McIntosh MC275 User manual

SERVICE MANUAL
Performance Specifications ........................................ 2
Notes ......................................................................... 2
Rear Panel .................................................................. 3
Section Location ........................................................ 4
BlockDiagram ........................................................... 5
Interconnection Diagram ...................................... 7 - 8
Amplifier Schematic and PCB............................. 9 - 12
Input Schematic and PCB .................................. 13 - 14
Parts List ............................................................ 15 - 16
ExplodedView and Parts List ............................. 17 - 18
Repacking Instructions ............................................. 19
CONTENTS
STEREO
POWERAMPLIFIER
STARTING WITH SERIAL NO. WV1536

PERFORMANCE SPECIFICATIONS
2
1. The heavy lines on the schematic denote the primary
signal path.
2. Unless otherwise noted, all voltages indicated on the
schematics are measured under the following conditions:
a. ACinputat120volts,50/60Hz.
b. All voltages are +/-10% with respect to ground. A
high impedance (10 megaohm) voltmeter must be used.
3. Unless otherwise specified:
a. Resistor values are in ohms.
b. Capacitorvaluesaremicrofarads(uF).
c. Inductor values are in microhenries (uH).
4. On PC board drawings, Square pad indicates:
a. PolarizedCapacitors-Positive
b. Diodes - Cathode
c. Others - Pin 1
5. WARNING
Parts marked with the symbol have critical
characteristics. Use only replacement parts recom-
mended by the manufacturer.
NOTES
PowerOutputStereo
Minimum sine wave continuous average power output
per channel, both channels operating is:
75 watts into 4, 8 or 16 ohm load
PowerOutputMono(Parallel)
Minimum sine wave continuous average power output
is:
150 watts into 2 ohm, 4 ohm or 8 ohm load
OutputLoadImpedance
4, 8, or 16 ohm (Stereo Mode)
2, 4, or 8 ohm (Mono Mode)
RatedPowerBand
20Hzto20,000Hz
TotalHarmonicDistortion
MaximumTotal HarmonicDistortionat any power level
from 250 milliwatts to rated power output is 0.5%
IntermodulationDistortion
Maximum Intermodulation Distortion if instantaneous
peak output per channel does not exceed twice the rated
output, for any combination of frequencies from 20Hz to
20,000Hz, with both channels operating is 0.5%
A-WeightedSignalToNoise Ratio
100dB
FrequencyResponse
+0,-0.5dBfrom20Hzto20,000Hz
+0,-3dBfrom10Hzto70,000Hz
Sensitivity
1.2 Volt unbalanced inputs
2.5 Volt balanced inputs
WideBandDampingFactor
Greaterthan14
InputImpedance
90,000 ohms unbalanced
180,000balanced
TubeCompliment
3 - 12AX7A Inputs and Phase Inverters
4-12AT7 VoltageAmplifier and Drivers
4- KT88/6550 Power Output
PowerRequirements
100Volts, 50/60Hzat360 watts
110Volts,50/60Hzat 3.6amps
120Volts, 50/60Hz at3.6 amps
220Volts, 50/60Hz at1.8 amps
230Volts, 50/60Hz at1.8 amps
240Volts, 50/60Hz at1.8 amps
Note: Refer to the right side panel of the MC275 for the correct
voltage.
OverallDimensions
Width is 16-1/2 inches (41.91cm),Heightis 8-1/4 inches
(20.96cm)including feet, Depthis 12 inches(30.48cm)
Weight
67 pounds (30.5kg) net, 75 pounds (34.lkg) in shipping
carton

3
SECTION LOCATIONS
BOTTOM VIEW WITH COVER REMOVED
TOP VIEW WITH COVER REMOVED
TERMINAL
BLOCK
AMPLIFIER
PCB
2
INPUT
PCB
3
KT88 (4X)
OUTPUT
TRANSFORMER
1
POWER
TRANSFORMER
1
12AT7
12AT7
12AX7A
12AX7A
CHOKE
FILTER
MC275

