McIntosh The Best Catalog

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YOU SHOULD OWN McIntosh BECAUSE TABLE OF CONTENTS Power Amplifiers: MC 2500, MC 2255, MC 2250, MC 2155, MC 2120, MC 502 2-16 PreAmplifiers: C 33, C 29, C 27, C 504 14-24 Tuners: MR 80, MR 78, MR 75 25-37 Tuner-Preamplifier: MX 117 38-45 Receiver: MAC4100 AM/FM Receiver 46-50 Preamplifier- Amplifier: MA6200 51 Loudspeakers: 52-65 The Mclntosh Story 66-67 Equalizers: MQ107, MQ 104 68 FM Guide. . . 69-76 - Mclntosh instruments are design- ed and manufactured for long life. - Mclntosh instruments have always been designed for long life with low maintenance costs and high quali- ty performance. Mclntosh in- struments have been and are the LABORATORY STANDARD for the world. - Until 1949 the performance re- quirements for a Mclntosh had long been an engineering dream. They became a reality with the in- troduction of the first Mclntosh amplifier. Through all these years Mclntosh has produced instru- ments that have exceptionally long life. Clinics held ail over North America have shown that most of the Mclntosh instruments ever manufactured still meet or exceed their original exacting specifica- tions. - Used McIntosh instruments have the highest resale value. Retailers report that customers are constant- ly searching for used Mclntosh in- struments. A Mclntosh does not re- main on the "Used" display long. You'll get more when you trade-in your Mclntosh assuring you of maximum return on your invest- ment, - Mclntosh dedication, not only to improvements, but also to fun- damentals, has justified many patents on basic circuit structures as well as refinements. - Doesn't it make good sense to deal with a company that wants to do as much for you as it possibly can? 1

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illuminated over a portion of its length. Also located within the dial opening are symmetrically positioned center-of- channel and signal-strength meters. To the left of the dial area are two rectangular areas denoted as "function" and "selectivity". Illuminated words "stereo", "filter", and "muting" appear (when selected) in the upper area, while the lower area is illuminated with either the notation "-7 dB", "-22 dB" or "-55 dB". These correspond to the three selectivity settings of the selectivity switch just below. The dB numbers represent adjacent channel selec- tivity and should not be confused with the more familiar alternate channel selectivity values which are, of course, much greater. A large tuning knob, coupled to a blacklash- free flywheel and dial string arrangement, is located to the right of the dial area opening. In addition to the selectivity switch, other rotary controls along the bottom section of the front panel include a meter selector switch which chooses either the signal strength or multipath indication function of the signal-strength meter, a filter switch which, in addition to having an "off" posi- tion, has two settings for noise reduction during weak-signal stereo FM reception, a muting switch, with positions for local and distant reception (which varies the muting thres- hold), a mode switch with "stereo only", mono, and "stereo auto" positions and a volume control which also turns power on and off to the tuner. The rear panel of the MR 78 has a pair of test points, as illustrated in Fig. 2., which are intended for use with the Mclntosh Maximum Performance Indicator, an acces- sory product marketed by that company. A fuesholder cap is also accessible from the rear for replacement, if necessary, of the tuner's 0.5 ampere slo-blow line fuse. Push-type Fig. 2 - View of back panel terminals are supplied for 300-ohm antenna transmission line connection, while a 75-ohm coaxial connector is offered for connection of that type of transmission line. Two sets of audio output jacks (one pair for fixed output, the other controlled by the front-panel volume control) and one convenience AC receptacle complete the rear panel layout. Internal Construction and Circuit Highlights As can be seen in the internal view of the chassis, Fig. 3, the Mclntosh MR 78 is extensively shielded. Six major circuit board modules are used in addition to the RF front end. These include the IF circuit board, the selectivity selec- tion junction board, the multiplex section, the detector cir- cuit board, the output amplifier board and the power supply circuit board. The front end utilizes a 5-section tuning capacitor. A junction FET is used as impedance converter to drive a 5-watt power transistor in the RF stage for high overload capability. An antenna matching circuit at the RF input has a two-position selectable switch which alters the RF bandpass characteristics of the input circuit. The switch positions are labelled "Lo Gain" and "Hi Gain", a bit con- fusing unless the user reads the manual carefully and dis- covers that the gain references refer to the antennas which might be used with the tuner. Thus, the Lo Gain position is intended for use in seeking out distant or weak signals Fig. 3. - View of chassis layout while, in most applications, the "Hi Gain" position should be used since it yields the lesser amount of RF signal at the input to the RF amplifier stage, as well as a sharper bandpass characteristic. A block diagram of the RF and IF sections of the MR 78 is reproduced in Fig. 4. A balanced integrated circuit mixer stage is used as a further safeguard against possible overload and to reduce oscillator pulling. Its 0.7 MHz output is coupled to the IF amplifier section by means of a bifilar transformer. Linear phase filters are used in both the NORMAL and NARROW selectivity settings of the MR 78, while for the SUPER-NARROW selectivity setting, a 4-pole, 4-zero crystal filter having constant delay, is intro- duced into the IF chain. Mclntosh developed a new type of FM detector for this tuner which they call a linear phase bridge discriminator. It uses a balanced transmission line bridge in conjunction with a differential voltage doubling circuit to achieve ultra-low orders of distortion in the demodulated FM audio signals. A block diagram of the Multiplex and Audio Sections is illustrated in Fig. 5. An IC audio amplifier with over 120 dB of negative feedback in two feedback loops is used to drive the stereo demodulator. Muting, "stereo only" tuning and automatic mono/stereo switching are all functions which are performed within the stereo decoder circuitry. A stereo filter circuit follows the matrix decoder and de- emphasis networks to reduce noise when tuning to weak stereo stations. This filter employs a twin-T bandpass filter design to suppress noise while only minimally affecting stereo separation and imaging. The audio amplifier section consists of a pair of two-transistor amplifiers, one for each channel. Each amplifier delivers 2.5 volts to the fixed output jacks and to the volume control sections which feed the 29

