Power Amplifier
MC252
Owner’s Manual
McIntosh Laboratory, Inc. 2 Chambers Street Binghamton, New York 13903-2699 Phone: 607-723-3512 FAX: 607-724-0549
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Thank You
Table of Contents
Your decision to own this McIntosh MC252 Power Ampli-
fier ranks you at the very top among discriminating music
listeners. You now have “The Best.” The McIntosh dedica-
tion to “Quality,” is assurance that you will receive many
years of musical enjoyment from this unit.
Please take a short time to read the information in this
manual. We want you to be as familiar as possible with all
the features and functions of your new McIntosh.
Safety Instructions ............................................................ 2
Thank You and Please Take a Moment............................. 3
Technical Assistance and Customer Service .................... 3
Table of Contents and Important Information .................. 3
Connector Information ..................................................... 4
Introduction ...................................................................... 4
Performance Features ....................................................... 4
Dimensions ....................................................................... 5
Installation ........................................................................ 6
Top Panel Connections and Switch .................................. 7
How to Connect in Stereo................................................. 8
How to Connect in Mono Bridged Mode ....................... 10
How to Connect in Mono Bi-Amp (Parallel) ................. 12
Front Panel Displays and Controls ................................. 14
How to Operate............................................................... 15
Technical Description ..................................................... 16
Notes ............................................................................... 20
Specifications ................................................................. 22
Packing Instruction ......................................................... 23
Please Take A Moment
The serial number, purchase date and McIntosh Dealer
name are important to you for possible insurance claim or
future service. The spaces below have been provided for
you to record that information:
Serial Number:
Purchase Date:
Dealer Name:
Technical Assistance
Important Information
If at any time you have questions about your McIntosh
product, contact your McIntosh Dealer who is familiar with
your McIntosh equipment and any other brands that may
be part of your system. If you or your Dealer wish addi-
tional help concerning a suspected problem, you can re-
ceive technical assistance for all McIntosh products at:
Caution: The MC252 Amplifier weight is 94.5 pounds
(42.87 kilograms). It requires two or more persons
to safely handle when moving the amplifier.
1. The following Connecting Cable is available from the
McIntosh Parts Department:
Power Control Cable Part No. 170-202
Six foot, 2 conductor shielded, with two 1/8 inch stereo
mini phone plugs.
2. For additional connection information, refer to the owner’s
manual(s) for any component(s) connected to the MC252.
3. The MC252 mutes the speaker outputs for approximately two
seconds when first turned on.
4. It is very important that loudspeaker cables of adequate size
be used, so that there will be no power loss. The size is
specified in Gauge Numbers or AWG, (American Wire Gauge).
The smaller the Gauge number, the larger the wire size:
If your loudspeaker cables are 50 feet (38.1m) or less,
use at least 14 Gauge.
McIntosh Laboratory, Inc.
2 Chambers Street
Binghamton, New York 13903
Phone: 607-723-1545
Fax: 607-723-3636
Customer Service
If it is determined that your McIntosh product is in need of
repair, you can return it to your Dealer. You can also return
it to the McIntosh Laboratory Service Department. For as-
sistance on factory repair return procedure, contact the
McIntosh Service Department at:
If your loudspeaker cables are 100 feet (76.2m) or less,
use at least 12 Gauge.
5. In the event the MC252 over heats, due to improper
ventilation and/or high ambient temperature, the protection
circuits will activate. The Power Guard LED will stay ON and
the audio will be muted. When the MC252 has returned to a
safe operating temperature, normal operation will resume.
McIntosh Laboratory, Inc.
2 Chambers Street
Binghamton, New York 13903
Phone: 607-723-3515
Fax: 607-723-1917
Copyright 2003 by McIntosh Laboratory, Inc.
3
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Connector Information
XLR Connectors
• Balanced and Unbalanced Inputs
Below is the Pin configuration for the XLR Balanced Input
Connectors on the MC252. Refer to the diagram for con-
nection:
Balanced connections guard against induced noise and al-
low long cable runs without compromising sound quality.
PIN 1: Shield/Ground
PIN 2: + Input
PIN 3: - Input
Pin 1
Pin 2
• Patented Sentry Monitor with Thermal Protection
McIntosh Sentry Monitor power output stage protection
circuits ensure the MC252 will have a long and trouble free
operating life. Built-in Thermal Protection Circuits guard
against overheating.
Pin 3
Power Control and Trigger Connectors
The MC252’s Power Control Outputs provide a 5 volt sig-
nal. Use a 1/8 inch stereo mini
phone plug to connect to the
Power Control Input on other
McIntosh Components.
