McIntosh MX 110 User manual

CONTENTS
GENERAL DESCRIPTION. 1
TECHNICAL DESCRIPTION. 1
INTRODUCTION. 3
FM ALIGNMENT. 4
MULTIPLEX ALIGNMENT. 6
SCHEMATIC. 8
DIAL STRINGING. 11
PARTS LIST. 12
SPECIFICATIONS.. 16
CHASSIS LAYOUT. . 18
OPERATING CURVES. 20
M AND X SERIES SCHEMATICS.POCKET
2 CHAMBERS ST.
BINGHAMTON, N.Y.
WARRANTY STATION
MX 110
SERVICE MANUAL
nWntosh
mx

MX 110 TUNER PREAMPLIFIER
GENERAL DESCRIPTION
The MX 110 combines in one unit an extremely
low-distortion preamplifier with a highly sensitive
FM multiplex stereo tuner. Every desirable
feature of a tuner and a preamplifier is included
in this design. Interstation noise suppression,
tuning indicator, FM multiplex indicator, indi¬
vidual channel bass controls, individual channel
treble controls, electronic phase switch have all
been engineered into the MX 110. The INPUT
SELECTOR gives you a choice of six different
program sources. The MODE SELECTOR is a
newly developed control which makes it very
easy to balance a stereo system. It is designed to
add left to right for monophonic operation, to
control the left to right stereo perspective or to
compare the left and right channels of a stereo
program. The loudness of the phono channels and
the auxiliary channel may be balanced to the
TECHNICAL
The radio-frequency amplifier of the MX 110 is
a “cascode” type circuit. The circuit is specially
designed to amplify weak signals with less noise
and distortion. By carefully tuning this RF
amplifier during manufacturing and controlling
other circuit constants, spurious response rejec¬
tion is improved. The high-frequency oscillator
mechanical layout is engineered for minimum
response to temperature variations. In fact the
combination of mechanical and electronic design
is so unusually good in this circuit that automatic
frequency control is not needed in the MX 110.
The mixer output is amplified by four inter¬
mediate frequency amplifiers. The transformers
used in the I.F. amplifiers are designed for max¬
imum adjacent channel rejection, for electrical
stability, and for electrical and mechanical
resistance to shock and vibration.
tuner loudness. These adjusting controls are
located on the top of the MX 110 behind the
front panel. By releasing the PANLOC buttons
on the front panel, you can slide the MX 110
out of its mounting until the second latch en¬
gages. The top mounted LEVEL set controls are
now available.
The McIntosh designed PANLOC system is
the first professional installation technique to be
used on stereo instruments. The PANLOC sys¬
tem gives you absolute ease of installation,
operation, and maintenance.
The McIntosh MX 110 is a beautifully engi¬
neered control center for the finest stereo sound
systems. The extreme care in manufacturing, in
layout design and in thermal engineering prom¬
ises the usual McIntosh extra values of reliability,
performance, and long life.
DESCRIPTION
The R.F. and I.F. circuits of the MX 110
are completely shielded and exceed the FCC
requirements for suppression of oscillator radia¬
tion. Either a 300 ohm or 75 ohm antenna may
be used with the MX 110. A VHF television
antenna which is suitable for FM reception can
be connected to the MX 110.
In the MX 110, a new type of mechanical
tuning assembly gives smooth flywheel tuning.
By controlling the relations between mass and
mechanical resistance, and dividing work loads in
the dial drive system, it becomes nearly impossi¬
ble to detect any backlash. Yet the entire dial
drive is a model of mechanical stability. For
smooth, quiet action and extended life with
virtually' no wear, a teflon lined dial pointer
carriage and nylon pulleys are used in the dial
cord assembly.
1

