McIntosh MC 50 User manual

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THE MciNTOSH Me 50 SOLID STATE POWER AMPLIFIER
READING TIME 20 MINUTES
Price $1.25

YourMe 50 Solid State Power
Amplifier will give you many years
of pleasant and satisfactory per-
formance. If you have any questions
please contact:
CUSTOMER SERVICE
Mcintosh Laboratory Inc.
2 Chambers Street
Binghamton, New York 13903
Phone: [phone]
WARNING:TO PREVENT FIRE ORSHOCK
HAZARD,DO NOT EXPOSE THIS UNIT TO RAIN
ORMOISTURE.
Take Advantage of 3 years
.of FREE Factory Service ...
Fill in the Application NOW.
CONTENTS
SERVICE CONTRACT 1
INSTALLATION 2
HOW TO CONNECT 2,3
ADJUSTMENTS 2
PERFORMANCE LIMITS AND RATINGS 4
TYPICAL PERFORMANCE CHARTS 5
TECHNICAL DESCRIPTION 6
BLOCK DIAGRAM 7
THREE YEAR FACTORY SERVICE CONTRACT
Theterms ofthe contract are:
Anapplicationfor a FREE THREE YEARFACTORYSERVICE CONTRACTis included with this manual.
1. Mcintosh will provide all parts, materials and
labor needed to return the measured perform-
ance of the instrument to the original per-
formance limits free of any charge.The
SERVICE CONTRACTdoes not cover anyship-
ping costs to and from the authorized service
agency or the factory.
2. Any Mcintosh authorized service agency will
repairall Mcintoshinstruments at normal
service rates.To receivethe free service under
theterms of the SERVICE CONTRACT,the
SERVICE CONTRACT CERTIFICATE must ac-
company the instrument when taken tothe
service agency.
3. Always have service doneby a Mcl ntosh
authorized service agency. If the instrument
is modified or damaged, asa result of un-
authorized repair the SERVICECONTRACT
will be cancelled. Damage byimproper use
Copyright © 1972 By Mcintosh Laboratory Inc.
ormishandling is not covered by the SERV-
ICE CONTRACT.
4. The SERVICE CONTRACT is issued toyou as
the original purchaser. To protectyou from
misrepresentation this contract cannot be
transferred to a second owner.
5. For your protection Mcintosh selects its
dealers carefully.Only one dealer inten
qualifies for a Mcintosh franchise. To receive
the SERVICE CONTRACTyour purchase must
be made from a Mcintosh franchised dealer.
6. Your completely filled in application for a
SERVICE CONTRACT mustbe postmarked
within 30 days of the date of purchase of
the instrument.
7. To receive the SERVICE CONTRACTall in-
formation on the application must befilled
in.The SERVICE CONTRACT will beissued
when the completely filled in application
is received at Mcintosh Laboratory Incor-
porated in Binghamton, New York.
1

