THE MclNTOSH C 26 SOLID STATE STEREO PREAMPLIFIER · 2018. 5. 31. · Drill the two locating holes. Be certain the drill is perpendicular to the panel. Now position the template on

READING TIME: 32 Minutes Price $1.25

THE MclNTOSH C 26 SOLID STATE STEREO PREAMPLIFIER

Your C 26 stereo preamplifier willgive you many years of pleasantand satisfactory performance.If you have any questions concerningthis instrument, please contact:

CUSTOMER SERVICE

Mclntosh 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 Service . . .Fill in the Application NOW.

CONTENTS

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

The terms of the contract are: or mishandling is not covered by the SERV-ICE CONTRACT.

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

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 onlydealers who have technical competence toguide purchasers fairly, and provide servicewhen necessary. To receive the SERVICECONTRACT your purchase must be madefrom 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.

How to Connect ... 4, 5, 6

What the Controls Do ... 7, 8

Using the Front Panel Controls ... 8, 9

Using the Pushbuttons ... 10

Adjusting the Top Panel Controls ... 11

Listening to Your Stereo System ... 11

Performance Limits ... 12, 13

Performance Charts ... 14

Technical Description ... 15

Block Diagram ... 16

Service Contract ... 1

Installation ... 2, 3

THREE YEAR SERVICE CONTRACT

1

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 break-down that results from unnecessarily high operat-ing temperatures. The direct benefit of adequateventilation is longer, trouble-free life.

Allow at least 15 inches deep x 17½ inches widex 6 inches high for mounting the C 26. Alwaysallow for air flow by either ventilation holes orspace next to the bottom of the preamplifier anda means for a warm air to escape at the top.

It is recommended that the C 26 be mounted ina normal or horizontal position. However, withadequate ventilation the preamplifier can bemounted in any position.

To prepare the C 26 for installation remove theplastic protective covering. Turn the C 26 upsidedown so that it rests on its top on the shippingpallet. Remove the four plastic feet fastened tothe bottom of the chassis.

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

The PANLOC professional mounting design elimi-nates the need for any shelf or bracket to supportthe C 26. It is completely supported by its ownmounting 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 step 2. If the cutout is to belocated from the rear of the panel, begin here.1. On the back of the cabinet panel, scribe a

vertical 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 lineof the cutout area on the template and anyshelf or 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 onthe template with the drill holes.

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

With the template in place against the cabi-net panel, mark the "A" and "B" drill holes andthe four small holes that identify the corners ofthe cutout. Join the corner marks with a pencil.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 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.

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instrument in until the front panel is against thecabinet panel. At the bottom front corners of thePANLOC instruments are the PANLOC buttons.Depressing the PANLOC buttons will lock the in-strument firmly in the installation. Depressing thePANLOC buttons a second time (as with a ball-point pen) will release the instrument. You canthen slide the instrument forward to the inspec-tion-adjustment position. Depressing the inspec-tion-adjustment position latches will allow the in-strument to be slid completely out of the installa-tion.

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 ¾ inch long screws for panels under ½inch, or two 1¼ inch long screws for panels ½ inchthick and larger.)

Attach the mounting brackets to the cabinetusing 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, loosenthe screws and push the brackets into alignmentand retighten.

Insert the power cord through the opening.Carefully slide the C 26 into the opening so therails on the bottom of the equipment slide in thetrack of the mounting brackets. Slide the instru-ment in until it stops at the adjust position latches.Press the latches in and continue to slide the

3

How to ConnectCONNECTING A RECORD PLAYER TO PHONO 1

Connect the cable from the "left" channel of therecord player into the "L" PHONO 1 input jack.

Connect the cable from the "right" channel ofthe record player into the "R" PHONO 1 jack.

PHONO 2 is provided for the use of a secondrecord player.

Connect the cable from the "left" channel of therecord player into the "L" PHONO 2 input jack.

