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
The lightning flash with arrowhead,
within an equilateral triangle, is intended
to alert the user to the presence of
uninsulated “dangerous voltage” within
the product’s enclosure that may be of
sufficient magnitude to constitute a risk
of electric shock to persons.
The exclamation point within an equilateral triangle is intended to alert the
user to the presence of important
operating and maintenance (servicing) instructions in the literature accompanying the appliance.
WARNING - TO REDUCE RISK OF
FIRE OR ELECTRICAL SHOCK, DO
NOT EXPOSE THIS EQUIPMENT TO
RAIN OR MOISTURE.
IMPORTANT SAFETY
INSTRUCTIONS!
PLEASE READ THEM BEFORE
OPERATING THIS EQUIPMENT.
1. Read these instructions.
2. Keep these instructions.
3. Heed all warnings.
4. Follow all instructions.
5. Do not use this apparatus near water.
6. Clean only with a dry cloth.
7. Do not block any ventilation openings. Install in
accordance with the manufacturer’s instructions.
8. Do not install near any heat sources such as
radiators, heat registers, stoves, or other
apparatus (including amplifiers) that produce
heat.
9. Do not defeat the safety purpose of the polarized
or grounding-type plug. A polarized plug has two
blades with one wider than the other. A grounding
type plug has two blades and a third grounding
prong. The wide blade or the third prong are
provided for your safety. If the provided plug
does not fit into your outlet, consult an electrician
for replacement of the obsolete outlet.
10. Protect the power cord from being walked on or
pinched particularly at plugs, convenience
receptacles, and the point where they exit from
the apparatus.
NO USER-SERVICEABLE PARTS
INSIDE. REFER SERVICING TO
QUALIFIED PERSONNEL.
To prevent the risk of electric shock, do not remove cover or
back. No user serviceable parts inside.
11. Only use attachments/accessories specified by the
manufacturer.
12. Use only with the cart, stand, tripod, bracket, or
table specified by the manufacturer,
or sold with the apparatus. When a
cart is used, use caution when moving
the cart/apparatus combination to
avoid injury from tip-over.
13. Unplug this apparatus during lightning storms or
when unused for long periods of time.
14. Refer all servicing to qualified service personnel.
Servicing is required when the apparatus has
been damaged in any way, such as power-supply
cord or plug is damaged, liquid has been spilled
or objects have fallen into the apparatus, the
apparatus has been exposed to rain or moisture,
does not operate normally, or has been dropped.
15. Do not expose this equipment to dripping or
splashing and ensure that no objects filled with
liquids, such as vases, are placed on the
equipment.
16. To completely disconnect this equipment from
the a.c. mains, disconnect the power supply cord
plug from the a.c. receptacle.
17. The mains plug of the power supply cord shall
remain readily operable.
2
Thank You
Your decision to own this McIntosh MC252 Power Amplifier ranks you at the very top among discriminating music
listeners. You now have “The Best.” The McIntosh dedication 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.
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:
Table of Contents
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
Technical Assistance
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 additional help concerning a suspected problem, you can receive technical assistance for all McIntosh products at:
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 assistance on factory repair return procedure, contact the
McIntosh Service Department at:
McIntosh Laboratory, Inc.
2 Chambers Street
Binghamton, New York 13903
Phone: 607-723-3515
Fax: 607-723-1917
Important Information
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.
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.
Copyright 2003 by McIntosh Laboratory, Inc.
3
Connector Information
XLR Connectors
Below is the Pin configuration for the XLR Balanced Input
Connectors on the MC252. Refer to the diagram for connection:
PIN 1: Shield/Ground
PIN 2: + Input
PIN 3: - Input
Power Control and Trigger Connectors
The MC252’s Power Control Outputs provide a 5 volt signal. Use a 1/8 inch stereo mini
phone plug to connect to the
Power Control Input on other
McIntosh Components.
Pin 2
Positive
Pin 1
Pin 3
N/C
Ground
Introduction
Now you can take advantage of traditional McIntosh standards 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 absolutely accurate. The McIntosh Sound is “The Sound of the
Music Itself.”
Performance Features
• Power Output
The MC252 consists of two separate power amplifier channels, 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.
