THE MCINTOSH MC 2105 SOLID STATE STEREO POWER AMPLIFIERberners.ch/McIntosh/Downloads/MC2105_own.pdf · THE MCINTOSH MC 2105 SOLID STATE STEREO POWER AMPLIFIER Reading Time: 28 Minutes

THE MCINTOSH MC 2105 SOLID STATE STEREO POWER AMPLIFIER

Price $1.25Reading Time: 28 Minutes

Your MC 2105 Stereo Power Amplifierwill give you many years of pleasantand satisfactory performance. If youhave any questions, please contact:

CUSTOMER SERVICEMclntosh Laboratory Inc.2 Chambers StreetBinghamton, New York 13903Phone: 607-723-3512

WARNING: TO PREVENT FIRE OR SHOCKHAZARD, DO NOT EXPOSE THIS UNIT TORAIN OR MOISTURE.

Take Advantage of 3 yearsof FREE Factory Service . . .Fill in the Application NOW.

SERVICE CONTRACT 1

INSTALLATION 2,3

HOW TO CONNECT 4,5

HOW TO USE THE DYNAMICPEAK LOCKING METERS . . . 6

FRONT PANEL INFORMATION . . . 8

PERFORMANCE LIMITSAND RATINGS 9

TYPICAL PERFORMANCE CHARTS .. 10

TECHNICAL DESCRIPTION 11

BLOCK DIAGRAM 12

THREE YEAR FACTORY SERVICE CONTRACTAn application for a FREE THREE YEAR FACTORY SERVICE CONTRACT is included with this manual.

The terms of the contract are:

1. Mclntosh will provide all parts, materials andlabor needed to return the measured perform-ance of the instrument to the original per-formance limits free of any charge. TheSERVICE CONTRACT does not cover any ship-ping costs to and from the authorized serviceagency or the factory.

2. Any Mclntosh authorized service agency willrepair all Mclntosh instruments at normalservice rates. To receive the free service underthe terms of the SERVICE CONTRACT, theSERVICE CONTRACT CERTIFICATE must ac-company the instrument when taken to theservice agency.

3. Always have service done by a Mclntoshauthorized service agency. If the instrumentis modified or damaged, as a result of un-authorized repair the SERVICE CONTRACTwill be cancelled. Damage by improper use

or mishandling is not covered by the SERV-ICE CONTRACT.

4. The SERVICE CONTRACT is issued to you asthe original purchaser. To protect you frommisrepresentation this contract cannot betransferred to a second owner.

5. For your protection Mclntosh selects itsdealers carefully. Only one dealer in tenqualifies for a Mclntosh franchise. To receivethe SERVICE CONTRACT your purchase mustbe made from a Mclntosh franchised dealer.

6. Your completely filled in application for aSERVICE CONTRACT must be postmarkedwithin 30 days of the date of purchase ofthe instrument.

7. To receive the SERVICE CONTRACT all in-formation on the application must be filledin. The SERVICE CONTRACT will be issuedwhen the completely filled in applicationis received at Mclntosh Laboratory Incor-porated in Binghamton, New York.

Copyright © 1970 By Mclntosh Laboratory Inc.

1

CONTENTS

Adequate ventilation extends the trouble-freelife of electronic instruments. It is generally foundthat each 10° centigrade (18° F) rise in tempera-ture reduces the life of electrical insulation by onehalf. Adequate ventilation is an inexpensive andeffective means of preventing insulation breakdownthat results from unnecessarily high operating tem-peratures. The direct benefit of adequate ventila-tion is longer, trouble-free life.

Allow at least 15 inches deep x 17 inches widex 8 inches high for mounting the MC2105. Alwaysallow for air flow by either ventilation holes orspace next to the bottom of the amplifier and ameans for a warm air to escape at the top. Withadequate ventilation the amplifier can be mountedin any position.

To prepare the MC 2105 for installation removethe plastic protective covering. Turn it upside downso that it rests on its top on the shipping pallet.Remove the four plastic feet fastened to the bot-tom of the chassis.

Next, place the mounting brackets, the partsbag and the mounting template at hand.

The PANLOC professional mounting designeliminates the need for any shelf or bracket tosupport the MC 2105. It is completely supportedby its own mounting brackets.

The design of the mounting template allows youto position or locate the cutout from the front orrear of the panel to which the instrument is to bemounted. Position the plastic mounting templateover the area of the panel to be cut out for installa-tion.