BLOCK DIAGRAM
4

5 6
MC275
INTERCONNECT
1

7 8
AMPLIFIER 750675
2A

AMPLIFIER 750675
2B
910
AMPLIFIER 750675
2
MC275

11
INPUT 750082
3
12

13
PARTS LIST
MC275
1
2
Ref. No. Description Part No.
INTERCONNECT
F1 FUSE 4A 250V SLO-BLO 5X20 IEC 089135
L1 CHOKE FILTER 0.5H 800MA SLOTS 122379
RT1 ASSEMBLY THERMISTOR CL-40 5R 052008
S1 CABLEASSYPWR SWCH 171729
T1 POTTED TRANSFORMER POWER 750086
T2 POTTED TRANSFORMER OUTPUT 750085
T3 POTTED TRANSFORMER OUTPUT 750085
750675AMPLIFIERPCB
C1 CAP ELECT 47UF 450V 066560
C2 CAP MPF 0.1UF 630VDC 064431
C3 CAP MPF 0.1UF 630VDC 064431
C4 CAP ELECT 100UF 25V 066573
C5 CAP ELECT 100UF 25V 066573
C6 CAP MPF 0.1UF 5% 63VDC 064325
C7 CAP MPF 0.1UF 5% 63VDC 064325
C8 CAP MPF 0.1UF 5% 63VDC 064325
C9 CAP MPF 0.1UF 5% 63VDC 064325
C10 CAP ELECT 470UF 16V 066508
C11 CAP ELECT 470UF 16V 066508
C12 CAP PF 0.001UF 5% 63VDC 064453
C13 CAP PF 0.001UF 5% 63VDC 064453
C14 CAP MPF 0.0022UF 5% 63VDC 064454
C15 CAP MPF 0.0022UF 5% 63VDC 064454
C16 CAP MPF 0.1UF 630VDC 064431
C17 CAP MPF 0.1UF 630VDC 064431
C18 CAP MPF 0.1UF 630VDC 064431
C19 CAP MPF 0.1UF 630VDC 064431
C20 CAP ELECT 470UF 50V 066469
C21 CAP ELECT 470UF 50V 066469
C22 CAP POLYPROP 0.22UF 20% 1KVDC 064432
C23 CAP POLYPROP 0.22UF 20% 1KVDC 064432
C24 CAP POLYPROP 0.22UF 20% 1KVDC 064432
C25 CAP POLYPROP 0.22UF 20% 1KVDC 064432
C26 CAP POLY .047UF 10% 1000VDC 064434
C27 CAP POLYPROP .047UF 10% 250VDC 064364
C28 CAP ELECT 680UF 315V 066549
C29 CAP ELECT 680UF 315V 066549
C30 CAP ELECT 4700UF 35V 066541
C31 CAP ELECT 680UF 315V 066549
C32 CAP ELECT 680UF 315V 066549
C33 CAP ELECT 47UF 450V 066560
C34 CAP ELECT 47UF 450V 066560
C35 CAP ELECT 47UF 450V 066560
C36 CAP MPF 0.22UF 5% 63VDC 064329
C37 CAP MPF 0.22UF 5% 63VDC 064329
D1 DIODE ZENER 200V 1.5W 070177
D2 DIODE ZENER 200V 1.5W 070177
D3 DIODE ZENER 200V 1.5W 070177
D4 DIODE ZENER 200V 1.5W 070177
D5 DIODE ZENER 200V 1.5W 070177
D6 DIODE ZENER 200V 1.5W 070177
D7 DIODE ZENER 200V 1.5W 070177
D8 DIODE ZENER 200V 1.5W 070177
D9 DIODE ZENER 200V 1.5W 070177
D10 DIODE BRIDGE RECT 1000V 6A 070180
