The McIntosh Audio Compensator is a complete control unit for professional
and home entertainment systems. Five input channels are provided; three which
produce constant amplification over the audio spectrum of 20 cycles to 20, 000
cycles, and two which are equalized for use with magnetic phonograph cartridges.
The C-108 Audio Compensator requires an external power source. A
McIntosh 50W-2, 20W-2, or A-116 Power Amplifier, or D-101 power supply may
be used for this purpose.
UNIT
C-108
C-108a
(C-108 in wooden
enclosure)
C-108h
(C-108 with cabinet
mounting panel
11" x 4-1/4")
1. Connect speaker to output of amplifier.
PHYSICAL SPECIFICATIONS
DIMENSIONS
10" x 3-1/2" x 7-1/2"
11-1/2" x 4-1/4" x 8"
10" x 3-1/2" x 7-1/2"
INSTALLATION WITH McINTOSH AMPLIFIERS
WEIGHT
6 lbs.
7 lbs.
6 lbs.
2. Insert Power Amplifier line cord into socket labeled
"PWR AMP" on C-108.
3. Insert inter-unit cable of C-108 into socket labeled
"PRE-AMP" on power amplifier.
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4. Turn the power amplifier volume control (50W-2 or
20W-2) to full volume setting. The volume control on
the A-116, 30 watt power amplifier, is inoperative
when the pre-amp socket is used and this step may be
disregarded when using this amplifier.
5. Turn the volume control on the C-108 to "OFF".
6. Insert the power cord of the C-108 into a 117 V.A.C.
power outlet.
7. Turn the selector switch of the C-108 to "5" and bass
fully clockwise.
8. Turn the volume control on the C-108 clockwise until
the power switch is activated.
9. Allow thirty seconds for warm-up, then advance the
volume control to full volume.
10. Adjust the hum centering potentiometer on the power
amplifier for minimum hum.
11. Turn the volume control of the C-108 to a minimum
and all other controls to the desired settings.
12. Insert inputs into their proper jacks at the rear of
the C-108.
INSTALLATION WITH McINTOSH D-101 POWER SUPPLY
1. Connect speaker to power amplifier.
2. Insert power amplifier power cord in socket labeled
"PWR AMP" on D-101.
3. Insert D-101 power cord into socket labeled "PWR
AMP" of the C-108.
4. Insert inter-unit cable of C-108 into socket labeled
"PRE-AMP" of the D-101.
5. Connect "OUTPUT" of D-101 to the input of power
amplifier (socket labeled "PRE-AMP" on McIntosh
Power Amplifier). J-107 series cables may be used
for this purpose.
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6. Follow steps 4 through 9 above.
7. Adjust the hum centering potentiometer on the D-101
for minimum hum.
8. Follow steps 11 and 12 above.
INPUT CONNECTING PROCEDURE
The inherent hum and noise voltages applied to the input of the C-108 is
-110 DBM, or less than 3 microvolts. To avoid lowering the signal to hum ratio
of the C-108 by adding hum voltages to the input, extreme care must be taken in
its installation. We offer the following recommendations as a guide to installa-
tion:
1. Connect input to C -108 as outlined on the table
below.
High Level Magnetic
cartridges. (Terminated for
Pickering Cartridge)
Low Level magnetic
cartridges.
(Terminated for
Audax polyphase
cartridge and
Weathers FM
cartridge.)
INPUT
(For 3 v. output)
Min. Max.
.1V 20 V.
12 MV. 60 MV.
30 MV. .15 V.
12 MV. 60 MV.
GAIN
30 db
48 db
40 db from
Turn-over to
20,000 cps.
48 db from
Turn-over to
20,000 cps.
FREQUENCY
RESPONSE
(20-20,000 cps.)
+ .25 db
+ .25 db
Rises at the
rate of 6 db
per octave below turn-over
frequency to
20 cps.
REMARKS
Input levels in excess of . 1V should
be reduced by
potentiometer on
back panel.
Input not to exceed
60 MV.
Cartridge of other
manufacturers may
be used but input
must be terminated
as recommended by
manufacturer. Alter
R6 & R7 or R8.
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2. The C-108 and magnetic phonograph cartridges should
be mounted at least two feet from power transformers.
3. Inter-unit cables provide a complete ground system.
Alternate ground wires create ground loops which will
usually increase hum level.
4. The heaters of the 12AX7 tubes used in the C-108 are
returned to ground through a hum balancing potentiometer in the power amplifier (or D-101 power supply if
used). This control requires an initial adjustment for
minimum hum, and should be readjusted each time one
or more tubes are replaced.
5. Grounding the turntable motor frame to the C-108
chassis near the input jacks may reduce the hum level
on the phonograph channels.
The output stage of the C-108 is a cathode follower. The generator resis-
tance of this tube is 600 ohms, but should not be loaded with a capacitive reactance
of less than 10, 000 ohms at 20, 000 cycles. This is the reactance presented by
750 micromicrofarads, and is equal to that of a cable 30 feet long and having a
capacity of 25 mmf per foot. Under special circumstances where the C-108 must
be connected to the power amplifier by a longer cable, either lower capacity
must be employed, or the output must be reduced.
REDUCE TURNTABLE RUMBLE,
OR LOW FREQUENCY DISTURB-
ANCES ON ALL CHANNELS.
SELECT DESIRED BASS
COMPENSATION ON
CHANNELS 4 AND 5.
OPERATION
SELECT DESIRED TREBLE
ROLL-OFF ON ALL CHANNELS.
