Reading Time: 32 Minutes Price: $2.00

THE MclNTOSH MR 80 DIGITAL FM TUNER

VARIOUS REGULATORY AGENCIES REQUIRE THAT WE BRING THE FOLLOWINGINFORMATION TO YOUR ATTENTION. PLEASE READ IT CAREFULLY.

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

The Mclntosh you have purchased is a Model

MR 80. It has a serial number located on the rear

panel of the chassis. Record that serial number

here:

Serial Number

The model, serial number and purchase date are

important to you for any future service. Record the

purchase date here:

Purchase date

Upon application, Mclntosh Laboratory provides a

Three-Year Service Contract. Your Mclntosh author-

ized service agency can expedite repairs when you

provide the Service Contract with the instrument for

repair. To assist, record your Service Contract

number here:

Service Contract Number

Your MR 80 Digital FM Tunercan give you many years ofsatisfactory performance. If youhave any questions, please contact:

CUSTOMER SERVICEMclntosh Laboratory Inc.2 Chambers StreetBinghamton, New York 13903-9990Phone: 607-723-3512

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

ContentsSERVICE CONTRACT INFORMATION . . . 1

INSTALLATION . .2HOW TO CONNECT AND

BACK PANEL INFORMATION...4FRONT PANEL INFORMATION

AND USE OF CONTROLS. . .6TOP PANEL INFORMATION

AND SECONDARY CONTROLS . . .8PERFORMANCE LIMITS . . .9

PERFORMANCE CHARTS. -10TECHNICAL DESCRIPTION. 14

BLOCK DIAGRAM..20

MclNTOSH THREE YEAR SERVICE CONTRACTAn application for A THREE YEAR SERVICE CONTRACT is included with this manual.

The terms of the contract are:1. Mclntosh will provide all parts, materials

and labor needed to return the measuredperformance of the instrument to theoriginal performance limits. The SER-VICE CONTRACT does not cover anyshipping costs to and from the authoriz-ed service agency or the factory.

2. Any Mclntosh authorized service agencywill repair Mclntosh instruments at nor-mal service rates. To receive serviceunder the terms of the SERVICE CON-TRACT, the SERVICE CONTRACT CER-TIFICATE must be presented when theinstrument is taken to the service agency.

3. Always have service done by aMclntosh authorized service agency. Ifthe instrument is modified or damagedas a result of unauthorized repair, theSERVICE CONTRACT will be cancelled.Damage by improper use or mishandl-ing is not covered by the SERVICECONTRACT.

4. The SERVICE CONTRACT is issued toyou as the original purchaser. To pro-tect you from misrepresentation, this

contract cannot be transferred to a se-cond owner.

5. To receive the SERVICE CONTRACT,your purchase must be made from aMclntosh franchised dealer.

6. Your completely filled in application forthe SERVICE CONTRACT must be post-marked within 30 days of the date ofpurchase of the instrument.

7. To receive the SERVICE CONTRACT, allinformation on the application must befilled in. The SERVICE CONTRACT willbe issued when the completely filled inapplication is received by MclntoshLaboratory Incorporated in Binghamton,New York.

8. Units in operation outside the UnitedStates and Canada are not covered bythe Mclntosh Factory Service Contract,irrespective of the place of purchase.Nor are units acquired outside theU.S.A. and Canada, the purchasers ofwhich should consult with their dealerto ascertain what, if any, service con-tract or warranty may be available locally.

Copyright 1980 © by Mclntosh Laboratory Inc. 1

How to Connect andBack Panel InformationRefer to page 5.

AUDIO OUTPUTSUse the FIXED OUTPUT jacks on the rear panel to

feed program to a stereo control preamplif ier orother equipment which has its own volume control.The front panel VOLUME control does not a f fec t theloudness of the tuner at the FIXED OUTPUT jacks.The output level is a nominal 1 volt for 100% FMmodulation.

Use the VARIABLE OUTPUT jacks to connect toequipment such as a power ampl i f ier or a taperecorder where control of the volume at the tuner isdesired. The output at the VARIABLE OUTPUT jacksis a nominal 2.5 vol ts for 100% FM modulation.There is no dif ference in the signal qual i ty at eitherpair of output jacks.

Both pairs of OUTPUT jacks may be used simul-taneously. The output impedance at both outputs isvery low so that long audio cables can be usedwithout a loss of high frequencies due to cablecapacity.

RF INPUTS — ANTENNA CONNECTIONSTwo of four d i f ferent antenna systems can be

used with your MR 80. 1) an outdoor FM antenna, 2)an a l l channel (UHF-VHF-FM) antenna, 3) a cable in-put from your local cable company, or 4) the indoordipole supplied wi th the MR 80. A switch is providedon the top level set panel to select between two ofthe four systems mentioned.

An outdoor antenna is recommended for optimumperformance in all areas. In fr inge areas, best resultswi l l be obtained with a highly direct ional FM an-tenna used in connection with a rotator. Rotate theantenna unt i l the best reception is obtained. Con-nect a 300 ohm outdoor antenna to the 300W AN-TENNA (red) terminals. Connect a 75 ohm antennaand/or 75 ohm cable system to the coaxial antennajack.

