INSTRUCTION MANUAL
MclNTOSH MODEL C-8 and C-8P
AUDIO COMPENSATORS
McINTOSH LABORATORY, INC.
320 Water St. Binghamton, N. Y.
U.S.A.
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INSTRUCTION MANUAL
McINTOSH MODEL C-8 and C-8P
AUDIO COMPENSATORS
The McIntosh Audio Compensator is a complete control unit for professional
or home entertainment systems. The Model C-8 derives its power from any
McIntosh power amplifier: the Model C-8P is self-powered.
Five input channels are provided: three which produce constant amplification over the audio spectrum of 20-20, 000 cycles, and two which are equalized for
magnetic phonograph cartridges.
THE AUDIO COMPENSATOR IS A COMPLETE PRE-AMPLIFIER AND
RECORD COMPENSATOR: THEREFORE, THE USE OF AN AUXILIARY EQUALIZER OR PRE-AMPLIFIER WITH THIS UNIT IS NOT RECOMMENDED.
INSTALLATION OF MODEL C-8 and C-8P,
AUDIO COMPENSATORS
The C-8 and C-8P Audio Compensator may be mounted in any type equipment cabinet, relay rack panel, door, wall, etc., or in its own cabinet for chair
side operation. It is not necessary to disassemble the Audio Compensator for
mounting. Cut a rectangular hole in the panel to be used for mounting, insert the
Audio Compensator, and secure with wood or machine screws. Mounting tem-
plates are provided with this manual for the C-8 and C-8P.
When installing the C-8P, the power supply section should be mounted at
least two feet from the Audio Compensator.
After these units have been secured in their desired location, proceed as
follows:
1. Connect speaker to output of power amplifier.
2. Insert power amplifier line cord into one of the Auxiliary A.C.
receptacles provided at the rear chassis of the Audio Compensator.
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3. C-8: Connect inter-unit cable to socket labeled "PRE-AMP.
INPUT" on McIntosh power amplifiers.
CAUTION: THE INTER-UNIT CABLE MUST NOT BE REMOVED
FROM THE C-8.
C-8P: Insert cable of D-8 power supply into socket labeled "INTERUNIT CABLE" on C-8P. Connect audio cable provided between
RETMA pin jack labeled "MAIN OUTPUT" on C-8P and 2.5V input
of power amplifier. (Socket labeled "PRE-AMP INPUT" on McIntosh
power amplifiers.)
4. The Audio Compensator delivers 2.5 volts of audio signal at full
output. The gain control of the power amplifier should be
adjusted as outlined in the amplifier instruction manual for this
sensitivity.
5. Turn the volume control on the Audio Compensator to "OFF".
6. Insert power cord of the Audio Compensator into a 117 V.A.C.
power outlet.
7. Turn the Selector switch on the Audio Compensator to "5" and
Bass control fully clockwise.
8. Turn the volume control on the Audio Compensator clockwise
until the power switch is activated. Allow thirty seconds for
warm-up, then advance the volume control to "10".
9. C-8: Adjust the hum reducing potentiometer on the power
amplifier for minimum hum.
C-8P: Adjust the hum reducing potentiometer on the power
supply for minimum hum.
10. Turn the volume control on the Audio Compensator to off.
11. Insert inputs into their proper jacks at the back of the Audio
Compensator, and all A.C. power cords into the A.C. outlets
provided.
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INPUT CONNECTING PROCEDURE
The inherent hum and noise voltages applied to the input of the Audio
Compensator are -110 DBM, or less than 3 microvolts. To avoid lowering the signal to hum ratio of the Audio Compensator, by adding hum voltages to the input,
extreme care must be taken in its installation. We offer the following recommendations as a guide to installation:
1. Connect inputs of Audio Compensator as outlined on the table below.
CHANNEL
1 & 2
3
4
5
FOR USE WITH
AM-FM Tuners
Wire Reproducers
Tape Reproducers
Crystal or Ceramic
cartridges
Crystal Microphones
Low Impedance
Microphone
High level Magnetic
cartridges. (Termi-
nated for Pickering
cartridge)
Low level magnetic
cartridges or amplitude responsive
cartridges such as
FM or ceramic
(FOR 2.5 V. OUTPUT)
INPUT
MIN. MAX.
70 MV. 20 V.
10 MV. 1 V.
30 MV. 150 MV.
10 MV. 50 MV.
GAIN
32 db
50 db
40 db
50 db
REMARKS
Input levels in excess
of .07V should be re-
duced by potentiometers
on back panel.