COMPENSATE FOR EAR
CHARACTERISTIC AT
REDUCED VOLUME ON
ALL CHANNELS.
SELECT ANY ONE OF FIVE
INPUT CHANNELS. UNUSED
CHANNELS ARE GROUNDED
TO PREVENT CROSSTALK.
CONTROL BASS RESPONSE
ON ALL CHANNELS.
CONTROL TREBLE RESPONSE
ON ALL CHANNELS.
CONTROL VOLUME ON
ALL CHANNELS. ON-OFF
CONTROL FOR C-108
AND ITS POWER SUPPLY.
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Channels 1 and 2:
Channels 1 and 2 are each terminated by a potentiometer. These potentiom-
eters are screw driver adjustments on the back panel and should be used to reduce
signal input to these channels if in excess of . 1 volts. Correct adjustment occurs
when the sound level of channels 1 and 2 is equivalent to that of channels 4 or 5.
High impedance sources, such as crystal microphones and the detector output of
tuners, may be connected directly to these channels since they have an input
impedance of 660, 000 ohms.
Channel 3:
Channel 3 is a high gain microphone channel having an input impedance of
100, 000 ohms. The input to this channel should not exceed 60 MV. Low impedance
microphones in conjunction with an input transformer, such as the McIntosh M-107
(ATI-1), may be used on this channel.
Channels 1, 2 and 3 provide flat amplification from 20 cycles to 20, 000
cycles with the bass and treble controls in their central position, and the treble
compensation switches in the up position. These controls may be used to alter the
response of these channels as shown on page 9.
Channels 4 and 5:
Channels 4 and 5 are equalized for use with magnetic phonograph cartridges.
The degree of equalization may be varied with the bass and treble compensation
switches as shown on pages 8 and 9. The bass and treble tone controls may be
used to supplement these compensation switches.
The inputs of channels 4 and 5 have been terminated to give flat response from
the Pickering and Audax Polyphase cartridges respectively. If cartridges of other
manufacturers are used, the terminating resistors should be replaced by values
recommended by the manufacturer. For example, the 47, 000 ohm terminating
resistance of channel 5 should be replaced by 12, 000 ohms if the G.E. reluctance
cartridge is used. If it is desirable not to alter the C-108 an 18, 000 ohm resistor
may be connected across the G.E. cartridge in the line to the cartridge.
Page 8
— 6 —
The Aural Compensator may be used to compensate for the response characteristic of the ear as loudness is adjusted. The response of this control is
plotted on page 9. This control should not be used until all other adjustments
have been made.
The Rumble Filter may be used to eliminate turntable rumble and other low
frequency disturbances. The response of this control is plotted on page 9.
An additional output jack has been provided at the rear of the C-108. This
jack may be used for recording tape while the signal is being monitored by the
power amplifier. The selector switch, rumble filter, and bass compensation
switches are effective at the auxiliary output.
GUARANTEE
We guarantee the performance of the C-108 and the mechanical and electrical workmanship to be free of serious defects for a period of 90 days with the
exception that we do not guarantee the tubes and filter capacitor beyond that of
their manufacturers.
McINTOSH LABORATORY, INC
320 Water Street
Binghamton, New York
Page 9
For convenience of installation, we have made the following connectors and
cables available from your dealer.
- 7 -
J-100 Output Plug
J-101 Input plug
*J-102 J-100 Output plug fitted with 6 foot length of two
conductor cable, connected for 4 ohm output of
McIntosh 50W-2 or 20W-2.
*J-103 Same as J-102, but connected for 8 ohms.
*J-104 Same as J-102, but connected for 16 ohms.
*J-105 Same as J-102, but connected for 32 ohms.
* For use with 20W-2 or 50W-2 Amplifiers only.
J-109 J-100 output plug fitted with 6 foot length of two
conductor cable connected for 4 ohm output of
McIntosh A-116.
J-110 Same as J-109, but connected for 8 ohms.
J-111 Same as J-109, but connected for 16 ohms.
J-106 Same as J-102, but connected for 600 ohms, for
use with 50W-2, 20W-2 or A-116.
J-107 J-101 input plug fitted with 6 feet of 25 MMF
capacity per foot cable and phono pin jack. For
2.5V input of 50W-2, 20W-2, or A-116.
J-101
J-103
J-104
J-105
J-106
J-101
J-100
J-107a Same as J-107, but 12 ft. long.
J-107b Same as J-107, but 18 ft. long.
J-107c Same as J-107, but 24 ft. long.
J-107d Same as J-107, but 30 ft. long.
J-108 Phono pin jack fitted with 6 feet of 25 MMF capa-
city per foot cable, with shield and center
conductor stripped and tinned.
J-112 Input plug fitted with 6 feet of 25 MMF capacity
per foot cable and phono pin jack. For . 5V input
of A-116.
J-107
J-107a
J-107b
J-107c
J-107d
J-108
Page 10
8
-
Page 11
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10-21-53
AUDIO COMPENSATOR
CONTROL POSITION
CONTROL CURVES FOR MODEL C-108
EQUALIZATION CONTROLS
MCINTOSH LABORATORY, INC.
(ALL CHANNELS)
RUMBLE FILTER
(ALL CHANNELS)
TONE CONTROLS
(ALL CHANNELS)
AURAL COMPENSATOR
Page 12
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10-13-53
MCINTOS H LABORATORY , IN C
C-10 8 AUDI O COMPENSATO R
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