Clockwise rotation increases lows and counterclockwise decreases lows.
Turn the control to the center position for flat response.
When the volume is reduced, the music will seem to lose
much of its bass and some of its treble. This effect is due
to the sensitivity characteristic of human hearing. The response of the human ear to bass and treble pitch decreases
6
more rapidly than its response to pitch centered in the midtonal range. The LOUDNESS switch converts the volume
control to a loudness compensated control. Use LOUDNESSIN to listen at low volume and still hear full-frequency range.
TAPE
The TAPE pushbutton allows instantaneous comparison
of recorded material and the program source. With the pushbutton at the IN position, the recorded tape is heard. With
the pushbutton at the OUT position the program being
recorded is heard.
VOLUME ON/OFF
The VOLUME control regulates the loudness in both
channels. The VOLUME control has been precision tracked
throughout the listening range (0 to -65 dB) for accurate
stereo balance. When rotated to the counterclockwise position the AC power to the MX 113 is turned off.
IMPORTANT: When the MX 113 is operated with the
TAPE pushbutton at the IN position, signal from any
other source will not be heard from the loudspeakers.
To hear any other program source, the pushbutton must
be at the OUT position.
Using the Pushbuttons
MUTING
MODE SELECTOR
MUTING suppresses the background noise and hiss
normally heard between FM stations. With the pushbutton
at the IN position the muting is turned on. Weak stations
that may not override noise and interference are also suppressed by the muting. With the pushbutton at the OUT
position, the muting is turned off. This allows conventional
FM tuning with the between station noise and interference
present.
Stereo
With the pushbutton at the OUT position the left channel
is heard from the left loudspeaker and the right channel is
heard from the right loudspeaker.
Mono (L + R)
With the pushbutton at the IN position the left and right
channels are added together and are heard from both
loudspeakers.
SELECT
With the SELECT pushbutton at the IN position the selectivity of the MX 113 is increased in both FM and AM. The
sides of the IF curve are compressed which increases the
ability of the tuner to separate a weak (distant) station
from a strong (local) station on adjacent channels.
LF FILTER
With the pushbutton at the IN position the low frequency
response is attenuated below 50 Hz. The slope is 12 dB
per octave. Use of the LF filter reduces unwanted low frequency noise such as rumble. With the pushbutton released,
the response of the MX 113 is flat.
PANLOC
Mclntosh developed PANLOC mounting brings professional installation technique to stereo. Depressing the
PANLOC buttons will lock the instrument firmly in the
installation. Depressing the PANLOC buttons a second time
will release the instrument. It can then be pulled toward
you to the "adjustment" position. In this position the top
panel controls can be adjusted.
HF FILTER
With the pushbutton at the IN position high frequency
response is attenuated above 5000 Hz. The slope is 12 dB
per octave. Use of the HF filter reduces unwanted high frequency noise like hiss or scratch. With the pushbutton released, the response of the MX 113 is flat.
7
Balancing Your Stereo
The performance and enjoyment of a stereo system is
greatly increased when the sound is properly balanced.
The balance of the stereo system is affected by many things
including room acoustics, furniture placement, room shape,
small differences in loudspeakers, etc. To assist you in
balancing your stereo system in your room, here is the
procedure to determine correct phase and program loudness.
TO ADJUST PHASE
1. Play a familiar record.
2. Press the MODE pushbutton to the MONO position.
3. Turn BALANCE control to 12 o'clock position.
4. Stand about 10 feet in front of and midway between the
loudspeakers. The sound should appear to come from
directly in front of you. If the sound is not directly in
front of you with the phase switch in the 0° NORMAL
position, reverse the leads on one loudspeaker. When
the sound comes from directly in front of you the
speakers are in PHASE. Use the PHASE switch to correct
for out of phase program sources.