••
• Balanced and Unbalanced Inputs
••
Balanced connections guard against induced noise and allow long cable runs without compromising sound quality.
••
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.
••
•
Power Control
••
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 additional 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.
••
• 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.
••
• Fiber Optic Solid State Front Panel Illumination
••
The Illumination of the Front Panel is accomplished by the
combination of custom designed Fiber Optic Light Diffusers and Light Emitting Diodes (LEDs). This provides even
Front Panel Illumination, together with the extra long life
LEDs.
••
• Patented Autoformers
••
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
••
• 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.
Connector Information, Introduction, Performance Features and Dimensions
The following dimensions can assist in determining the
best location for your MC252. There is additional information on the next page pertaining to installing the MC252
into cabinets.
Front View of the MC252
17-
1/2
44.45cm
16-
13/16
42.70cm
"
8-
13/16
"
7/16
22.38cm
9-
23.97cm
"
"
Rear View of the MC252
Side View of the MC252
13-
1/4
33.66cm
14-
36.83cm
"
1/2
"
13-
5/8
34.61cm
"
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
Installation
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.
The MC252 can be placed upright on a table or shelf,
standing on its four feet. The
four feet may be removed
from the bottom of the
MC252 when it is custom
installed as outlined below.
The four feet together with
the mounting screws should
be retained for possible future use if the MC252 is removed from the custom installation and used free
standing. It also can be custom 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 instrument. Do not install the
MC252 directly above a heat
generating component such
as a high powered amplifier.
If all the components are installed 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 temperature.
A custom cabinet installation should provide the following minimum spacing
dimensions for cool operation. 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 obstructed. Allow 16 inches
MC252 Front Panel
Custom Cabinet Cutout
Opening
for Ventilation
MC252 Side View
in Custom Cabinet
MC252 Bottom View
in Custom Cabinet
Cabinet
Front
Panel
Support
Shelf
Installation
(40.64 cm) depth behind the front panel. Allow 1-3/16
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.
17-
1/16
"
43.34cm
8-
5
/16
"
21.11cm
Cutout Opening
for Custom Mounting
6"
15.24cm
Cutout Opening for Ventilation
1
-1/4
"
3.18cm
11-
1/2
"
29.21cm
Cutout Opening
for Ventilation
Alternate Rear Foot Location
14-
3/8
"
36.51cm
6
Top Panel Connections and Switch
Main Fuse holder,
refer to information
on the top back
panel of the MC252
to determine the correct fuse size and
rating
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
UNBALANCED INPUTS for an audio cable
from a preamplifier or
control center audio outputs
RIGHT Channel OUTPUTs
connections for 2 ohm, 4 ohm
and 8 ohm Loudspeakers
Connect the MC252
power cord to a live
AC outlet. Refer to
information on the
back panel to determine the correct
voltage
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
BALANCED INPUTS for
an audio cable from a
preamplifier or control
center audio outputs
7
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.
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 McIntosh 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:
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.
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.
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
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 Loudspeaker, being careful to observe the correct polarities. Output impedance connections of 2S (ohm), 4S (ohm) and
8S (ohm) are provided. 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.
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.
Terminal Connection Covers
Cable Openings
Cover Mounting
Screw Locations
Figure 9
8
Cover Mounting
Screw Location
McIntosh C45 Audio Control Center
How to Connect in Stereo
MC252 Top Rear View
4 ohm
Loudspeaker
To AC Outlet
4 ohm
Loudspeaker
9
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.
There are two different ways of operating the MC252 monaurally, 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 connected 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, proceed 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 McIntosh Preamplifier or Control Center to the MC252
Unbalanced R/MONO Input.
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:
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.
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.
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.
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 correct polarities. If the Loudspeaker’s impedance is inbetween 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.
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.
Terminal Connection Covers
Cable Openings
10
Cover Mounting
Screw Locations
Cover Mounting
Screw Location
Figure 9
McIntosh C45 Audio Control Center
How to Connect in Mono Bridged Mode
MC252 Top Rear View
4 ohm
Loudspeaker
To AC Outlet
Mono Bridge Hookup Connections
Loudspeaker
Impedance
4S (Ohm)
8S (Ohm)
16S (Ohm)
Loudspeaker Negative
(-) Connection
Left Outp ut 2
Positive (+ ) Connection
Left Outp ut 4
Positive (+ ) Connection
Left Outp ut 8
Positive (+ ) Connection
S
S
S
Loudspeaker Positive
(+) Connection
Right Outp ut 2
Positive (+ ) Connection
Right Outp ut 4
Positive (+ ) Connection
Right Output 8
Positive (+) Connection
S
S
S
11
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.