D11 DIODE SIL 400 PIV @ 1.5A 070031
D12 DIODE SIL 400 PIV @ 1.5A 070031
D13 DIODE RECTIFIER 070178
D14 DIODE RECTIFIER 070178
F1 FUSE 2A 250V SLO-BLO 5X20 IEC 089123
F2 FUSE 2A 250V SLO-BLO 5X20 IEC 089123
F3 FUSE T8AL 250V SLO-BLO 5X20 IEC 089134
F4 FUSE T8AL 250V SLO-BLO 5X20 IEC 089134
J1 CONN MALE 6 POS FRICTION LOCK 117218
J2 CONN 3 POS MALE MTS100 NORMAL 117214
J3 CONN 3 POS MALE MTS100 NORMAL 117214
J4 BLADE FASTON W/FEET 117708
J5 BLADE FASTON W/FEET 117708
J6 BLADE FASTON W/FEET 117708
J7 BLADE FASTON W/FEET 117708
J8 BLADE FASTON W/FEET 117708
J9 BLADE FASTON W/FEET 117708
J10 BLADE FASTON W/FEET 117708
J11 BLADE FASTON W/FEET 117708
J12 BLADE FASTON W/FEET 117708
J13 BLADE FASTON W/FEET 117708
J14 BLADE FASTON W/FEET 117708
J15 BLADE FASTON W/FEET 117708
J16 BLADE FASTON W/FEET 117708
J17 BLADE FASTON W/FEET 117708
J18 BLADE FASTON W/FEET 117708
J19 BLADE FASTON .187 117726
J20 BLADE FASTON .187 117726
J21 BLADE FASTON W/FEET 117708
J22 BLADE FASTON W/FEET 117708
J23 BLADE FASTON W/FEET 117708
J24 BLADE FASTON W/FEET 117708
J25 BLADE FASTON W/FEET 117708
J26 BLADE FASTON W/FEET 117708
J27 BLADE FASTON W/FEET 117708
J28 BLADE FASTON W/FEET 117708
J29 BLADE FASTON W/FEET 117708
J30 BLADE FASTON W/FEET 117708
J31 BLADE FASTON W/FEET 117708
J32 BLADE FASTON W/FEET 117708
L1 CHOKE 2.2 UH 122405
L2 CHOKE 2.2 UH 122405
L3 CHOKE 2.2 UH 122405
L4 CHOKE 2.2 UH 122405
R1 RES MF 1M 1% 1/4W 144577
R2 RES MF 1M 1% 1/4W 144577
R3 RES MF 221K 1% 1/4W 144629
R4 RES MO 100K 5% 2W 144698
R5 RES MO 100K 5% 2W 144698
R6 RES MF 221K 1% 1/4W 144629
R7 RES MF 221K 1% 1/4W 144629
R8 RES MF 221K 1% 1/4W 144629
R9 RES MF 1K 1% 1/4W 144513
R10 RES MF 1K 1% 1/4W 144513
R11 RES MF 100K 1% 1/2W 144635
R12 RES MF 100K 1% 1/2W 144635
R13 RES MF 1M 1% 1/4W 144577
R14 RES MF 1M 1% 1/4W 144577
R15 RES MF 1M 1% 1/4W 144577
R16 RES MF 1M 1% 1/4W 144577
R17 RES MF 10K 1% 1/4W 144504
R18 RES MF 10K 1% 1/4W 144504
R19 RES MF 10K 1% 1/4W 144504
R20 RES MF 10K 1% 1/4W 144504
R21 RES MF 100 OHM 1% 1/4W 144568
R22 RES MF 100 OHM 1% 1/4W 144568
Ref. No. Description Part No.