TO BALANCE LOUDNESS
1. Press the MODE pushbutton to the MONO position.
2. Play a familiar recording,
3. Turn the BALANCE control to the 12 o'clock position.
4. While the program is playing, stand between the two
loudspeakers. Listen for a difference in loudness between speakers. Balance the system by adjusting the
controls on the power amplifiers. Next, set the MODE
selector to STEREO. If there is then a difference in loudness turn the BALANCE control toward the speaker that
is not as loud. Adjust the BALANCE control until the
sound is satisfactory between both speakers.
8
Listening to Your Stereo
The recording process continues as usual. When the TAPE
pushbutton is at the OUT position the program being recorded is heard.
LISTENING TO A STEREO RECORD
LISTENING TO AM
Turn the INPUT SELECTOR to PHONO 1 or PHONO 2,
whichever is connected to the record player you wish
to hear.
Turn the INPUT SELECTOR to AM.
Rotate the tuning knob to the station of your choice.
Adjust the volume to a comfortable level.
Make certain the MODE PUSHBUTTON is in the OUT or
STEREO position.
Separation of a weak station from a strong adjacent
station can be improved with the SELECT button at the
IN position.
Adjust the VOLUME control to desired volume.
LISTENING TO A MONOPHONIC RECORD
LISTENING TO FM OR FM STEREO
Turn the INPUT SELECTOR to PHONO 1 or PHONO 2,
whichever is connected to the record player you wish
to hear.
Turn the INPUT SELECTOR to FM.
Rotate the tuning knob to the station of your choice.
Push the MODE pushbutton IN to MONO.
Separation of a weak station from a strong adjacent
station can be improved with the SELECT button at
the IN position.
Adjust the VOLUME control to desired volume.
LISTENING TO A STEREO TAPE RECORDER
When the STEREO indicator is lighted, the station is
broadcasting a 19,000 Hz pilot signal for stereo and the
MX 113 will automatically switch to stereo. If a station is
not transmitting the 19,000 Hz pilot signal for stereo,
the STEREO indicator will remain off and the tuner will
automatically switch to mono. The MX 113 uses a new
Mclntosh developed automatic mono-stereo switching circuit. The circuit action is electronic and prevents switching
clicks or transients.
Turn the INPUT SELECTOR to TAPE.
Set the MODE pushbutton to STEREO or MONO, depending on the program on the tape.
Adjust the VOLUME control to desired volume.
TO RECORD ON A STEREO TAPE RECORDER
All program sources are available at the TAPE OUTPUT
jacks. The program material is unaffected by all front panel
controls except the INPUT SELECTOR, and the use of the
SELECT button on AM and FM.
The ultrasonic muting circiut suppresses all noise between FM stations. It also suppresses all weaker stations
not strong enough to override the background noise. The
muting threshold setting determines the strength of the
signal which can be heard with muting in operation. Casual
adjustment of the muting threshold is not recommended.
To monitor while recording, the tape recorder must have
separate record and playback or monitor heads. The TAPE
pushbutton permits monitoring the tape recordings while
in the process of recording. When the TAPE pushbutton is
at the IN position it will play the sound from the tape as
it passes the playback head, a moment after it is recorded.
While tuning FM you may notice that the tuning meter
will show a station yet no program is heard from the
speakers. The muting circuit in the tuner has rejected the
station because there is objectionable noise with the weak
signal from the station. Push the MUTING pushbutton to
the OUT position and the station will be heard. Most programs that can be tuned in this manner are of poor quality
due to interfering noise.
The ability to separate a weak station from a strong station will be improved by the use of the SELECT pushbutton. With the pushbutton at the IN position a Mclntosh
developed circuit compresses the sides of the IF curve
which improves the separation of weak stations from strong
stations on adjacent channels.
9
Performance Limits and Ratings
Performance limits are the maximum deviation from
perfection permitted for a Mclntosh instrument. We promise
you that the MX 113 you buy must be capable of performance at or exceeding these limits or you get your money
back. Mclntosh is the only manufacturer that makes this
guarantee.