There are two different ways of operating the MC252 monaurally, 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 connected 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 McIntosh 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 Operation requires a Hookup Cable and jumper wires for connection 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:
Carefully remove sufficient insulation from the
cable/wire ends, refer to
figures 1, 2 & 3. If the
cable/wire 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.
Spade lug or prepared wire connection:
Insert the spade lug connector or prepared
section of the cable/wire end into the terminal side access hole, and tighten the terminal cap until the cable/wire is firmly
clamped into the terminal so they cannot
slip out. Refer to figures 4, 5 & 6.
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.
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 Connections” Chart on the next page for making the following 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 impedance of the Loudspeaker (1S [ohm], 2S [ohm] or
4S [ohm]), being careful to observe the correct 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
Terminal Connection Covers
Cable Openings
Cover Mounting
Screw Locations
Figure 9
Cover Mounting
Screw Location
12
How to Connect in Mono Bi-Amp (Parallel) Mode
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
McIntosh C45 Audio Control Center
4 ohm
Loudspeaker
To AC Outlet
Jumper Wires
Mono Bi-Amp (Parallel) Hookup Conne ctions
Loudspeaker
Impedance
1S (Ohm)
2S (Ohm)
4S (Ohm)
Loudspeaker Negative
(-) Connection
Left and Right O utput 2
Negative (- ) Connection
Left and Right O utput 4
Negative (- ) Connection
Left and Right O utput 8
Negative (- ) Connection
Loudspeaker Positive
(+) Connection
Left and Right O utput 2
S
Positive (+ ) Connection
Left and Right O utput 4
S
Positive (+ ) Connection
Left and Right O utput 8
S
Positive (+) Connection
S
S
S
13
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
14
METER Switch selects
the display modes of the
Power Output Meter
POWER GUARD LED
lights when the amplifier
Left Channel POWER
GUARD circuit activates
POWER Switch Turns
AC power On/Off, or
On/Remote
POWER GUARD LED
lights when the amplifier
Right Channel POWER
GUARD circuit activates
How to Operate
Power On
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 operation, rotate the power switch
to the On or Off position as desired. Refer to figure 10.
Note: There must be a power
control connection
between the MC252 and
the McIntosh Control
Center, in order for the remote power turn-on to
function.
Meter Selection
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 meter will
continue to indicate the power
output.
Watts- The meters re-
spond to all the
musical information being produced by the amplifier. 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 electronically held to this power level until a
Figure 10
Figure 11
How to Operate
slowly return to its rest position or lower
power level. The decay rate is approximately
6dB per minute.
Mode Switch
The STEREO/MONO BRIDGED/MONO BI-AMP (Parallel) Mode Switch, which is located to the left of the R/MONO
BALANCED INPUT (XRL Connector) 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 is additional
information for connecting
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.
“How to Connect for Mono Bi-Amp (Parallel)” on
pages 12 and 13.
Figure 13
Figure 12
higher power peak passes through the amplifier. The meter pointer will then rise to the
newer higher indication. If no further power
peaks are reached, the meter pointer will very
15
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 created a power amplifier without compromise, using the most
advanced McIntosh circuit design concepts.
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 powerful amplifiers McIntosh has ever manufactured. The distortion 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 performance from any type of high quality loudspeaker system.
Creating an amplifier with this level of performance did
not come easily. Many months of design, testing and measuring were required. Extensive controlled listening tests,
the ultimate form of measuring, were made before the final
design was accepted.
Design Philosophy
The design philosophy incorporated in the MC252 involved several different techniques, all based on sound scientific 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 expected 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-
16
Inside View of the MC252
Technical Description
rent gain over the entire current range they must cover.
Output transistors in particular, have matched uniform current gain, high current-bandwidth product and large active
region safe operating area. An automatic tracking bias system completely eliminates any trace of crossover distortion. Precision metal film resistors and low dielectric absorption film capacitors are used in all critical circuit locations.