If the cutout is to be located from the front ofthe panel, begin at 2. If the cutout is to be locatedfrom the rear of the panel, begin here.

1. On the back of the cabinet panel, scribe avertical centerline through the exact center ofthe area in which the cutout is to be made.

Place the template against the back of thepanel and match the template centerline withthe centerline on the cabinet panel.

Make sure that there is at least ¼ inch clear-ance between the bottom of the dashed line ofthe cutout area on the template and any shelfor brace below the proposed cutout.

Mark the two locating holes ("C" holes onthe mounting template).

Drill the two locating holes. Be certain thedrill is perpendicular to the panel.

Now position the template on the front of thepanel by aligning the "C" locating holes on thetemplate with the drill holes.

2. If the cutout is to be located from the front ofthe panel:

With the template in place against the cabinetpanel, mark the "A" and "B" drill holes andthe four small holes that identify the cornersof the cutout. Join the corner marks with a pen-cil. The edge of the template can be used as astraight edge.

IMPORTANT: DRILL THE 6 HOLES BEFOREMAKING THE CUTOUT.

Accurately drill the three holes on each side ofthe cutout area with a 3/16 inch drill.

With the saw on the INSIDE OF THE PENCILLINES carefully cut out the rectangular opening.

Secure the mounting strips to the rear of thecabinet panel using two screws from the hardwarepackage.

Insert the screws in the center holes of the cabi-net panel ("B" holes on the template) and tighten.The screw head should pull into the wood slightly.(Use two % inch long screws for panels under ½inch, or two 1¼ inch long screws for panels ½ inchthick and larger.)

2

Attach the mounting brackets to the cabinetpanel using four screws.

Place the template over the mounting screws.The mounting screws should be centered in the"A" and "B" holes on the template. The sides ofthe mounting brackets should match the verticaldash lines on the template. If necessary, loosen thescrews and push the brackets into alignment andretighten.

Insert the power cord through the opening. Care-fully slide the MC 2105 into the opening so the railson the bottom of the equipment slide in the trackof the mounting brackets. Slide the instrument inuntil it stops at the adjust position latches. Pressthe latches in and continue to slide the instrumentin until the front panel is against the cabinet panel.At the bottom front corners of the PANLOC instru-ments are the PANLOC buttons. Depressing thePANLOC buttons will lock the instrument firmly inthe installation. Depressing the PANLOC buttonsa second time (as with a ballpoint pen) will releasethe instrument. You can then slide the instrumentforward to the inspection-adjustment position. De-pressing the inspection-adjustment position latcheswill allow the instrument to be slid completely outof the installation.

3

HOW to Connect

INPUT STEREO

The shielded cable from the left output of theMclntosh preamplifier is plugged into the left jack.The shielded cable from the right output of theMclntosh preamplifier is plugged into the rightjack.

SPEAKERS

Speakers are connected at the barrier stripsmarked OUTPUT on the back panel of the ampli-fier. Use lamp cord, bell wire, or wire with similartype of insulation to connect the speakers to theamplifier. For the normally short distances of under50 feet between the amplifier and speaker, #18wire or larger can be used. For distances over 50feet between the amplifier and speaker use largerwire.

The loudspeaker impedance is usually identifiedon the loudspeaker itself. Connect one of the leadsfrom the left loudspeaker to the screw markedCOM on the LEFT OUTPUT barrier strip. Connectthe other lead from the left loudspeaker to thescrew marked with the number corresponding tothe speaker impedance on the LEFT OUTPUTbarrier strip. Connect one of the leads from theright loudspeaker to the screw marked COM on theRIGHT OUTPUT barrier strip. Connect the otherlead from the right loudspeaker to the screwmarked with the number corresponding to thespeaker impedance on the RIGHT OUTPUT barrierstrip.

The only adverse effect on the operation of aMclntosh amplifier when it is improperly matchedis a reduction in the amount of distortion-freepower available to the loudspeaker. Close imped-ance matching is desirable for maximum distor-tion-free power.

SPEAKER CONNECTIONS

Use this table to determine proper speaker con-nection.