• Power Control
Positive
The McIntosh Power Control Circuit allows for remote
turn-on of the MC252 Power Amplifier from a McIntosh
Audio/Video Control Center or Preamplifier. If any addi-
tional McIntosh Power Amplifiers are part of the system, a
delayed Power Control Output Trigger is available. This
delayed Trigger reduces the strain on the house’s electrical
wiring and protection devices.
N/C
Ground
Introduction
Now you can take advantage of traditional McIntosh stan-
dards of excellence in the MC252 Power Amplifier. The
250 watt high current outputs will drive any high quality
Loudspeaker System to its ultimate performance. The
MC252 reproduction is sonically transparent and abso-
lutely accurate. The McIntosh Sound is “The Sound of the
Music Itself.”
• Illuminated Power Meters
The Illuminated Power Output Watt Meters on the MC252
are peak responding, and indicate the power output of the
amplifier. The Peak Watt Hold Mode allows the meter to
temporarily stay at the highest power output and then
slowly decay. The Front Panel Meter Illumination may be
switched Off at any time.
Performance Features
• Power Output
• Fiber Optic Solid State Front Panel Illumination
The Illumination of the Front Panel is accomplished by the
combination of custom designed Fiber Optic Light Diffus-
ers and Light Emitting Diodes (LEDs). This provides even
Front Panel Illumination, together with the extra long life
LEDs.
The MC252 consists of two separate power amplifier chan-
nels, each capable of 250 watts into 2, 4 or 8 ohm speakers
with less than 0.005% distortion. The two channels can be
combined into a single channel with 500 watts into 1, 2, 4,
8 or 16 ohm speakers with less than 0.005% distortion.
• Patented Autoformers
• Glass Front Panel and Super Mirror Chassis Finish
The famous McIntosh Illuminated Glass Front Panel with a
three dimensional look and the Stainless Steel Chassis with
Super Mirror Finish ensures the pristine beauty of the
MC252 will be retained for many years.
The McIntosh designed and manufactured Output
Autoformers provide an ideal match between the amplifier
output stage and speaker loads of 2, 4 and 8 ohms. The
Autoformers also provide perfect DC protection for your
valuable Loudspeakers.
• Patented Power Guard
The patented McIntosh Power Guard Circuit prevents the
amplifier from being over driven into clipping, with its
harsh distorted sound that can also damage your valuable
Loudspeakers.
4
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Connector Information, Introduction, Performance Features and Dimensions
The following dimensions can assist in determining the
best location for your MC252. There is additional informa-
tion on the next page pertaining to installing the MC252
into cabinets.
17-1/2"
44.45cm
8-13/16"
22.38cm
9-7/16"
23.97cm
Front View of the MC252
16-13/16"
42.70cm
Rear View of the MC252
13-1/4"
33.66cm
14-1/2"
36.83cm
13-5/8"
34.61cm
Side View of the MC252
8-1/8"
20.64cm
8-3/16"
21.11cm
7/8"
2.22cm
9-1/2"
24.13cm
1-1/16"
2.70cm
5
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Installation
Installation
Caution: The MC252 Amplifier weight is 94.5 pounds
(40.64 cm) depth behind the front panel. Allow 1-3/16
(42.87 kilograms). It requires two or more persons
to safely handle when moving the amplifier.
The MC252 can be placed upright on a table or shelf,
standing on its four feet. The
inches (3.02 cm) in front of the mounting panel for knob
clearance. Be sure to cut out a ventilation hole in the
mounting shelf according to the dimensions in the drawing.
four feet may be removed
from the bottom of the
MC252 when it is custom
installed as outlined below.
17-1/16"
43.34cm
The four feet together with
the mounting screws should
be retained for possible fu-
ture use if the MC252 is re-
moved from the custom in-
8-5/16"
21.11cm
MC252 Front Panel
Custom Cabinet Cutout
stallation and used free
standing. It also can be cus-
tom installed in a piece of
furniture or cabinet of your
choice. The required panel
cutout, ventilation cutout
and unit dimensions are
shown.
Always provide adequate
ventilation for your MC252.
Cool operation ensures the
longest possible operating
life for any electronic instru-
ment. Do not install the
Alternate Rear Foot Location
Cutout Opening
for Custom Mounting
6"
15.24cm
Cabinet
Front
Panel
Opening
for Ventilation
MC252 directly above a heat
generating component such
as a high powered amplifier.