Connect the cable from the "right" channel ofthe record player into the "R" PHONO 2 input jack.

CONNECTING A STEREO TUNER

Connect the cable from the "left" channel tuneroutput to the "L" tuner input jack.

Connect the cable from the "right" channeltuner output to the "R" tuner jack.

AUX

Any high level program source such as anothertuner or a TV set is connected to the input jacksmarked AUX.

CONNECTING A TAPE RECORDER

To Record:

Connect a cable from the L TAPE OUTPUT jackmarked TAPE 1 to the left high level input of a taperecorder.

Connect a cable from the R TAPE OUTPUT jackmarked TAPE 1 to the right high level input of thetape recorder.

Connect a second tape recorder in the samefashion to the TAPE 2 outputs.

To Playback/Monitor:

Connect the cable from the left channel outputof a tape recorder to the high level inputs . . . LTAPE 1.

Connect the cable from the right channel outputof a tape recorder to the high level input . . . RTAPE.

Connect a second tape recorder in the samefashion to the TAPE 2 input jacks.

CONNECTING THE C 26 to POWER AMPLIFIERS

Connect the MAIN output jacks to the input of astereo power amplifier. The L jack is connectedto the left amplifier input jack. The R jack is con-nected to the right amplifier input jack.

The output impedance at the MAIN output is 200ohms. Longer cables than are supplied can beconnected between the C 26 and the amplifiers.The length of the cable is limited by the capacityof the cable. The total capacity must not exceed1,000 pF. For instance: cables with a capacity of25 pF per foot may be 40 feet long. 13.5 pF perfoot cable may be 75 feet long. The input imped-ance of the amplifiers should be 47,000 ohms orgreater.

CTR OUTPUT (L + R)

Use the CTR output to feed left plus right signalto a separate power amplifier for monophonicbackground music or for a center channel speaker.

AC POWER OUTLETS

There are 4 black AC power outlets, and one redAC outlet. The power to the black AC power out-lets is controlled by the front panel switch. Usethese outlets for a tuner, tape recorder, etc. Thered receptacle is on at all times. Use the red outletfor a turntable or record changer. The turntable orrecord changer is protected by this arrangement.It is necessary to turn off the turntable or recordchanger with its own AC power switch.

GROUND CONNECTION

A single ground post is provided. Grounds forturntables, record changers, tape decks, etc.should be connected to this post. The left andright program cables and the ground wire fromthat source should be wound or twisted together.To avoid hum, make sure the ground wire doesnot make any connections to the shields of the leftand right program cables between the programsource and the C 26.

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What theControls Do

LOUDNESS CONTROL

FLAT position: (Maximum counterclockwise ro-tation) Normal flat frequency response. The loud-ness compensation is totally inoperative at thisposition.

A loudness control provides low-frequency boostto compensate for the behavior of the human earat low listening levels. The ear is less sensitive tolow frequencies at low levels. The loudness con-trol fills in low-frequency tones that the ear wouldnormally hear only at higher listening levels. In-creased loudness compensation is therefore de-sirable as the listening level is reduced.

The C26 LOUDNESS CONTROL automaticallycompensates for the lack of sensitivity in the ear asthe listening level is reduced. The low frequenciesare then heard in correct proportion to the mid-range and highs. Turning clockwise toward MAXposition reduces the listening volume, and auto-matically increases the compensation by boostingbass. Use the loudness control for full frequencyrange listening at even the softest listening levels.

TAPE MONITOR SWITCH

The C26 TAPE MONITOR switch makes it pos-sible to instantaneously compare recorded materialwith the source signal from either of two taperecorders used with the C 26. The recorders usedwith the C 26 should have separate record andplayback heads and separate record and playamplifiers.

MONITOR

With the button pushed in, the signal source be-comes the program as recorded and is fed throughthe main preamplifier outputs to the power ampli-fiers and loudspeakers.