MULTIPLEX DECODER
The multiplex decoder uses a special McIntosh
developed detecting circuit. One of the advan¬
tages of this circuit is the elimination of the
critical adjustments necessary with commonly
used matrixing methods. This circuit detects the
L+R sidebands and automatically matrixes the
recovered information with the L+R main
carrier signal. This circuit then yields the left and
the right program with maximum separation.
A temperature stabilized 19KC amplifier
locks-in a highly stable push-pull synchronous
oscillator. Apart from other advantages, this
method provides greatest noise immunity. Bal¬
anced detectors cancel the 38KC component
in the output and insure low distortion.
A three-section sharp cut off filter rejects SCA
interference and reduces susceptibility to spuri¬
ous signals.
The MX 110 has an MPX stereo indicator
that lights when the dial pointer crosses a station
broadcasting MPX stereo. A unique circuit using
a transistor operates the MPX stereo indicator.
The transistor is controlled by a differential
detecting circuit that amplifies the 19KC pilot
signal. This circuit automatically discriminates
between the 19KC signal and noise.
AUDIO
The MX 110 audio amplifier consists of three
negative-feedback amplifying sections in dupli¬
cate for the left and right stereo channels and a
separate L+R monophonic amplifier. The first
section in each channel is a feedback preamplifier
used to amplify and compensate for the input
signals coming from phonograph pickups or tape
heads. Level set controls are connected into the
output circuit of this preamplifier section when
the INPUT SELECTOR is switched to PHONO
1 or PHONO 2. These controls may be used to
maintain uniform loudness between phono and
tuner inputs. Skillful layout, grounding, and
shielding for low-hum pickup, metal film resistors,
low-noise tubes and extreme care in manufactur¬
ing combine to reduce noise and hum in t
input amplifiers.
octave) rumble and high-frequency filters are
associated with this section.
The third amplifier section is a two stage
negative feedback amplifier. The variable bass
and treble controls are included in the feedback
loop to maintain the lowest possible distortion.
For example a wave meter analysis of the three
amplifier sections of the MX 110 shows less
than 1/10 of 1% distortion at 3 volts output.
The MODE SELECTOR, balance controls and
left and right outputs are associated with the
third amplifier section.
The L+R monophonic amplifying section is a
feedback summing amplifier. It supplies mono¬
phonic output as well as L+R output.
The second amplifier section in each channel is
a cathode follower. The sharp cut-off (18db per
POWER SUPPLY
The power supply of the MX 110 has received
very special design attention. Two separate
rectifier circuits are used.
A full-wave rectifier supplies D.C. to the
heaters of all audio stages.
A bridge rectifier supplies D.C. to the anodes
of the audio stages.
A half-voltage tap on the bridge rectifier
supplies D.C. to the tuner stages.
This elaborate power supply design insures the
lowest possible background hum level and also
the maximum stability. In addition to this care¬
ful work the power transformer uses special
magnetic shielding to minimize possible hum
pickup in the MX 110 as well as in any other
equipment used with it.
Hi
2

INTRODUCTION
All McIntosh tuners are carefully aligned and tested at the factory using the
finest available test equipment. All McIntosh tuners will meet their published
specifications when shipped from the factory.
After extensive operation, especially when tubes have been replaced,
it may be desirable to realign the tuner circuits for best performance. This
manual gives complete information on the circuit realignment procedure for
the MX 110 tuner-preamplifier.
The test equipment listed below (or its equivalent) is necessary to properly
align an MX 110. The accuracy of the alignment will be directly related to
the accuracy and calibration of the test equipment used.
FM Signal Generator (Measurements 210A or equivalent)
VTVM
Multiplex Generator (RCA WR-51A or equivalent)
10.7 MC Generator (Preferably crystal controlled)
Oscilloscope (Hewlett-Packard 120B or equivalent)
Harmonic Distortion Analyzer, desirable but not essential—(Hewlett-
Packard 330B or equivalent)
If the necessary test equipment is not available, alignment should not be
attempted. You may contact the McIntosh Customer Service Department
for additional information.
Customer Service
McIntosh Laboratory, Inc.
2 Chambers Street
Binghamton, New York
Our telephone number is 723-5491
The direct dial area code is 607

T
MX 110 FM
STEPS
TUNER
DIAL
SETTING
SIGNAL GENERATOR
INDICATOR
FREQ
COUPLING
MODULATION
TYPE
CONNECTED
TO
Point of no
interference
or signal
10.7MC Through external
.01 MF cap to
pin 7 of
12AT7 mixer
cw
VTVM
TP #1
SAME SAME SAME
SAME MX 110
tuning eye
SAME SAME
SAME SAME VTVM TP #2 or
(discriminator
output on
"M" series)
SAME
SAME
SAME SAME
SAME
Pin 6 of
discriminator
transformer
105MC 105MC
300 ohm antenna
terminals with
* matching network
400 cycles
75KC deviation
(100% modulation)
VTVM connected to TP1
and
scope connected to
L or R audio output
90MC
90MC SAME
SAME
SAME
105MC 105MC SAME
SAME SAME
90MC
90MC SAME SAME
SAME
Point of no
interference
Scope
L or R output
105MC
105MC
SAME
400 cycles
75KC deviation
(100% modulation)
attenuated to 2.5
microvolts output
VTVM connected to TP #1
and
Scope connected to
L or R audio, output
ANTENNA MATCHING NETWORK
FM SIGNAL
GENERATOR
100 OHMS
-AAA—
-O
-AAA—
150 OHMS
TUNER
300 OHM
ANTENNA
° TERMINALS
* IF SIGNAL GENERATOR HAS OTHER THAN 50 OHM INTERNAL IMPEDANCE,
USE A RESISTOR OF 150 OHMS, LESS INTERNAL GENERATOR IMPEDANCE.

