McIntosh MC-2200 Owners manual

THE MclNTOSH MC 2200 SOLID STATE STEREO POWER AMPLIFIER

Reading Time: 29 Minutes

Price $1.25

Your MC 2200 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: [phone]

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

INSTALLATION

HOW TO CONNECT

FRONT PANEL INFORMATION

REAR PANEL INFORMATION

PERFORMANCE LIMITS AND RATINGS

PERFORMANCE CHARTS

TECHNICAL DESCRIPTION

BLOCK DIAGRAM

1

2

4
8

10
11
12
14
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 ship-

ping 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.

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 in-

formation 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

so be sure that the panel and its mounting can also handle
the weight.

INSTALLATION IN MclNTOSH CABINET

Remove the instrument and hardware package from the
carton. Remove the MC 2200 from its plastic bag and place
it upside down on the shipping pallet; unscrew the four

plastic feet from the bottom of the chassis. Use the screws

from the plastic feet to secure the instrument to the cabi-

net. Do not substitute longer screws. Longer screws may
penetrate the electronic components in the chassis which

would cause severe damage. Do not overtighten the screws.

INSTALLATION IN A CUSTOM CABINET

The trouble-free life of an electronic instrument is
greatly extended by providing sufficient ventilation to pre­vent the buildup of high internal temperatures that cause
deterioration. Allow enough clearance so that cool air can
enter at the bottom of the cabinet and be vented from the
top. With adequate ventilation the instrument can be

mounted in any position. The recommended minimum
space for installation is 15 inches (38.1 cm) deep, 17 inches
(43.2 cm) wide, and 8 inches (30.3 cm) high.

The MC 2200 can be housed in the Mclntosh L22 cabinet,
installed in a custom cabinet or, with the addition of RACK
MOUNTING ADAPTERS (RMA 7), mounted in a standard 19
inch rack panel. The MC 2200 weighs 85 pounds (38.6 kg).
In any installation it is necessary to provide proper support
for the weight. The mounting methods described and the
amplifier have been designed to accommodate the weight

1/4" DIA. (2 HOLES)

Vertical mounting the MC 2200 requires careful con­sideration. The total weight is transmitted to the panel and
shelf on which the amplifier is to be mounted. Thought
should be given to providing a means for raising the MC
2200 out of the panel. More consideration should be given

to providing adequate ventilation at the panel in vertical

mounting. The heat sinks are at the rear of the chassis
permitting the heat to pass over the entire chassis. It is then
trapped behind the panel causing the overall temperature
to rise. In any case, air flow for cooling can be improved by
the use of a properly installed low noise fan. Adequate
cooling will extend the life of the components.

CUTOUT

Fig. 1. Top view of the panel cutout and mounting shelf.

2

FRONT PANEL
MTG. SURFACE

6 9/16"

DEPTH REQUIRED

15".

TOP OF SHELF & BOTTOM

OF CUTOUT SHOULD COINCIDE.

SHELF

Fig. 2. Views showing mounting shelf in position.

INSTALLATION PROCEDURE

1. Mark for Position
Mark cabinet panel where the instrument is to be

installed. The solid lines in Fig. 2 represent the outline of
the rectangular cutout and also represent the outside
dimensions of the chassis. Make sure these lines clear
shelves, partitions, or any equipment. The broken line
represents the outside dimension of the panel.

2. Drill Holes
Using a drill bit slightly wider than the tip of your saw

blade, drill one hole at each of two diagonally opposite
corners. The holes should barely touch the inside edge of
the outline.

3. Saw Panel Cutout
Sawing carefully on the inside of the lines, first make

the two long cuts and then the two short. After the

rectangular opening has been cut out, use a file to

square the corners and smooth any irregularities in the

cut edges.

3"

MOUNTING SCREWS

DIFFERENCE BETWEEN SCREW
LENGTH & TOTAL SHELF THICKNESS
MUST NOT EXCEED 1/2"

INSTALLATION IN A 19 INCH RACK

• The RACK MOUNTING ADAPTERS install on each end of

the front panel. On each side of the amplifier, three screws

secure the front panel bracket to the chassis. These three
screws are removed, the RACK MOUNTING ADAPTER

placed over the screw holes and the screws replaced. The
entire weight is transmitted through the RACK MOUNTING
ADAPTERS to the rack. No weight is carried by the front
panel. Additional support for the weight can be provided

at the rear of the chassis as desired.

4. Shelf Installation
Install the shelf on which the MC 2200 will sit. It

must be capable of supporting the total weight of the
instrument. Drill the two ¼" holes shown in Fig. 1.