The TAPE MONITOR switches are mechanicallyinterlocked to prevent simultaneous monitoringfrom two tape recorders. If one button is at the INposition, it must be pushed again to release it tothe OUT position before the other button can bepushed.

USING ONE TAPE RECORDER

The output of a tape recorder can be connectedto either TAPE 1 or TAPE 2 input. The correspond-ing tape output of the C 26 should then be con-nected to the input of the tape recorder. Anysource can be recorded without being affected bythe tone control or volume control settings. Theplayback of the tape recording can be monitoredby pushing the corresponding tape monitor button.

TWO TAPE RECORDERS

Two tape recorders can be used with the C 26preamplifier. Recordings can be made from re-corder 1 to recorder 2, or from recorder 2 torecorder 1.

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Example: Connect the output of recorder 1 toTAPE 1 input on the C 26. Connect the TAPE 1output on the C 26 to the input of recorder 1. Inthe same way, connect the output of recorder 2 toTAPE 2 input on the C 26. Connect TAPE 2 outputof the C 26 to the input of recorder 2.

By setting the C 26 input selector switch atTAPE 1, a recording can be made on tape recorder2 from a tape playing on tape recorder 1. The re-cording can be monitored from the playback oftape recorder 2 by pushing the TAPE 2 monitorbutton.

The tape recorder functions can be reversed bysetting the input selector switch at TAPE 2. A re-cording can then be made on tape recorder 1,from a tape playing on tape recorder 2. The re-cording on tape recorder 1 can be monitored fromthe playback of tape recorder 1 by pushing theTAPE 1 monitor button.

The C 26 preamplifier can also be used with onerecorder for recording other program sources whileplaying tapes from a second recorder.

Example: Connect the output of tape recorder 1to the TAPE 1 inputs of the C 26. Connect the out-puts of tape recorder 2 to the TAPE 2 inputs of theC 26. Connect the TAPE 2 outputs of the C 26 tothe inputs of tape recorder 2.

A recording from AUX, TUNER, PHONO 1 orPHONO 2 can be made on tape recorder 2 if theselector switch is set to the corresponding sourceposition. The recording on tape recorder 1 can bemonitored for playback by pushing the TAPE 2monitor button. At the same time, the C 26 can beused to play a tape from tape recorder 1 by releas-ing the monitor button for TAPE 2 and pushing themonitor button for TAPE 1. The signal of taperecorder 1 will then go to the main preamplifieroutputs without affecting the recording being madeon tape recorder 2.

Tape recordings can be made simultaneously ontwo tape recorders by using PHONO 1, PHONO 2,AUX or TUNER as a program source. The taperecorders should be connected as described inexample 1. Set the input selector switch to thedesired source. The recording on either tape re-corder can be monitored for playback by pushingthe appropriate tape monitor button.

CAUTION: When recording with two tape recordersat the same time from the same program source,mutual interference of the recorder bias oscillatorscan result. This can be heard as a howl or squealin the background when the recordings are playedback. This noise is caused by insufficient filteringof the bias oscillator circuits in the tape recorders.A test run should be made for the particular re-corders intended for this use.

SPEAKER SWITCHES

To switch the main and remote stereo speakersusing the pushbuttons on the front panel, thepower amplifier output leads must be connectedto the amplifier output terminals on the rear of theC 26. The main speakers must be connected to themain speaker terminals and the remote speakersto the remote speaker terminals. If either main orremote speaker button is pushed to OFF, loadresistors are automatically connected to the poweramplifier to compensate for the speaker. Theheadphone output is always connected throughlevel matching resistors to the amplifier terminalsregardless of the position of the main or remoteswitches.

8

Using theFront Panel Controls

In the upper right of the front panel is the VOL-UME-ON/OFF control.

Turning the VOLUME totally counterclockwiseturns the C 26 OFF. The VOLUME control regu-lates the loudness in both channels. The VOLUMEcontrol has been precision tracked throughout thelistening range (0 to -65 dB) for accurate stereobalance.

