McIntosh MC-275 Mk4 Owners manual

Stereo Power Amplifier

MC275

Owner’s Manual

McIntosh Laboratory, Inc. 2 Chambers Street Binghamton, New York 13903-2699 Phone: [phone] FAX: [phone]

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 Y ou

Table of Contents

Your decision to own this McIntosh MC275 Stereo 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:

T echnical 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:

Safety Instructions ............................................................ 2

Thank You and Please Take a Moment............................. 3

Technical Assistance and Customer Service .................... 3

Table of Contents.............................................................. 3

Important Information ...................................................... 4

Connector Information ..................................................... 4

Introduction ...................................................................... 4

Performance Features ....................................................... 4

Dimensions ....................................................................... 5

Installation of Tubes and Tube Cover............................... 6

Location and Ventilation................................................... 7

Left Side Panel Connections ............................................ 8

Right Side Panel Connection and Fuse Holder ................ 9

How to Connect for Stereo ............................................. 10

How to Connect for Mono Parallel ................................ 11

Left Side Panel Controls and Switches .......................... 12

How to Operate............................................................... 13

Specifications ................................................................. 14

Packing Instructions ....................................................... 15

McIntosh Laboratory, Inc.
2 Chambers Street
Binghamton, New York 13903
Phone: [phone]
Fax: [phone]

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: [phone]
Fax: [phone]

Copyright 2004 © by McIntosh Laboratory, Inc.

3

Introduction and Performance Features

Important Information

1. Caution: To prevent electrical shock make sure that the AC
POWER CORD IS NOT CONNECTED TO THE
MC275 when inserting or removing Vacuum Tubes,
as there are hazardous voltages present at the pins of
the Tube Sockets.

2. When Vacuum Tubes are installed or removed make sure to
reattach the Tube Cover to the MC275 Chassis.

3. If the MC275 has been On, please allow the Hot Vacuum
Tubes to cool first before removing them.

4. For additional connection information, refer to the owner’s
manual(s) for any component(s) connected to the MC275.

5. It is very important that loudspeaker cables of adequate size
be used, so that there will be minimum power loss. The size is
specified in Gauge Numbers or AWG (American Wire Gauge).
The smaller the Gauge number, the larger the wire size.
Connection Terminals will accept up to a 8 AWG 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.

Connector Information

XLR Connectors

Below is the Pin configuration for the XLR Balanced Input
Connectors on the MC275. Refer to the diagram for con­nection:

PIN 1: Shield/Ground
PIN 2: + Input
PIN 3: - Input

Pin 2
Pin 1
Pin 3

Introduction

Now you can take advantage of traditional McIntosh stan­dards of excellence in the MC275 Stereo Power Amplifier.
Two 75 watt output channels will drive any high quality
Loudspeaker System to its ultimate performance. The
MC275 reproduction is sonically transparent and abso­lutely accurate. The McIntosh Sound is “The Sound of the
Music Itself.”

Performance Features

••

• Power Output

••

The MC275 consists of two separate power amplifier chan­nels, each capable of 75 watts into 4, 8 or 16 ohm Loud­speakers in stereo. It may also be operated in mono at 150
watts into 2, 4, or 8 ohm Loudspeakers.

••

• Bifilar Wound Transformers and Output Circuit

••

The Power Output Sections utilize the famous McIntosh
Patented Unity Coupled Circuit with a Bifilar Wound Out­put Transformer for low distortion, extended frequency re­sponse and cool operating output tubes.

••

• Balanced and Unbalanced Inputs

••

Balanced connections guard against induced noise and al­low long cable runs without compromising sound quality.

••

• Gold Plated Connectors and Tube Socket Contacts

••

Gold Plated Input Jacks and Output Binding Posts provide
trouble free connections. Ceramic tube sockets with gold
plated contacts provide protection from atmospheric con­tamination. Output Tube Sockets include Air-Pipe cooling
at their bases.

••

• Super Mirror Chassis Finish

••

The famous McIntosh Stainless Steel Chassis with Super
Mirror Finish ensures the pristine beauty of the MC275
will be retained for many years.

4

MC275 Dimensions

The following dimensions can assist in determining the
best location for your MC275. There is additional informa­tion on page 7 pertaining to installing the MC275 into cabi­nets.