A f l ex ib le fo lded dipole antenna supplied wi thyour MR 80 may be used in urban or in high signalstrength areas. The f l ex ib i l i t y of the th in f l a t wireassembly permits it to be placed under a rug. tackedbehind the stereo or placed in any other convenientlocation. In some cases it may be necessary to posi-tion the antenna for best signal reception. Thisshould be done before it is permanently located.

Avoid locating th is antenna next to other w i res ormetal objects. This antenna may not prove e f fec t i vein houses having metal siding or metal clad insula-t ion.

The cable signal from a local cable company or asecond FM antenna with 75 ohms impedance maybe connected to the coaxial cable jack.

REMOTE SCANThe REMOTE SCAN CONTROL SIGNAL jack is to

be connected to the cable push button assemblysupplied wi th the MR 80 for remote tuning. Plug thecable into the CONTROL SIGNAL jack. Pressing thepush button at the end of the cable causes the MR80 to scan to the next stat ion. The mode of scan canbe selected by the STATION'S sl ide switch. In thePRESET position every time the push but ton isdepressed the MR 80 w i l l scan to the next preset sta-tion. In the ALL posit ion depressing the but ton wi l lcause the MR 80 to scan to the next station.

If REMOTE tuning is not used, leave the jack freeof any connection.

SCOPEThe vert ical and horizontal scope jacks are pro-

vided to connect to a maximum performance in-dicator or an osci l loscope for indication of FMmult ipath and signal strength. Connect the ver t ica ljack to the vert ical input of the indicator and thehorizontal jack to the horizontal input.

UNSWITCHED AC POWER OUTLETThis outlet may be used to power aux i l ia ry equip-

ment such as an antenna rotator or a maximum per-formance indicator. Power is available whenever theMR 80 is connected to a power source.

4

FM CABLEINPUT OR

2ND 75W ANTENNALEAD-IN

FM ANTENNA

OPTIONAL75W ANTENNA

LEAD-IN

REMOTE CONTROLPUSH BUTTON

POWER AMPLIFIER

PREAMPLIFIER

LEFT SPEAKER RIGHT SPEAKER

5

MAXIMUM PERFORMANCEINDICATOR

OROSCILLOSCOPE

TO ACPOWER

SOURCE

Front Panel Information andUse of Controls

The MR 80 Tuner has the most f lex ib le controlsystem ever designed in a stereo FM tuner. Correctuse of these controls will yield a higher level of per-formance than previously possible wi th conven-tional tuners.

VOLUME CONTROL AND AC POWER SWITCHThe VOLUME control has been precision tracked

throughout the listening range (0 to - 65 dB) for ac-curate stereo balance.

It sets the output level of the VARIABLE OUTPUTjacks and the front panel HEADPHONE jack. TheFIXED OUTPUT jacks are not af fected by the posi-tion of the VOLUME control. The AC power switch ispart of the VOLUME control. Turning the VOLUMEcontrol fu l l y counterclockwise turns the AC poweroff .

TUNING CONTROLS AND FREQUENCY DISPLAY

Frequency DisplayThe Frequency Display indicates the received fre-

quency to the nearest 100 kHz.Tuning

There are four methods of tuning your MR 80.Automatic selection of the tuning method is pro-vided by touch sensors associated with each of thetuning controls.

Manual TuningWhen power is applied to the MR 80, the circuitry

automatically selects the manual or knob tuningcontrol mode. Turning the tuning knob clockwisewil l increase the received frequency. Counterclock-wise decreases the received frequency.

Note: When the MR 80 is operated but is not con-nected to any other device (preamp, power amp,antenna, test equipment, etc.), there is a chance thefrequency display will blank out when tuning withthe main tuning knob. This is normal and can easilybe corrected by reversing the 120V AC line plug or byconnecting the MR 80 to any other equipment.

Auto ScanAUTO SCAN is provided by two touch pads im-

mediately to the left of the tuning knob. These twotouch pads start the tuner searching for a new sta-tion. The small arrow wi l l light next to the padtouched and indicate the direction of scanning. Itwill scan in the direction chosen until it stops at astation or reaches the end of the band. At the bandend the tuner will reverse its scan direction.

Preset 1, 2, 3 & 4These touch pads located to the left of the fre-

quency display select one of the four preset sta-tions. Just touch to operate. A small rectangle willlight above the pad indicating which preset has beenselected.Remote SCAN

Remote SCAN of either the presets or all stationsis provided for as described under back panel infor-mation.