14
PARTS LIST con’t
3
R23 RES MF 100 OHM 1% 1/4W 144568
R24 RES MF 100 OHM 1% 1/4W 144568
R25 RES MF 8.25K 1% 1/4W 144549
R26 RES MF 8.25K 1% 1/4W 144549
R27 RES MF 121K OHM 1% 1/2W 144588
R28 RES MF 121K OHM 1% 1/2W 144588
R29 RES MF 121K OHM 1% 1/2W 144588
R30 RES MF 121K OHM 1% 1/2W 144588
R31 RES 698 OHM 1% 1/4W 144511
R32 RES 698 OHM 1% 1/4W 144511
R33 RES 698 OHM 1% 1/4W 144511
R34 RES 698 OHM 1% 1/4W 144511
R35 RES MF 2.21M 1% 1/4W 144576
R36 RES MF 2.21M 1% 1/4W 144576
R37 RES MF 2.21M 1% 1/4W 144576
R38 RES MF 2.21M 1% 1/4W 144576
R39 RES MF 221K 1% 1/4W 144629
R40 RES MF 221K 1% 1/4W 144629
R41 RES MF 221K 1% 1/4W 144629
R42 RES MF 221K 1% 1/4W 144629
R43 RES MF 10K 1% 1/4W 144504
R44 RES MF 10K 1% 1/4W 144504
R45 RES MF 10K 1% 1/4W 144504
R46 RES MF 10K 1% 1/4W 144504
R47 RES MO 46.4K 1% 1W 144637
R48 RES MO 46.4K 1% 1W 144637
R49 RES MO 46.4K 1% 1W 144637
R50 RES MO 46.4K 1% 1W 144637
R51 RES MF 90.9K 1% 1/4W 144557
R52 RES MF 90.9K 1% 1/4W 144557
R53 RES MF 1M 1% 1/4W 144577
R54 RES MF 1M 1% 1/4W 144577
R55 RES MF 1M 1% 1/4W 144577
R56 RES MF 1M 1% 1/4W 144577
R57 RES MF 200K 1% 1/4W 144531
R58 RES MF 200K 1% 1/4W 144531
R59 RES MF 200K 1% 1/4W 144531
R60 RES MF 200K 1% 1/4W 144531
R61 RES MO 100K 5% 2W 144698
R62 RES MO 100K 5% 2W 144698
R63 RES MO 100K 5% 2W 144698
R64 RES MO 100K 5% 2W 144698
R65 RES MO 100K 5% 2W 144698
R66 RES MO 100K 5% 2W 144698
R67 RES MO 100K 5% 2W 144698
R68 RES MO 100K 5% 2W 144698
R69 RES WW 220 OHM 10% 5W 139256
R70 RES WW 220 OHM 10% 5W 139256
R71 RES WW 220 OHM 10% 5W 139256
R72 RES WW 220 OHM 10% 5W 139256
R73 RES MO 10K 5% 2W 144638
R74 RES MO 2.2K 5% 2W 144666
R75 RES MO 100K 5% 2W 144698
R76 RES MO 100K 5% 2W 144698
(F1) HOLDER FUSE 5X20MM PCB MOUNT 178159
(F2) HOLDER FUSE 5X20MM PCB MOUNT 178159
(F3) HOLDER FUSE 5X20MM PCB MOUNT 178159
(F4) HOLDER FUSE 5X20MM PCB MOUNT 178159
(V1) SOCKET 9 PIN TUBE CERAMIC 178170
(V2) SOCKET 9 PIN TUBE CERAMIC 178170
(V3) SOCKET 9 PIN TUBE CERAMIC 178170
(V4) SOCKET 9 PIN TUBE CERAMIC 178170
(V5) SOCKET 9 PIN TUBE CERAMIC 178170
(V6) SOCKET 9 PIN TUBE CERAMIC 178170
(V7) SOCKET 9 PIN TUBE CERAMIC 178170
(V8) SOCKET OCTAL TUBE CERAMIC 178169
(V9) SOCKET OCTAL TUBE CERAMIC 178169
(V10) SOCKET OCTAL TUBE CERAMIC 178169
(V11) SOCKET OCTAL TUBE CERAMIC 178169
750082 INPUT PCB
J1 JACK PHONO GOLD 117862
J2 XLR FEMALE HORIZ PCB WITH LATCH 117814
J3 XLR FEMALE HORIZ PCB WITH LATCH 117814
J4 CONN 3 POS MALE MTS100 NORMAL 117214
J5 CONN 3 POS MALE MTS100 NORMAL 117214
J6 CONN MALE 6 POS FRICTION LOCK 117218
R1 RES MF 221K 1% 1/4W 144629
R2 RES MF 100K 1% 1/4W 144528
R3 RES MF 221K 1% 1/4W 144629
R4 RES MF 100K 1% 1/4W 144528
S1 SWITCH SLIDE DPDT 148076
S2 SWITCH SLIDE DPDT 148076
Ref. No. Description Part No. Ref. No. Description Part No.