Front View of the MC275

1

-3/4

"

4.45cm

16-1/2

41.91cm

13

-5/8

34.61cm

MC275 Dimensions

"

-7/8

"

7

20.00cm

"

8

-1/4

"

20.96cm

Top View of the MC275

Left Side View
of the MC275

1

-3/4

"

4.45cm

4

-3/8

"

11.11cm

5

-9/16

"

14.13cm

12"

30.48cm

Right Side View
of the MC275

1

-1/4

"

3.18cm

5

Installation of Tubes and Tube Cover

Caution: To prevent electrical shock make sure that the AC

POWER CORD IS NOT CONNECTED TO THE
MC275 when inserting or removing Tubes, as there
are hazardous voltages present at the pins of the
Tube Sockets.

Your MC275 has gone through an extensive series of per­formance tests during the manufacturing process. The
MC275 is supplied with the actual Tubes that were used to
test and confirm the performance of this amplifier. To pro­tect the Vacuum Tubes from possible shipping damage,
they are packed in four layers of foam and placed into the
Tube Cover. It is secured to the MC275 Chassis.

Note: Gloves or a soft cloth will prevent “fingerprinting” of

the Tubes during their installation.

1. Orient the MC275 so the Front Panel is facing you.

2. Remove the Tube Cover from the MC275 Chassis by
lifting up on both sides. Refer to figure 1.

3. Orient the Tube Cover to the wide opening along one
side of its longer dimension. Refer to figure 2.

4. Remove the first layer of foam to expose the Tubes.
Refer to figure 3.

5. Carefully remove the Tubes from the remaining
pieces of foam and temporarily place them in a safe
location.

6. Remove the remaining foam from the Tube Cover
and retain all four pieces for possible future use.

Tinnerman Clip Fasteners

Tube Cover with
Layers of Foam
and Tubes

Tube Cover

Figure 1

Figure 1

Figure 2

The MC275 Chassis has nomenclature screened on it to
specify both the circuit location and Tube Type for each
channel. Refer to figure 4.

Note: It is extremely important to insert the Tubes in the

correct location.

Power Output Tubes:

1. Orient the Chassis so the Front Panel of the Amplifier
is facing you.

2. Locate a KT88 or 6550 Power Output Tube.

3. On the top left side of the amplifier, locate the Tube
Socket that has the nomenclature V8 KT88/6550
next to it on the chassis.

4. Orient the Tube so the key on the base of the Tube is
aligned with the corresponding key on the Tube
Socket.

5. Carefully insert the Tube into the socket until the base
of the Tube is fully seated in the Tube Socket.

6. Repeat the above the steps for the remaining 4 Power
Output Tubes.

There are two different types of Small Signal Tubes
(12AX7A and 12AT7) used in each channel. Tube type can
be found on the outside of the Tube. The MC275 will not
function if they are inserted into the wrong socket.

Power Output Tubes

Figure 3

V8 KT88/6550 Tube

V1 12AX7A Tube

Figure 4

Small Signal Tubes

6

Installation of Tubes, Tube Cover, Location and V entilation

Small Signal Tubes:

1. Locate a 12AX7A Tube.

2. On the top left side of the amplifier, locate the Tube
Socket that has the nomenclature V1 12AX7A next
to it on the chassis. Refer to figure 4 and 5.

3. Orient the Tube so the area where no pins are located
on the base of the Tube is aligned with the corre­sponding area on the Tube Socket.

4. Carefully insert the Tube into the socket until the base
of the Tube is fully seated in the Tube Socket.

5. Repeat the above steps for the remaining two
12AX7A Tubes at locations V2 and V5.

6. Locate a 12AT7 Tube.

7. On the top center of the amplifier, locate the Tube
Socket that has the nomenclature V3 12AT7A next to
it on the chassis.

8. Insert the Tube, following the same procedure as in
steps 3 and 4.

9. Repeat steps 6-9 for the remaining three 12AT7
Tubes at locations V4, V6 and V7.

Caution: To prevent electrical shock make sure the MC275

Tube Cover is installed before connecting the AC
Power Cord.

Before operating the MC275, locate the previously re­moved Tube Cover and perform the following steps:

Installing the Tube Cover:

1. The Tube Cover has a wide opening along one side
of its longer dimension. Orient this wide opening so
it is facing towards the three large transfomers.

