McIntosh MX 112 Operating and installation instructions

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MX 112
FM/AM TUNER PREAMP
SERVICE INFORMATION
FROM SERIAL NO. 10S01 TO 39S99
MclNTOSH LABORATORY INC. 2 CHAMBERS STREET BINGHAMTON, NEW YORK
MX
112

1
* a I ! C
ELECTRICAL SPECIFICATIONS
FM TUNER SECTION
PREAMPLIFIER SECTION
USABLE SENSITIVITY
Better than 2.5pF (IHF usable sensiti¬
vity)
SIGNAL TO NOISE RATIO
Better than 65dB
HARMONIC DISTORTION
Mono, less than 0.5%- Stereo, less than
0 . 8 %.
FREQUENCY RESPONSE
Flat from 20Hz to 20kHz with standard
de-emphasis and 19kHz pilot filter
CAPTURE RATIO
Better than 1.5dB
SPURIOUS REJECTION
90dB or greater
IMAGE REJECTION
75UB or greater (at 100MHz)
STEREO SEPARATION
Better than 30dB at 1 kHz
AM TUNER SECTION
SENS1TIVITY
Better than 12pV at 1000kHz (using ex¬
ternal antenna input)
SIGNAL TO NOISE RATIO
Better than 55dB
HARMONIC DISTORTION
Less than l%.at 30% modulation
FREQUENCY RESPONSE
Down 6d8 at 5kHz
SELECTIVITY
10kHz at -6dB
IMAGE REJECTION
60dB or greater at 1000kHz
FREQUENCY RESPONSE
+0.5dB, 20Hz to 20,OOOHz
DISTORTION
Less than 0.1% at 2.5 volts 20Hz to 20kHz
INPUT SENSITIVITY (phono 1 and phono 2)
2 millivolts for 2.5 volts output at 1 kHz
INPUT SENSITIVITY (aux, tape)
0.25 volts for 2.5 volts output
HUM AND NOISE (phono 1 and phono 2)
72dB below 10 millivolt input
HUM AND NOISE (aux, tape)
85dB below rated output
OUTPUT (main)
2.5 volts with rated input. Up to 10
volts can be developed without distor¬
tion. FM and AM will produce up to 10
volts output at 100% modulation.
OUTPUT (tape)
0.25 volts with rated input. Phono input
signal of 10 millivolts produces 1.2
volts output. FM and AM will produce 1
volt output at 100% modulation.
OUTPUT (center channel)
2 volts with rated input to both channels
BASS CONTROL
-18dB to +16dB at 20Hz
TREBLE CONTROL
+20dB to 20,OOOHz
LF FILTER
Flat or roll off below 50Hz, down 12dB
at 20Hz
HF FILTER
Flat or roll off above 5000Hz, down 12dB
at 20,OOOHz

FM/AM
TUNER
SECTION
PREAMPLIFIER
SECTION

MX 112

SCHEMATIC NOTES
Unless otherwise specified: Resistance values are
in ohms, 1/4 watt, and 10% tolerance; capacitance
values smaller than 1 are in microfarads (pF);_
capacitance values greater than 1 are in picofarads
(pF); inductors are in microhenries (pH).
Printed circuit board components are outlined on
the schematics by dotted lines. The circled num¬
bers around the dotted lines correspond to the
numbers on the PC Board layouts.
The heavy lines on the schematics denote the pri¬
mary signal path.
The terminal numbering of rotary switches is for
reference only.
All voltages indicated on the schematics are mea¬
sured under the following conditions:
a. Use of an 11 megohm input impedance VTVM.
b. All voltages +10% with respect to chassis
g round.
c. No signal at input or antenna terminals.
d. AC input at 117 volts, 50/60Hz.
e. Front panel controls at:
Tuning indicator 100MHz (no signal)
Volume Ful 1 y CCW
Mode Stereo
Muting
Input Selector
Panel Lights
Out
AM (to measure AM section)
FM (to measure FM section)
Bright
]. In units with serial numbers below 11S00: C25
is connected to pin 4 of T3; pin 3 of T3 is
connected to ground; C31 is connected to pin 4
of T5; pin 3 of T5 is connected to ground.
2. In units with serial numbers below 11S17 : C25
and C31 are 2.2pF; C33 is 6.8pF and is con¬
nected to pin 5 of T3; C35 is .OOlpF; C60 is
not used; R20 is 33k; R23 is 33k and is con¬
nected as shown by clotted line; L9 (part num¬
ber 122-013) is used in place of R62; D7 and
C61 are not used; R225 is 470k; R206 and C203
(part number 064-069) are used and are con¬
nected as shown by dotted line. R2 is con¬
nected to the other end of Rl as shown by
dotted line.
3. R221 is used in units with serial numbers be-
1ow 14S01.
4. In units with serial numbers from 17S40 to
22S65: R63 is used in place of L10; R64 and
C 1 2 8 are used.
5. In units with serial numbers from 17S25 to
17S75. C73 is used.
6. In units with serial numbers below 17S25: R35,
R38, R41 , R43, and R44 are used; LI 5 is used;
R37 is 470k; R55 Is lk; R52 is 1M and R15 is
6.8M.
7. In units with serial numbers below 17S40: C345
is used; R397 and R398 are not used.
8. In units with serial numbers below 1 8S35, C1 29
is not used.
9. In units with serial numbers below 20S00: R53
and R59 are lOOP; R 65 is not used; Ll, R6, R61,
and CIO are used; there is no connection from
C12 to pin number 1 on the mixer and local
oscillator PC Board; and C7 is connected to L3
as shown by dotted line.
10. In units with serial numbers from 19S63 to
31S34, R66 is used.
11. In units with serial numbers from 20S72 to
31S35, R67 and R68 are used.
12. In units with serial numbers below 26S01 : R55
is 270Q; R69 and SI are not used.
13. In units with serial numbers below 25S1I, R399
and R400 are not used.
(continued on alignment page)