If all the components are in-
stalled in a single cabinet, a
quiet running ventilation fan
can be a definite asset in
maintaining all the system
components at the coolest
possible operating tempera-
ture.
A custom cabinet instal-
lation should provide the fol-
lowing minimum spacing
dimensions for cool opera-
tion. Allow at least 6 inches
(15.24 cm) above the top, 2
inches (3.81cm) below the
bottom and 1 inch (2.54 cm)
on each side of the amplifier,
so that airflow is not ob-
structed. Allow 16 inches
MC252 Side View
in Custom Cabinet
Cutout Opening for Ventilation
Support
Shelf
1-1/4"
3.18cm
11-1/2"
29.21cm
MC252 Bottom View
in Custom Cabinet
14-3/8"
36.51cm
Cutout Opening
for Ventilation
6
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Top Panel Connections and Switch
Main Fuse holder,
refer to information
on the top back
panel of the MC252
to determine the cor-
rect fuse size and
rating
UNBALANCED IN-
PUTS for an audio cable
from a preamplifier or
control center audio out-
puts
POWER CONTROL IN receives
a turn On/Off Trigger from a
McIntosh component. POWER
CONTROL OUT sends a turn On/
Off Trigger to the next McIntosh
component
RIGHT Channel OUTPUTs
connections for 2 ohm, 4 ohm
and 8 ohm Loudspeakers
MODE switch selects
between three modes of
operation; STEREO,
MONO (BRIDGED) or
MONO (BI-AMP)
Parallel
LEFT Channel OUTPUTs
connections for 2 ohm, 4 ohm
and 8 ohm Loudspeakers
Connect the MC252
BALANCED INPUTS for
an audio cable from a
preamplifier or control
center audio outputs
power cord to a live
AC outlet. Refer to
information on the
back panel to deter-
mine the correct
voltage
7
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How to Connect in Stereo
Caution: The supplied AC Power Cord should not be
connected to the Rear Panel of the MC252
Amplifier until after the Loudspeaker Connections
have been made and the supplied protective
Terminal Connection Covers have been installed.
Failure to observe this could result in Electric
Shock.
Banana plug connection:
Insert the banana plug into the hole at the top of the
terminal. Tighten the top portion of the terminal post
and the set screw to secure the banana plug in place.
Note: The use
of
Banana
1. For Remote Power Control, connect a power control
cable from the Control Center or Preamplifier Power
Control Out to the MC252 Power Control In.
2. Connect cables from the Unbalanced Output of a McIn-
tosh Preamplifier or Control Center to the MC252
Unbalanced Inputs.
Note: An optional hookup is to use balanced cables.
3. Prepare the Loudspeaker Hookup Cables that attach to
the MC252 Power Amplifier by choosing one of the
methods below:
Plugs is
for use in
the
United
States
and Canada only.
4. Connect the Loudspeaker hookup cables to the output
terminals that match the impedance of the Loudspeak-
er, being careful to observe the correct polarities. Out-
put impedance connections of 2S (ohm), 4S (ohm) and
8S (ohm) are provided. If the Loudspeaker’s imped-
ance is in-between the available connections, use the
nearest lower impedance connection.
WARNING: Loudspeaker terminals are hazardous live
and present a risk of electric shock. For
additional instruction on making
Bare wire cable ends:
Carefully remove sufficient insulation from the cable
ends, refer to figures 1,
2 & 3. If the cable is
stranded, carefully twist
the strands together as
tightly as possible.
Note: If desired, the twisted ends can be tinned with
solder to keep the strands together, or attach spade
lug and/or banana connector.
Loudspeaker Connections contact your
McIntosh Dealer or McIntosh Technical
Support.
5. Attach the supplied Terminal Connection Covers with
the four Mounting Screws (6-32 x 1/4 inch Phillips
Head) to the Rear Panel of the MC252 Amplifier. Refer
to figure 9.
Spade lug or prepared wire connection:
Insert the spade lug connector or prepared section of
the cable end into the terminal side access hole, and
tighten the terminal cap until the cable is firmly
clamped into the terminal so the wires cannot slip out.
Refer to figures 4, 5 & 6.
Note: The illustration in figure 9 is for the purpose of
installing the Terminal Connection Covers, showing
the opening on the covers for the Loudspeaker
Cables to exit the MC252. It is not intended to show
which terminal connections to use.