2. Carefully place the Tube Cover onto the MC275
while at the same time aligning the two chassis
mounted ball studs with the Tinnerman Clips in the
cover. Refer to figure 6.

Location and V entilation

12AX7A

KT88/6550

12AX7A12AT7

Figure 5

Ball Stud Fasteners

Figure 6

12AT7

The MC275 can be placed upright on a table or shelf,
standing on its four feet. It also can be installed in a piece
of furniture of your choice. Do not install the MC275 di­rectly above a heat generating component. Adequate venti­lation extends the trouble free life of the MC275. The sug­gested minimum space for operating the MC275 is 22
inches (55.88cm) in width, 18 inches (45.72cm) depth, and
21 inches (53.34cm) in height. Always allow air to flow
through the ventilation holes on the bottom of the amplifier
and a means for the warm air to escape at the top. If the
MC275 is installed in a cabinet, a quiet running ventilation
fan can be a definite asset in maintaining the coolest pos­sible operating temperature. Refer to figure 7.

Warm Air

Cool Air

Figure 7

7

Left Side Panel Connections

LEFT OUTPUT
Connections for
loudspeakers

BALANCED INPUTS
for audio cables from a
preamplifier or control
center audio outputs

RIGHT OUTPUT
Connections for
loudspeakers

UNBALANCED INPUTS
for audio cables from a
preamplifier or control
center audio outputs

8

Right Side Panel Connection and Fuse Holder

Connect the MC275
power cord to a live
AC outlet. Refer to
information on the
back panel to deter­mine the correct volt­age

Main Fuse holder,
refer to information
on the back panel
of your MC275 to
determine the cor­rect fuse size and
rating

9

How to Connect for Stereo

How to Connect for Stereo

1. Connect cables from the Balanced Outputs of a McIn­tosh Preamplifier or Control Center to the MC275 Left
and Right Balanced Inputs.

Note: An optional hookup is to use unbalanced cables.

2. Prepare the Loudspeaker Hookup Cables that attach to
the MC275 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.

Spade lug or prepared wire connection:
Insert the spade lug connector or prepared section of
the cable end under the terminal strip screw and
tighten the screw until the cable is firmly clamped
into the ter­minal strip
so the
wires can­not slip
out. Refer
to figures 4, 5 & 6.

3. 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 4S (ohm), 8S (ohm) and
16S (ohm) are provided. If the Loudspeaker’s imped-
ance is in-between the available connections, use the
nearest lower impedance connection.

4. Place the MC275 POWER Switch to the OFF Position
and connect the supplied power cord to an active AC
outlet.

McIntosh Preamplifier

Left
Loudspeaker
4 ohm

10

Right
Loudspeaker
4 ohm

How to Connect for Mono Parallel

How to Connect for Mono Parallel

1. Connect cables from the Balanced Output of a McIn­tosh Preamplifier or Control Center to the MC275
Right Balanced Input.

Note: An optional hookup is to use unbalanced cables.

2. Prepare the Loudspeaker Hookup Cable and Jumper
Wires for connection to the Power Amplifier Output
Terminals; two 4-1/2 inch (11.43 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
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.

Spade lug or prepared wire connection:
Insert the spade lug connector or prepared section of
the cable end under the terminal strip screw and
tighten the screw until the cable is firmly clamped
into the ter­minal strip
so the
wires can­not slip
out. Refer to figures 4, 5 & 6.

3. Connect the hookup cables to the output terminals that
match the connections in the chart below, 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.

4. Place the MC275 POWER Switch to the OFF Position
and connect the supplied power cord to an active AC
outlet.

Mono (Parallel) Hookup Connections

Loudspeaker

Impedance

2S (Ohm)

4S (Ohm)

8S (Ohm)

Loudspeaker Negative

(-) Connection

Left a nd Right Output 4

Negative (- ) Connection

Left a nd Right Output 8

Negative (- ) Connection

Left and Right Output 16

Negative (- ) Connection

McIntosh Preamplifier

Loudspeaker Positive

(+) Con nec tion

Left a nd Right Output 4

S

Posit ive (+ ) Connection

Left a nd Right Output 8

S

Posit ive (+ ) Connection

Left and Right Output 16

S

Positive (+) Connection

S

S

S

4 ohm
Loudspeaker

Jumper Cables

11

Left Side Panel Controls and Switches

UNBALANCED
LEVEL Controls for
each channel when us­ing the Unbalanced In­puts

12

Power Switch turns all
AC power On or Off

MODE switch selects
MONO (Parallel) or
STEREO Modes of
operation

INPUTS switch se­lects between the
BALanced or
UNBALanced Inputs

How to Operate the MC275

Power On and Off

Press the POWER switch to the ON position and sound
will be heard from the Loudspeakers when the tubes have
reached their operating temperature. The amount of time it
takes is dependent upon the temperature of the Tubes.
Press the POWER Switch to the Off posi­tion to stop amplifying the audio signal.
Refer to figure 7.

