McIntosh MC-2255 User Manual
THE
MclNTOSH
MC
2255
SOLID STATE STEREO POWER AMPLIFIER
Reading Time: 31 Minutes
Price $2.00
VARIOUS REGULATORY AGENCIES REQUIRE THAT WE BRING THE FOLLOWING
INFORMATION TO YOUR ATTENTION. PLEASE READ IT CAREFULLY.
WARNING: TO PREVENT FIRE OR SHOCK
HAZARD, DO NOT EXPOSE THIS UNIT TO
RAIN OR MOISTURE.
The Mclntosh you have purchased is a Model
MC 2255. It has a serial number located on the rear panel
of the chassis. Record that serial number here:
Serial Number
The model, serial number and purchase date are important to you for any future service. Record the purchase date here:
Purchase date
Upon application, Mclntosh Laboratory provides a
Three-Year Service Contract. Your Mclntosh authorized
Service Agency can expedite repairs when you provide
the Service Contract with the instrument for repair. To
assist, record your Service Contract number here:
Service Contract Number
Your MC 2255 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
Take Advantage of 3 years
of Contract Service...
Fill in the Application NOW.
MclNTOSH THREE YEAR SERVICE CONTRACT
An application for A 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. The SERVICE CONTRACT does not cover any
shipping costs to and from the authoriz-
ed service agency or the factory.
2. Any Mclntosh authorized service agency
will repair Mclntosh instruments at nor-
mal service rates. To receive service
under the terms of the SERVICE CONTRACT, the SERVICE CONTRACT CERTIFICATE must be presented when the
instrument is 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 mishandl-
ing is not covered by the SERVICE
CONTRACT.
4. The SERVICE CONTRACT is issued to
you as the original purchaser. To protect you from misrepresentation, this
Contents
SERVICE 1
INSTALLATION 2
HOW TO CONNECT 4
FRONT PANEL INFORMATION 9
REAR PANEL INFORMATION 11
PERFORMANCE LIMITS AND RATINGS 12
PERFORMANCE CHARTS 13
TECHNICAL DESCRIPTION 15
BLOCK DIAGRAM 17
contract cannot be transferred to a second owner.
5. To receive the SERVICE CONTRACT,
your purchase must be made from a
Mclntosh franchised dealer.
6. Your completely filled in application for
the 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 by Mclntosh
Laboratory Incorporated in Binghamton,
New York.
8. Units in operation outside the United
States and Canada are not covered by
the Mclntosh Factory Service Contract,
irrespective of the place of purchase.
Nor are units acquired outside the
U.S.A. and Canada, the purchasers of
which should consult with their dealer
to ascertain what, if any, service con-
tract or warranty may be available locally.
Copyright 1981 (c) by Mclntosh Laboratory Inc.
1
How to Connect
INPUT
STEREO OPERATION
Use shielded cables to connect the signal from
the preamplifier or signal source to the power
amplifier. To minimize the possibilty 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 2255.
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 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 jack of the MC 2255
only. The MODE SWITCH on the back panel of the
amplifier must be placed in one of the MONO positions. In the MONO positions 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.
Be certain that the MC 2255 is never operated in
the stereo mode with the outputs connected for
monophonic operation. Should the MODE SWITCH
be left in the STEREO position and the outputs remain strapped for a mono parallel load, one channel
will attempt to drive the other which causes high circulating currents and overheating.
duction for which the loudspeakers have been designed. If undersize wire is used, resistance is added
to the amplifier/loudspeaker combination which
adversely affects the performance. Added resistance causes depreciation of damping characteristics, modification of frequency response and reduction in power output.
Use lamp cord or wire with similar insulation to
connect the speakers to the amplifier. In all cases,
the leads to and from the speaker should be twin
conductor or twisted together. 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 use larger diameter wire. Select the correct size
wire from the chart below. It is recommended that
the DC resistance of the speaker leads be less than
5% of the speaker impedance. Resistance of the
leads should be computed for the length of wire both
to and from the speaker or speakers.