6. Connect the MC252 power cord to an active AC outlet.
Terminal Connection Covers
Cable Openings
Cover Mounting
Screw Locations
Cover Mounting
Screw Location
Figure 9
8
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How to Connect in Stereo
McIntosh C45 Audio Control Center
MC252 Top Rear View
To AC Outlet
4 ohm
Loudspeaker
4 ohm
Loudspeaker
9
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How to Connect in Mono Bridged Mode
Caution: The supplied AC Power Cord should not be
connected to the Rear Panel of the MC252
Amplifier until after the Loudspeaker Connections
have been made and the supplied protective
Terminal Connection Covers have been installed.
Failure to observe this could result in Electric
Shock.
Banana plug connection:
Insert the banana plug into the hole at the top of the
terminal. Tighten the top portion of the terminal post
and the set
screw to secure
the banana plug
in place. Refer
to figures 7 and
8.
There are two different ways of operating the MC252 mon-
aurally, Mono Bridged Mode and Mono Bi-Amp (Parallel)
Mode. The Mono Bridge Mode allows for Loudspeakers of
4S (ohm), 8S (ohm) or 16S (ohm) impedance to be con-
nected to the MC252. The Mono Bi-Amp (Parallel) Mode
allows for Loudspeakers of 1S (ohm), 2S (ohm) or 4S
(ohm) impedance to be connected to the MC252.
Choose the appropriate Mono Mode determined by the
impedance of your Loudspeakers. If the Mono Bi-Amp
(Parallel) Mode is appropriate for the Loudspeakers, pro-
ceed to page 12 for proper connections.
1. For Remote Power Control, connect a power control
cable from the Control Center or Preamplifier Power
Control Out to the MC252 Power Control In.
2. Connect cables from the Unbalanced Output of a McIn-
tosh Preamplifier or Control Center to the MC252
Unbalanced R/MONO Input.
Note: The use
of Banana Plugs is for use in the United States and
Canada only.
4. Referring to the “Mono Bridge Hookup Connections”
Chart on the next page, connect the Loudspeaker
hookup cables to appropriate output terminals based on
the impedance of the Loudspeaker (4S [ohm], 8S
[ohm] or 16S [ohm]), being careful to observe the cor-
rect polarities. If the Loudspeaker’s impedance is in-
between the available connections, use the nearest
lower impedance connection.
WARNING: Loudspeaker terminals are hazardous live
and present a risk of electric shock. For
additional instruction on making
Loudspeaker Connections contact your
McIntosh Dealer or McIntosh Technical
Support.
Note: An optional hookup is to use balanced cables.
3. Prepare the Loudspeaker Hookup Cables that attach to
the MC252 Power Amplifier by choosing one of the
methods below:
5. Attach the supplied Terminal Connection Covers with
the four Mounting Screws (6-32 x 1/4 inch Phillips
Head) to the Rear Panel of the MC252 Amplifier. Refer
to figure 9.
Bare wire cable ends:
Carefully remove sufficient insulation from the cable
ends, refer to figures 1, 2 & 3. If the cable is stranded,
carefully twist the strands
together as tightly as pos-
sible.
Note: If desired, the
Note: The illustration in figure 9 is for the purpose of
installing the Terminal Connection Covers, showing
the opening on the covers for the Loudspeaker
Cables to exit the MC252. It is not intended to show
which terminal connections to use.
6. Connect the MC252 power cord to an active AC outlet.
twisted ends can be
tinned with solder to keep the strands
together, or attach spade lug and/or
banana connector.
Terminal Connection Covers
Spade lug or prepared wire connection:
Insert the spade lug connector or prepared
section of the cable end into the terminal
side access hole, and tighten the terminal
cap until the cable is firmly clamped into
the terminal so the wires cannot slip out.
Refer to figures 4, 5 & 6.
Cable Openings
Cover Mounting
Screw Locations
Cover Mounting
Screw Location
Figure 9
10
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How to Connect in Mono Bridged Mode
McIntosh C45 Audio Control Center
MC252 Top Rear View
To AC Outlet
Mono Bridge Hookup Connections
Loudspeaker Loudspeaker Negative Loudspeaker Positive
Impedance
(-) Connection
(+) Connection
Left Output 2
Right Output 2
S
S
4
8
(Ohm)
(Ohm)
S
S
Positive (+ ) Connection
Positive (+ ) Connection
Left Output 4
Right Output 4
S
S
4 ohm
Loudspeaker
Positive (+ ) Connection
Positive (+ ) Connection
Left Output 8
Right Output 8
S
S
16 (Ohm)
S
Positive (+ ) Connection
Positive (+) Connection
11
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How to Connect in Mono Bi-Amp (Parallel)
Mode
Caution: The supplied AC Power Cord should not be
connected to the Rear Panel of the MC252 Amplifier
until after the Loudspeaker Connections have been
made and the supplied protective Terminal
Connection Covers have been installed. Failure to
observe this could result in Electric Shock.