INDICATOR LIGHTSThree indicator lights are provided immediately to

the lef t of the preset touch pads. The uppermostSTEREO indicates when a stereo broadcast is beingreceived. The second, LOCK, indicates when thetuner is locked to the station. The lock circuit in theMR 80 is unique in that tuned frequency is locked tothe station, not to an internal standard as in the caseof many digital tuners. This allows the MR 80 to betuned to any frequency within the FM band and lockon that frequency. Other digital tuners can only lockon specif ic channel assignments. This lock circuit isso powerful that it must be disabled in order to tunethe tuner. You will notice that the moment that youtouch any one of the tuning controls the lock lightextinguishes and only comes on when the station isproperly tuned. Once lock has been established itwi l l remain on even if the station being receivedshould drift up to 2 megacycles either side of thecenter of the carrier. Thus, perfect tuning is alwaysassured. The third indicator light, FILTER, indicateswhen the stereo noise filter is in operation. The in-dicator lights are in three different colors: red forSTEREO, amber for LOCK, and green for FILTER.

SELECTIVITY SWITCHTwo degrees of IF selectivity are selectable by the

SELECTIVITY switch. The NARROW or normal posi-tion provides adequate selectivity for stereo recep-tion even under severe receiving conditions. Fivelinear phase piezoelectric IF f i l ters provide lowdistortion reception with this high degree of selec-t iv i ty . Setting the SELECTIVITY switch to SUPERNARROW adds an additional 4-pole 4-zero quartzcrystal f i l ter to the five previously mentioned filters.Use the SUPER NARROW position to receive sta-tions from distant cities which are on channels adja-cent to local stations. There may be useable signalswhich were never heard before with ordinary FMtuners.

6

SIGNAL COLUMNA column of LED lamps respond to the signal

strength of the stat ion being received. The strongerthe signal the higher the column reaches. There is acontrol on the tuner top panel to adjust the columnheight for fu l l scale when receiving the strongestsignal in your l istening area.

FILTER SWITCH AND FUNCTION INDICATORThe MR 80 FILTER switch provides automatic

stereo noise reduction on weak stereo stations. Withthe switch in the AUTO position the f i l t e r w i l l be ononly when the station is broadcasting a stereo pilottone and the signal strength is below 100 microvol ts.With the swi tch in the IN posit ion the f i l ter is con-nected at al l t imes. The f i l te r has no af fect on monostat ions. The f i l te r funct ion indicator light glowsgreen when the f i l te r is on.

MODE SWITCHA two posit ion MODE switch is provided so that

you may select either automatic stereo or monoreception. In the STEREO position the tunerautomatically switches from mono to stereo modewhen a pre-determined signal to noise ratio has

been reached. In the MONO position all stations wi l lbe received monophonically but the STEREO indicatorwil l l ight if the stat ion is broadcasting in stereo.

HEADPHONE JACKA HEADPHONE jack is provided to drive low im-

pedance dynamic headphones from an internalpower amplf ier.

SCAN CONTROLThe SCAN control adjusts the speed at which the

tuner searches for the next station, when using theAUTO SCAN mode of tuning. If the dial is crowdedwith stat ions use a slow scan speed. If there are fewstations fast scanning can be used.

MUTING CONTROLMUTING suppresses the background noise and

hiss normally heard between stations. Turning thecontrol counterclockwise to the OUT position dis-ables the muting c i rcui ts. Turning the control clock-wise increases the signal level required to unmute.This control also adjusts the sensi t iv i ty of the AUTOSCAN tuning circui ts and the number of stat ionsyou wi l l receive when using this tuning mode.

7

Top Panel Information andSecondary Controls

On the top of the chassis behind the front panel arecessed panel contains the secondary controls.When the MR 80 is installed in the cabinet access tothis panel may be gained by depressing the twoPANLOC buttons and slipping the unit partially for-ward.

Preset 1 thru 4The PRESET tuning adjustments are used to set

the received frequency for each preset. To set apreset to the desired station, touch the correspond-ing preset pad and at the same time adjust thepreset control on the top panel for the desired fre-quency indication. You must touch the pad whiletuning to hold the frequency lock circuit inactive,otherwise erroneous tuning will result.

PreselectThe RF PRESELECT switch switches an addi-

tional tuned circuit between the antenna and thefirst RF stage to immunize against overload. Use thepreselector in very strong signal areas.

InputThe INPUT switch selects either an antenna or

cable as the RF input source. The CABLE input mayalso be used as a second antenna input.

LockThis switch wi l l disable the lock c i rcui ts only

when the main tuning knob is in use. Use the ONposition for all normal reception. Switch to the OFFposition when the received station has a deep fade.This prevents the frequency lock circuit from chang-ing tuning to lock to an adjacent stronger station.

De-emphasisThe 50/75ms button selects the correct de-

emphasis for your country. 75ms is used on the NorthAmerican continent and 50ms is used in WesternEurope and the Far East. 25ms de-emphasis is alsoavailable by depressing the button marked

Note: The normal operating position of the fivepushbutton switches is for the switches to be in theout or up position.

Signal StrengthUse this control to set the signal strength column

to f u l l scale for the strongest station in your area.This control is a sensitivity adjustment for the solidstate signal strength indicator. It merely adjusts theheight of the column. It does not affect the sensitiv-ity of the tuner.