15 16
EXPLODEDVIEW and PARTS LIST
1 005653 CHASSIS
2 005650 RCASPACER
3 101197 SCREW HI/LO 4-24 X 3/8 PH RD BLK
4 404007 WASHER LOCK 6 X .288 INT STAR
5 104165 WASHER 3/8 INTERNAL TOOTH GOLD
6 402003 NUT KEP 6-32
7 750082 ASSY INPUT PCB
8 084219 POST BINDING DUAL 4MM THREAD
9 404198 LOCK WASHER
10 410015 NUT M4 INT STAR SS
12 171729 CABLE ASSYPOWER SWITCH
13 104165 WASHER 3/8 INT TOOTH GOLD
19 400157 SCREW MACH 6-32 X 1/4 PH PN
20 114012 BALL STUD
21 165065 TUBE 12AX7A McINTOSH
22 165067 TUBE 12AT7
23 165070 TUBE KT88 WITH McINTOSH LOGO
24 017761 AIR PIPE
25 400292 SCREW MACH 6-32 X 3/8 PH FH BLK
26 750085 POTTED TRANSFORMER OUTPUT
27 750086 POTTED TRANSFORMER POWER
28 166126 DECAL OUTPUT TRANSFORMER
29 166127 DECAL POWER TRANSFORMER
30 005651 TUBE COVER
31 017862 PUSH-ON FOOT
32 125667 NAMEPLATE
33 106012 SPRING CLIP: PUSH-ON
35 017452 KLIP WIRE
36 178161 HOLDER FUSE 5 X 20mm IEC
37 404016 WASHER INT STAR .5 X .630 X .022
38 102006 NUT MACH 10-32 W/LOCK
39 078024 GROMMET RUBBER 1” ID
40 078025 GROMMET RUBBER 3/4” ID
41 017859 SPACER NYLON 6-32 X 7/16
42 117487 RECEPTACLE AC LINE
43 074091 TERMINAL BLOCK AC
Ref.No. DescriptionPartNo.
44 404001 WASHER FLAT STEEL 4 X 9/32 X .025
45 402022 NUT MACH 4-40 X 3/16 X 1/16
46 122379 CHOKE FILTER
47 402005 NUT MACH 8-32 W/LOCK
48 005425 SUPPORT BRACKET
49 750675 ASSYAMPLIFIER PCB
50 005426 BOTTOM COVER
51 401078 SCREW TAP 8-32 X 5/16 PH PN BLK
52 017542 PLASTIC FOOT
53 400153 SCREW MACH 8-32 X 1/2 PH PN
54 401109 SCREW TT 6-32 X 5/16 PH PN BLK
MC275

REPACKING INSTRUCTIONS
17
The continuous improvement of its products is the policy of McIntosh Laboratory Incorporated, who reserve the right to improve design without notice.
Because of the constant upgrading of McIntosh products’ circuitry and components, the Company cannot insure, and does not warrant, the accuracy of the
within schematic material, which is intended for information only.
McINTOSH LABORATORY, INC., 2 CHAMBERS STREET, BINGHAMTON, NEW YORK 13903 Printed in U.S.A. Part Number 041046
STEREO POWER AMPLIFIER
SERVICE MANUAL
STARTING WITH SERIAL NO. WV1536
MC275