1
] ALIGNMENT
ADJUST
TEST
LIMITS
REMARKS
Top (secondary)
and bottom,
(primary) of 1st,
2nd and 3rd
IF transformers
Maximum
possible
negative
voltage
Shunt to ground the winding not being adjusted with a .01 MF capacitor in
series with a 1 K resistor. Attenuate signal generator until output voltage at
TP #1 is less than 1.5 volts with one IF transformer winding shunted. IF
transformers have terminal #1 marked with a green dot and are numbered
clockwise.
4th IF
transformer, top
and bottom.
Eye should close to approx, ’/is” with strong signal. Make additional adjustments of eye
closure by varying the length of parallel conductors connected to pins 1 and 4 of the 4th IF
transformer. (This changes the capacitive coupling between pins 1 and 4.)
Discriminator
transformer
upper core
(secondary)
Adjust
for 0 volts
! - -
Discriminator
transformer
lower core
(primary)
Maximum
negative voltage
Repeat step 3 if a large change is made in the setting of the lower core.
i
Oscillator
trimmer cap.
Maximum
negative voltage
As output increases, attenuate signal generator to keep maximum output at
TP #1 to less than 2 volts.
Oscillator coil
tuning slug
SAME Repeat steps 5 and 6 until dial calibration is accurate. j
Mixer trimmer
and
RF trimmer
SAME
1
|
Mixer coil tuning
slug and
RF coil tuning slug
SAME
Repeat steps 7 and 8 until output is as high as possible.
Muting adj.
control
Turn muting switch to "in'' position. Adjust muting control until background
noise just disappears. i
IHFM
sensitivity
2.5 microvolt
for 3 % total
noise and
distortion
Step 10 is an overall sensitivity check, and requires a distortion analyzer and i
FM signal generator with attenuator.
With 2.5 microvolts input at the 300 ohm antenna terminals,
TP #1 voltage should be .6 volts or more.

MX IIO MULTIPLEX
TUNER
SIGNAL GENERATOR
_
INDICATOR
STEPS
DIAL
SETTING
FREQ.
COUPLING
MODULATION
TYPE
CONNECTED
TO
i
Point of no
interference
or signal
Audio generator
set to 67KC,
0.5 volts output
or less
TP H2
(MPX input
on "M" series)
Audio VTVM
Pin 6 of 38KC
transformer
(yellow wire
connected at
this pin)
2
SAME MPX generator
with 19KC pilot
attenuated to
approx. 5% level
(5% level is 14 of
normal 10% level)
1 9KC pilot must
be attenuated for
correct alignment
SAME
SAME
Pin 3 or 8
of 12AU7
MPX oscillator
100MC
100MC modulated 300 ohm antenna 1 KC 100%
SAME
Pin 1 or 2 of
by MPX generator, terminals with
19KC pilot at approx. 1000
normal output microvolt signal
modulation (34KC
deviation)
modulating left or
right only
38KC transformer
4
SAME SAME
SAME
SAME Audio VTVM
and scope
L or R
output jack
5
SAME SAME
SAME SAME
SAME
SAME
6
SAME SAME
SAME
SAME SAME SAME
7
SAME
SAME
SAME
Turn off 1 KC
audio modulation
SAME
SAME
8
SAME SAME
SAME Same as step 3 SAME
SAME

DECODER ALIGNMENT
ADJUST
TEST
LIMITS
REMARKS
67KC trap Adjust for
minimum voltage
1 9KC phase coil
and
1 9KC transformer
1. Disable local 38KC oscillator by placing a jumper wire across 6.8K resistor connected to pins
1 and 6 of 12AU7 MPX oscillator.
2. Shunt pin 2 of 19KC transformer to ground with .01 capacitor in series with 1 K resistor.
3. Adjust 19KC phase coil for maximum output. Proper adjustment places core approx. %"
from bottom of coil form.
4. Adjust lower core of 19KC transformer for maximum output.
5. Shunt pin 3 of 19KC transformer to ground with .01 capacitor in series with 1 K resistor.
6. Adjust upper core of 19KC transformer for maximum output.
7. Remove jumper used in step 1 above.
38KC transformer
bottom core
Adjust for
maximum voltage
38KC transformer
upper core
Adjust for
stable scope
display
1. Turn off 19KC pilot on MPX generator.
2. Adjust upper core of 38KC transformer to obtain a stable and uniform
1 KC signal scope display. This adjustment may be critical, so turn core
very slowly.
3. Turn 19KC pilot back on.
19KC phase coil 30db separation
or more
Modulate left channel and measure right channel output. Adjust 19KC
phase coil for minimum right channel output (maximum separation).
Remove all test leads from TP #2 for separation checks.
SAME
Modulate right channel and measure left channel output.
Separation in steps 5 and 6 should be at least 30db
This step checks the rejection of 19KC and 38KC frequencies. Residual output should be at
least 40db below modulated output.
1 ' ' .
Check for MPX indicator light
1. MPX light should turn on with MPX signal
2. Tuning slowly across dial, MPX light should turn on only with MPX signal.