8

Performance LimitsPerformance Guarantee

Performance limits are the maximum deviation fromperfection permitted for a Mclntosh instrument. Wepromise you that the MR 80, at the time of its pur-chase, is capable of performance at or exceedingthese limits or you get your money back. Mclntosh isthe only manufacturer that makes this guarantee.

Tuning:88 to 108MHz

Antenna Inputs:One 300W balanced and two 75W unbalanced.

Intermediate Frequency:10.7MHz

Sensitivity:9.3dBf (1.6mV) for 35dB of quieting

14.7dBf (3mV) for 50dB of quieting13.2dBf (2.5mV) for 3% total noise and harmonic dis-tortion

Signal to Noise Ratio:75dB below 100% modulation

Harmonic Distortion:0.2% 20Hz to 15kHz, mono or stereo

Typically, 0.08% at 1000Hz

Intermodulation Distortion:0.15% mono or stereo for any combination of fre-

quencies from 20Hz to 15,000Hz with peak modula-tion equal to 100% or less. Typically 0.1%

Frequency Response:Mono and Stereo ± 1dB 20Hz to 15kHz with 75, 50

or 25mS deemphasis

Capture Ratio:1.5dB

Selectivity:

Adjacent channelAlternate channel

Spurious Rejection:110dB

Narrow8dB

90dB

Super Narrow60dB

110dB

Tuner IM (RF):-23dBm for 2 signals 1MHz apart

Tuner Intercept Point:-10dBm 75W

Image Rejection:90dB

Maximum Signal Input:8 volts across 75W (1W) antenna terminal wi l l not

increase harmonic or intermodulation distortion.

Audio Hum:75 dB down from 100% modulation

Muting:70dB noise reduction between stations

Muting Threshold:2mV to 1000mV

SCA Rejection:60dB minimum

Stereo Separation:50dB to 1000Hz

Stereo Filter:10dB noise reduction

Audio Output:Variable:

2.5V into 47kFixed:

1V into 47k

General Information

Power Requirements:120 volts 50/60Hz. 25 watts

Semiconductor Complement:57 Transistors68 Integrated Circuits81 Diodes4 LED Displays

18 LED's7 Neon Lamps

Mechanical InformationSIZE: Front panel measures 16 inches wide (40.6 cm)by 5 7/16 inches high (13.8 cm). Chassis measures14 3/4 inches wide (37.5 cm) by 4 13/16 inches high(12.2 cm) by 13 inches deep (33 cm), including con-nectors. Knob clearance required is 1 1/4 inches (3.2cm) in front of mounting panel.FINISH: Front panel is anodized gold and black withspecial gold/teal nomenclature i l luminat ion.Chassis is black.MOUNTING: Exclusive Mclntosh developed profes-sional PANLOCWEIGHT: 27 pounds (12.2 kg) net, 39 pounds (17.7 kg)in shipping carton

9

Performance Charts

SIGNALINPUT

10

SIGNAL INPUT

11

FREQUENCY IN HERTZ

FREQUENCY IN HERTZ

FREQUENCY IN HERTZ

12

FREQUENCY IN HERTZ

FREQUENCY IN HERTZ

FREQUENCY IN HERTZ

13

FREQUENCY IN HERTZ

FREQUENCY IN HERTZ

FREQUENCY IN HERTZ

Technical DescriptionEngineering direction dictated a tuner design

governed by insistence on great f lexibi l i ty and easeof use. This had to be done while designing an RFsection with great sensitivity and the world's bestselectivity in keeping with the needs of low distor-tion. These values were achieved and they retain theMclntosh reputation of outstanding performance,long l i fe and reliability.

RF-IF SECTIONIn the ANT SWITCH six RF PIN diodes are con-

nected as a single pole double throw switch. Thisallows the use of two antennas or the use of anantenna and a cable. Input to output isolation of thisswitch is greater than 75dB.

Following the ANT SWITCH is an RF tuner of ex-ceptional performance. This performance is achiev-ed by the use of a low noise junction FET and a highpower bipolar transistor (a heatsink is used) con-nected as a cascode amplifier. This connectionallows high gain, low noise, and high output levelswithout the need for neutralization. Two additionalPIN diodes are used to insert a second tuned anten-na Preselector circuit during strong signal recep-tion. For lower intermodulation distortion the tunedcircuits are tuned by a series parallel connection offour matched varactor diodes. This circuit and thehigh tuning voltage (5-26 volts) eliminates the RF in-termodulation distort ion caused by diode non-linearities.

Af ter the RF amplifier two parallel tuned circui tsare used to provide the proper load impedance forthe bipolar transistor. The use of two tuned circuitsat this location greatly improves the image rejectionand overload performance of the tuner, as well as in-creasing the RF select iv i ty.

The following balanced mixer is a matched dualJ-FET and bipolar transistor circuit. A low losstoroidal phase splitting transformer is used as animpedance matching network in the gate circuit ofthe mixer. At the output a balanced double tunedtransformer is used as the drain load. This arrange-ment gives great immunity to mixer overload in thepresence of a very strong signal. A bipolar transistoris used as an osci l lator buffer to prevent oscillatorpulling on strong signals, and as the constant cur-rent source for the dual J-FET mixer.

