McIntosh MX110Tuner-Preamp Service Manual.pdf

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1、CONTENTS GENERAL DESCRIPTION. 1 TECHNICAL DESCRIPTION. 1 INTRODUCTION. 3 FM ALIGNMENT. 4 MULTIPLEX ALIGNMENT. 6 SCHEMATIC. 8 DIAL STRINGING. 11 PARTS LIST. 12 SPECIFICATIONS. 16 CHASSIS LAYOUT. . 18 OPERATING CURVES. 20 M AND X SERIES SCHEMATICS.POCKET 2 CHAMBERS ST. BINGHAMTON, N.Y. WARRANTY STATIO

2、N MX 110 SERVICE MANUAL nWntosh mx MX 110 TUNER PREAMPLIFIER GENERAL DESCRIPTION The MX 110 combines in one unit an extremely low-distortion preamplifier with a highly sensitive FM multiplex stereo tuner. Every desirable feature of a tuner and a preamplifier is included in this design. Interstation

3、noise suppression, tuning indicator, FM multiplex indicator, indi vidual channel bass controls, individual channel treble controls, electronic phase switch have all been engineered into the MX 110. The INPUT SELECTOR gives you a choice of six different program sources. The MODE SELECTOR is a newly d

4、eveloped control which makes it very easy to balance a stereo system. It is designed to add left to right for monophonic operation, to control the left to right stereo perspective or to compare the left and right channels of a stereo program. The loudness of the phono channels and the auxiliary chan

5、nel may be balanced to the TECHNICAL The radio-frequency amplifier of the MX 110 is a “cascode” type circuit. The circuit is specially designed to amplify weak signals with less noise and distortion. By carefully tuning this RF amplifier during manufacturing and controlling other circuit constants,

6、spurious response rejec tion is improved. The high-frequency oscillator mechanical layout is engineered for minimum response to temperature variations. In fact the combination of mechanical and electronic design is so unusually good in this circuit that automatic frequency control is not needed in t

7、he MX 110. The mixer output is amplified by four inter mediate frequency amplifiers. The transformers used in the I.F. amplifiers are designed for max imum adjacent channel rejection, for electrical stability, and for electrical and mechanical resistance to shock and vibration. tuner loudness. These

8、 adjusting controls are located on the top of the MX 110 behind the front panel. By releasing the PANLOC buttons on the front panel, you can slide the MX 110 out of its mounting until the second latch en gages. The top mounted LEVEL set controls are now available. The McIntosh designed PANLOC system

9、 is the first professional installation technique to be used on stereo instruments. The PANLOC sys tem gives you absolute ease of installation, operation, and maintenance. The McIntosh MX 110 is a beautifully engi neered control center for the finest stereo sound systems. The extreme care in manufac

10、turing, in layout design and in thermal engineering prom ises the usual McIntosh extra values of reliability, performance, and long life. DESCRIPTION The R.F. and I.F. circuits of the MX 110 are completely shielded and exceed the FCC requirements for suppression of oscillator radia tion. Either a 30

11、0 ohm or 75 ohm antenna may be used with the MX 110. A VHF television antenna which is suitable for FM reception can be connected to the MX 110. In the MX 110, a new type of mechanical tuning assembly gives smooth flywheel tuning. By controlling the relations between mass and mechanical resistance,

12、and dividing work loads in the dial drive system, it becomes nearly impossi ble to detect any backlash. Yet the entire dial drive is a model of mechanical stability. For smooth, quiet action and extended life with virtually no wear, a teflon lined dial pointer carriage and nylon pulleys are used in

13、the dial cord assembly. 1 MULTIPLEX DECODER The multiplex decoder uses a special McIntosh developed detecting circuit. One of the advan tages of this circuit is the elimination of the critical adjustments necessary with commonly used matrixing methods. This circuit detects the L+R sidebands and auto