Connect theIf the speaker impedance speaker leadsis between: between COM and:

3.2 to 6.5 ohms 4 ohms6.5 to 13 ohms 8 ohms13 to 26 ohms 16 ohms

Connect as follows:Connect oneright speaker

Connect one lead to theIf the left speaker tospeaker screw LEFT-imped- COM andance is: other to:4 ohms LEFT-48 ohms LEFT-816 ohms LEFT-16

screw markedRIGHT-COMand the otherto:RIGHT-4RIGHT-8RIGHT-16

DO NOT CONNECT A MONOPHONIC LOUD-SPEAKER TO BOTH TERMINALS. THE LOUD-SPEAKER CAN BE DAMAGED.

For 25 volt line operation connect one of the leftleads to the screw marked COM on the LEFT OUT-PUT barrier strip. The other left lead is connectedto the screw marked 8W on the LEFT OUTPUTbarrier strip. Connect the right leads in the samemanner on the RIGHT OUTPUT barrier strip.

AC POWER:

The MC 2105 operates on 117 to 130 volt, 50/60Hz. The amplifier will be turned on and off if itspower cord is plugged in one of the auxiliary ACpower outlets on the program source.

4

5

HOW to Use theDynamic Peak

Locking Meters

Ordinary meters lack the capability of indicatingthe short interval power in a sound wave. Themass of the meter movement is too great to re-spond to instantaneous changes in music programmaterial. Mclntosh superior engineering has de-veloped new circuitry that permits the meters onthe MC 2105 to respond to the short interval powerin a sound wave to an accuracy of 98% of the truevalue. This is another Mclntosh development thatrepresents a major step forward in the use ofpower level meters.

There are two circuits that give these metersthe indicating capability of the short interval powerin a sound wave. The first circuit is an acceleratingcircuit that compensates for the inertia character-istics of the meter movement. Because the shortinterval power fluctuation is so rapid, the eyemight not perceive the instantaneous power read-ing. This caused the development of the secondcircuit, which is a "time stretching" circuit. Thetime stretching circuit delays the movement of themeter needle at peak reading for a few milli-seconds.

With the aid of the CBS test record STR1000 thefrequency response of your phono cartridge canbe measured. The graph on page 7 shows theideal RIAA curve using the CBS record STR100.

Follow these steps to plot the performance ofyour phonograph cartridge.

1. Set the "METER RANGE SWITCH" to the-20 position.

2. Play the 1000 Hz test tone recorded on theCBS Test Record STR100 on your phono-graph.

3. Turn the LEFT GAIN control until the leftmeter indicates "0."

4. Turn the RIGHT GAIN control until the rightmeter indicates "0."

5. Write down the meter indication at each fre-quency as the record plays.

6. Transfer the readings by frequency to thegraph.

7. The graph shows the ideal RIAA responsecurve using the CBS STR1000 test record.Compare your curve with the curve on thegraph. A deviation of 3 dB from the ideal isacceptable. By making this check at regularintervals, (for instance, every 6 months) anydeterioration in the cartridge or system willbe quickly detected.

A tape recorder can be checked in the samefashion.

1. Use a standard frequency response tapeas the signal source.

2. Complete all steps outlined for phono cart-ridges.

3. You now have a graph of the playback char-acteristics of your tape recorder.

To find the record characteristics of the taperecorder follow this procedure:

1. Record the CBS Test Record STR1000 onyour tape recorder. Adjust the record volumeonly on the 1000 Hz signal for proper record-ing level. DO NOT ADJUST THE RECORDVOLUME CONTROL DURING THE RECORD-ING.

2. Play back the tape just recorded. Completeall steps outlined for tape playback charac-teristics.

3. A comparison of the two curves will give therecording characteristics of your tape re-corder. A deviation of 3 dB is acceptable.

Similar checks can be made on all programsources in your stereo system. Follow the samegeneral procedure for any program source forwhich a standard reference is available.

6

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-2020,00010,0001,00010020

IDEAL RIAA SYSTEM RESPONSE USING CBS STR 100 TEST RECORD

4

2

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-2

-4

-6

-8

-10

-12

14

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-2020,00010,000

FREQUENCY IN Hz

7

1,00010020

Front Panel informationLEFT GAIN

Use the left gain control to adjust the volume in theleft channel to the desired listening level. Turn thecontrol clockwise to increase the volume.

RIGHT GAIN

Use the right gain control to adjust the volume in theright channel to the desired listening level. Turn thecontrol clockwise to increase the volume.

METER RANGE

The meter switch has four positions. The first positionis OFF. With the switch in the OFF position there isno indication on the meters.