The MR 80 has the narrowest IF bandwidth everused in a stereo tuner. It is the correct width to letjust one FM station through. The excellent selectivi-ty of the MR 80 (210kHz wide at 60dB down) permitstuning to stations that are impossible to receive onordinary tuners.

Constant delay design techniques are used in the4-pole 4-zero crystal f i l ter used in the SUPER NAR-ROW position. However, due to the extreme selec-tivity, delay distortion is very slightly increased overthe NARROW selectivity position.

Four dif ferential amplif iers, coupled with PHASE-LINEAR monolithic fi lters, comprise the NARROWselectivity and signal strength sections of the IFamplifier. One half of each dif ferential amplifier out-put drives a fi l ter and the second output drives a fu l lwave rectif ier circuit. The outputs of these fourrectifier circuits are summed at the inverting input ofan operational ampl i f ier. A f i f t h rect i f ier circuit thatis driven from the limiter is also summed at the inputto the operational amplifier. The output of the opera-tional amplif ier is a voltage that is proportional tothe log of the RF input level. Dynamic range is from2mV to over 2V, that is, greater than 120dB. A solidstate signal strength meter is used as a front panelindication of the incoming RF signal level. TwelveLED's are used in place of the conventional metermovement. The LED's have an almost unlimited life.The fast response of the LED's plainly showsmultipath signals and antenna misorientation. Tobetter use the wide dynamic range of the f ive signalstrength detectors, an adjustment is provided toreduce the ful l scale signal from 100,000mV to anyvalue below that. This meter can be set to give a fullscale indication on a signal as low as 2mV. Thisallows setting the signal meter to indicate full scaleon the strongest station in the users area. Then thesignal strength meter indicates the RF level of allstations received relative to the strongest in thelistener's area.

The signal strength voltage is also used to controlmono/stereo switching, stereo f i l ter insertion,muting, and automatic scan stop. Because of it'swide range and high repeatabil ity this controlvoltage is also used to adjust the stereo separationat low RF signal levels. This produces the maximumsignal to noise ratio possible for all signal levels.

Following the selectivity section of the IF ampli-f ier is the LIMITER. A total gain of 80dB is used inthis circuit. The use of very high gain in the limitercircuit produces hard limiting with very good im-pulse noise rejection. Limiter bandwidth is greaterthan 50MHz, producing excellent detector capturecharacteristics.

A broadband Foster-Seeley discriminator is usedas the detector. This detector coupled with thebroadband limiter produces unmeasurable noiseand distortion. A high speed buffer amplifier fol low-ing the detector isolates the detector from all varia-

14

tions in load impedance. This prevents changes inaudio cable lengths outside the tuner from affectingthe detector performance.

FM STEREO MULTIPLEXThe heart of the multiplex section is a new third

generation phase locked loop (PLL) stereo decoderintegrated circuit (IC). This PLL IC incorporates twospecial systems, an automatic variable separationcontrol circuit to reduce background noise whenreceiving weak stereo stations, and tri-level digitalwaveform generation which eliminates interferencefrom SCA signals and from the sidebands of adja-cent channel FM signals.

The variable separation control is operated fromthe IF amplifier's signal strength detector. A smoothtransition is provided from mono to stereo or fromstereo to mono at weak signal levels to provide theoptimum signal to noise ratio and best stereoseparation for the prevailing signal conditions. Thecircuit operates only during stereo reception. It swit-ches automatically to monophonic if the 19kHz pilottone is absent.

In the PLL the internal oscillator operates at228kHz, locked onto the 19kHz pilot tone. The228kHz feeds a 3 stage Johnson countervia a binarydivider to generate a series of square waves.Suitably connected NAND gates and exclusive ORgates produce the tri-level drive waveform for thevarious demodulators in the circuit. The usualsquare waveforms have been replaced in the PLLand decoder sections by tri-level waveforms. Thesetri-level forms contain no harmonics which aremultiples of 2 or 3. This eliminates frequencytranslation and detection of interference from theside-bands of adjacent stations since the third har-monic of the sub-carrier (114kHz) is excluded. It alsoeliminates interference from SCA broadcasts sincethe third harmonic of the pilot tone (57kHz) is exclud-ed. Unwanted spurious audible components andphase j i t ter in the PLL are inherently eliminated bythis technique.

Additional advantages of the phase locked loopstereo demodulation are the elimination of induc-tors to minimize drift, integral lamp driving capabili-ty to indicate the presence of the 19kHz pilot carrier,excellent channel separation over the entire audiofrequency range, extremely low distortion, low out-put impedance, and transient-free mono/stereoswitching.

AUDIO CIRCUITSFollowing the MPX decoder is the three position

deemphasis switch. The three different positionsallow the MR 80 to be used in North America withstandard 75ms deemphasis and in Western Europeand the Far East with 50ms deemphasis. The 25msposition is for use with an external noise reductionadapter.