Installation
Adequate ventilation extends the trouble-
free life of electronic instruments. It is gen-
erally found thateach 10° centigrade (18
0
F)
rise in temperature reduces the life of elec-
tricalinsulation by one half. Adequate ven-
tilation is an inexpensive and effective means
ofpreventing insulation breakdownthat re-
sults fromunnecessarily high operating tem-
peratures. The direct benefit of adequate
ventilation is longer, trouble-free life.
The suggested minimum space for mount-
ingthe Me 50 is 14 inches long X 8112inches
wide X91,12inches high. Always allow for air
flow by either ventilation holes or space next
to the bottomof the amplifierand a means
for the warm air to escape at the top.
It is recommended that the Me 50 be
mounted in a normal or horizontalposition.
However with adequate ventilation, the ampli-
fiercan be mounted in any position except
upside down.If the amplifier is to be installed
on a vertical surface it is recommended that
the autoformer be on the down side. This
position permits greater air flow around the
transistors and component parts extending
the trouble-free life ofthe amplifier.
How to Connect
INPUT
The input sensitivity of the MC 50 is 0.5 volt for
50 watts output. The input impedance is 200,000
ohms. There is a GAIN control in the input circuit to
permit the use of input voltages up to 30 volts. The
inputjack marked 0.5 VOLT INPUT is located below
the GAIN control. Plug the shielded lead from the
program source in the INPUT jack.
OUTPUT
Speakers are connected at the barrierstrips
marked OUTPUT on the sloped panel of the amplifier.
Use lamp cord, bell wire, or wire with similar type of
insulation to connect the speakers to the amplifier.
Forthe normally short distances of under 50 feet be-
tween the amplifier and speaker, #18 wire or larger
can be used.For distances over 50 feet between the
amplifier and speaker use larger wire.
The loudspeaker impedance is usually identified on
the loudspeaker. Connect one of the leads from the
loudspeaker to the screw marked COM on the OUT-
PUT barrier strip.Connect the other lead from the
loudspeakerto the screwmarkedwith thenumber
corresponding to the speaker impedance on the
OUTPUT barrier strip.
The only adverse effect on the operation of a Mc-
Intosh amplifier when it is improperly matched is a
reduction in the amount of distortion-free power
available to the loudspeaker. Close impedance
matching is desirable formaximum distortion-free
power.
SPEAKER CONNECTIONS
Use this table to determine properspeakercon-
nection:
If the speaker impedance
is between:
Connect the
speaker leads
between COMand:
3.2 to 6.5 ohms 4 ohms
6.5 to 13 ohms 8 ohms
13to 26 ohms 160hms
For 25 volt line operation connect one of the leads
to the screw marked COM on the OUTPUT barrier
strip. The other lead is connected to the screw
marked 16 on the OUTPUT barrier strip.
AC POWER
The MC 50 operates on 105 volt to 130 volt,50
to 60 Hz.The amplifier will be turned on and off if its
power cord is plugged in one of the auxiliary AC
power outlets on the program source.
FUSE
The MC 50 is fused with a slo-blo type fuse rated
at 1.5 amperes.For maximum protection always re-
place with fuses of the same rating, never larger.The
AC power outlet on the MC 50 is not fused.
AdjUstments
For maximum flexibility set the amplifier gain con-
trol as follows:turn the volume control on the pro-
gram source equipment (i.e. tape recorder,tuner,
preamplifier,etc). to the 12 o'clock position. Turn the
gain control on the MC 50 until the loudness ofthe
sound from the speaker is just a little louder than you
normally like to listen.The volume control on the
program source equipment now has the most con-
venient amount of loudness change in eitherdirec-
tion from the 12 o'clock position:
2

How to Connect
AC LINE
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performance Limits
PERFORMANCE GUARANTEE
Performance Limits arethemaximum deviation from
perfection permittedfor aMcintosh instrument. We
promise you that theMe 50 you buy must becapable
of performanceat or exceeding theselimits or you get
your money back. Mcintosh is the only manufacturer
that makes thisguarantee.
PERFORMANCE
Mcintosh audio power ratingsarein accordance with
the FederalTradeCommission Regulation of Novem-
ber 4,1974 concerningpower output claims for ampli-
fiers used in home entertainment products.
POWER OUTPUT
50 watts minimum sine wave continuous
average power output,operating into 4
ohms, 8 ohms, or 16 ohms load impe-
dance, whieh is:
14.1 volts RMS across 4ohms
20.0 volts RMS across 8 ohms
28.3 volts RMS across 16 ohms
OUTPUT LOAD IMPEDANCE
4ohms,8ohms,or 16 ohms; separate ter-
minals are provided for each output
RATED POWER BAND
20 Hz to 20,000 Hz
TOTAL HARMONIC DISTORTION
0.25% maximum harmonic distortion at
any power level from 250 milliwatts to 50
watts from 20Hz to 20,000 Hz
INTERMODULATION DISTORTION
0.25% if instantaneous peak power outputis 100 watts
or less for any combination of frequencies 20 Hzto
20,000 Hz
FREQUENCY RESPONSE
20 Hz to 20,000 Hz + 0 -0.25 db
10 Hz to 100,000 Hz +0 -3.0 dB atone watt output
NOISE AND HUM
90 dB below rated output
RATINGS
OUTPUT VOLTAGES
25 volts for distribution lines
DAMPING FACTOR
25at 4 ohms output
50at 8 ohmsoutput
17 at 16 ohmsoutput
INPUT IMPEDANCE
200,000 ohms
INPUT SENSITIVITY
0.5 volt. Level control provided for higher input voltage
GENERAL INFORMATION
POWER REQU'IREMENTS
120 volts, 50/60 Hz, 15 watts at zero signal output,
120 watts at rate output
SEMICONDUCTOR COMPLEMENT
12 silicon transistors
12 siliconrectifiers and diodes
MECHANICAL INFORMATION
SIZE
5V2 inches high (13.97 cm), 8 inches wide (20.32 cm),
12V2 inches deep (31.75 cm)
CHASSIS
Chrome and bl.ack
WE'IGHT
20 pounds (9.07 kg) net, 24 pounds (10.89 kg) inship-
ping carton
SPECIAL FEATURES
The amplifier is completely stable whenconnected to
any loudspeaker system or eventoany reactive loads.
The Me 50 has specialcircuits to prevent damage
by short circuit oropen circuit of the outputload, or
by any amount of output impedance mismatch.
Thermalcutouts are mounted on the output transistor
heatsinks to provide protection in the event ofina,de-
quate ventilation.
4