MODE SELECTOR: Connects the program to theloudspeaker in the following seven ways:

L to L & R: Connects the "left" input to bothloudspeakers.

R to L & R: Connects the "right" input to bothloudspeakers.

STEREO REV: Connects the "left" input to the"right" loudspeaker and the "right" input tothe "left" loudspeaker.

STEREO: Connects the "left" input to the "left"loudspeaker and the "right" input to the"right" loudspeaker.

MONO (L + R): adds the "left" input and the"right" input and then connects the L + Rprogram to both amplifiers and loudspeakers.

L + R to L: Connects the "left plus right" pro-gram to the "left" loudspeaker only.

L + R to R: Connects the "left plus right" pro-gram to the "right" loudspeaker only.

INPUT SELECTOR:

Aux: Connects the output from any high level pro-gram source requiring flat amplification to the highlevel input stage. Such a source could be a tele-

vision set or other source that has output of 0.25volts or more. In the AUX position the gain is 20 dBto the MAIN outputs, 0 dB to the TAPE outputs.The input impedance is 250,000 ohms.

TAPE 1: Connects the output from a complete taperecorder to the high level input stage of the C 26.In the TAPE 1 position the C 26 has flat amplifica-tion. There is 20 dB of gain to the MAIN outputs,0 dB to the TAPE OUTPUTS.

TAPE 2: Connects the output from a complete taperecorder to the high level input stage of the C 26.In the TAPE 2 position the C 26 has flat amplifica-tion. There is 20 dB of gain to the MAIN outputs,0 dB to the TAPE OUTPUTS.

TUNER: Connects the output from any AM, FM orFM STEREO tuner to the high level input stage ofthe C 26. In the TUNER position the C 26 has flatamplification. There is 20 dB of gain to the MAINoutputs, 0 dB to the TAPE outputs. The input im-pedance is 250,000 ohms.

PHONO 1: Connects the output of any magneticphono cartridge to the low level input stage of theC 26. The response has been shaped to compen-sate for the characteristics of the magnetic phonocartridge. The gain at 1000 Hz is 62 dB to the MAINoutputs, 42 dB to the TAPE outputs. The inputimpedance is 47,000 ohms.

PHONO 2: Same as PHONO 1.

LOUDNESS

The C 26 LOUDNESS control automaticallyboosts the bass as it turns down the listening vol-ume. The bass is then heard in correct proportionto the mid-range.

Turning clockwise toward MAX position reducesthe listening volume, while automatically boostingthe bass for full frequency listening at even thelowest volume levels.

The C 26 LOUDNESS control automaticallyboosts the bass as it turns down the listening vol-ume. The bass is then heard in correct proportionto the mid-range.

Turning clockwise toward MAX position reducesthe listening volume, while automatically boostingthe bass for full frequency listening at even thelowest volume levels.

BALANCE

The BALANCE control adjusts for unequal loud-ness in either the left or right channels. The loud-ness of the channels can be varied relative to eachother without affecting their combined loudness.

Left . . . turning the control to the left accentsthe left channel by reducing the right channel out-put.

Right. . . turning the control to the right accentsthe right channel by reducing the left channel out-put.

BASS

The C 26 has concentric 11 position tone controlswitches for adjusting the bass. The outer knobadjusts the left channel bass response. The centerknob adjusts the right channel bass response.

Left: Adjusts the bass loudness from the leftloudspeaker. Clockwise rotation increases thebass loudness while counterclockwise rotation de-creases the bass loudness. Each step of the tonecontrol adjusts the bass loudness 4 dB.

Right: Has the same effect on the sound fromthe right loudspeaker.

TREBLE

The C 26 has concentric 11 position tone controlswitches for adjusting the treble. The outer knobadjusts the left channel response. The center knobadjusts the right channel treble response.