Banana plug connection:
There are two different ways of operating the MC252 mon-
aurally, Mono Bridged Mode and Mono Bi-Amp (Parallel)
Mode. The Mono Bridge Mode allows for Loudspeakers of
4S (ohm), 8S (ohm) or 16S (ohm) impedance to be con-
nected to the MC252. The Mono Bi-Amp (Parallel) Mode
allows for Loudspeakers of 1S (ohm), 2S (ohm) or 4S
(ohm) impedance to be connected to the MC252.
Choose the appropriate Mono Mode determined by the
impedance of your Loudspeakers. If the Mono Bridge
Mode is appropriate for the Loudspeakers, proceed to page
10 for proper connections.
1. For Remote Power Control, connect a power control
cable from the Control Center or Preamplifier Power
Control Out to the MC252 Power Control In.
2. Connect cables from the Unbalanced Output of a McIn-
tosh Preamplifier or Control Center to the MC252
R/MONO Unbalanced Input.
Note: An optional hookup is to use balanced cables.
3. The MC252 Mono Bi-Amp (Parallel) Mode of Opera-
tion requires a Hookup Cable and jumper wires for con-
nection to the Power Amplifier Output Terminals; two
22 inch (55.88 cm) Jumper wires, and one Loudspeaker
Hookup Cable cut to the desired length. Prepare the
cable and wires by choosing one of the methods below:
Bare wire cable ends:
Insert the banana plug into the hole at the top of the
terminal. Tighten the top portion of the terminal post
and the set screw to secure the banana plug in place.
Refer to figures
7 and 8.
Note: The use
of
Banana
Plugs is
for use in
the
United States and Canada only.
4. Refer to the “Mono Bi-Amp (Parallel) Hookup Con-
nections” Chart on the next page for making the fol-
lowing connections.
5. Insert the Loudspeaker Hookup Cable Ends through
the opening of both supplied Terminal Connection
Covers and connect the one of prepared Jumper Wire
between the two - Output Terminals and the other
Jumper Wire between the two appropriate Impedance
+ Output Terminals. Connect the Loudspeaker hookup
cable to appropriate output terminals based on the im-
pedance of the Loudspeaker (1S [ohm], 2S [ohm] or
4S [ohm]), being careful to observe the correct polari-
ties. If the Loudspeaker’s impedance is in-between the
available connections, use the nearest lower impedance
connection.
Carefully remove suffi-
cient insulation from the
WARNING: Loudspeaker terminals are hazardous live
and present a risk of electric shock. For
cable/wire ends, refer to
figures 1, 2 & 3. If the
cable/wire is stranded, carefully twist the
strands together as tightly as possible.
Terminal Connection Covers
Note: If desired, the twisted ends can be tinned
with solder to keep the strands together,
or attach spade lug and/or banana
connector.
Spade lug or prepared wire connection:
Insert the spade lug connector or prepared
section of the cable/wire end into the termi-
nal side access hole, and tighten the termi-
nal cap until the cable/wire is firmly
Cable Openings
clamped into the terminal so they cannot
slip out. Refer to figures 4, 5 & 6.
Cover Mounting
Screw Locations
Cover Mounting
Screw Location
Figure 9
12
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How to Connect in Mono Bi-Amp (Parallel) Mode
McIntosh C45 Audio Control Center
additional instruction on making
Loudspeaker Connections contact your
McIntosh Dealer or McIntosh Technical
Support.
5. Attach the supplied Terminal Connection Covers with
the four Mounting Screws (6-32 x 1/4 inch Phillips
Head) to the Rear Panel of the MC252 Amplifier. Refer
to figure 9.
Note: The illustration in figure 9 is for the purpose of
installing the Terminal Connection Covers, showing
the opening on the covers for the Loudspeaker
Cables to exit the MC252. It is not intended to show
which terminal connections to use.
6. Connect the MC252 power cord to an active
AC outlet.