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POWER OUTPUT IN AVERAGE WATTS
1000
Harmonic Distortion versus Power
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Technical DescriPtion
A two stage preamplifier with three transistors in-
creases the input voltage 16db.
There are 13 transistors in the power amplifier
section. The two stage preamplifier is fed to a pair of
matched transistors arranged as an emitter coupled
amplifier with two inputs and one output. The signal
from the preamplifier section connects to one of
these inputs. Both AC and DC negative feedback are
applied to the other input. This large quantity of feed-
back is used to reduce noise and distortion. The
signal is then fed to a voltage amplifier. The voltage
amplifier is followed by two driver transistors.
The output section is arranged as a series push-
pull amplifier. The power transistors used in the out-
put section of your MC 50 are selected for their high
power dissipation capabi lity, wide frequency response,
and large "safe operating area." In addition, each
power transistor is given four separate tests before
it is put in your MC 50. This additional testing makes
sure your MC 50 will deliver its rated power from
20 Hz to 20,000 Hz with low distortion and complete
reliability.
The power transistors are mounted on oversized
anodized heat sinks. The heat sinks assure that un-
der normal operation the transistors will operate at a
low temperature. If temperatures increase due to a
shorted speaker, or restricted ventilation, an auto-
matic temperature sensing device turns off the power
to the MC 50. The device operates automatically at a
preset temperature. The MC 50 will turn on again
when the temperature has returned to normal limits.
This additional feature gives your MC 50 complete
reliability under the most extreme operating con-
ditions.
The output stages are matched to the load by the
Mcintosh autoformer. The Mcintosh autoformer is
carefully wound using Mcintosh trifilar winding and
interleaving techniques. Trifilar winding and inter-
leaving gives the autoformers exceptional band-
width. The autoformers properly match the power
transistors to 4, 8 and 16 ohm loads at all audio
frequencies.
The use of the Mcintosh designed trifilar auto-
former makes the Mcintosh solid state amplifiers the
only amplifiers that deliver FULL POWER AT ALL
SPEAKER IMPEDANCES. You have not been power
penalized for your choice of loudspeakers when
using the Mcintosh MC 50.
Another of the advantages of the autoformers is
the 25 volt output for a constant voltage distribution
system.With the MC 50 several sets of speakers can
be operated independently throughout your home.
To further insure reliability a special power output
SENTRY MONITORING CIRCUIT prevents failure of
the power output transistors due to excessive mis-
match of the output. When your MC 50 operates
normally the SENTRY MONITORING CIRCUIT has no .
effect on signals passing through the power ampli-
fier. If the power dissipation should rise above nor-
mal operation, the SENTRY MONITORING CIRCUIT
restricts the drive to the output transistors.The
SENTRY MONITORING CIRCUIT acts instantaneous-
ly for any input signal or load combination. This ar-
rangement assures complete circuit reliability.Only
Mcintosh gives you this degree of protection.
There are three separate power supply sections.
One positive and one negative high current supply is
used for the output stages.The other positive supply
is used for the driving amplifier stages. All supplies
are full wave and use silicon rectifiers. Adequate
filtering is used to assure an absolute minimum of
hum. The power output stage filter capacitors have
very high capacity, which allows full power output
below 20 Hz.The power transformer is generous in
size and runs cool,even under heavy use.