ADJACENT CHANNEL SELECTIVITY
35 dB with SELECT button at the OUT position
45 dB with SELECT button at the IN position
FM
USEABLE SENSITIVITY
2.5 microvolts at 100% modulation (±75 kHz deviation)
for less than 3% total noise and harmonic distortion
IMAGE REJECTION
65 dB; 540 kHz to 1600 kHz
SIGNAL TO NOISE RATIO
70 dB at 100% modulation
PREAMPLIFIER
HARMONIC DISTORTION
Mono: 0.3% at 100% modulation ±75 kHz deviation
Stereo: 0.5% at 100% modulation ±75 kHz deviation
FREQUENCY RESPONSE
±0.5 dB, 20 to 20,000 Hz
FREQUENCY RESPONSE
±1dB from 20 Hz to 15,000 Hz with standard de-emphasis
DISTORTION
0.1% at 2.5 volts output, 20 to 20,000 Hz
CAPTURE RATIO
1.5 dB
INPUT SENSITIVITY
PHONO 1 and PHONO 2: 2 millivolts for 2.5 volts output
at 1,000 Hz
AUX and TAPE: 0.25 volts for 2.5 volts output
SPURIOUS REJECTION
90 dB IHF
INPUT IMPEDANCE
PHONO 1 and PHONO 2: 47,000 ohms
AUX and TAPE: 250,000 ohms
IMAGE REJECTION
95 dB; 88 to 108 MHz (IHF)
STEREO SEPARATION
35 dB at 1000 Hz
SELECTIVITY
Adjacent Channel—6 dB
normal; 15 dB IHF with
position
Alternate Channel—58 dB
normal; 88 dB IHF with
position
VOLTAGE AMPLIFICATION
PHONO 1, PHONO 2 to MAIN output 62 dB, to TAPE
output 42 dB
AUX andTAPEtoMAINoutput20dB;to TAPE output 0dB
IHF with SELECT button in
SELECT button at the IN
HUM AND NOISE
PHONO 1 and PHONO 2: 72 dB below 10 millivolt
input; equivalent to less than 3 microvolts at the input
terminals.
AUX and TAPE; 85 dB below 2.5 volts output, unweighted
IHF with SELECT button in
SELECT button at the IN
TUNING INDICATOR
D'Arsonval movement meter
BASS CONTROL
-18 dB to +16 dB at 20 Hz
STEREO INDICATOR
Stereo light activated by 19,000 Hz pilot signal only
TREBLE CONTROL
±20 dB at 20,000 Hz
AM
SENSITIVITY
75 microvolts at 1,000 kHz (using external antenna
input)
LF FILTER
Flat or roll off below 50 Hz, down 12 dB at 20 Hz
HF FILTER
Flat or roll off above 5,000Hz, down 12 dB at 20,000 Hz
SIGNAL TO NOISE RATIO
45 dB
OUTPUT
Main: 2.5 volts with rated input. Up to 10 volts can be
developed without increase in distortion. FM and AM
will produce 10 volts output at 100% modulation.
HARMONIC DISTORTION
1% at 30% modulation
FREQUENCY RESPONSE
Down 6 dB at 3,500 Hz
Tape: 0.25 volts with rated input. Phono input signal of
10
10 millivolts produces 1.2 volts output. FM and
will produce 1.2 volts output at 100% modulation.
WEIGHT: 26 pounds (11.79 kg) net, 38 pounds (17.24 kg)
in shipping carton.
L + R: 2 volts with rated input
FINISH: Front panel: Anodized gold and black with special
gold/teal panel nomenclature illumination.
GENERAL
CHASSIS: Chrome and black.
MOUNTING: Mclntosh developed professional PANLOC.