MC252 Top Rear View
To AC Outlet
Jumper Wires
Mono Bi-Amp (Parallel) Hookup Connections
Loudspeaker Loudspeaker Negative Loudspeaker Positive
Impedance
(-) Connection
(+) Connection
Left and Right Output 2
Left and Right Output 2
S
S
1
2
4
(Ohm)
(Ohm)
(Ohm)
S
S
S
Negative (- ) Connection
Positive (+ ) Connection
Left and Right Output 4
Left and Right Output 4
S
S
4 ohm
Loudspeaker
Negative (- ) Connection
Positive (+ ) Connection
Left and Right Output 8
Left and Right Output 8
S
S
Negative (- ) Connection
Positive (+) Connection
13
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Front Panel Displays and Controls
METER indicates the
Power Output of the Left
Channel Amplifier
METER indicates the
Power Output of the Right
Channel Amplifier
Remote On Indicator lights
when the amplifier is in the
Remote Turn-On Mode
METER Switch selects
the display modes of the
Power Output Meter
POWER Switch Turns
AC power On/Off, or
On/Remote
POWER GUARD LED
POWER GUARD LED
lights when the amplifier
Left Channel POWER
GUARD circuit activates
lights when the amplifier
Right Channel POWER
GUARD circuit activates
14
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How to Operate
How to Operate
Power On
slowly return to its rest position or lower
power level. The decay rate is approximately
6dB per minute.
To have the MC252 automatically turn On or Off when a
control center turns on or off,
rotate the power switch to the
remote position. For manual op-
eration, rotate the power switch
to the On or Off position as de-
sired. Refer to figure 10.
Mode Switch
The STEREO/MONO BRIDGED/MONO BI-AMP (Paral-
lel) Mode Switch, which is lo-
cated to the left of the R/MONO
BALANCED INPUT (XRL Con-
nector) on the Top Rear Panel of
the MC252 and allows selection
of either Stereo or two different
Mono Modes of Operation. Refer
to figures 13.
Note: There must be a power
control connection
between the MC252 and
Figure 10
the McIntosh Control
Center, in order for the remote power turn-on to
function.
Meter Selection
Figure 13
Note: There is additional
information for connecting
Rotate the meter mode switch to select the meter operation
mode you desire. Refer to figures 11 and 12.
Lights Off - Meter lights are
turned off and
the MC252 and pertaining to all modes of operation:
“How to Connect for Stereo” on pages 8 and 9.
“How to Connect for Mono Bridged” on pages 10
and 11.
the meter will
continue to indi-
cate the power
output.
“How to Connect for Mono Bi-Amp (Parallel)” on
pages 12 and 13.
Watts- The meters re-
spond to all the
musical informa-
tion being pro-
duced by the am-
Figure 11
plifier. They indicate to an accuracy of at least
95% of the power output with only a single
cycle of a 2000Hz tone burst.
Hold - The meter pointer is locked to the highest
power peak in a sequence of peaks. It is elec-
tronically held to this power level until a
Figure 12
higher power peak passes through the ampli-
fier. The meter pointer will then rise to the
newer higher indication. If no further power
peaks are reached, the meter pointer will very
15
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Technical Description
McIntosh Laboratory, the company who introduced the
world’s first amplifier that could be called “High Fidelity”,
has done it again. The McIntosh engineering staff has cre-
not come easily. Many months of design, testing and mea-
suring were required. Extensive controlled listening tests,
the ultimate form of measuring, were made before the final
ated a power amplifier without compromise, using the most design was accepted.
advanced McIntosh circuit design concepts.
Design Philosophy
A continuous average power output rating of 250 watts
and with an output current of greater than 50 amperes per
channel, making this one of the most advanced and power-
ful amplifiers McIntosh has ever manufactured. The distor-
tion limits for the MC252 are no more than 0.005% at rated
power output for all frequencies from 20Hz to 20,000Hz.
Typical performance at mid frequencies is less than
0.002%. The true distortion readings on the MC252 are so
low, it takes special measuring techniques to make accurate
readings. The MC252 can deliver the best possible perfor-
mance from any type of high quality loudspeaker system.
Creating an amplifier with this level of performance did
The design philosophy incorporated in the MC252 in-
volved several different techniques, all based on sound sci-
entific logic. Refer to figure 14. Every stage of voltage or
current amplification must be as linear as possible prior to
the use of negative feedback. McIntosh engineers know
how to properly design negative feedback circuits so they
contribute to the extremely low distortion performance ex-
pected from a McIntosh amplifier. The typical McIntosh
owner would never accept the approximately 100 times
higher distortion of many non-feedback designs.
All transistors are selected to have nearly constant cur-
Inside View of the MC252
16
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Technical Description
rent gain over the entire current range they must cover.