-0 In this position of the meter range switch, theamplifier will deliver 100 watts when the meter indi-cates +3dB, with meter indication of "0", the ampli-fier delivers 50 watts, with a meter indication of —3dB,

-10 In this position of the meter range switch, theamplifier will deliver 5 watts output when the meterindicates "0". With a meter indication of —3dB, theamplifier delivers 2½ watts output and a -10dB meterindication, the amplifier delivers ½ watt.

-20 In this position of the meter range switch, theamplifier will deliver ½ watt (500 milliwatts) when themeter indicates "0". With a meter indication of —3dB,the amplifier delivers ¼ watt (250 milliwatts) and a-10dB meter indication the amplifier delivers 50milliwatts.

the amplifier delivers 25 watts; and a meter indicationof -10dB, the amplifier delivers 5 watts.

(A meter reading of +3.2dB indicates 105 watts poweroutput.)

HEADPHONE

Use the jack for low impedance stereo headphones.The headphone jack is on at all times.

SPEAKERS

OFF: The loudspeakers are turned off when theSPEAKER switch is in the OFF position. You canlisten to headphones in private.

THIS SWITCH MUST BE IN THE "ON" POSITIONTO HEAR MUSIC FROM THE LOUDSPEAKERS.

ON: Music will be heard through the loudspeakers.Use this as the normal listening position.

POWER

The power switch turns the MC2105 on or off. Theswitch does not control the power outlet on the backpanel. If you wish to control the operation of theon/off switch from a preamplifier control center leavethe switch in the ON position. In this case be sure toplug the AC cord of the MC 2105 into the controlledoutlets on the rear of the preamplifier control center.

OFF: In the OFF position the AC to the amplifier isturned off.

8

Performance Limits and Ratings

PERFORMANCE GUARANTEEPerformance Limits are the maximum deviation fromperfection permitted for a Mclntosh instrument. Wepromise you that the MC 2105 you buy must be capableof performance at or exceeding these limits or you getyour money back. McIntosh is the only manufacturerthat make this guarantee.

PERFORMANCEMcIntosh audio power ratings are in accordance withthe Federal Trade Commission Regulation of Novem-ber 4, 1974 concerning power output claims for ampli-fiers used in home entertainment products,POWER OUTPUT105 watts minimum sine wave continuousaverage power output, per channel, bothchannels operating into 4 ohms, 8 ohms,or 1.6 ohms load impedance, which is:

20.5 volts RMS across 4 ohms29.0 volts RMS across 8 ohms41.0 volts RMS across 16 ohms

OUTPUT LOAD IMPEDANCE4 ohms, 8 ohms, or 16 ohms; separate ter-minals are provided for each outputRATED POWER BAND20 Hz to 20,000 HzTOTAL HARMONIC DISTORTION0.25% maximum harmonic distortion atany power level from 250 milliwatts to 105watts per channel from 20 Hz to 20,000Hz, both channels operatingINTERMODULATION DISTORTION0.25% if instantaneous peak power output is 210 wattsor less per channel with both channels operating forany combination of frequencies 20 Hz to 20,000 Hz

FREQUENCY RESPONSE20 Hz to 20,000 Hz +0 -0.25 dB10 Hz to 100,000 Hz +0 -3.0 dB at one watt output

NOISE AND HUM90 dB below rated outputOUTPUT POWER MONITOR METERMeter is calibrated to read +3 dB when amplifier pro-duces 105 watts. Meter range switch is provided toincrease meter sensitivity by 10 dB or 20 dBCalibration accuracy at 0 dB reading is ±2% at allfrequencies; meter range accuracy is ±5%

9

OUTPUT VOLTAGES25 volts for distribution lines

DAMPING FACTOR13 at 8 ohms output18 at 4 ohms output10 at 16 ohms output

INPUT IMPEDANCE200.00 ohms

INPUT SENSITIVITY0.5 volt. Level control provided for higher input voltage

GENERAL INFORMATIONPOWER REQUIREMENTS120 volts 50 60 Hz, 75 watts at zero signal output,430 watts at rated output

SEMICONDUCTOR COMPLEMENT34 silicon transistors18 silicon rectifiers and diodes

MECHANICAL INFORMATIONSIZEFront panel measures 16 3/16 inches wide (41,12 cm)by 7 1/8 inches high (18,1 cm). Chassis measures 15inches wide (38,1 cm) by 6 9/16 inches high (16.67 cm)by 14½ inches deep (36.83 cm), including connectors.Knob clearance required is 1½ inches (3.81 cm) infront of mounting panel