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PROTECTION
FIRST PROTECTION •.••
Inthese dark days of hurry up-percentage analy-
sis-production rush-and limited personalresponsi-
bility the Mcintosh policy of"Performance Limits" is
a bitofbright blue sky. Every Mcintosh instrument-
everyone-is tested to be equalto or better than the
performance limits advertised.When a performance
limit of 0.25% harmonic distortion is established for
an instrument, Mcintosh means that every, each, all
ofthe instruments manufactured mustbe capable of
performance to that limit-orbetter-or your full
purchase price is refunded.
One of the reasons Mcintosh can make this prom-
ise is: we 100% test every product for maximum per-
formance. We are notcontent knowing that 10% of
our products are tested and meet the performance
requirements established by our engineering group.
We must knowthateveryone meets its requirements.
This vigorous pursuit of excellence takes time. At
Mcintosh more time means more care, more protec-
tionfor you. There's no production rush at Mcintosh.
The Mcintoshinvestment inprofessional testing
instruments is staggering. Onapercentage basis
Mcintosh probably invests more ofits sales dollars
in testing facilities thatanyone else in alike busi-
ness.For instance, Mcintoshhas one professional
distortion analyzerforevery 10 employees. This kind
ofstatistic is repeated forall sorts of testinstru-
ments. As new testing instruments are produced that
update the Mcintosh abilitytoknow, Mcintoshin-
vests in them-wave form analyzers-real time ana-
lyzers-lowest distortion signal generators-etc.,
etc. Even so faras a small FMtransmitterso thatthe
entire transmissionreception systemcan be ana-
lyzed.
"What does this mean tome?" you ask. Only
through this impressive investment;throughcon-
tinuous testing andresearch; through product analy-
sis;and endlessmeasurement can wepromise and
deliver to you reliability, 'Iong life, performance, high-
est value, and freedom from service.
SECOND PROTECTION ••••
BECAUSEMciNTOSH MANUFACTURES THE BEST ELECTRONIC MUSIC
REPHODLJCING INSTRUMENTS, AND BECAUSE MciNTOSHINSTRUMENTS
ARE DESI(;NED TOHAVE LONG, TROUBLE FHEELIFE, AND BECAUSE
McfNTOSHWANTS TO ASSUREYOU THAT yOUOWN THEFINEST INSTRU.
MENTMADE,
MciNTOSH LABORATORY ISSUES THIS THREE YEARCONTRACT TO:
State Zip
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Mcintosh Laboratory has great belief
in itsengineering,product development,
manufacturing and quality control. To
offer you strong evidence of this confi-
denceMcintosh offers you a FREE
THREE YEAR SERVICE CONTRACT.
During thefirst three years you can't
spend one dime for service. Mcintosh
quarantees partsand labor. It costs you
nothing. The extended life of a Mcintosh,
theconservativeratings,and the sophisti-
cated appearancemake a Mcintosh in-
strument a greater value when you are
ready totrade.

(IOIOS
MciNTOSH LABORATORY INC.
2 CHAMBERS ST., BINGHAMTON, N. Y. 13903
607-723-3512
Design subject to change without notice.
Printed in U.S.A.
038·794

POWER AMPLIFIER
II
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STARTING WITH SERIAL NO. lOUOl
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MciNTOSH LABORATORY INC. 2 CHAMBERS STREET BINGHAMTON,NEW YORK I 0