For multiple speaker operation, run separate
leads from the amplifier to the speakers.
MAXIMUM WIRE LENGTHS
Wire
Gauge
18
16
14
12
10
Wire lengths above represent the wire resistance
equal to 5% of the speaker impedance.
For 4 Ohm Load
Feet
15
25
40
60
100
Meters
4.57
7.62
12.19
18.29
30.48
For 8 Ohm Load
Feet
30
50
80
120
200
Meters
9.14
15.24
24.38
36.58
60.96
OUTPUT
Be certain the loudspeakers connected to the MC
2255 are capable of handling the power output of the
amplifier.
Selection of the proper gauge wire to connect the
loudspeakers preserves the quality of sound repro-
STEREO OPERATION
Check the impedance of the speaker which is
usually identified on the speaker itself or in the
owner's manual. Connect a lead from the common
terminal of the left speaker to the amplifier LEFT
OUTPUT terminal strip COMmon screw. Connect
4
another lead from the other terminal of the
loudspeaker to the left output terminal marked for
the impedance of the speaker on the LEFT OUTPUT
terminal strip. The right channel speaker is connected in the same manner to the RIGHT OUTPUT
terminal strip.
When multiple speakers are to be connected to
either or both outputs, the combined load impedance must be caluclated. The load must be connected to the appropriate impedance tap. Use this
table to aid in selecting the correct impedance
match:
Load
impedance
in ohms
0.8 to 1.6
1.6 to 3.2
3.2 to 6.4
6.4 and up
Connect for:
1 ohm output
2 ohm output
4 ohm output
8 ohm output
For monophonic operation using the MONO
PARALLEL mode, output impedances of ½, 1, 2, and
4 ohms are accomodated. Connect as listed below.
The common output terminal is at ground potential.
Load Impedance
In Ohms
½
1
2
4
Connect - Speaker
Lead To:
Either Left or Right
Common Terminal
Either Left or Right
Common Terminal
Either Left or Right
Common Terminal
Either Left or Right
Common Terminal
Connect + Speaker
Lead To:
Both Left and Right
1 Ohm Terminals
Both Left and Right
2 Ohm Terminals
Both Left and Right
4 Ohm Terminals
Both Left and Right
8 Ohm Terminals
FOR MONOPHONIC CONSTANT VOLTAGE LINE
OPERATION
For output
voltage of
Connected for:
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 reduced.
FOR STEREO CONSTANT VOLTAGE OPERATION:
For output
voltage of
25 volts
Connect for:
4 ohms
MONOPHONIC OR SINGLE CHANNEL OPERATION
When the MC 2255 is used as a monophonic or
single channel power amplifier the two channels are
combined to produce output up to 500 watts. The
outputs must be connected as described below.
For monophonic operation using the MONO
BRIDGE mode, output impedances of 2, 4, 8, and 16
ohms are accomodated. Output connections are
made by connecting to the output terminals as
listed below. Note that neither output terminal is at
ground potential.
25 volts
2 ohm output (mono)
Be certain that the MC 2255 is never operated in
the stereo mode with the outputs connected for
monophonic operation. Should the MODE SWITCH
be left in the STEREO position and the outputs re-
main strapped for a mono parallel load, one channel
will attempt to drive the other which causes high circulating currents and overheating.
AC POWER
The MC 2255 operates on 120 volts 50/60 Hz. The
auxiliary AC OUTLET on the MC 2255 is not fused or
switched.
Load Impedance
In Ohms
2
4
8
16
Connect - Speaker
Lead To:
Left 1 Ohm Terminal
Left 2 Ohm Terminal
Left 4 Ohm Terminal
Left 8 Ohm Terminal
Connect + Speaker
Lead To:
Right 1 Ohm Terminal
Right 2 Ohm Terminal
Right 4 Ohm Terminal
Right 8 Ohm Terminal
5
Stereophonic
Connections
PROGRAM SOURCE
LEFT
SPEAKER
MUST BE IN STEREO
POSITION FOR
STEREO PROGRAMS
6
RIGHT
SPEAKER
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