Output transistors in particular, have matched uniform cur-
rent gain, high current-bandwidth product and large active
region safe operating area. An automatic tracking bias sys-
tem completely eliminates any trace of crossover distor-
tion. Precision metal film resistors and low dielectric ab-
sorption film capacitors are used in all critical circuit loca-
tions.
The output signal of the circuit is coupled together in
the unique McIntosh MC252 Output Autoformer. It pro-
vides low distortion power transfer at frequencies from be-
low 20Hz to well beyond 20,000Hz with optimum imped-
ance points of two ohms, four ohms and eight ohms. The
unequaled expertise of McIntosh in the design and manu-
facturing of autoformers is legendary in the high fidelity
industry.
The high efficiency circuit design of the MC252 con-
tributes to low operating temperatures. More than 621
square inches of heat sink area keep the MC252 operating
safely with convection cooling. No fans are needed.
Autoformers
All solid state power amplifier output circuits work best
into what is called an optimum load. This optimum load
may vary considerably from what a loudspeaker requires.
In the case of more than one loudspeaker connected in par-
allel, the load to the power amplifier may drop to two ohms
or even less. A power amplifier connected to a load that is
Block Diagram of the Amplifiers
and
Meter Circuitry
Figure 14
17
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lower than optimum, causes more output current to flow,
which results in extra heat being generated in the power
output stage. This increase in temperature will result in a
reduced life expectancy for the amplifier.
The Autoformer creates an ideal match between the
power amplifier output stage and the loudspeaker. Refer to
figure 15. There is absolutely no performance limitation
amplifier under even the most extreme operating condi-
tions. The different types of protection circuits incorpo-
rated in the MC252 insure a long and safe operating life.
The MC252 also
includes the unique
patented McIntosh
Input Test Signal
Power Guard circuit.
Power Guard elimi-
nates the possibility of
ever overdriving the
amplifier into clipping.
Refer to figures 17, 18
and 19. An overdriven
amplifier can produce
both audible and inau-
dible distortion levels
exceeding 40%. The
audible distortion is
Figure 17
unpleasant to hear, but
the inaudible ultra-
sonic distortion is also
Without Power Guard
undesirable, since it
can damage valuable
loudspeaker system
tweeters. You will
never experience the
harsh and damaging
distortion due to clip-
ping.
Figure 15
with an Autoformer. Its frequency response exceeds that of
the output circuit itself, and extends well beyond the au-
dible range. Its distortion level is so low it is virtually im-
possible to measure. In the rare event of a power amplifier
output circuit failure, the McIntosh Autoformer provides
absolute protection from possible damage to your valuable
loudspeakers.
The Power Guard
circuit is a waveform
comparator, monitor-
ing both the input and
output waveforms.
Under normal operat-
ing conditions, there
Figure 18
With Power Guard
are no differences
between the shape of
these waveforms. If
an amplifier channel
is overdriven, there
will be a difference
between the two sig-
nal waveforms.
Protection Circuits
The MC252 incorporates its version of the McIntosh Sen-
try Monitor out-
put transistor
protection cir-
cuit. Refer to
figure 16. There
is absolutely no
compromise in
When the difference
exceeds 0.3%
sonic perfor-
mance with this
circuit, and it
ensures safe op-
eration of the
(equivalent to 0.3%
harmonic distortion),
the Power Guard ac-
tivates the PG light
and a dynamic elec-
Figure 19
Figure 16
18
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Technical Description, con’t
tronic attenuator at the amplifier input reduces the input
volume just enough to prevent any further increase in dis-
tortion. The Power Guard circuit acts so fast that there are
absolutely no audible side effects and the sonic purity of
the music reproduction is perfectly preserved. The MC252
Power Amplifier with Power Guard is not limited to just
the rated power output, but will actually produce distortion
free output well above its rated power due to the McIntosh
philosophy of conservative design.
your McIntosh Preamplifier or Control Center. When you
turn on your preamplifier a digital “1” (+5V) signal oper-
ates the power relay in the MC252. The MC252 also has a
remote Power Control Out Jack. The Power Control signal
from this jack is delayed by a fraction of a second so that
the turn on power surge of the next power amplifier occurs
at a later time. This helps prevent power circuit overload
that could trip circuit breakers or blow fuses, a very impor-
tant feature in a high power Home Theater System employ-
ing three MC252 Power Amplifiers.
Power Supply Circuits
The MC252 can provide greater than 50 amperes peak
output current to drive uneven speaker loads. Some poor
speaker designs have input impedance that dip to 1 or 2
ohms at various frequencies and the MC252 has the output
To compliment the design of the MC252, there is a high
voltage power supply for both channels. Refer to figure 20.