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MC 50
ELECTRICAL SPECIFICATIONS
PERFORMANCE
McIntosh audio power ratings arein accordance with
the Federal TradeCommission Regulationof Novem-
ber 4,1974 concerning power output claimsfor ampli-
fiers used in homeentertainment products.
POWER OUTPUT
50 watts minimum sine wave continuous
average power output,operating into 4
ohms, 8 ohms,or 16ohms load impe-
dance, whieh is:
14.1volts RMS aeross 4ohms
20.0 volts RMSaeross 8 ohms
28.3 volts RMS across 16 ohms
OUTPUT LOAD IMPEDANCE
4ohms,8ohms,or16 ohms; separate ter-
minals areprovided foreach output
RATED POWER BAND
20 Hz to 20,000 Hz
TOTAL HARMONIC DISTORTION
0.25%maximum harmonie distortion at
any power level from 250 milliwatts to 50
watts from 20Hz to 20,000 Hz
INTERMODULATION DISTORTION
0.25% if instantaneouspeak power output is100 watts
or less for any combination offrequencies 20 Hz to
20,000 Hz
FREQUENCY RESPONSE
20 Hz to 20,000 Hz + 0-0.25 db
10Hzto 100,000 Hz + 0-3.0 dB at one watt output
NOISE AND HUM
90 dB belowratedoutput
RAT'INGS
OUTPUT VOLTAGES
25 volts for distribution lines
DAMPI.NG FACTOR
25 at 4 ohms output
50 at 8 ohms output
17 at 16 ohmsoutput
INPUT IMPEDANCE
200,000 ohms
INPUT SENSITIVITY
0.5 volt. Level control provided for higher input voltage
GENERAL INFORMATION
POWER REQUIREMENTS
120 volts, 50/60 Hz, 15watts at zero signal output,
120 watts atrateoutput
SEMICONDUCTOR COMPLEMENT
12 silicontransistors
12 silicon rectifiers anddiodes
MECHANICAL INFORMATION
SIZE
51/2inches high (13.97cm), 8 inches wide(20.32cm),
121/2inches deep(31.75 cm)
CHASSIS
Chromeand black
WEIGHT
20 pounds (9.07 kg) net, 24 pounds (10.89 kg) in ship-
ping carton

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POWER SUPPLY
SECTION
MC 50 154-349

MC 50
SCHEMAHC NOTES
1.Unless otherwise specified:Resistance values are in ohms,1/2 watt,and 10%tolerance;capacitance
values smaller than 1 are in microfarads (µF);capacitance values greater than 1 arein picofarads
(pF);inductors are in microhenries (µH).
2.Printedcircuit board components are outlined on the schematics by dotted lines.The circled numbers
on the dotted 1 ines correspond to the numbers on the PC board layouts.
3.Theheavy1 ines on the schematics denote the primary signal path.
4.All voltages indicated on the schematics are measured under the following conditions:
a.Use of an 11 megohm impedance VTVM. d. ACinput at 117 volts AC,SO/60Hz.
b.All voltages ±10% with respect to e.Front panel controls at:
chassis ground.
Gain FULL CCW
c.No signal at input terminals.
5.In units with Serial No.'s below 10U51,C14 is not used;R1S and R19 are 5% resistors.
6.In units with Serial No.
IS
from 13UOO to 1SUSS,C7 is lSOpF.
7.Inunits with Serial No.
IS below 14USO,Qll and Q12 are Mcintosh Part No.132-536.
S.In units with Serial No.ls below 12U50,R16 is 3.3k;R24is160Q; R25 is 220Q;and R21 and R22
are used.
9·
InunitswithSerial
No1s.
below201J7SR26
is
·120Q.
10. Inunits with SerialNo's.below 2?1J79R4 andR5 are 3.3k.
Q II TOP
Q 9 BOTTOM
LOCATION OF TRANSISTORS NOT ON PRINTED CIRCUIT BOARDS
Q 12 TOP
Q 10 BOTTOM