Note: If the MC275 is connected to a

McIntosh Preamplifier, Control
Center or A/V Center, the addition of a McIntosh
Power Controller such as a PC4 will allow the
MC275 to switch On and Off automatically.

Mode Switch

The MODE Switch, which is located on the Left Side
Panel of the MC275, allows se­lection of either Stereo or Mono
(Parallel) Modes of Operation. Refer
to figure 8 and pages 10 and 11 for
connection information.

Figure 7

How to Operate the MC275

Input Switch

Figure 8

When BALANCED Input Connections are used, place the
MC275 INPUT Switch to the
BALanced position. If UNBAL­ANCED connections are used,
place the INPUT Switch to the
UNBALanced position. Refer to
figure 9.

Figure 9

Unbalanced Level Controls

The MC275 UNBALANCED Input Connections allow for
adjusting the volume level of the incoming Audio Signal
by using the
UNBAL­ANCED
LEVEL Con­trols, one for
each of the
channels. Refer
to figure 10.

Figure 10

13

Specifications

Specifications

Power Output Stereo

Minimum sine wave continuous average power output per
channel, both channels operating is:
75 watts into 4, 8 or 16 ohm load

Power Output Mono (Parallel)

Minimum sine wave continuous average power output is:
150 watts into 2 ohm, 4 ohm or 8 ohm load

Output Load Impedance

4, 8, or 16 ohm (Stereo Mode)
2, 4, or 8 ohm (Mono Mode)

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

0.5%

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 both chan­nels operating is 0.5%

Power Requirements

100 Volts, 50/60Hz at 3.6 amps
110 Volts, 50/60Hz at 3.6 amps
120 Volts, 50/60Hz at 3.6 amps
220 Volts, 50/60Hz at 1.8 amps
230 Volts, 50/60Hz at 1.8 amps
240 Volts, 50/60Hz at 1.8 amps

Note: Refer to the right side panel of the MC275 for the

correct voltage.

Overall Dimensions

Width is 16-1/2 inches (41.91cm)
Height is 8-1/4 inches (20.96cm) including feet
Depth is 12 inches (30.48cm)

Weight

67 pounds (30.5kg) net, 75 pounds (34.lkg) in shipping car­ton

A-Weighted Signal To Noise Ratio

100dB

Frequency Response

+0, -0.25dB from 20Hz to 20,000Hz
+0, -3dB from 10Hz to 70,000Hz

Sensitivity

1.2 Volt unbalanced inputs

2.5 Volt balanced inputs

Wide Band Damping Factor

Greater than 14

Tube Compliment

3 - 12AX7A Inputs and Phase Inverters
4 - 12AT7 Voltage Amplifier and Drivers
4 - KT88/6550 Power Output

14

Packing Instructions

Packing Instructions

In the event it is necessary to repack the equipment for
shipment, the equipment must be packed exactly as de­scribed and shown below.
The MC275 Vacuum Tubes must be removed from the Am­plifier Tube Sockets and placed into the inside open­ings of the four layer foam packing material. The foam
with the tubes located inside are placed into the Amplifier
Tube Cover and secured to the Chassis. Failure to do this
will result in damage to the Vacuum Tubes and possibly the
MC275.
It is very important that the four plastic feet are attached to
the bottom of the equipment. 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 034005 Shipping carton outside
2 033718 Foam Pad (side)

2 034266 Foam pack tube (ends)
2 034265 Foam pack tube (inside with

tube cutouts)

1 034006 Shipping carton inside
1 033707 Top pad
1 033712 Foam pad (tube cover)
1 033704 Bottom pad
1 033705 Front pad
1 033706 Rear pad
1 033711 Side pads

4 017862 Plastic foot

15

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. 04091200