Input levels in excess
of 10 MV should be
reduced by potentiometer on back panel.
See text for operation
of these channels.
The Audio Compensator and magnetic phonograph cartridges should
be mounted at least two feet from power transformers.
Inter-unit cables provide a complete ground system. Alternate
ground wires create ground loops which will usually increase hum
level.
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4. The heaters of the 12AX7 tubes used in the C-8 are returned to
ground through a hum reducing potentiometer in the power
amplifier. Heaters of tubes used in the C-8P are returned to
ground through a hum reducing potentiometer in the power
supply. 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 Audio Compensator
chassis near the input jacks may reduce the hum level on the
phonograph channels.
OUTPUT CONNECTIONS
Three outputs are provided: one auxiliary and two main outputs.
The auxiliary output may be used for recording tape from any source connected to the Audio Compensator. The Selector switch, Bass and Treble
compensation switches, and Rumble Filter are effective at this output. Adjustment of the Bass and Treble tone controls, Aural Compensator and Volume
control may be made for monitoring purpose and will not affect the recorded
signal. The auxiliary output delivers a signal of one volt.
All controls are effective at the main outputs, which are available at the
octal socket labeled "INTER-UNIT CABLE" between pins #1 and #2 (pin #1 is
ground), and at the RETMA pin jack labeled "MAIN OUTPUT". The inter-unit
cable connecting the C-8 to any McIntosh power amplifier uses the octal socket
output. The pin jack output may be used for driving a second power amplifier
if so desired.
The main and auxiliary output jacks are fed from cathode followers. The
input impedance of devices connected to these outputs should be 50, 000 ohms
or greater, and the capacitive reactance of audio cables connecting these
devices should not be less than 8, 000 ohms at 20, 000 cycles. This is the
reactance of a capacity of 1000 mmf. Audio cable having a capacity of 25 mmf
per foot may be 40 feet long.
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TYPICAL INSTALLATION
AUDIO COMPENSATOR, C-8
TYPICAL INSTALLATION
AUDIO COMPENSATOR, C-8P
(SELF POWERED)
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REDUCE TURNTABLE RUMBLE,
OR LOW FREQUENCY DISTURB-
ANGES ON ALL CHANNELS.
SELECT ANY ONE OF FIVE
INPUT CHANNELS. UNUSED
CHANNELS ARE GROUNDED
TO PREVENT CROSSTALK.
SELECT DESIRED BASS
COMPENSATION ON
CHANNELS 4 AND 5.
CONTROL BASS RESPONSE
ON ALL CHANNELS
SELECT DESIRED TREBLE
ROLL-OFF ON ALL CHANNELS.
CONTROL TREBLE RESPONSE
ON ALL CHANNELS.
COMPENSATE FOR EAR
CHARACTERISTIC AT
REDUCED VOLUME ON
ALL CHANNELS.
CONTROL VOLUME ON
ALL CHANNELS, ON-OFF
CONTROL.
Channels 1 and 2:
Channels 1 and 2 are each terminated by a potentiometer mounted on the back
panel which should be used to reduce signal input to these channels if in excess of
.07 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 terminated by a 100, 000 ohm potentiometer mounted on the back
panel which should be used to reduce signal input to this channel if in excess of
10 MV. Low impedance microphones in conjunction with an input transformer,
such as McIntosh M-107, may be used on this channel.
Channels 1, 2 and 3 provide flat amplification from 20 to 20, 000 cycles. All
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front panel controls are effective, with the exception of the Bass Compensation
switches, and may be used to alter the response as desired.
Channel 4:
Channel 4 is equalized for use with high level magnetic cartridges delivering
30 MV of signal. It is terminated for use with the Pickering cartridge.
Channel 4 may be modified for use with other high level magnetic cartridges by
changing the terminating pad of R6 and R7, or may be used for a second low level
cartridge by replacing R6 and R7 with a single terminating resistor as recommended
by the cartridge manufacturer.
Channel 5:
Channel 5 is equalized for use with low level magnetic cartridges such as
G.E., Audax, or Fairchild with input transformer. A variable terminating con-
trol is provided, and a switch for selecting either magnetic cartridges (velocity
responsive), or amplitude responsive cartridges, such as a ceramic or F.M. type.
When using a magnetic cartridge this switch should be in the "MAG" position
and the control labeled "LOAD" should be adjusted to the resistance recommended
by the manufacturer. High frequency roll-off of the cartridge may be obtained by
decreasing the recommended load. The load control is calibrated from "0" to
"100" with each calibration representing thousands of ohms.