TRANSISTOR COMPLEMENT
2-JFET
3—MOSFET
30—Silicon Planar
31—Diodes
2 Integrated Circuits—(each contains the equivalent of
16 transistors and 8 diodes)
POWER REQUIREMENTS
120 volts, 50/60 Hz, 30 watts
FACILITIES AND FEATURES
VOLUME CONTROL: Precision "tracked" at all listening
levels. (0 to -65 dB). Does not change stereo balance as
loudness is changed. The AC power ON/OFF switch is
coupled with this control.
BALANCE CONTROL: Natural balance at center position,
attenuation of left or right channel by rotating control.
LOUDNESS: Loudness compensated or f a t response—
Loudness position boosts low frequencies for low level
listening. Operates as a function of volume control position.
Full compensation is obtained at lower volume levels and
flat response is obtained at full volume.
SELECTIVITY: Increases the ability of the tuner to separate
a weak (distant) station from a strong (local) station on
adjacent channels.
MUTING: Suppresses the background noise and hiss normally heard between FM stations.
TAPE MONITOR: Pushbutton; compares recorded tape with
program source while recording.
MODE: Selects either stereo or mono operation.
PHASE CONTROL: Electronically reverses phase in the left
channel to correct "out of phase" program sources.
MUTING ADJUST: Modifies the noise rejection threshold
on FM
DIAL SCALE INTENSITY: Modifies the brightness of the
illumination of the front panel
MECHANICAL
SIZE: Front panel: 16 inches wide (40.64 cm) by 5-7/16
inches high (13.81 cm); Chassis: 15 inches wide (38.1 cm)
by 13 inches deep (33.02 cm), including PANLOC shelf
and back panel connectors; Knob Clearance: 1½ inches
(3.81 cm) in front of mounting panel.
11
RELATIVE OUTPUT IN dB
Performance
Charts
FM SIGNAL PERFORMANCE
0
10
20
30
40
50
60
70
0.1
10
1.0
100
1K
10K
RF INPUT SIGNAL IN MICROVOLTS ACROSS 300 OHMS
FM-IF CHARACTERISTIC
0
-10
FM HARMONIC DISTORTION
-40
-50
PER CENT HARMONIC DISTORTION
-30
AMPLITUDE RESPONSE EN dB
-20
3
2
-60
1
-70
0
20
-80
-90
-100
0
100
200
FREQUENCY IN KILOHERTZ
12
300
400
100
1000
FREQUENCY IN HERTZ
10000
AM FREQUENCY RESPONSE
RELATIVE OUTPUT IN dB
0
-10
-20
-30
-40
20
100
1000
10000
FREQUENCY IN HERTZ
AM SELECTIVITY AT 1000 kHz
0
RELATIVE OUTPUT IN dB
-20
-40
-60
-80
-85
-100
1030
1020
1010
1000
FREQUENCY IN kHz
13
990
980
970
20000
PHONO EQUALIZATION
20
15
Response in dB
10
5
0
-5
-10
-15
-20
20
100
1000
10000
20000
1000
10000 20000
FREQUENCY IN HERTZ
TONE CONTROLS
20
15
Response in dB
10
5
0
-5
-10
-15
-20
20
100
FREQUENCY IN HERTZ
LOUDNESS AND FILTER CHARACTERISTICS
15
Response in dB
10
5
0
-5
-10
-15
-20
20
100
1000
FREQUENCY IN HERTZ
14
10000
20000
Technical Description
signal to two double-tuned transformers, a ceramic filter
network, and a single-gate MOS-FET. The sides of the IF
curve are compressed by this circuit narrowing the IF bandpass. In this mode of operation weak stations adjacent to
strong stations can be tuned with surprising clarity.
TUNING MECHANISM AND DIAL DRIVE
In the MX 113, the unique design and careful manufacture of the mechanical assembly gives smooth flywheel
tuning.
All of the RF circuits, including the selectivity circuit
and the AM sections of the variable capacitor are encased
in a metal module. Each FM-RF section is isolated in a
separate compartment by metal shielding. Careful design
and manufacturing increase the protection against radiation
and interference. The MX 113 exceeds the FCC requirements for suppression of local oscillator radiation.