Left: Adjusts the treble loudness from the leftloudspeaker. Clockwise rotation increases thetreble loudness while counterclockwise rotationdecreases the treble loudness. Each step of thetone control adjusts the treble loudness about4 dB.

Right: Has the same effect on the sound fromthe right loudspeaker.

HEADPHONES

Low impedance dynamic headphones are plug-ged into the HEADPHONE jack.

The output of the power amplifiers must be prop-erly connected to the C 26 back panel for programmaterial to be available at the HEADPHONE jack.

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Using the PushbuttonsThe C 26 is designed to be used with two com-

plete tape recorders. The pushbuttons permit nor-mal playback of either recorder, or monitor ofeither recorder as recordings are being made.

TAPE 1

PUSHBUTTON OUT . . . The program source isfed to the power amplifiers and heard through theloudspeakers.

IN . . . The program source becomes the re-corded tape on the tape recorder connected toTAPE INPUT 1. The recorded program from taperecorder 1 is fed to the power amplifiers and heardfrom the loudspeakers.

TAPE 2

The second complete tape recorder can beoperated in the same fashion.

L F (LOW FREQUENCY FILTER)

Use the L F filter switch to reduce objection-able low-frequency noise created by a turntable orrecord changer or acoustically coupled feedback.

OUT . . . filter disconnected.

IN . . . low-frequency rumble and noise below 50Hz are reduced when the switch is pushed to theIN position.

H F (HIGH FREQUENCY FILTER)

Use the H F filter switch to reduce objection-able high-frequency noise such as record scratch.

OUT . . . filter disconnect.

IN . . . rolls off response sharply at 7000 Hz.

SPEAKER

When the output of the power amplifier and thespeakers have been connected to the proper pushconnecters on the back panel, the pushbuttonsturn the speakers ON or OFF. (See Diagram Page6).

If the program is to be heard from the mainspeakers only, the REMOTE pushbutton is pushedIN. This turns off the remote loudspeakers.

If the program is to be heard from the remotespeakers only the MAIN pushbutton is pushed IN.This turns off the main speakers.

To hear program from both main and remotespeakers, both the MAIN and REMOTE pushbut-tons must be in the OUT position.

MAIN

PUSHBUTTON OUT . . . the program materialis heard from the MAIN speakers.

IN . . . the MAIN loudspeakers are turned OFF.

REMOTE

PUSHBUTTON OUT . . . the program materialis heard from the REMOTE loudspeakers.

IN . . . the REMOTE loudspeakers are turnedOFF. (These pushbuttons do not affect the head-phone jack.)

PANLOC

Mclntosh developed PANLOC mounting bringsprofessional installations technique to stereo.When the C 26 has been installed on PANLOCbrackets, pressing the PANLOC buttons locks theamplifier firmly in position. Depressing the buttons(as with a ballpoint pen) will release the instru-ment. It can then be slid forward to the "adjust-ment" position. In the "adjust" position the toppanel controls PHASE and CENTER CHANNELLEVEL can be adjusted. The PANLOC system givesabsolute ease of installation, operation, and main-tenance.

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Adjusting theTop Panel ControlsPHASE —The PHASE is a two-position switch

that reverses the phase in the left channel. Im-properly phased program sources can be cor-rected with this switch.

1. Set the MODE SELECTOR switch to MONO.

2. Stand about 10 feet in front of and mid-waybetween your loudspeakers. The soundshould appear to be directly in front of you.If the sound is not directly in front of youwith the PHASE switch in the 0° reverse theleads on one loudspeaker. When the soundcomes from the mid-point between thespeakers they are in PHASE.

CENTER CHANNEL LEVEL — Left and rightchannels are added to make a center channel pro-gram source. The program can be fed to a thirdamplifier for a center channel speaker or for mono-phonic remote speakers. The CENTER CHANNELLEVEL control adjusts the volume on CTR CHAN-NEL output jack only. Adjustment is from —6 dB to+6 dB with respect to the MAIN output. Clockwiserotation increases the loudness.