5. Install Instrument
Guide the AC power cord through the panel opening

to the back of the cabinet; then, slide the instrument into
the opening until its front panel is flush with the cabinet
panel. Secure the MC 2200 to the shelf with #10 wood
screws of the proper length.

½" thick shelf—use 1" screws

5

"

/

thick shelf—use 11/

8

"

screws

8

¾" thick shelf—use 1¼" screws

Do not use screws longer than this recommended
length. They may penetrate electronic components
inside the chassis and cause severe damage. In any
event, the screw length must not exceed the shelf
thickness by more than ½".

Insert two proper length screws through the mount­ing shelf and into the holes in the bottom of the ampli­fier. Do not overtighten the screws.

Fig. 3. Rack Mounting Adapters installed.

3

INPUT

STEREO OR TWIN AMPLIFIER OPERATION

Use shielded cables to connect the signal from the pre-

amplifier 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 2200.

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 2200, large diameter speaker leads
must be used. Use lamp cord, bell wire, or wire with similar

type of 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 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

be less than 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 jack of the MC 2200 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. Mono output is obtained by strapping

both outputs in parallel. 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 2200 is never operated in the stereo

mode with the outputs connected for monophonic opera-

tion.

OUTPUT

Be certain the loudspeakers connected to the MC 2200

are capable of handling the power output of the ampli-

fier.

For multiple speaker operation, run separate leads from

each speaker to the amplifier. Because of the high power

MAXIMUM WIRE

Wire
Gauge

22

20

18
16
14
12
10

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 termi-

nal of the left speaker to the screw with the number cor-

responding 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

For 4 Ohm Load

Feet

10

15
25
40
60

100

Meters

6

1.83

3.05

4.57

7.62

12.19

18.29

30.48

LENGTHS

For 8

Feet

12
20
30

50
80

120

200

Ohm Load

Meters

3.66

6.10

9.14

15.24

24.38

36.58

60.96

4

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 im­pedance tap. Use this table to aid in selecting the correct
impedance match:

FOR MONOPHONIC CONSTANT VOLTAGE LINE
OPERATION
For output
voltage of Connected for
25 volts 2 ohm output (mono)

For multiple speaker operation, run separate leads from

each speaker to the amplifier.

Load
impedance
in ohms

0.8 to 1.6

1.6 to 3.2
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 4 ohms

MONOPHONIC OR SINGLE CHANNEL OPERATION

When the MC 2200 is used as a monophonic or single
channel power amplifier the two channels are combined to
produce output up to 400 watts. The outputs must be tied

together at the appropriate load impedance tap. In connect-

ing a load to the MC 2200 for single channel operation
connect the common side of the load to the LEFT CHANNEL
OUTPUT terminal marked COM., the other lead is con­nected:

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

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 2200 is never operated in the stereo mode with the

outputs connected for monophonic operations.

AC POWER

The MC 2200 operates on 120 volts 50/60 Hz. The aux-

iliary AC OUTLET on the MC 2200 is not fused or switched.

If the speaker
or load

impedance is

0.5 ohm
1 ohm

2 ohms
4 ohms

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

0.4 to 0.8

0.8 to 1.6

The hot side
of the line is
connected to
Left 1
Left 2
Left 4
Left 8

Connect for

0.5 ohm output
1 ohm output

Connect a
wire between
Left 1 and
Left 2 and
Left 4 and
Left 8 and

Load
impedance
in ohms

1.6 to 3.2

3.2 and up

jumper

Right 1
Right 2
Right 4
Right 8

Connect for
2 ohm output
4 ohm output

5

Front Panel

Information

LEFT GAIN

Use the LEFT GAIN control to adjust the volume in the

left channel to the desired listening level. Turn the control

clockwise to increase the volume.

RIGHT/MONO GAIN

Use the RIGHT/MONO GAIN control to adjust the volume
in the right channel to the desired listening level. Turn the
control clockwise to increase the volume.

MONO

With the output of MC 2200 connected for monophonic

operation and the rear panel MODE SWITCH in MONO the

volume is controlled by the RIGHT/MONO GAIN control
only.

LIMIT/NORMAL

The NORMAL (green) and LIMIT (red) indicators are a
new Mclntosh development. As long as the amplifier

operates without overload the NORMAL indicator illu-

8

minates. A waveform comparator in the MC 2200 con­stantly compares the amplifier input and output waveform.
Waveform difference of the output wave is converted to

a voltage which is used as a control signal to "turn off" the

NORMAL indicator and to "turn on" the LIMIT indicator.
The LIMIT indicator turns on whenever the waveform dif-

ference exceeds 0.5%. Generally, these waveform differ-

ences are the result of applying voltages at the input in

excess of its rating. Because the limit indicator circuit can

show an overload condition as short as one cycle of a

20,000 Hz signal a holding circuit keeps the red indi-

cator on long enough for the eye to see.