FINISHFront panel is anodized gold and black with specialgold teal nomenclature illumination. Chassis is chromeand black

MOUNTINGExclusive Mclntosh developed professional PANLOC

WEIGHT65 pounds (29.48 kg) net, 77 pounds (34,93 kg) in ship-ping carton

SPECIAL FEATURESThe amplifier is completely stable when connected toany loudspeaker system or even to any reactive loads;The MC 2105 has special circuits to prevent damageby short circuit or open circuit of the output loads, orby any amount of output impedance mismatch,Thermal cutouts are mounted on the output transistorheat sinks to provide protection in the event of inade-quate ventilation.

Peak reading - peak locking meters feature special cir-cuit to respond to peak value of complex input signal.

RATINGS

Technical DescriptionA two stage amplifier with three transistors in

each channel increases the input voltage 16 dB.There are 13 transistors in each power amplifier

section. The two stage preamplifier is fed to a pairof matched transistors arranged as an emittercoupled amplifier with two inputs and one output.The signal from the preamplifier section connectsto one of these inputs. Both AC and DC negativefeedback are applied to the other input. This largequantity of feedback is used to reduce noise anddistortion. The signal is then fed to a voltage ampli-fier. The voltage amplifier is followed by two drivertransistors.

The output section is arranged as a series push-pull amplifier. The power transistors used in theoutput section of your MC 2105 are selected fortheir high power dissipation capability, wide fre-quency response, and large "safe operating area."In addition, each power transistor is given fourseparate tests before it is put in your MC 2105. Thisadditional testing makes sure your MC 2105 willdeliver its rated power from 20 to 20 kHz with lowdistortion and complete reliability.

The power transistors are mounted on oversizedanodized heat sinks. The heat sinks assure thatunder normal operation the transistors will operateat a low temperature. If temperatures increase dueto a shorted speaker, or restricted ventilation, anautomatic temperature sensing device turns off theMC 2105. The device operates automatically at apreset temperature. The MC 2105 will turn on againwhen the temperature has returned to normallimits. This additional feature gives your MC 2105complete reliability under the most extreme oper-ating conditions.

The output stages are matched to the load bythe Mclntosh autoformer. The Mclntosh autoformeris carefully wound using Mclntosh trifilar windingand interleaving techniques. Trifilar winding andinterleaving gives the transformers exceptionalbandwidth. The autoformers properly match thepower transistors to 4, 8, and 16 ohm loads at allaudio frequencies.

The use of the Mclntosh designed trifilar auto-former makes the Mclntosh solid state amplifiersthe only amplifiers that deliver FULL POWER ATALL SPEAKER IMPEDANCES. You have not beenpower penalized for your choice of loudspeakerswhen using the Mclntosh MC 2105.

Another of the advantages of the autoformersis the 25 volt output for a constant voltage distribu-tion system. With the MC 2105 several sets ofspeakers can be operated independently through-out your home.

To further insure reliability a special power out-put SENTRY MONITORING CIRCUIT prevents fail-ure of the power output transistors due to exces-

sive mismatch of the output. When your MC 2105operates normally the SENTRY MONITORING CIR-CUIT has no effect on signals passing through thepower amplifier. If the power dissipation shouldrise above normal operation, the SENTRY MONI-TORING CIRCUIT restricts the drive to the outputtransistors. The SENTRY MONITORING CIRCUITacts instantaneously for any input signal or loadcombination. This arrangement assures completecircuit reliability. Only Mclntosh gives you this de-gree of protection.

POWER SUPPLY SECTION

There are three separate power supply sections.One positive and one negative high current supplyis used for the output stages. The other positivesupply is used for the driving amplifier stages. Allsupplies are full wave and use silicon rectifiers.Adequate filtering is used to assure an absoluteminimum of hum. The power output stage filtercapacitors have very high capacity, which allowsfull power output below 20 Hz. The power trans-former is generous in size and runs cool, evenunder heavy use.

11

BlockDiagram

12

MCINTOSH LABORATORY INC.2 CHAMBERS ST., BINGHAMTON, N. Y. 13903

607-723-3512

Design subject to change without notice.Printed in U.S.A.

038-799