McIntosh MC-2125 User Manual
THE MclNTOSH MC 2125 SOLID STATE STEREO POWER AMPLIFIER
Reading Time: 31 Minutes
Price $1.25
Your MC 2125 Stereo Power Amplifier
will give you many years of pleasant
and satisfactory performance. If you
have any questions, please contact:
CUSTOMER SERVICE
Mclntosh Laboratory Inc.
2 Chambers Street
Binghamton, New York 13903
Phone: 607-723-3512
WARNING: TO PREVENT FIRE OR SHOCK
HAZARD, DO NOT EXPOSE THIS UNIT TO
RAIN OR MOISTURE.
Take Advantage of 3 years
of FREE Service ...
Fill in the Application NOW.
Contents
SERVICE . . . . 1
INSTALLATION . . . . 2
HOW TO CONNECT . . . . 4
FRONT PANEL INFORMATION . . . . 8
REAR PANEL INFORMATION . . . . 10
PERFORMANCE LIMITS AND RATINGS . . . . 11
PERFORMANCE CHARTS . . . . 12
TECHNICAL DESCRIPTION . . . . 14
BLOCK DIAGRAM . . . . 16
THREE YEAR SERVICE CONTRACT
An application for a FREE THREE YEAR SERVICE CONTRACT is included with this manual.
The terms of the contract are:
1. Mclntosh will provide all parts, materials and labor
needed to return the measured performance of the Instrument to the original performance limits free of any
charge. The SERVICE CONTRACT does not cover any
shipping costs to and from the authorized service
agency or the factory.
2. Any Mclntosh authorized service agency will repair all
Mclntosh instruments at normal service rates. To receive the free service under the terms of the SERVICE
CONTRACT, the SERVICE CONTRACT CERTIFICATE must
accompany the instrument when taken to the service
agency.
3. Always have service done by a Mclntosh authorized
service agency. If the instrument is modified or damaged, as a result of unauthorized repair the SERVICE
CONTRACT will be cancelled. Damage by improper use
or mishandling is not covered by the SERVICE CONTRACT.
The SERVICE CONTRACT is issued to you as the original
purchaser. To protect you from misrepresentation this
contract cannot be transferred to a second owner.
For your protection Mclntosh selects only dealers who
have technical competence to guide purchasers fairly,
and provide service when necessary. To receive the
SERVICE CONTRACT your purchase must be made from
a Mclntosh franchised dealer.
Your completely filled in application for a SERVICE
CONTRACT must be postmarked within 30 days of
the date of purchase of the instrument.
To receive the SERVICE CONTRACT all information on
the application must be filled in. The SERVICE CONTRACT will be issued when the completely filled in
application is received at Mclntosh Laboratory Incorporated in Binghamton, New York.
Copyright © 1976 by Mclntosh Laboratory Inc.
1
INPUT
STEREO OR TWIN AMPLIFIER OPERATION
Use shielded cables to connect the signal from the preamplifier or signal source to the power amplifier. To minimize the possibility of hum the shielded cables should be
run parallel to each other or loosely twisted together. Locate the cables away from speaker leads and AC power
cords. All connections are made on the back panel of the
MC
2125.
For stereo operation, the left output of the preamplifier
should be plugged into the Left input jack of the power
amplifier. The right output of the preamplifier should be
plugged into the Right (MONO) input jack of the power
amplifier.
In stereo or twin amplifier operation the MODE SWITCH
must be in the STEREO position. For twin amplifier operation a separate signal source can be connected to each
input.
MONOPHONIC OR SINGLE CHANNEL OPERATION
A shielded cable from the signal source is plugged into
the Right (MONO) input |ack of the MC 2125 only. The
MODE SWITCH on the back panel of the amplifier must be
placed in the MONO position. In the MONO position the
output of the right channel input amplifier is fed to both
left and right power amplifiers. The Left INPUT is disconnected. Only the signal fed into the Right (MONO) input
will be amplified. Should the MODE SWITCH be left in the
STEREO position and the output transformers remain
strapped for a monophonic load, one channel will attempt
to drive the other which causes high circulating currents
and overheating.
Be certain that the MC 2125 is never operated in the
stereo mode with the outputs connected for monophonic
operation.
speaker should be twin conductor or twisted together. Use
lamp cord, bell wire, or wire with similar type of insulation
to connect the speakers to the amplifier. For the normally
short distances of under 20 feet between the amplifier and
speaker, #18 wire or larger can be used. For distances
over 20 feet between the amplifier and speaker use larger
diameter wire. Select the correct size wire for the wire distance from the chart. It is recommended that the DC resistance of the speaker leads not be over 5% of the speaker
impedance. Up to 10% can be tolerated. Resistance of the
leads should be computed for the length of wire both to
and from the speaker or speakers.