An electronically switched f i l te r circuit, im-plemented with two J-FETs of a quad J-FETpackage, is used to reduce out of phase noise whenin the stereo mode and tuned to a weak station. Thisfilter is actually a twin-T bandpass that blends thehigh and low frequencies, leaving separation unaf-fected at mid-frequencies. This results in a greatlyimproved stereo image when the fi l ter is required.

A combination of three inputs are used to controlthe switch point of the filter. The first is the frontpanel switch. The f i l ter is only active when thisswitch is in the AUTO or ON position. In the ON posi-tion the filter is in the circuit for all stations mono orstereo. In the AUTO position the filter will switch inwhen the station is transmitting a stereo pilot signaland the signal strength is below 100mV.

In the same quad J-FET package are the two FETsthat are used for the muting circuit. These FETs arecontrolled by the logical ANDing of three signals.The first signal is the deviation or center tune, thisdetects when the tuner is correctly tuned to thecenter of the FM channel. The second signal is thesignal to noise ratio. Only when there is suff icientsignal wil l the tuner be allowed to unmute. Signal tonoise ratio is measured by a special bandpassamplifier centered around 138kHz. This frequency isused to prevent false triggering due to adjacentchannel and overmodulation products. The thirdsignal is the RF signal level that is derived from thef ive signal detector circuits. A front panel control(MUTING LEVEL) adjusts the reference level to avoltage comparator. The other input to the com-parator is the signal strength voltage. When the RFlevel exceeds the preset reference level, a signal issent to the muting logic to be ANDed with the othertwo signals. This adjustment al lows the unmutelevel to be set to any value from 2mV to greater than1000mV.

This wide range is necessary for the tuner to scanproperly in all signal conditions and provide the bestcombination of ease of use with maximum intersta-tion noise suppression.

19 AND 38kHz FILTERAn LC tuned notch fi l ter is used to eliminate any

beatnote interference with the bias oscillator in ausers tape recorder. This filter is driven from a fi l terbuffer amplifier and terminated by the output opera-tional amplifier. These amplif iers provide thenecessary input and output impedances for properphase response. The output amplifier is also used asan audio bandpass filter to prevent unwanted noiseand transients from being passed on to the head-phone amplifier.

HEADPHONE AMPLIFIERThe headphone amplifier is capable of driving a

pair of dynamic headphones with less than .02%

15

harmonic distortion. Because of its extremely lowTHD and power capability, it is also the main outputamplifier.

TOUCH SENSORThe touch sensor consists of three functional

elements: 1) Input buffers and static protection cir-cuits. 2) Latches, and 3) Encoder. The seven sensors:KNOB, PRESET 1 to 4, UP and DOWN SCAN are in-puts to the seven input buffer amplifiers. These per-form a dual function. First the inputs are biased to ahigh level by a very high resistance. Second the buf-fers are designed to detect a negative transitionfrom a reference level. When a sensor is touched,the stray capacity of the human body shunts someof this reference signal to ground. This referencesignal is derived from the 228kHz osci l lator on themultiplex circuit board. This means a l t noise com-ponents of the reference signal are a multiple of19kHz, and wi l l be f i l tered out by the 19 and 38kHzfi l ters. The second phase of this reference signal isused to transfer the output of the buffer amplifiersinto the latches. The latches are used as temporarystorage to prevent false triggering due to static andvoltage transients.

The output from the latched inputs are supplied tothe encoder, which performs two functions. First, itputs in order the inputs, assigning highest priority tothe tuning knob and the lowest to the down scansensor. Second, it encodes the input with thehighest priority into a binary coded decimal wordand outputs this to the decoder circuit. This decoderreconverts the BCD word back into a 1 of seven linecode, indicating the sensor that is touched. An addi-tional input to the decoder is the reference phase in-put that inhibits the decoder during clock edge tran-sitions. This is done to prevent false triggering dueto noise glitches and partial contact with the touchsensor.

PRESET SCANThe seven outputs from the touch control and

decoder go to the preset scan circuits. In the presetscan is an electronic switch and a counter. A switchon the rear panel selects whether the tuner scans allstations or only the preset stations. The circuitoperates in the preset scan mode as follows: When apulse is received at the rear panel connector thecounter is indexed by one, then the seven pole dou-ble throw switch connects the input to the tuningcontrol logic to the output of the counter. The con-trol logic then selects the preset that is representedby the counter output. At the end of the pulse thecounter is disconnected and the lock circuit auto-matically fine tunes the tuner to the center of thechannel.

When in the scan all stations mode, the inputpulse is routed to the scan circuitry on the tuning

control logic board. The logic circuitry will thenselect the auto scan circui t and start searching forthe next acceptable station. The direction of scanwi l l be the last selected scan direction and wi l lchange when the band limit is reached.

The remote input to the tuner is a ground assertedlogic level that is normally at + 15 volts. When thisl ine is grounded the tuner wi l l start scanning. Theuse of this logic permits any number of remotecables to be connected to the MR 80.