Listening to YourStereo system

LISTENING TO A STEREO RECORD

1. Turn the INPUT SELECTOR to PHONO 1, orPHONO 2, whichever is connected to therecord player you wish to hear.

2. Set the MODE SELECTOR to STEREO.

3. Adjust the VOLUME control to the desiredvolume.

LISTENING TO MONOPHONIC RECORDS

1. Turn the INPUT SELECTOR to PHONO 1, orPHONO 2, whichever is connected to therecord player you wish to hear.

2. Turn the MODE SELECTOR to MONO.

3. Adjust the VOLUME control to the desiredvolume.

LISTENING TO A TAPE RECORDER

The TAPE input is used:

1. Turn the INPUT SELECTOR to TAPE.

2. Turn the MODE SELECTOR switch toSTEREO or MONO, depending on the pro-gram on the tape.

3. Adjust the VOLUME control to the desiredvolume.

Two tape recorders can be used with the C 26.Connect a three head tape recorder to TAPE 1inputs. Connect a second three head tape recorderto TAPE 2. Recording and monitoring can be donewith both tape recorders.

To monitor while recording your tape recordermust have separate record and playback headsand separate electronics. The pushbutton switchlets you monitor the quality of tape recordingsmade during the recording process. When theTAPE switch is in the IN position it will play thesound from the tape as it passes the playbackhead, a moment after it is recorded. The recordingprocess continues as usual. When the switch is inthe OUT position normal program from the sourceis heard.

HOW TO COPY TAPE

1. Put the tape on the recorder connected toTAPE 1 input.

2. Turn the input selector to TAPE 1.

3. The signal available at the TAPE OUTPUTjacks is the playback of TAPE 1.

4. Record on the recorder connected to TAPE2. The recording can be monitored by press-ing in the TAPE 2 pushbutton. Instantaneouscomparison on the recorded program withthe original can be heard.

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Performance Limits POWER REQUIREMENT

120 volts, 50/60 Hz, 15 watts

Performance Limits are the maximum deviationfrom perfection permitted for a Mclntosh instru-ment. We promise you that your C 26 must becapable of performance at or exceeding theselimits or you get your money back. Mclntosh isthe only manufacturer that makes this guarantee.

FREQUENCY RESPONSE+0 -0.5 dB 20 Hz to 20,000 Hz

DISTORTIONWill not exceed 0.1% at rated output level, 20

Hz to 20,000 Hz

INPUT SENSITIVITY AND IMPEDANCEAUXILIARY, TUNER, TAPE 1, TAPE 2 0.25 volts

at 250,000 ohms

HUM AND NOISE

AUXILIARY, TUNER, TAPE 1, and TAPE 2 85 dBbelow rated output

PHONO 1, PHONO 2 74 dB below 10 millivoltsinput, equivalent to less than 2 microvolts atthe input terminals

OUTPUT LEVEL AND IMPEDANCE

MAIN OUTPUT 2.5 volts with rated input, 200ohms source impedance, to operate into 47,-000 ohms or greater

TAPE OUTPUT 0.25 volts from low level inputs,200 ohms source impedance, to operate into47,000 ohms or greater

CENTER CHANNEL OUTPUT (L + R) 2.5 voltswith rated input to both channels, 1,200 ohmssource impedance, to operate into 47,000ohms or greater

A level control adjusts the CENTER CHANNELoutput from -6 dB to +6 dB with respect toMAIN output

VOLTAGE AMPLIFICATION IN DECIBELS:

AUXILIARY, TUNER, TAPE 1 and TAPE 2to MAIN OUTPUT 20 dBto TAPE OUTPUT 0 dBPHONO 1 and PHONO 2 (at 1,000 Hz)to MAIN OUTPUT 62 dBto TAPE OUTPUT 42 dB

AC POWER OUTLETS:

1 unswitched (Red)4 switched

FACILITIES AND FEATURES

BASS

Separate 11 position rotary switches for eachchannel. -20 dB to +16 dB at 20 Hz

TREBLE

Separate 11 position rotary switches for eachchannel. -20 dB to +20 dB at 20,000 Hz

LOUDNESS

Flat response, or continuously variable loudnessequalization as volume level is reduced

BALANCE

Natural balance at center position, attenuationof left or right channel by rotating control

VOLUME

Precision "tracked" at all listening levels. (0 to-65 dB). Does not change stereo balance as loud-

ness is changed. The AC power ON/OFF switch iscoupled with this control

INPUT

Six positions —AUXILIARY, TAPE 1, TAPE 2,TUNER, PHONO 1, and PHONO 2

MODE

Seven positions — Left channel only to bothspeakers. Right channel only to both speakers,Stereo Reverse, Stereo, Mono, L + R, L + R toright speaker only, and L + R to left speaker only

TAPE MONITOR

Two pushbutton switches. Either of two taperecorders can be monitored by selecting the TAPE1 pushbutton or TAPE 2 pushbutton. They are me-chanically interlocked to accept only one push-button at the IN position at one time

LF FILTER (Rumble Filter)

Flat or roll-off 6 dB perdown to 12 dB at 20 Hz

HF FILTER (Scratch Filter)

octave below 50 Hz,

Flat or roll-off 6 dB per octave above 6,000 Hz,down 12 dB at 20,000 Hz

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SPEAKER

Main — Switch the MAIN loudspeaker systemON or OFF without affecting the performanceof REMOTE speakers.

Remote — Switch the REMOTE loudspeakersystem ON or OFF without affecting the per-formance of MAIN speakers.

HEADPHONE JACK

The output of the power amplifiers must beproperly connected to the C 26 back panel forprogram material to be available at the HEAD-PHONE jack.

SECONDARY CONTROLS

These controls are located behind the frontpanel on top of the C 26. They are readily accessi-ble by depressing the PANLOC buttons and slidingthe C 26 forward on the PANLOC brackets.

CENTER CHANNEL LEVEL

Top of chassis control to adjust the output levelof the left plus right program material at the CEN-TER CHANNEL output on the back panel.

PHASE CONTROL

Electronically reverse phase in the left channelto correct "out of phase" program sources.

TRANSISTOR COMPLEMENT

18 silicon-planar transistors, and 3 silicondiodes.

SIZE: Front panel measures 16 inches wide (40.64cm) by 5-7/16 inches high (13.81 cm). Chassismeasures 15 inches wide (38.1 cm) by 5 incheshigh (12.7 cm) by 13 inches deep (33.02 cm),including PANLOC shelf and back panel con-nectors. Knob clearance required is 1½ inches(3.81 cm) in front of the mounting panel.

FINISH: Front panel is anodized gold and blackwith special Mclntosh gold/teal panel nomencla-ture illumination. Chassis is black.

MOUNTING: Exclusive Mclntosh developed pro-fessional PANLOC.

WEIGHT: 18 pounds (8.16 kg) net, 33 pounds(14.97 kg) in shipping carton.

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MECHANICAL INFORMATION

PerformanceCharts

LOW AND HIGH FREQUENCY FILTER CHARACTERISTICS

PHONO EQUALIZATION CHARACTERISTIC (RIAA)100 1000 10000 20000

20

15

10

5

0

-5

-10

-15

-20

FREQUENCY IN HERTZ

20FREQUENCY IN HERTZ BASS AND TREBLE TONE CONTROL CHARACTERISTICS

LOUDNESS CONTROL CHARACTERISTICS10000 20000

14100

FREQUENCY IN HERTZ10000 20000100020

RE

SP

ON

SE

IN

dB

0

-5

-10

-15

-20

-25

20 100

FREQUENCY IN HERTZ

1000

20

15

10

5

0

-5

-10

-15

-20

Res

pons

e in

dB

1000 10000 20000100

Res

pons

e in

dB

20

0

-5

-10

-15

-20

Res

pons

e in

dB

The C 26 preamplifier functions can be dividedinto 5 sections. They are: phono preamplifier,main preamplifier, power supply, center channelamplifier, and speaker control.