The output signal of the circuit is coupled together in
the unique McIntosh MC252 Output Autoformer. It provides low distortion power transfer at frequencies from below 20Hz to well beyond 20,000Hz with optimum impedance 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 contributes 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 parallel, 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
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
Figure 15
with an Autoformer. Its frequency response exceeds that of
the output circuit itself, and extends well beyond the audible range. Its distortion level is so low it is virtually impossible 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.
Protection Circuits
The MC252 incorporates its version of the McIntosh Sentry Monitor output transistor
protection circuit. Refer to
figure 16. There
is absolutely no
compromise in
sonic performance with this
circuit, and it
ensures safe operation of the
Figure 16
amplifier under even the most extreme operating conditions. The different types of protection circuits incorporated in the MC252 insure a long and safe operating life.
The MC252 also
includes the unique
Input Test Signal
patented McIntosh
Power Guard circuit.
Power Guard eliminates the possibility of
ever overdriving the
amplifier into clipping.
Refer to figures 17, 18
and 19. An overdriven
amplifier can produce
both audible and inaudible distortion levels
exceeding 40%. The
audible distortion is
unpleasant to hear, but
the inaudible ultrasonic distortion is also
Without Power Guard
Figure 17
undesirable, since it
can damage valuable
loudspeaker system
tweeters. You will
never experience the
harsh and damaging
distortion due to clipping.
The Power Guard
circuit is a waveform
comparator, monitoring both the input and
output waveforms.
Figure 18
Under normal operating conditions, there
are no differences
With Power Guard
between the shape of
these waveforms. If
an amplifier channel
is overdriven, there
will be a difference
between the two signal waveforms.
When the difference
exceeds 0.3%
(equivalent to 0.3%
harmonic distortion),
the Power Guard activates the PG light
and a dynamic elec-
Figure 19
18
Technical Description, con’t
tronic attenuator at the amplifier input reduces the input
volume just enough to prevent any further increase in distortion. 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.
Power Supply Circuits
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
into the wall outlet.
Also, most owners desire that there be one power
switch for the whole audio system. The MC252 is equipped
with a circuit that provides remote Power Control from
your McIntosh Preamplifier or Control Center. When you
turn on your preamplifier a digital “1” (+5V) signal operates 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 important feature in a high power Home Theater System employing three MC252 Power Amplifiers.
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
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
range that “Digital Audio” demands.
Block Diagram
of the
Power Supply
Figure 20
19
20
Notes
21
Specifications
Specifications
Power Output Stereo
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
Power Output Mono Bridged
Minimum sine wave continuous average power output is:
500 watts into 4 ohm load
500 watts into 8 ohm load
500 watts into 16 ohm load
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
Output Load Impedance
2, 4 or 8 ohms (Stereo Mode)
1, 2, 4, 8 or 16 ohms (Mono Modes)
Rated Power Band
20Hz to 20,000Hz
Total Harmonic Distortion
Maximum Total Harmonic Distortion at any power
level from 250 milliwatts to rated power output is
0.005%
A-Weighted Signal To Noise Ratio
112dB below rated output
Input Impedance
10,000 ohms Unbalanced Inputs
20,000 ohms Balanced Inputs
Wide Band Damping Factor
Greater than 40
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
Note: Refer to the rear panel of the MC252 for the correct
voltage.
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
Weight
94.5 pounds (42.87 kg) net, 108.5 pounds (49.22 kg) in
shipping carton
Intermodulation Distortion
Maximum Intermodulation Distortion if instantaneous peak output per channel does not exceed
twice the rated output, for any combination of frequencies 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
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 attached 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 ensure the proper equipment location on the bottom pad. Failure 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 Laboratory. Please see the Part List for the correct part numbers.
Quantity Part Number Description
1 034256 Shipping carton only
2 034250 Foam end cap
1 034198 Inner carton top
1 034199 Inner carton bottom
1 034188 Foam pad
1 034037 Inner carton pad
1 033699 Shipping skid
7 017218 Plastic foot
4 100159 #10-32 x 3/4” Machine screw
2 104083 #10 x 7/16” Flat washer
3 101204 #10 x 2-1/2” Wood screw
3 104033 #10 x 1-3/4” Flat washer
23
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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