By controlling the relationship of mass and mechanical
resistance, and by dividing the workloads in the dial drive
system, it becomes nearly impossible to detect any backlash.
Yet, the entire dial drive is a model of mechanical stability.
For added ease and increased tuning accuracy, a section
of the dial pointer is illuminated.
Antenna connections for either 300 ohm twin lead transmission line or 75 ohm coaxial cable are provided on the
back panel of the MX 113. The normal input impedance of
the RF amplifier is 75 ohms. Impedance match to 300 ohms
is provided by a Mclntosh designed, negligible loss, balun
transformer. Connections for both 300 ohm twin lead and
75 ohm coaxial cable are made with push type terminals.
FM SECTION
The Radio Frequency (RF) section houses the complete
FM-RF front-end and part of the AM RF circuit.
A seven-section variable capacitor is the heart of the RF
section. Four sections of the variable capacitor are in the
FM front end and the remaining three are in the AM section.
By interleaving the sections (AM-FM-AM-FM-etc.) spurious
responses are significantly reduced. The four FM sections
of the variable tuning capacitor provides a high degree of
RF selectivity and excellent spurious rejection. Using the
latest "state of the art" field effect transistors with a welldesigned variable tuning capacitor has provided the
MX 113 with an excellent RF front-end.
FM-IF AND DISCRIMINATOR SECTION
The MX 113 uses linear-phase IF filters. Each filter was
designed from a FORTRAN computer program for minimumphase and constant delay. The mathematical complexity of
the filter design procedure is almost beyond belief. Using
numerical integration in the S-Plane, an "IBM" 1130 high
speed computer spent eighteen minutes on the mathematics
for the design of the IF filter. It would have taken a human
engineer, working twenty-four hours a day, seven days a
week, and working error-free three-hundred years to perform the same mathematical calculations!
A dual insulated gate metal oxide silicon field effect
transistor (MOS-FET) is used as first and second RF amplifier. Each gate of the transistor is internally protected by
back-to-back diodes against incoming transients that may
occur due to severe external conditions. Use of MOS-FET's
greatly reduces the cross-modulation products over a
wider dynamic range. A wider dynamic range permits the
input circuits to accept extremely strong signals without
overload. Since both RF amplifiers have insulated gate
configurations, external neutralization is not required.
This design results in a very stable RF amplifier circuit.
The IF filter has equal time delay in its pass band region.
Any error in time delay causes FM distortion. All other IF
filters have delay distortion, some as much as 100% of
the 10.7 MHz transit delay. The MX 113 has less than 1.0%
delay distortion from antenna input to discriminator output!
This makes possible the overall low distortion performance
limit for the FM tuner and multiplex section of the MX 113.
Amplification of the intermediate frequency signal is
provided by two high gain integrated circuits, each containing 16 transistors, 3 zener diodes, 5 diodes, and 23 resistors, all on a signal monolithic silicon chip. The exceptionally high gain of the integrated circuit assures "hard
limiting" at very low levels of input signals.
Low temperature coefficient components for the FM local
oscillator prevent frequency drift. The frequency stability
inherent in the local oscillator makes automatic frequency
control (AFC) unnecessary. The rate of drift of the local
oscillator is less than ten parts per million per degree
centrigrade.
Paralleling the main signal path through the FM-IF and
detector module, a secondary amplifying and de-modulating process is used to activate the tuning meter and to provide testpoint TP1 and TP2 with a signal to be used with
the Mclntosh Maximum Performance Indicator.
The mixer design uses a JFET for high sensitivity and
freedom from overload. The mixer delivers the composite
FM signal at the 10.7 MHz intermediate frequency. The
path of the IF signal is controlled by the front panel
SELECTivity pushbutton.