MX 112
LEFT CHANNEL PREAMP. PRINTED C
RIGHT CHANNEL PREAMP. PRINTED CIF

MX 112

MPX PRINTED CIRCUIT BOARD 043-974
POINTER DRIVE
TUNING CONDENSER DRUM
POINTER
ADJUSTMENT
SCREW
jr
Before stringing unit,
turn pointer adjustment
screw until pulley "A"
is in the center of its
travel.
String unit as shown.
After stringing unit,
turn tuning shaft until
pointer is as far to
the left as it will go.
Turn the pointer adjust¬
ment screw until the
pointer coincides with
the zero bar of the
logging scale.
Turn the tuning knob
making the pointer move
back and forth from one
end of the dial scale
to the other. Return
pointer to the far left
and, if necessary, re¬
adjust pointer position.
TUNING CONDENSER DRUM
TUNING CONDENSER DRIVE
BLACK DIAL CORD
DIAL CORD SEQUENCE
( TO LEFT SIDE PULLEY 8) WHITE !=====
(TO IDLER PULLEY AND TUNING SHAFT) SLACK ]
* WHITE (TO RIGHT SIDE
PULLEY A )
- BLACK (TO TUNING SHAFT)
TUNING CONDENSER DRUM
POINTER DIAL STRINGING

ED CIRCUIT BOARD 043-954
COAX

IOZO

PRINTED
CIRCUIT
BOARD
043-983
POWER
SUPPLY
/
CENTER
CHANNEL
SECTION

SCHEMATIC NOTES (CONT.)
In units with serial numbers below 31S34, R130
is not used.
In units with serial numbers below 31S35: C25
is 1.2pF; C31 is ].5pF; C33 is .OOlpF; C73, C74,
C75, C76, R70, R71, R72, and R226 are not used.
In units with serial numbers below 31S35, the
drain of Q4 is connected directly to pin 17 on
the AM PC Board and gate 1 of Q4 is connected
directiy to C1 9 •
In units with serial numbers from 26S01 to 31S35,
R55 is 56k.
In units with serial numbers below 31S35, C20 is
.01pF.
In units with serial numbers below 31S56: R31
is 100k; R336 is 18k; C12 6 is used; Cl 30 and
Cl 31 are not used; C17, C24, C26, C27, C28, C29.
C30, C32, C36, C37, C38, C39, C45, C46, C47, C48,
C49, and C51 are .047 p F.
In units with serial numbers below 31S56: R23
is 15k; R27 is 1.5k; R62 is 2.7k, and Rl5 is 1M.
In units with serial numbers below 31S68, R57
is used; R52 is 100k and the AM sensitivity
switch is wired as shown by dotted lines.
In units with serial numbers from 31S35 to
31S86, C56 is 1.5pF.
In units with serial numbers below 37S50, Rl31
is not used and R105 is a 200k potentiometer
(McIntosh part number 134-205)*

MX 112 MX 112

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