Be certain the loudspeakers connected to the MC 2125
are capable of handling the power output of the am
plifier.
STEREO OR TWIN AMPLIFIER OPERATION
Check the impedance of the speaker which is usually
identified on the speaker itself or in the speaker owner's
manual. Connect a lead from the common terminal of the
left speaker to the amplifier LEFT OUTPUT terminal strip
COMmon screw. Connect another lead from the other termi-
nal of the left speaker to the screw with the number corresponding to the speaker impedance on the LEFT OUTPUT
terminal strip. The right channel speaker is connected in
the same manner on the RIGHT OUTPUT terminal strip. For
stereo or twin channel operation it is not necessary to use
the same impedance loudspeaker on each output. Connect
each channel for the impedance desired. Full power will
be delivered to each properly connected speaker.
When multiple speakers are to be connected to either or
both outputs, the combined load impedance must be calculated. The load must be connected to the appropriate im-
pedance tap. Use this table to aid in selecting the correct
impedance match:
OUTPUT
For multiple speaker operation, run separate leads from
the amplifier to the speakers. Because of the high power
available from the MC 2125, be sure to use large diameter
speaker leads. In all cases, the leads to and from the
4
Load
impedance
in ohms
1.6 to 3.2
3.2 to 6.4
Connect for
2 ohm output
4 ohm output
Load
impedance
in ohms
6.4 to 13
13 and up
Connect for
8 ohm output
16 ohm output
If a load impedance is used that is lower than the output
impedance tap, then reduced power and possible distortion
will result If a load impedance is used that is higher than
the output impedance tap, then neither the signal nor the
amplifier will be harmed but the power available is limited.
FOR STEREO OR TWIN AMPLIFIER CONSTANT VOLTAGE
OPERATION:
For output
voltage of Connect for
25 volts 8 ohms
MONOPHONIC OR SINGLE CHANNEL OPERATION
When the MC 2125 is used as a monophonic or single
channel power amplifier the two channels are combined to
produce output up to 240 watts. The outputs must be tied
together at the appropriate load impedance tap. In connect-
ing a load to the MC 2125 for single channel operation
connect the common side of the load to the LEFT CHANNEL
OUTPUT terminal marked COM., the other lead is connected:
If the speaker
or load
impedance is
1 ohm
2 ohms
4 ohms
8 ohms
The hot side
of the line is
connected to
Left 2
Left 4
Left 8
Left 16
Connect a jumper
wire between
Left 2 and Right 2
Left 4 and Right 4
Left 8 and Right 8
Left 16 and Right 16
Do not connect unequal impedance taps together
If the load impedance is between any of the above fig-
ures, select the best impedance match from:
Load
impedance
in ohms
0.8 to 1.6
1.6 to 3.2
FOR MONOPHONIC CONSTANT VOLTAGE LINE
OPERATION
For output
voltage of Connected for
25 volts 4 ohm output (mono)
For multiple speaker operation, run separate leads from
the amplifier to the speakers. Should the MODE SWITCH be
left in the STEREO position and the output transformers
be strapped to a monophonic load, one channel will attempt
to drive the other and cause circulating currents and
overheating. Be certain that the MC 2125 is never operated in the stereo mode with the outputs connected for
monophonic operations.
Connect for
1 ohm output
2 ohm output
Load
impedance
in ohms
3.2 to 6.4
6.4 and up
Connect for
4 ohm output
8 ohm output
AC POWER
The MC 2125 operates on 120 volts 50/60 Hz. The aux-
iliary AC OUTLET on the MC 2125 is not fused or switched.
Wire
Gauge
22
20
18
16
14
12
10
For 4
Feet
6
10
15
25
40
60
100
MAXIMUM
Ohm Load
Meters
1.83
3.05
4.57
7.62
12.19
18.29
30.48
WIRE
For
Feet
12
20
30
50
80
120
200
LENGTHS
8 Ohm Load
Meters
3.66
6.10
9.14
15.24
24.38
36.58
60.96
For 16
Feet
24
40
60
100
160
240
400
Ohm Load
Meters
7.32
12.20
18.30
30.50
48.80
73.20
122.00
These wire lengths represent the wire resistance equal to 5% of the speakers im-
pedance. Use of smaller wire sizes will produce more resistance which causes more
power loss and less loudspeaker damping.
5
Stereophonic
Connections
PROGRAM SOURCE
LEFT
SPEAKER
MUST BE IN STEREO
POSITION FOR STEREO
PROGRAMS
RIGHT
SPEAKER
STEREO
MODE
SWITCH
MONO
6
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