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if he could have heard FM the way we heard it over the Mac MR 78. There was only one instance where we found it necessary to use the SUPER-NARROW position of the selector switch, and that was when we were trying to listen to a weak sig- nal originating some 120 miles from our listening location - one nestled between a stronger signal 200 kHz below it, and a much stronger local station, 200 kHz on the higher side of the dial. If you've ever tried to receive that kind of signal on a lesser tuner, you'll know what we mean. In any case, when we did switch to the SUPER-NARROW position, we actually were able to listen to the desired distant station and distortion, though audibly higher, was still at tolerable levels. FREQUENCY - HZ Mono: (1) Total Harmonic Distortion (THD) Stereo: (2) Total Harmonic Distortion (THD) Fig. 9 - Separation and distortion versus frequency (with selectivity switch set to "NARROW") Previously, we had measured signal voltages of 2 to 3 volts at that location and found that most tuners did exhibit cross-modulation and other overload effects. With the "Mac" tuner, we were able to clearly separate closely spaced high-signal stations on the dial with nary a trace of interference from other strong-signal stations in the same vicinity. Other Use and Listening Tests Back in our lab (some 20 miles from the city), we began to appreciate the importance of that selectivity switch on the front panel. If you are an inveterate FM DX-er, you will be amazed (as we were) at how many signals you can separ- ate and receive clearly by using the narrow (and at times even the super-narrow) selectivity switch positions on the MR 78. Here is a tuner that doesn't compromise between low distortion and wide bandwidth. 55 dB of selectivity (that claimed in the NORMAL setting) is no problem if you are not plagued by adjacent and alternate channel signals. In fact, the normal setting, coupled with those linear phase filters in the IF section, rendered the kind of reception from the few good quality stations that we have in our lis- tening area that we had often dreamed about- Program quality varied, of course, but when we were fortunate enough to tune to a live concert (yes, we still do have some live FM programming in this area, albeit at midnight each night), the results were truly astounding. We had the feel- ing that the late Major Armstrong, too, would have smiled 31 FREQUENCY- HZ Mono: (1) Total Harmonic Distortion (THD) Stereo (2) Total Harmonic Distortion (THD) Fig. 8 - Separtion and distortion versus frequency (with selectivity switch set to "NORMAL")

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reference 0.5 volts output, and this too corresponds exactly to the 250 mV spec called for by Mclntosh for their referenced output level of 2.5 volts. Figure 9 illustrates the range of control of each of the three equalizer controls provided on the MX 117. The frequencies at which the three equalizer controls are centered make for an extremely ver- satile range of control. The action of the unique loudness control found in the MX 1 1 7 is illustrated in the series of response curves plotted by means of our spectrum analyzer and reproduced in the 'scope photo of Fig. 1 0. Note that only a moderate amount of treble compensation comes into play as the con- trol is advanced towards more contouring. Fig. 10-Response obtained at various settings of the independent loudness control of the Mclntosh MX 117 Tuner-Preamp Frequency response plots for the phono preamp- equalizer section of the MX 117 were accurately plotted using our new Sound Technology 1 500A test instrument and an associated video printer. In Fig. 1 1 we see the familiar RIAA playback curve ob- tained by feeding a constant amplitude frequency- swept signal into the phono inputs. The plot extends Fig. 12 -Expanded-scale phono response, using inverse RIAA input test signal from 20 Hz at the left to 40 kHz, with double vertical lines indicating 1 00, 1 000 and 1 0,000 Hz. 0 dB re- ference has been established at 1 kHz as shown. In Fig. 12 the vertical sensitivity of the plot has been expanded so that it is 2 dB per vertical division (in- stead of 10, as in the previous display). Also, the signal applied to the phono inputs has not been subjected to inverse RIAA equalization so that, in theory, if perfect RIAA equalization were incorporat- ed in the MX 1 1 7, a "straight line" response would be obtained. As you can see, maximum deviation from this ideal was 0.6 dB at 40 Hz (where the dot- ted line cursor is positioned for a read-out at the lower right of the display) while moving the cursor to the maximum deviation in the high frequency region (Fig. 13), shows a maximum deviation from "ab- solute RIAA accuracy" of only 0.5 dB at 1 8.5 kHz. Fig. 11-Phono preamp-equalizer response, Mclntosh MX 117 Tuner-Preamp Fig. 13 -Same as Fig. 12, except "cursor" has been moved to read relative response at 18.5 kHz Signal-to-noise ratio of the phono section was first measured in accordance with the IHF/EIA standard, which calls for a 5 mV input at 1 kHz and adjustment of the volume control so as to produce an output of 0.5 volts. Under these conditions, and using an "A-weighting" curve, a reading of 84.4 dB was ob- 44