MC 50
REPLACEMENT PARTS
Al I parts notIisted are common items obtain-
able fromradioparts jobbers.
Replacement partsmay be obtained when ordered
byPARTNUMBER from:
Mcintosh LaboratoryInc.
Customer Service Department
2 Chambers Street
Binghamton,New York13903
(telephone [phone]S12)
CAPAC ITORS
SymbolPa r t
NumberDescription Number
CIMylar .47µF 2S0V 064-069
C2,3EIec
t. 640µF2SV 066-135
CS E Iec t.
100lJF 15V066-127
c6 Elect.10µF 2SV 066-005
c8 EIec
t.
470µF 4v 066-136
CI0I,102EIec
t.
4000µF50V 066-096
CI03 E Iec t . 470µF40V 066-134
CI04E Iec t . 80/80/50/ISOµF 066-095
200/200/150/150V
DIODES
01Si . signal diode070-047
02 S i .I-eferencediode070-046
03,4Si.signal diode070-047
05,6 S i .I-ectifiel' 070-031
0101,102 Si.rectifier 070-031
0103,104S i .rectifier 070-031
010S,106S i .l-ectiFier070-031
FUSES
FIOIFuse I.S amp,slo-blo089-003
TRANSISTORS
Q 1,2
Q3,4
QS
Q6
Q7
Q8
Q9
QIO
QII ,12
Si.NPNtransistor132-092
132-0S6
132-0S6
132-S15
132-021
132-032
132-S24
132- 530
132-070
Si.PNP transistor
Si.PNP transistor
Si.NPNtransistor
Si.NPN transistor
Si.PNPtransistor
Si.NPN transistor
Si.PNP transistor
Si.NPN transistor
POTENTIOMETERS
RIGain control 134-206
MC 50 SCHEMATIC PART NO. 038-803
RT7
R27
R28
SIOI
Tl
TIOI
RESISTORS
Wi rewound3.6k 5W
SW
SW
139-096
139-048
139-080
Wirewound.S61l
Wirewound .331l
SW ITCHES
ThermaIcut-out153-007
TRANS FO RM ERS
Audio autoformer043-607
043-934
Power transformer
MISCELLANEOUS ITEMS
Plasticfeet 017-144
038-659
090-017
033-100
170-021
178-001
Owners manual
Gain control knob
Shippingcarton
AC powercord
Fuseholder
20C1025S7-M4803

SERVICE CONTRACT APPLICATION
1. Mcintosh will provide all parts, materials and labor needed to return the
measured performance of the instrument to the original performance
limitsfree of any charge. The SERVICE CONTRACTdoes notcover any
shipping costs to and from the authorized service agency or the factory;
2.Any Mcl ntosh authorized service agency will repairall McI ntosh instru-
ments at normal service rates. To receive the free service under the terms
oftheSERVICE CONTRACT, the SERVICE CONTRACT CERTIFICATE
must accompany the instrument when taken to the service agency.
3.Always have service done by a Mcintosh authorized service agency. If the
instrument is modified or damaged, as a result of unauthorized repair the
SERVICE CONTRACT will be cancelled. Instruments damaged by im-
proper use or mishandling are not covered by the SERVICE CONTRACT.
4. The SERVICE CONTRACT is issued to you as the original purchaser. To
protect you from misrepresentation th is contract cannot be transferred to
asecond owner.
5. The SERVICE CONTRACT is given to purchasers who live in the 50
United States or Canada only.
6.For yourprotection Mcintosh selects its dealers carefully. Only one dealer
in ten qualifies fora Mcintosh franchise. To receive the SERVICE CON-
TRACTyour purchase must be made from a Mcintosh franchised dealer.
7.Your completely filled in application for a SE RVICE CONTRACT must
be postmarked within 30 days of the date of purchase of the instrument.
8.To receive the SE RVICE CONTRACTall information on the application
must be filled in.The SERVICE CONTRACT will be issued when the
completely filled in application is received at Mcl ntosh Laboratory
Incorporated in Binghamton, New York. If the application is not received
at Mcl ntosh Laboratory, only the service offered under the gO-day
guarantee will apply.
Tear Off And Mail Remainder 038·617
PLEASE PRINT ALL INFORMATION
YOUR NAME: __
ADDRESS: _
CITY:_STATE:_ZIP:_
MODELNO: __ SERIAL NO: _
NAME OF DEALERFROM WHOM YOU BOUGHT:
CITY: _
DATE YOUBOUGHT: _
Iaccept the benefits and thetermsof theFactoryServiceContract.
Your Signature:
Fold HereFor Mailing