14、matically matrixes the recovered information with the L+R main carrier signal. This circuit then yields the left and the right program with maximum separation. A temperature stabilized 19KC amplifier locks-in a highly stable push-pull synchronous oscillator. Apart from other advantages, this method

15、provides greatest noise immunity. Bal anced detectors cancel the 38KC component in the output and insure low distortion. A three-section sharp cut off filter rejects SCA interference and reduces susceptibility to spuri ous signals. The MX 110 has an MPX stereo indicator that lights when the dial poi

16、nter crosses a station broadcasting MPX stereo. A unique circuit using a transistor operates the MPX stereo indicator. The transistor is controlled by a differential detecting circuit that amplifies the 19KC pilot signal. This circuit automatically discriminates between the 19KC signal and noise. AU

17、DIO The MX 110 audio amplifier consists of three negative-feedback amplifying sections in dupli cate for the left and right stereo channels and a separate L+R monophonic amplifier. The first section in each channel is a feedback preamplifier used to amplify and compensate for the input signals comin

18、g from phonograph pickups or tape heads. Level set controls are connected into the output circuit of this preamplifier section when the INPUT SELECTOR is switched to PHONO 1 or PHONO 2. These controls may be used to maintain uniform loudness between phono and tuner inputs. Skillful layout, grounding

19、, and shielding for low-hum pickup, metal film resistors, low-noise tubes and extreme care in manufactur ing combine to reduce noise and hum in t input amplifiers. octave) rumble and high-frequency filters are associated with this section. The third amplifier section is a two stage negative feedback

20、 amplifier. The variable bass and treble controls are included in the feedback loop to maintain the lowest possible distortion. For example a wave meter analysis of the three amplifier sections of the MX 110 shows less than 1/10 of 1% distortion at 3 volts output. The MODE SELECTOR, balance controls

21、 and left and right outputs are associated with the third amplifier section. The L+R monophonic amplifying section is a feedback summing amplifier. It supplies mono phonic output as well as L+R output. The second amplifier section in each channel is a cathode follower. The sharp cut-off (18db per PO

22、WER SUPPLY The power supply of the MX 110 has received very special design attention. Two separate rectifier circuits are used. A full-wave rectifier supplies D.C. to the heaters of all audio stages. A bridge rectifier supplies D.C. to the anodes of the audio stages. A half-voltage tap on the bridge

23、 rectifier supplies D.C. to the tuner stages. This elaborate power supply design insures the lowest possible background hum level and also the maximum stability. In addition to this care ful work the power transformer uses special magnetic shielding to minimize possible hum pickup in the MX 110 as w

24、ell as in any other equipment used with it. Hi 2 INTRODUCTION All McIntosh tuners are carefully aligned and tested at the factory using the finest available test equipment. All McIntosh tuners will meet their published specifications when shipped from the factory. After extensive operation, especial

25、ly when tubes have been replaced, it may be desirable to realign the tuner circuits for best performance. This manual gives complete information on the circuit realignment procedure for the MX 110 tuner-preamplifier. The test equipment listed below (or its equivalent) is necessary to properly align

26、an MX 110. The accuracy of the alignment will be directly related to the accuracy and calibration of the test equipment used. FM Signal Generator (Measurements 210A or equivalent) VTVM Multiplex Generator (RCA WR-51A or equivalent) 10.7 MC Generator (Preferably crystal controlled) Oscilloscope (Hewl

27、ett-Packard 120B or equivalent) Harmonic Distortion Analyzer, desirable but not essential(Hewlett- Packard 330B or equivalent) If the necessary test equipment is not available, alignment should not be attempted. You may contact the McIntosh Customer Service Department for additional information. Cus

28、tomer Service McIntosh Laboratory, Inc. 2 Chambers Street Binghamton, New York Our telephone number is 723-5491 The direct dial area code is 607 T MX 110 FM STEPS TUNER DIAL SETTING SIGNAL GENERATOR INDICATOR FREQ COUPLING MODULATION TYPE CONNECTED TO Point of no interference or signal 10.7MC Throug