PHONO PREAMPLIFIER

There are three transistors in each channel ofthe phono preamplifier. The input transistor, ahigh-gain amplifier, dives an emitter follower. Theemitter follower drives the third transistor whichis another high-gain amplifier. To reduce noiseand distortion the output of the third transistor isconnected by a negative feedback loop to theemitter of the input transistor. The feedback net-work also provides precision RIAA frequencycompensation required for magnetic phonographcartridges and a low output impedance for thetape output. Feedback remains in effect even at20 Hz, where gain is highest.

The phono input sensitivity is 2 millivolts. In theC 26, phono input overload is virtually impossible.For example, at 1,000 Hz, the phono input circuitwill accept 150 millivolts of signal without over-load.

Ten millivolts of signal at the phono input at1,000 Hz will produce 1.2 volts at the tape output.

MAIN PREAMPLIFIER

There are five transistors in each channel of theMAIN PREAMPLIFIER. The selector switch con-nects either the output of the phono amplifier ora high level input to the main preamplifier.

The high level input impedance is 250,000 ohms.The high-level input feeds through the volume con-trol to a pair of transistors connected as high-gainamplifier. In the left channel the second transistoris connected in a balanced output arrangement toprovide equal amplitude signals for the phaseswitch. With this arrangement the output leveldoes not vary when the phase switch is changed.Negative feedback is used to reduce noise and

distortion and to provide the low impedanceneeded to drive the highly selective filter networkswhich follow.

The filter networks are switch controlled. Thehigh-frequency filter network reduces treble re-sponse above 5,000 Hz. The low-frequency filterreduces bass response below 50 Hz. The slope ofthe filters is selected for maximum rejection ofobjectionable noises. Careful design has kept theloss of usable program material to a minimum.

The signal is then fed into the loudness andbalance controls. The loudness control is con-tinuously variable. It may be used in conjunctionwith the volume control. Rotating the loudnesscontrol produces any loudness compensation fora desired listening level. At 50% rotation, the loud-ness control will be effective below 150 Hz, gradu-ally increasing low-frequency output to a maximumof 6 dB at 20 Hz. At full rotation, the loudnesscontrol will be effective below 1,000 Hz graduallyincreasing low-frequency output to a maximum of15 dB at 20 Hz.

The output of the balance control is connectedto an emitter follower which is the first stage ofthe tone control section. The emitter follower pro-vides a high-input impedance required for loud-ness and balance circuits and a low-output imped-ance for the tone control circuits. The remainingtwo transistors are connected as a high-gain ampli-fier stage. Again negative feedback is used toassure low distortion and, in addition, accuratelyshapes the tone-control response curves and pro-vides a low output impedance for the main out-puts. Negative feedback is maintained at all fre-quencies, even with the tone controls turned tofull boost.

CENTER CHANNEL AMPLIFIER (L + R)

The center channel amplifier is a single transis-tor connected as a voltage amplifier. The main leftand right outputs are fed through mixing resistorsto the input of the voltage amplifier. The centerchannel level control is connected in a negativefeedback loop around the voltage amplifier. It per-mits adjusting the output ±6 dB compared to themain outputs. Feedback also provides a low out-put impedance for center channel.

POWER SUPPLY

Careful design of the power supply section in-sures proper supply voltages for the preamplifiercircuits. A wide variation of line voltage will notaffect the D.C. voltage output of the power supply.A series regulator transistor acts as a highly effec-tive filter for A.C. ripple as well. The voltage regu-lator transistor is stabilized by a zener referencediode for constant voltage output.

15

BlockDiagram

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

607-723-3512Design and Price subject to change without notice. Printed in U.S.A.

038-867

BE032003