CONTROL LOGICThe control logic portion of the tuner is made up

of very low power complementary MOS integratedcircuits. By using this logic family a very signif icantpower reduction was realized in the design. With thelower power consumption, a very real reduction inthe operating temperature and an improvement inthe operating l i fe is achieved.

A very important consideration in the design of adigital tuner is the amount of radiated noise from thedigital integrated circuits. To achieve low noise thecontrol logic was made to operate in a static modeto entirely eliminate any interference. This allowsthe control logic board to be built without theshielding necessary to reduce interference.

The seven touch sensor inputs from the presetscan board are stored in eight C-MOS flip-flop's. Thestate of the f l ip-f lop's indicate which input was ac-tive last. One bit is used for the main tuning knob, 4bits are used to represent the 4 presets. The scan cir-cuitry uses 3 bits to tell if the scan is on or off, set toscan up or down, and the third is set to a zero whenthe tuner reaches an acceptable station. This com-plex group of circuits provides a level of sophistica-tion and ease of operation not possible before in atuner.

Several timing circuits are used to provide thevarious time sequences and delays for the propernoise free operation of the preset and scan circuits.The first of these monostable circuits is used as apower on clear that resets the circuits to the maintuning knob mode. During the four second delay thelock circuit is inhibited and the high speed mutinginput to the multiplex is held high to mute the tunerand prevent any noise or transient from affecting therest of the users system. At the completion of thisfour second delay the lock circuit is enabled, lockingthe tuner to the incoming frequency and unmutingthe tuner.

When one of the four presets is activated, thedisplay and audio are inhibited for two seconds fromwhen the sensor is touched. The lock circui t isdisabled during the time the sensor is touched, toallow the presets to be set to the proper frequency.When the sensor is released the lock circuit thentunes to the center of the FM station. During normaloperation (not setting of the presets) the touch sen-

16

sor reacts in a small fraction of a second so thetuner appears to change stations instantaneously,without any interstation noise even with the mutingturned of f .

When either of the scan sensors is touched thetuner is muted and the display blanked for twoseconds, this allows the tuner to reach the next sta-tion under normal listening conditions without anyinterstation noise. If the scan speed is set to a slowsetting and the muting is turned off, interstationnoise and very weak stations will be heard after thetwo second delay, which is very useful when remotetuning is used.

Driven from the tuning control logic are six LEDlamps. Four are used to indicate which of thepresets are in use. The other two lamps indicate thedirection of scan. These six lamps and the frequencydisplay indicate at a glance how the tuner isoperating and what preset or scan direction hasbeen chosen.

LOCK CIRCUITAn innovative new circuit was developed for use in

the MR 80. This new circuit allows correct tuningwithout the use of a center tune meter. The MR 80will be correctly tuned even if the station or thecable company is not on its correct frequency. Thisis done by the use of two operational amplifiers,

A deviation signal from the detector is fed into thefirst amplifier. This circuit is a log amplifier that pro-duces an output voltage proportional to the log ofthe DC component in the detector output. Becausethe output voltage contains audio signals, a secondamplifier, connected as a switched gain low passfilter, removes the audio signals. This amplifier hasa very high gain when the lock circuit is on and unitygain when the lock circuit is off. An N-channel J-FETis used as the gain switching element in thenegative feedback path. The fi l ter output, now calledthe correction voltage, is fed into a scaling circuitthat compensates for the tuning diodes nonlinearfrequency to voltage response. Both of theamplifiers operate with greater than 50dB of gain atDC. With a closed loop gain of greater than 100dBthe tuning error when locked is less than 1kHz at100MHz, or 1 part in 100,000. This error is the sameas a crystal controlled synthesizer with the addi-tional benefit of being correctly tuned even if thestation or the cable signal is not on the properfrequency.

Because the lock circuit will track a station even ifit drifts 1MHz, the lock circuit must be turned off forthe operator to be able to tune the MR 80. This is thereason for the touch sensor on the main tuningknob. To prevent the tuner from locking onto astrong signal next to a weak signal, a circuit is usedto sense the strong adjacent channel signal and in-hibit the lock circuit under these conditions. On the

top cover control panel is a manual lock ON/OFFswitch that inhibits the lock circuit only if the tuneris in the main tuning knob mode. This provision ismade for testing the tuner and for cases where thestation being received has a deep fade to the pointof losing lock. If the switch is set to the off positionthe lock circuit will work normally for all the presetsand the scan circuit, but not for the tuning knob.

SCAN CIRCUITWith the voltage tuned RF section, automatic

scanning is implemented without any moving partssuch as motors, f lywheels, or strings. By the elimina-tion of all moving parts, a much greater degree ofreliabil i ty is achieved and tuning convenience im-proves.