HEADPHONES

The output of the front panel HEADPHONE jack has been

designed to feed low impedance dynamic stereo head-

phones. Electrostatic headphones generally require higher
power than dynamic headphones. Connect them to the
LEFT and RIGHT OUTPUT contacts on the back of the

MC 2200. Plug dynamic headphones into the front panel
HEADPHONE jack. Adjust the front panel LEFT GAIN and
RIGHT/MONO GAIN control for comfortable headphone
listening.

POWER

The power switch turns the MC 2200 ON or OFF. The
switch does not control the power outlet on the back panel.
If you wish to control the AC power from a preamplifier
control center leave the switch in the ON position. Be sure
the AC cord of the MC 2200 is plugged into the controlled
outlets on the rear of the preamplifier control center.

OFF: In the OFF position the AC power to the amplifier
is turned off.

9

Rear Panel Information

LEFT and RIGHT OUTPUT

For stereo operation, output impedances of 1, 2, 4 and
8 ohms have been provided on a secure, screw type barrier
strip. For monophonic operation proper interconnection
provides 0.5,1, 2 and 4 ohms from the same barrier strips.

POWER GUARD

Amplifiers are capable of delivering large quantities of

power when they are driven to clipping. Clipping is
caused when the amplifier is asked to produce more power
output than it can deliver with low distortion. A clipped
amplifier can have more than 40% harmonic distortion.
The extra energy content of the clipped signal will dam­age most speakers. A new Mclntosh advancement helps
to protect your speaker from this kind of damage. The
MC 2200 has a built in "waveform comparator" that com­pares the wave shape of the input signal with the output
signal. If the non-linearity between the two signals exceeds

0.5% a front panel signal illuminates in red (LIMIT}. With
the POWER GUARD switch in the NORMAL position, 1.0%
distortion will cause the POWER GUARD circuit to operate.
The POWER GUARD circuit limits the input dynamically so
that the amplifier cannot be overdriven. This eliminates

amplifier output clipping. Recommended operation is with
the POWER GUARD switch in the NORMAL position at all
times.

MODE SWITCH

The MC 2200 can be used in these different manners:

stereo (or as a twin amplifier) and mono. Because of the

excellent channel separation of the MC 2200, it can fulfill
all of these functions. When the instrument is properly con-

nected the MODE switch is used to select the method of
operation desired.

INPUT

In the stereo or twin amplifier mode of operation both

input jacks accept signal. In the mono mode of operation

the Left channel input jack is disconnected and only the

Right (MONO) channel input jack accepts signal.

INPUT LEVEL

The input sensitivity of the MC 2200 is 0.75 volts or

2.5 V depending on the position of the INPUT LEVEL switch.
With indicated voltage applied and the GAIN control clock­wise, the amplifier will deliver its rated power. All Mclntosh

preamplifiers have been designed to deliver 2.5 volts out­put with rated input. For the best signal to noise ratio when
using Mclntosh source equipment, always have the INPUT
LEVEL switch in the 2.5 V position and the front panel LEFT

and RIGHT/MONO GAIN controls in the fully clockwise

position. If more gain is desired the 0.75 V position may be

used. For source equipment other than Mclntosh set the
switch in the position nearest to the stated output rating of
the source equipment.

AC POWER

The MC 2200 is rated for 120 volts, 50/60 hertz. A

10 ampere fuse protects the MC 2200 electrically. An
auxiliary AC power outlet has been provided. The auxiliary
outlet is neither fused nor switched.

10

Performance Limits and Ratings

PERFORMANCE GUARANTEE

Performance Limits are the maximum deviation from per­fection permitted for a Mclntosh instrument We promise
you that the MC 2200 you buy must be capable of per­formance at or exceeding these limits or you get your

money back, Mclntosh is the only manufacturer that makes

this guarantee.

PERFORMANCE

Mclntosh audio power ratings are in accordance with the
Federal Trade Commission Regulation of November 4,1974
concerning power output claims for amplifiers used in home

entertainment products.