29、h external .01 MF cap to pin 7 of 12AT7 mixer cw VTVM TP #1 SAME SAME SAME SAME MX 110 tuning eye SAME SAME SAME SAME VTVM TP #2 or (discriminator output on M series) SAME SAME SAME SAME SAME Pin 6 of discriminator transformer 105MC 105MC 300 ohm antenna terminals with * matching network 400 cycles

30、75KC deviation (100% modulation) VTVM connected to TP1 and scope connected to L or R audio output 90MC 90MC SAME SAME SAME 105MC 105MC SAME SAME SAME 90MC 90MC SAME SAME SAME Point of no interference Scope L or R output 105MC 105MC SAME 400 cycles 75KC deviation (100% modulation) attenuated to 2.5 m

31、icrovolts output VTVM connected to TP #1 and Scope connected to L or R audio, output ANTENNA MATCHING NETWORK FM SIGNAL GENERATOR 100 OHMS -AAA -O -AAA 150 OHMS TUNER 300 OHM ANTENNA TERMINALS * IF SIGNAL GENERATOR HAS OTHER THAN 50 OHM INTERNAL IMPEDANCE, USE A RESISTOR OF 150 OHMS, LESS INTERNAL G

32、ENERATOR IMPEDANCE. 1 ALIGNMENT ADJUST TEST LIMITS REMARKS Top (secondary) and bottom, (primary) of 1st, 2nd and 3rd IF transformers Maximum possible negative voltage Shunt to ground the winding not being adjusted with a .01 MF capacitor in series with a 1 K resistor. Attenuate signal generator unti

33、l output voltage at TP #1 is less than 1.5 volts with one IF transformer winding shunted. IF transformers have terminal #1 marked with a green dot and are numbered clockwise. 4th IF transformer, top and bottom. Eye should close to approx, /is” with strong signal. Make additional adjustments of eye c

34、losure by varying the length of parallel conductors connected to pins 1 and 4 of the 4th IF transformer. (This changes the capacitive coupling between pins 1 and 4.) Discriminator transformer upper core (secondary) Adjust for 0 volts ! - - Discriminator transformer lower core (primary) Maximum negat

35、ive voltage Repeat step 3 if a large change is made in the setting of the lower core. i Oscillator trimmer cap. Maximum negative voltage As output increases, attenuate signal generator to keep maximum output at TP #1 to less than 2 volts. Oscillator coil tuning slug SAME Repeat steps 5 and 6 until d

36、ial calibration is accurate. j Mixer trimmer and RF trimmer SAME 1 | Mixer coil tuning slug and RF coil tuning slug SAME Repeat steps 7 and 8 until output is as high as possible. Muting adj. control Turn muting switch to in position. Adjust muting control until background noise just disappears. i IH

37、FM sensitivity 2.5 microvolt for 3 % total noise and distortion Step 10 is an overall sensitivity check, and requires a distortion analyzer and i FM signal generator with attenuator. With 2.5 microvolts input at the 300 ohm antenna terminals, TP #1 voltage should be .6 volts or more. MX IIO MULTIPLE

38、X TUNER SIGNAL GENERATOR _ INDICATOR STEPS DIAL SETTING FREQ. COUPLING MODULATION TYPE CONNECTED TO i Point of no interference or signal Audio generator set to 67KC, 0.5 volts output or less TP H2 (MPX input on M series) Audio VTVM Pin 6 of 38KC transformer (yellow wire connected at this pin) 2 SAME

39、 MPX generator with 19KC pilot attenuated to approx. 5% level (5% level is 14 of normal 10% level) 1 9KC pilot must be attenuated for correct alignment SAME SAME Pin 3 or 8 of 12AU7 MPX oscillator 100MC 100MC modulated 300 ohm antenna 1 KC 100% SAME Pin 1 or 2 of by MPX generator, terminals with 19K