FM STEREO MULTIPLEX SECTION
At the OUT position, the SELECTivity switch directs the
signal through an IF preamplifier stage, that uses a J-FET
and a double-tuned IF transformer. The signal then goes to
the FM-IF and discriminator module for further amplification. Activating the SELECTivity pushbutton routes the
Mclntosh has developed a special detecting circuit used
in the multiplex section. A particular 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
15
the recovered information with the L + R carrier signal.
This yields the left and right program output with maximum
separation.
A high-quality loopstick antenna is provided. It can be
rotated for maximum performance, optimum signal reception or minimum interference. In each MX 113 the loopsticks are individually tuned for optimum performance.
After tuning, the loopstick is then sealed. This custom
matching of the loopstick to the AM-RF front end maximizes the performance of the loopstick antenna. The antenna is rotatable through nearly 180 degrees in all directions. With this mobility you will not suffer loss of sensitivity
regardless of the angle at which the instrument is mounted.
A back panel antenna connector is provided for connecting
an external antenna if desired.
The 19,000 Hz pilot signal, broadcast by an FM station,
is filtered from the composite stereo input signal, amplified by a special limiting amplifier, doubled to the 38,000
Hz carrier frequency, and then amplified again by a limiting amplifier. The composite signal minus the 19,000 Hz
pilot is combined with the 38,000 Hz carrier signal.
The new combination of signals is fed to the special detector
circuit mentioned above. Balanced full wave detectors
are used to cancel the 38,000 Hz components in the output. The SCA (Subsidiary Communication Authorization)
signal must be removed from the composite output. This
is accomplished by the use of a new "Image Parameter"
band elimination filter that has been computer designed.
The SCA filter rejects SCA signals without impairing stereo
performance.
To maintain the excellent image rejection and lack of
spurious cross modulation of the AM-RF amplifier an autodyne converter circuit was used in producing the AM-IF.
AM-IF uses two double tuned IF transformers designed
to obtain a high degree of selectivity yet allowing good
audio fidelity. With the SELECT button IN a narrow band
ceramic filter is added between the AM-IF amplifier and the
detector.
When the 19,000 Hz carrier of a stereo signal is received, the automatic FM stereo switching circuit activates
the multiplex decoding circuit. This lights the stereo indicator. The circuit switching is all done electronically with
no clicks. The automatic stereo switching can be defeated
by depressing the mode selector switch to MONO. (In this
position the stereo indicator will still light to indicate the
presence of a stereo signal.) On monophonic transmissions
the stereo switching is inactive at all times, assuring
optimum signal to noise ratio. The stereo switching circuit
has been designed so that noise will not activate it.
A 10,000 Hz active filter eliminates the 10,000 Hz
whistle and irritating "Monkey Chatter" caused by an
adjacent station. The frequency response of all stations is
nearly flat from 20 Hz to around 3,500 Hz, then rolloff
begins. Because an active filter is used, the output level at
10,000 Hz, or the whistle frequency, is down over 20 dB
or one hundredth of what it would be without filtering.
With the select button IN, the active filter cutoff frequency
is lowered. The filter then effectively suppresses the 5,000
Hz whistle from nearby television receivers.
FM muting in the MX 113 operates by detecting ultrasonic noise which is present when tuning between stations
or when receiving a weak station. The muting circuit can
be activated or defeated by the use of the muting button
on the front panel. The threshold of muting desired can be
adjusted by the muting level control on the top panel.
Varying the muting control adjusts the threshold at which
the muting takes effect.
The AVC (automatic volume control) system was designed to prevent bursting or thumps when the AM is
tuned through a strong signal. Distortion at low audio frequencies is minimized by using two AVC filter sections
instead of the conventional one.
PHONO PREAMPLIFIER
There are three transistors in each channel of the phono
preamplifier. The output of the third transistor is connected
by a negative feedback loop to the emitter of the input
transistor. The feedback loop reduces noise and distortion.
It also provides precision RIAA frequency compenation
required for magnetic phonograph cartridges. Feedback
remains in effect even at 20 Hz, where gain is highest.
