THE MclNTOSH MC 2200 SOLID STATE STEREO POWER

THE MclNTOSH MC 2200 SOLID STATE STEREO POWER
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:
Contents
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.
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
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.
The terms of the contract are:
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.
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.
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.
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.
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.
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
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 cabinet. 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.
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.
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)
CUTOUT
FRONT PANEL
MTG. SURFACE
Fig. 1. Top view of the panel cutout and mounting shelf.
2
DEPTH REQUIRED
15".
TOP OF SHELF & BOTTOM
OF CUTOUT SHOULD COINCIDE.
6 9/16"
SHELF
3"
MOUNTING SCREWS
DIFFERENCE BETWEEN SCREW
LENGTH & TOTAL SHELF THICKNESS
MUST NOT EXCEED 1/2"
Fig. 2. Views showing mounting shelf in position.
INSTALLATION PROCEDURE
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.
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.
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 "
/8 thick shelf—use 11/8" screws
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".
Fig. 3. Rack Mounting Adapters installed.
Insert two proper length screws through the mounting shelf and into the holes in the bottom of the amplifier. Do not overtighten the screws.
3
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 2200.
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 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.
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.
MAXIMUM WIRE LENGTHS
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.
Wire
For 4 Ohm Load
For 8 Ohm Load
Gauge
22
20
18
16
14
12
10
Feet
6
10
15
25
40
60
100
Feet
12
20
30
50
80
120
200
Meters
1.83
3.05
4.57
7.62
12.19
18.29
30.48
Meters
3.66
6.10
9.14
15.24
24.38
36.58
60.96
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.
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 operation.
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
OUTPUT
Be certain the loudspeakers connected to the MC 2200
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
4
FOR MONOPHONIC CONSTANT VOLTAGE LINE
OPERATION
For output
voltage of
Connected for
25 volts
2 ohm output (mono)
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:
Load
impedance
in ohms
0.8 to 1.6
1.6 to 3.2
Connect for
1 ohm output
2 ohm output
Load
impedance
in ohms
3.2 to 6.4
6.4 and up
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 2200 is never operated in the stereo mode with the
outputs connected for monophonic operations.
Connect for
4 ohm output
8 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.
AC POWER
The MC 2200 operates on 120 volts 50/60 Hz. The auxiliary AC OUTLET on the MC 2200 is not fused or switched.
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 connecting 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:
If the speaker
or load
impedance is
0.5 ohm
1 ohm
2 ohms
4 ohms
The hot side
of the line is
connected to
Left 1
Left 2
Left 4
Left 8
Connect a jumper
wire between
Left 1 and Right 1
Left 2 and Right 2
Left 4 and Right 4
Left 8 and Right 8
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
impedance
in ohms
0.4 to 0.8
0.8 to 1.6
Load
impedance
Connect for
in ohms
0.5 ohm output 1.6 to 3.2
1 ohm output 3.2 and up
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 difference exceeds 0.5%. Generally, these waveform differences 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 indicator on long enough for the eye to see.
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.
HEADPHONES
The output of the front panel HEADPHONE jack has been
designed to feed low impedance dynamic stereo headphones. Electrostatic headphones generally require higher
power than dynamic headphones. Connect them to the
LEFT and RIGHT OUTPUT contacts on the back of the
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.
excellent channel separation of the MC 2200, it can fulfill
all of these functions. When the instrument is properly connected 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.
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.
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.
MODE SWITCH
The MC 2200 can be used in these different manners:
stereo (or as a twin amplifier) and mono. Because of the
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.
watts per channel from 20 Hz to 20,000
Hz, both channels operating
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.
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 clearance 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
MONO
0.1% maximum harmonic distortion at any
power level from 250 milliwatts to 400
watts from 20 Hz to 20,000 Hz
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 appropriate 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
11
Technical
Description
INPUT AMPLIFIER
Separate input amplifiers are used for the right and
left channels. Each input amplifier is a two transistor feedback 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.
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 control 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.
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 amplifiers.
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.
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 amplifier 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 distortion. 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.
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.
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 follower 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.
LIMIT INDICATOR AND POWER GUARD
The front panel NORMAL (green) and LIMIT (red) indicators 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 output 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 deliver designed maximum power.
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.
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 amplifier can be attenuated to as little as one tenth, if necessary, 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 CHAMBERS ST., BINGHAMTON, N. Y. 13903
607-723-3512
Design subject to change without notice.
Printed in U.S.A.
038-910
BE022004
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