Amplitude responsive cartridges may be used on channel 5 to allow full use
of the extremely flexible compensation available. By placing the slide switch in
position "F.M." and the "LOAD" control to "100", cartridges of this type may be
used.
All controls are effective on channels 4 and 5.
The Bass and Treble compensation switches may be used to compensate
recordings as recommended by the manufacturer or to adjust the compensation for a
more pleasing tonal balance for the listener. The Bass and Treble tone controls
are independent of the compensation switches and may be used as fine adjustments
in conjunction with these switches. In addition, a rumble filter is provided to
reduce turntable "wow" and "rumble".
•
The five position channel Selector switch may be used to select any of the
five input channels available.
The Volume control selects the desired listening level and since it is located
at the output of the Audio Compensator, the high signal to noise ratio of the unit is
maintained at all levels. By properly adjusting the input potentiometer on channels
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1, 2 and 3 the volume level can be held equal for all channels; the signal will
remain at a constant loudness when switching from one channel to another. The
master off-on switch is attached to the volume control. This switch controls the
three auxiliary A.C. outlets on the rear panel of the Audio Compensator as well as
the three auxiliary A.C. outlets on the power supply of the C-8P.
The aural compensator may be used to compensate for the response charac-
teristic of the ear at reduced volume. This control decreases the mid-range
frequencies while leaving the low and high frequencies at relatively constant
intensity. By reducing volume level with this control proper balance of the pro-
gram material can be maintained.
GUARANTEE
We guarantee the performance of this equipment and the mechanical and electrical workmanship to be free of serious defects for a period of 90 days. This
guarantee does not extend to components damaged by improper use nor does it
extend to transportation to and from the factory.
McINTOSH LABORATORY INC.
320 Water Street
Binghamton, N.Y., U.S.A.
ELECTRICAL AND MECHANICAL SPECIFICATIONS
Power Source C-8: Any McIntosh Power Amplifier
C-8P: Self-powered
Output Main: 2. 5 volts
Auxiliary: 1 volt
Input level Channels 1 & 2: 70 MV-20 volts
Channel 3: 10 MV
Channel 4: 30 MV (Magnetic Cartridge)
Channel 5: 10 MV (Magnetic or constant
amplitude cartridge)
Frequency Response See Graphs
Harmonic Distortion Less than . 3% at 2. 5 volts output, 20-20, 000 cycles
Hum and Noise -110 db (2. 5 microvolts) or lower, (referred to input)
0 db =.775 volts
Size C-8: 10" x 3-1/2" x 7-1/2
Front Panel 11" x 4-1/4"
C-8P: Same
D-8 (Power supply section of C-8P): 5-l/2"x4-3/4"x2-3/8"
11
Weight C-8: 6 lbs.
C-8P: 8 lbs.
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VOLTAGE AND RESISTANCE CHART
Resistances measured to ground with pin #4 of inter-unit cable socket shorted to pin #1
D.C. Voltages measured with VTVM to ground using D-8 power supply.
Signal voltage measured with all controls in flat position, 1000 cycle signal of
10 MV in channel 3, volume control fully on, and with a VTVM.
Tube
Input
Tube
Center
Tube
Output
Tube
Pin No.
1
2
3
4 & 5
6
7
8
9
1
2
3
4 & 5
6
7
8
9
1
2
3
4 & 5
6
7
8
9
Resistance
430K
1M
4. 1K
*0-65 ohms
440K
1M
1.8K
*0-65 ohms
110K
440K
330K
*0-65 ohms
110K
200K
102K
*0-65 ohms
340K
**0-l meg
1.8K
*0-65 ohms
12K
1.1M
102K
*0-65 ohms
D.C. Voltage
110V
0
1.2V
*0-4.8 V.A.C.
108V
0
1.2V
*0-6.3 V.A.C.
195V
108V
110V
*0-4.8 V.A.C.
195V
45V
55V
#0-6.3 V.A.C.
160V
0
1.2V
*0-4.8 V.A.C.
95V
25V
350V
*0-6.3 V.A.C.
Signal Voltage
17 MV
10 MV
9.5 MV
--
1.25V
17 MV
0
--
0
1.25V
1.2V
__
0
1.0V
1.1V
--
2.7V
95 MV
14 MV
--
0
2.65
2.85
--
* Depends on position of hum reducing potentiometer.
** Depends on position of Bass potentiometer. 100K, Bass at "0"
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7-7-54
MCINTOSH LABORATORY, INC.
320 Water Street, Binghamton , New Yor k
MODEL C-8P, AUDI O COMPENSATO R
C-l 1.3 45
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