POWER OUTPUT

STEREO

200 watts minimum sine wave continuous

average power output, per channel, both
channels operating into 1 ohm, 2 ohms, 4
ohms, or 8 ohms load impedance, which is:

14.1 volts RMS across 1 ohm

20.0 volts RMS across 2 ohms

28.3 volts RMS across 4 ohms

40.0 volts RMS across 8 ohms

MONO

400 watts minimum sine wave continuous
average power output into 0.5 ohm, 1

ohm, 2 ohms, or 4 ohms load impedance,

which is:

14.1 volts RMS across 0.5 ohm

20.0 volts RMS across 1 ohm

28.3 volts RMS across 2 ohms

40.0 volts RMS across 4 ohms

OUTPUT LOAD IMPEDANCE

STEREO

1 ohm, 2 ohms, 4 ohms, and 8 ohms; sepa­rate terminals are provided for each output

MONO

0.5 ohm, 1 ohm, 2 ohms, and 4 ohms; ob­tained by connecting together the appro-

priate terminals of both channels

RATED POWER BAND

20 Hz to 20,000 Hz

TOTAL HARMONIC DISTORTION

STEREO

0.1% maximum harmonic distortion at any
power level from 250 milliwatts to 200

watts per channel from 20 Hz to 20,000
Hz, both channels operating

MONO

0.1% maximum harmonic distortion at any
power level from 250 milliwatts to 400
watts from 20 Hz to 20,000 Hz

INTERMODULATION DISTORTION

STEREO

0.1% maximum if instantaneous peak power output is 400
watts or less per channel with both channels operating for
any combination of frequencies, 20 Hz to 20,000 Hz

MONO

0.1% maximum if instantaneous peak power output is 800
watts or less for any combination of frequencies, 20 Hz to
20,000 Hz

FREQUENCY RESPONSE (at one watt output)

20 Hz to 20,000 Hz, +0 -0.25 dB

10 Hz to 100,000 Hz +0 -3.0 dB

NOISE AND HUM

95 dB below rated output

RATINGS

OUTPUT VOLTAGES

25 volts for distribution lines

DAMPING FACTOR

STEREO

16 at 1 ohm output, 50 at 2 ohms output, 30 at 4 ohms out­put, 16 at 8 ohms output

MONO

16 at 0.5 ohms, 50 at 1 ohm, 30 at 2 ohms, and 16 at 4

ohms output

INPUT IMPEDANCE

100,000 ohms

INPUT SENSITIVITY

Switchable: 0.75 volt or 2.5 volts—Level control provided
for higher input voltages

GENERAL INFORMATION

POWER REQUIREMENTS

120 volts 50/60 Hz, 70 to 550 watts

SEMICONDUCTOR COMPLEMENT

43 silicon transistors
24 silicon rectifiers and diodes

2 integrated circuits

MECHANICAL INFORMATION

SIZE

Front panel measures 16 inches wide (40.7 cm) by 6 31/32
inches high (17.7 cm). Chassis measures 14 5/8 inches
wide (37.2 cm) by 6 9/16 inches high (16.7 cm) by 14 1/2

inches deep {36.8 cm), including connectors. Knob clear-

ance required is 1 1/2 inches (3.8 cm) in front of mounting

panel

FINISH

Front panel is anodized gold. Chassis is chrome and black
Weight

73 pounds (38.6 kg) net, 87 pounds (44.0 kg) in shipping

carton

11

Technical

Description

INPUT AMPLIFIER

Separate input amplifiers are used for the right and

left channels. Each input amplifier is a two transistor feed-

back amplifier which has unity gain. They are used to pro­vide high input impedance and low output impedance for
driving the power amplifier sections. In addition, impe­dance matching is provided for the POWER GUARD system

input attenuator.

When the MODE selector is switched to MONO, only the

right channel input, GAIN control, POWER GUARD attenua­tor, and input amplifier is used to drive both power am-

plifiers.

POWER AMPLIFIER

There are two identical power amplifier sections. At the

input to each power amplifier is a monolithic differential
transistor selected for low noise. The monolithic design

yields closely matched transistors for low distortion. The

input and the feedback signals are applied to this differen­tial amplifier. The second stage is a class A voltage ampli-

fier using a single transistor with feedback.

The predriver, driver, and output sections follow and are

fully complimentary with high efficiency and negligible dis­tortion. The predriver is a complimentary transistor pair

biased to nearly class A operation for low crossover dis-

tortion. Bias is supplied by a transistor which serves as

a temperature tracking circuit so the predriver is properly

biased regardless of temperature. The predriver has a

generous amount of emitter degeneration for low distortion.

Another complimentary pair of power transistors biased
for class AB operation make up the output driver stages.
Their bias is developed across a termistor which holds the
bias current stable regardless of temperature.