40、C pilot at approx. 1000 normal output microvolt signal modulation (34KC deviation) modulating left or right only 38KC transformer 4 SAME SAME SAME SAME Audio VTVM and scope L or R output jack 5 SAME SAME SAME SAME SAME SAME 6 SAME SAME SAME SAME SAME SAME 7 SAME SAME SAME Turn off 1 KC audio modulat

41、ion SAME SAME 8 SAME SAME SAME Same as step 3 SAME SAME DECODER ALIGNMENT ADJUST TEST LIMITS REMARKS 67KC trap Adjust for minimum voltage 1 9KC phase coil and 1 9KC transformer 1. Disable local 38KC oscillator by placing a jumper wire across 6.8K resistor connected to pins 1 and 6 of 12AU7 MPX oscil

42、lator. 2. Shunt pin 2 of 19KC transformer to ground with .01 capacitor in series with 1 K resistor. 3. Adjust 19KC phase coil for maximum output. Proper adjustment places core approx. % from bottom of coil form. 4. Adjust lower core of 19KC transformer for maximum output. 5. Shunt pin 3 of 19KC tran

43、sformer to ground with .01 capacitor in series with 1 K resistor. 6. Adjust upper core of 19KC transformer for maximum output. 7. Remove jumper used in step 1 above. 38KC transformer bottom core Adjust for maximum voltage 38KC transformer upper core Adjust for stable scope display 1. Turn off 19KC p

44、ilot on MPX generator. 2. Adjust upper core of 38KC transformer to obtain a stable and uniform 1 KC signal scope display. This adjustment may be critical, so turn core very slowly. 3. Turn 19KC pilot back on. 19KC phase coil 30db separation or more Modulate left channel and measure right channel out

45、put. Adjust 19KC phase coil for minimum right channel output (maximum separation). Remove all test leads from TP #2 for separation checks. SAME Modulate right channel and measure left channel output. Separation in steps 5 and 6 should be at least 30db This step checks the rejection of 19KC and 38KC

46、frequencies. Residual output should be at least 40db below modulated output. 1 . Check for MPX indicator light 1. MPX light should turn on with MPX signal 2. Tuning slowly across dial, MPX light should turn on only with MPX signal. ALL SWITCHES SHOWN IN CCW POSITION STEREO INPUT SELECTOR SWITCH,S2 M

47、ODE SELECTOR SWITCH. S3 ALL VOLTAGES MEASURED UNDER FOLLOWING CONDITIONS: UNLESS OTHERWISE SPECIFIED I -USE OF II MEGOHMS INPUT IMPEDANCE VTVM VOLTMETER. ALL RESISTORS 1/2 W 20% 2 - ALL VOLTAGES 10%,WITH RESPECT TO GROUND. ALL CAPACITORS IN PF 3-A.C. INPUT AT MTV 50 - 60 CPS. ALL INDUCTORS IN MICRON

48、 4-NO SIGNAL AT ANTENNA AND OTHER INPUT TERMINALS 5 - FRONT PANEL CONTROLS AT FMIFHOTMC MODE SELECTOR -STEREO MUTING -OUT INPUT SELECTOR - yPX lF/HF FILTERS - OUT VOLUME CONTROL -MAX LOUD -OUT BALANCE CONTROL-ZERO TAPE MONITOR-OUT TONE CONTROLS -FLAT PHASE - 0# MX 110 PARTS LIST TUBES ITEM NO. USE I

49、DENTIFICATION NUMBER VI RF Amplifier 1 6DS4 V2 RF Amplifier 2; Mixer 12AT7 V3 Oscillator 6AB4 V4 IF Amplifier 1 6AU6 V5 IF Amplifier 2 6AU6 V6 IF Amplifier 3; Limiter 1 6AU6 V7 Limiter 2 6CS6 V8 Muting; L+R Amplifier 12AT7 V9 Tuning Indicator 6HU6/EM87 (X, Z series) 6FG6 (EM84A) M series VI0 FM Audio (Left and Right); 1st Audio Amplifier 6D10 VII MPX. Amplifier and 19KC Separator/Indicator contro