The MR 80 scan circuit consists of f ive sections:1) switching circuit; 2) bipolar current source; 3) in-tegrator; 4) band limit detector; and 5} the auto-trackcircuit. The scan switching circuit controls the scanfunction by switching two flip-flops, the scan on/offf l ip- f lop and the scan run/stop f l ip-f lop. When eitherof the scan buttons or the remote control starts ascan cycle, the preset buttons and tuning knob cir-cuits are switched off, the lock circuit is inhibited,the display is blanked, the audio is muted, and thescan on/off f l ip-f lop turns on. The display is blankedand the audio is muted for two seconds. The scanon/off f l ip-f lop switches the RF tuning control to thescan ramp voltage.

Depending on the scan sensor touched, thebipolar current source is set to the proper value(negative for scan up, positive for scan down). Thiscurrent is adjusted by the front panel SCAN SPEEDcontrol for the proper search speed. The run/stopfl ip-f lop stops or starts the scan sequence. This f l ip-flop is set whenever a scan stop signal is sent fromthe multiplex. To reset the flip-flop one of the scansensors must be touched.

In the integrator portion of the scan circuit the cur-rent is converted into a time dependent ramp voltageuntil a stop signal is received from the multiplex.When the tuner has stopped on a station the tuningvoltage is stored on a special low leakage capacitor.To prevent drif t due to leakage currents, guardtracks were employed around the negative input tothe integrator operational amplif ier. This amplifier isa special type with MOS-FET input transistors thathave an input resistance of greater than 100 millionmegohms. With special circuit components andprinted circuit layout, drift in the scan circuit hasbeen eliminated. The positive input to the opera-tional amplifier is used as the input for the lock cor-rection voltage. The correction voltage is only ap-plied after the tuner has stopped scanning and finetunes the tuner to the center of the station.

Two comparators connected to the tuning voltageinput in the RF section are used for band limit detec-

17

tion. The comparators sense when the tuningvoltage exceeds the value needed for 87.5 or108.1MHz and generates a pulse that toggles thefl ip-f lop controlling the bipolar current source,changing the direction of scan. If a person attemptsto scan past the band ends, both scan indicators willlight and the tuner will hang at the band limit unti lthe sensor is released.

When any of the presets or the tuning knob are ac-tive the auto track circuit is used to force the outputof the integrator to a value equal to the current tun-ing voltage. During the turn on delay the auto trackensures that the integrator's output voltage is withinthe band limits. This circuit allows the tuner to startsearching for the next station from the current loca-tion.

FREQUENCY COUNTERThe counter and display form the digital

equivalent to the slide rule dial and pointer, but withgreater accuracy and readability. In the RF section asmall portion of the oscillator signal is coupled intothe buf fer amplif ier on the counter circuit board.This buffer amplifier is made with emitter coupledlogic circuits and is used to change the smalloscillator signal into a level acceptable by the highspeed ECL divide-by-four circuit. The output of thedivider is level shifted to low power Schottky levelsfor use in the rest of the counter circuit. The dividedlocal oscillator signal is sampled for 40.96mS by asynchronous gate, made from a J-K f l ip- f lop toeliminate the ± 1 count error. The actual counting isdone by low power Schottky integrated decadecounters. IF frequency offset is accomplished bypresetting the counters to the complement of the IFfrequency, 893. This allows subtracting the IF offsetby adding the negative of the IF frequency.

The gate signal is derived from a stable 200kHzcrystal oscillator and a binary divider made from LSintegrated circuits. Two other signals are derivedfrom the divider chain. The f i rst is used to transferthe information in the decade counters to thedisplay buffer. The second is used to reset thecounter to the complement of the IF frequency.

In the display portion, three TTL integrated cir-cuits are used as a latch to store the frequency infor-mation and as constant current sources to drive theLED frequency displays. By using the latches, aflicker free display is assured even when the displayis changing. The constant current sources improvereliabil i ty by reducing the number of components.LED displays were used because of their v is ib i l i ty ,character font, and very long life.

POWER SUPPLYSpecial design attention has been given to the

power supply section. Nine separate power circuitsare used. Six of these are regulated to prevent lossof performance during a brown out. The - 15, - 5.2.

5, 15 and 30v use integrated circuit 3 terminalregulators, while the 3ma current source is madewith discrete transistors because of the high voltageon the input terminal. The remaining voltages are us-ed for the headphone amplifier and the touch controlreference signal driver.

LAMP DRIVERSMclntosh, recognizing the need for improved relia-

bility, has designed a new circuit to drive incande-cent lamps. This new circuit prevents the fi lamentsfrom fai l ing due to notching when operated on directcurrent. This failure mode can reduce lamp l i fe fromone half to one tenth of the data sheet value. In theMR 80 the three lamps that are used for STEREO,LOCK and FILTER indicators are operated on AC atlower than rated voltage to extend the useful l i fe towell in excess of 15 years. Only Mclntosh brings youthis feature.

18

19

Block Diagram

20

MclNTOSH MR 80

DIGITAL FM TUNER

21

MclNTOSH LABORATORY INC.2 CHAMBERS ST., BINGHAMTON, N.Y. 13903-9990

607-723-3512The continuous improvement of its products is the policy ofMclntosh Laboratory Incorporated who reserve the r ight to

improve design and price wi thout notice.Printed in U.S.A.

039227