The output stage consists of 6 rugged complimentary
power transistors connected in single ended push-pull
parallel. This stage is connected as a balanced emitter fol-

lower which allows great stability and low distortion. Due

to a unique arrangement of the output bias network, the

output transistors are operated class B free of crossover
distortion. Heat is not produced by these transistors when

there is no output. The bias network for the output stage

is temperature compensated assuring class B operation
at any temperature or power level.

The output transistors and drivers are mounted on gener­ous sized black anodized aluminum heat sinks. The free
flow of room temperature air that passes through the over­sized heat sinks provides the cooling necessary for the long
life of components.

The MC 2200 has transient free turn on and turn off
characteristics. This is because the output of the amplifier is
switched by a heavy duty relay to the output auto trans­former. The relay is driven by a transistor switch. The con-

trol to this transistor is derived from a long time constant
capacitor charging network. The switch turns on the relay
approximately two seconds after the MC 2200 is turned on.
The same circuit has a short turn-off time constant which
turns off the relay before the amplifier's main power supply

has had a chance to drop. The output signal is fed through a
matching network to the front panel HEADPHONE jack. The
HEADPHONE output is designed to feed low impedance
dynamic stereo headphones.

The amplifier output signal is fed to the output terminals
through the autotransformer. The Mclntosh designed inter­leaved multifilar wound autotransformer is used to properly
match the amplifier to any output impedance tap. The MC
2200 will deliver full power over the entire audio frequency

range at any of these impedances. The MC 2200 will not
overheat when driving low impedance loads {1 ohm, 2
ohms or 4 ohms). The autotransformer also protects speak­ers from damage in the event of amplifier failure. Should a
direct current component appear in the output it is shunted
by the autotransformer and cannot damage the speaker.

The Mclntosh patented Sentry Monitoring circuit con­stantly monitors the output signal and instantly reacts to

prevent overload of the output transistors. At signal levels
up to rated output this circuit has high impedance and has
no effect upon the output. If the power output exceeds
design maximum, the Sentry monitoring circuit oper­ates to limit the signal to the output transistors. In the
event of a short circuit across the amplifier output or
severe impedance mismatch the Sentry Monitoring
circuit will protect the output transistors from failure.
The positive and negative halves of the output signal are

monitored independently.

LIMIT INDICATOR AND POWER GUARD

The front panel NORMAL (green) and LIMIT (red) indica-

tors are activated by a newly designed Mclntosh circuit. The

MC 2200 has a built in "waveform comparator." The wave­form comparator electrically compares the amplifier's out-

put waveform with the input waveform. Should the wave­form differences reach 0.5%, the red LIMIT indicator on the
front panel is turned on and the NORMAL indicator is
turned off. If the differences increase to 1% the POWER
GUARD circuit is activated. POWER GUARD provides an

unusual margin of safety for loudspeakers by the preven­tion of amplifier clipping yet permits the amplifier to de-

liver designed maximum power.

14

The input waveform and the output waveform are
compared in an integrated circuit differential amplifier.
Any differences, due to distortion of the output waveform,
are converted to a control voltage. This control voltage is
applied differentially to a high gain operational amplifier
where it is amplified about 100 times. The amplified
control voltage is detected by a full wave bridge rectifier
then enters a Schmidt trigger which is programmed to
sequence the front panel indicators from NORMAL (green)
to LIMIT (red} at a preset distortion level. Also built into
the trigger circuit is a timing capacitor which holds the

LIMIT indicator on long enough to be visible even when the
duration of the overload is much shorter. The LIMIT indica­tor will be illuminated for an overload condition as short
as one cycle of a signal at 20,000 Hz.

The same control voltage used to activate the LIMIT

indicator also actuates the POWER GUARD system. If the
control voltage is greater than is needed to illuminate
the LIMIT indication then the POWER GUARD begins op­erating. The control voltage is used to operate a light
emitting diode/light dependent resistor (LOR) network.
The LDR is part of an attenuator between the volume con­trol and the input amplifier. The input to the power am-

plifier can be attenuated to as little as one tenth, if neces-

sary, in order to maintain low distortion in the event of

excessive input signal.

The POWER GUARD circuit is activated when the rear
panel switch is in the NORMAL position. POWER GUARD
protection is disabled in the OUT position. The LIMIT indi­cator operates regardless of the position of the POWER
GUARD switch.

15

MclNTOSH LABORATORY INC.

2 CHAMBER S ST., BINGHAMTON, N. Y. 13903

607-723-3512

Design subject to change without notice .

Printed in U.S.A.

038-910