The power amplifiers draw high current from the AC
power line. Therefore, it is important that they plug directly current reserve to drive them. The MC252 has main filter
capacitors that guarantee an excellent signal to noise ratio
and the energy storage necessary for the wide dynamic
into the wall outlet.
Also, most owners desire that there be one power
switch for the whole audio system. The MC252 is equipped range that “Digital Audio” demands.
with a circuit that provides remote Power Control from
Block Diagram
of the
Power Supply
Figure 20
19
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20
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Notes
21
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Specifications
Specifications
Power Output Stereo
A-Weighted Signal To Noise Ratio
112dB below rated output
Minimum sine wave continuous average power output per
channel, all channels operating is:
250 watts into 2 ohm load
250 watts into 4 ohm load
250 watts into 8 ohm load
Input Impedance
10,000 ohms Unbalanced Inputs
20,000 ohms Balanced Inputs
Power Output Mono Bridged
Minimum sine wave continuous average power output is:
500 watts into 4 ohm load
Wide Band Damping Factor
Greater than 40
500 watts into 8 ohm load
500 watts into 16 ohm load
Power Requirements
100 Volts, 50/60Hz at 8.0 amps
110 Volts, 50/60Hz at 7.2 amps
120 Volts, 50/60Hz at 6.6 amps
220 Volts, 50/60Hz at 3.3 amps
230 Volts, 50/60Hz at 3.3 amps
240 Volts, 50/60Hz at 3.3 amps
Power Output Mono Bi-Amp (Parallel)
Minimum sine wave continuous average power output is:
500 watts into 1 ohm load
500 watts into 2 ohm load
500 watts into 4 ohm load
Note: Refer to the rear panel of the MC252 for the correct
voltage.
Output Load Impedance
2, 4 or 8 ohms (Stereo Mode)
1, 2, 4, 8 or 16 ohms (Mono Modes)
Overall Dimensions
Width is 17-1/2 inches (44.45cm)
Height is 9-7/16 inches (23.97cm) including feet
Depth is 14-13/16 inches (37.62cm) including the Front
Panel and Knobs
Rated Power Band
20Hz to 20,000Hz
Total Harmonic Distortion
Weight
94.5 pounds (42.87 kg) net, 108.5 pounds (49.22 kg) in
shipping carton
Maximum Total Harmonic Distortion at any power
level from 250 milliwatts to rated power output is
0.005%
Intermodulation Distortion
Maximum Intermodulation Distortion if instanta-
neous peak output per channel does not exceed
twice the rated output, for any combination of fre-
quencies from 20Hz to 20,000Hz, with all channels
operating is 0.005%
Dynamic Headroom
2.0dB
Frequency Response
+0, -0.25dB from 20Hz to 20,000Hz
+0, -3dB from 10Hz to 100,000Hz
Sensitivity
1.6 Volts Unbalanced Input
3.2 Volts Balanced Input
22
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Packing Instructions
Packing Instructions
In the event it is necessary to repack the equipment for
shipment, the equipment must be packed exactly as shown
below. It is very important that the four plastic feet are at-
tached to the bottom of the equipment. Three #10 x 2-1/2
inch screws and washers must be used to fasten the unit
securely to the bottom pad and shipping skid. This will en-
sure the proper equipment location on the bottom pad. Fail-
ure to do this will result in shipping damage.
Use the original shipping carton and interior parts only
if they are all in good serviceable condition. If a shipping
carton or any of the interior part(s) are needed, please call
or write Customer Service Department of McIntosh Labo-
ratory. Please see the Part List for the correct part numbers.
Quantity Part Number
Description
Shipping carton only
Foam end cap
1
2
034256
034250
1
1
1
1
1
034198
034199
034188
034037
033699
Inner carton top
Inner carton bottom
Foam pad
Inner carton pad
Shipping skid
7
4
2
3
3
017218
100159
104083
101204
104033
Plastic foot
#10-32 x 3/4” Machine screw
#10 x 7/16” Flat washer
#10 x 2-1/2” Wood screw
#10 x 1-3/4” Flat washer
23
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McIntosh Laboratory, Inc.
2 Chambers Street
Binghamton, NY 13903
The continuous improvement of its products is
the policy of McIntosh Laboratory Incorporated
who reserve the right to improve design without
notice.
Printed in the U.S.A.
McIntosh Part No. 040815
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