McIntosh MC-2120 User Manual
THE MCINTOSH MC 2120 SOLID STATE STEREO POWER AMPLIFIER
Reading Time: 29 Minutes
Price $1.25
Your MC 2120 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.
THREE YEAR SERVICE CONTRACT
An application for a FREE THREE YEAR SERVICE CONTRACT is included with this manual.
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
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 ac-
company 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 SERV-
ICE CONTRACT.
4. 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.
5. 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.
6. Your completely filled in application for a
SERVICE CONTRACT must be postmarked
within 30 days of the date of purchase of
the instrument.
7. 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 input. 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
2120.
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.
available from the MC 2120, be sure to use large diameter
speaker leads. In all cases, the leads to and from the
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. When using 8 ohm
speakers and for the normally short distances of under 30
feet between the amplifier and speaker, #18 wire or
larger can be used. For distances over 30 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.
For twin amplifier operation a separate signal source
can be connected to each input. In stereo or twin amplifier
operation the MODE SWITCH must be in the STEREO position.
MONOPHONIC OR SINGLE CHANNEL OPERATION
A shielded cable from the signal source is plugged into
the Right (MONO) input lack of the MC 2120 only. The
MODE SWITCH on the back panel of the amplifier must be
placed in the MONO position. In the MONO position the
right channel input jack connects to both left and right
power amplifiers. The Left INPUT is disconnected. Only the
signal fed into the Right (MONO) input will be amplified.
Mono output is obtained by strapping both outputs in
parallel. 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 over-
heating. Be certain that the MC 2120 is never operated in
the stereo mode with the outputs connected for monophonic operation.
OUTPUT
Be certain the loudspeakers connected to the MC 2120
are capable of handling the power output of the amplifier.
For multiple speaker operation, run separate leads from
each speaker to the amplifier. Because of the high power
Wire
Gauge
22
20
18
16
14
12
10
For 4
Feet
10
15
25
40
60
100
MAXIMUM
Ohm Load
Meters
6
1 83
3.05
4.57
7.62
12.19
18.29
30.48
WIRE
For 8
Feel
12
20
30
50
80
120
200
LENGTHS
Ohm Load
Meters
3.66
6.10
9 14
15.24
24.38
36.58
60.96
For 16
Feel
24
40
60
100
160
240
400
Ohm Load
Meters
7.32
12.20
18.30
30.50
48.80
73.20
122.00
Wire lengths above represent the wire resistance equal to
5% of the speakers impedance. Use of smaller wire sizes
will produce more resistance which causes more power
loss and less loudspeaker damping.
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 terminal 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.
4
When multiple speakers are to be connected to either or
both outputs, the combined load impedance must be calcu-
lated. The load must be connected to the appropriate im-
pedance tap. Use this table to aid in selecting the correct
impedance match:
Load Load
impedance impedance
in ohms Connect tor in ohms Connect for
1.6 to 3.2 2 ohm output 6.4 to 13 8 ohm output
3.2 to 6.4 4 ohm output 13 and up 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
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
each speaker to the amplifier.
Should the MODE SWITCH be left in the STEREO position
and the output transformers be strapped for a monophonic
load, one channel will attempt to drive the other and cause
circulating currents and overheating. Be certain that the
MC 2120 is never operated in the stereo mode with the
outputs connected for monophonic operations.
AC POWER
The MC 2120 operates on 120 volts 50/60 Hz. The aux-
iliary AC OUTLET on the MC 2120 is not fused or switched.
MONOPHONIC OR SINGLE CHANNEL OPERATION
When the MC 2120 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 connecting a load to the MC 2120 for single channel operation
connect the common side of the load to the LEFT CHANNEL
OUTPUT terminal marked COM., the other lead is con-
nected:
If the speaker
or load
impedance is
1 ohm
2 ohms
4 ohms
8 ohms
Do not connect unequal impedance taps together
If the load impedance is between any of the above figures, select the best impedance match from;
Load Load
impedance impedance
in ohms Connect for in ohms Connect for
0.8 to 1.6 1 ohm output 3.2 to 6 4 4 ohm output
1.6 to 3.2 2 ohm output 6.4 and up 8 ohm output
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
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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