The negative feedback also provides a low output impedance for the tape output.
AM SECTION
The AM-RF amplifier circuit includes a three section
variable tuning capacitor in the metal enclosed shielded
RF module which also houses the FM-RF front end. A three
section variable capacitor is used for greater spurious
rejection. The RF amplifier is unique. The circuit has constant sensitivity, constant selectivity, high image rejection
across the complete AM band. Ordinary AM-RF circuits
cannot do all of these simultaneously. This circuit design
achieves equal sensitivity even at the low end of the band.
Spurious, image, and intermediate frequency rejection are
all superior. The same circuit delivers equal selectivity
across the entire band. The Mclntosh circuit is unique in a
superheterodyne AM receiver.
Phono input overload is virtually impossible. For example, at 1,000 Hz, the phono input can accept 150
millivolts of signal without overload. Ten millivolts of signal
at the phono input at 1,000 Hz will produce 1.2 volts at
the tape output.
The selector switch connects either the output of the
phono amplifier, the FM tuner section, the AM tuner
section or one of two high level inputs (TAPE or AUX)
to the main preamplifier. The input impedance of the high
level input is 250,000 ohms. The high level inputs feed
In addition, there is no loss of audio frequency response
at the low end of the band, common in AM receivers. Another advantage of the Mclntosh circuit is freedom from
cross-modulation and overloading by strong local stations.
16
directly to the volume control. A loudness circuit is connected to a tap on the volume control to provide loudness
compensation. Compensation can be switched in or out.
The high level signal then feeds to a pair of transistors
connected as high gain amplifiers. Negative feedback is
used around this pair of transistors to reduce noise and
distortion. The negative feedback provides the low impedance needed to drive the highly selective filter networks
which follow.
In the left channel the second transistor is connected
in a balanced output arrangement. This circuit provides
equal amplitude signals but of opposite phase for the phase
switch.
The filter networks can be switched in or out. The highfrequency filter network reduces treble response above
5,000 Hz. The low-frequency filter reduces bass response
below 50 Hz. The slope of the filters is selected for maximum rejection of commonly encountered noise. Careful
design keeps the loss of useable program material to a
minimum.
The output from the filter circuits is fed to the balance
control. The output of the balance control drives the first
stage of the tone control section. The remaining two transistors are connected as a high-gain amplifier stage. The
high-gain of this stage is used to advantage for the tone
control negative feedback circuits. Negative feedback in
the tone control circuits assures low distortion and accurate
shape of the tone-control response curves. Negative feedback is maintained at all frequencies, even with tone controls turned to full boost. Overall distortion is low at all
frequencies including frequenices where maximum boost
occurs. The negative feedback also provides the low impedance output required for the main preamplifier outputs.
L + R AMPLIFIER
The L + R amplifier consists of a single transistor connected as a voltage amplifier. Negative feedback is used
around the summing amplifier to maintain low distortion
and provide a low impedance for the center channel output.
POWER SUPPLY
The power supply of the MX 113 has received very special attention.
Three separate rectifier circuits are used. First, a fullwave rectifier supplies DC to all audio circuits. The second
full-wave rectifier supplied DC to all tuner and multiplexdecoder circuits. The third supply provides DC to the AM
circuit.
The power supplies are elaborate in design. They use
electronic filtering to insure the lowest possible background hum level, maximum stability, and extremely good
regulation.
17
18
FM-AM BLOCK DIAGRAM
19
STATION LOG
CALL
LETTERS
FREQUENCY
LOCATION
CALL
LETTERS
ANTENNA
DIRECTION
20
FREQUENCY
LOCATION
ANTENNA
DIRECTION
MclNTOSH AUDIO DIVISION
2 CHAMBERS ST., BINGHAMTON, N. Y. 13903
607-723-3512
Design subject to change without notice.
Printed in U.S.A.
038-876
BE022003
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