McIntosh MX 113

 The McIntosh Tuner-Preamplifier unit concept accommodates all regular inputs of tuner, phono, tape, etc.,  and allows the selection of the right power amplifier needed for your system. The MX 113 is the most advanced version of this remarkable AM-FM/FM Stereo Tuner preamplifier with switchable selectivity. It has performance beyond any other manufacturer's equipment available today.

Special Features

Multiple "selectivity" switchable from the front panel. An elegant solution to a tough problem.

Linear Phase (constant delay) IF amplifier for low distortion at even high selectivity and low distortion.

Steggered tuning condenser elements to improve RF front and behavior, less interstage coulping, lower spurious effect, higher Q circuits.

Tremendous accomodiation of strong RF input signals - up to 10 volts without overload - overcoming an aggravating limitation of conventional tuners.

Highest spurious rejection 90 dB (IHF) and highest image rejection 95 dB (88 to 108 MHz). This means you receive the stations at the right place on the dial only. You don't receive the same stations or some mixture as you tune across the dial.

Ultra Sonic "muting" provides smooth inter channel FM noise suppression. Has complete connection to McIntosh Maximum performance Indicator to maximize your listening pleasure.

McIntosh developed a special detecting circuit used in the multiplex section. An advantage of this circuit is the elimination of the critical adjustments necessary with commonly used matrixing circuits. The circuit detects the L - R side-bands, then automatically matrixes the recovered information with the L + R carrier signal. This yialds the left and right program output with maximum separation.

 TUNING MECHANISM AND DIAL DRIVE

In the MX 113, the unique design and careful manufacture of the mechanical assembly gives smooth flywheel tuning. By controlling the relationship of mass and mechanical resistance, and by dividing the workloads in the dial drive system, it becomes nearly impossible to detect any backlash. Yet, the entire dial drive is a model of mechanical stability. For added ease and increased tuning accuracy, a section of the dial pointer is illuminated.

FM SECTION

The Radio Frequency (RF) section houses the complete FM-RF front-end and part of the AM RF circuit. A seven-section variable capacitor is the heart of the RF section. Four sections of the variable capacitor are in the FM front end and the remaining three are in the AM section. By interleaving the sections (AM-FM-AM-FM-etc.) spurious responses are significantly reduced. The four FM sections of the variable tuning capacitor provides a high degree of RF selectivity and excellent spurious rejection. Using the latest "state of the art" field effect transistors with a welldesigned variable tuning capacitor has provided the MX 113 with an excellent RF front-end ….

FM-IF AND DISCRIMINATOR SECTION

The MX 113 uses linear-phase IF filters. Each filter was designed from a FORTRAN computer program for minimumphase and constant delay. The mathematical complexity of the filter design procedure is almost beyond belief. Using numerical integration in the S-Plane, an "IBM" 1130 high speed computer spent eighteen minutes on the mathematics for the design of the IF filter. It would have taken a human engineer, working twenty-four hours a day, seven days a week, and working error-free three-hundred years to perform the same mathematical calculations! ...

FM STEREO MULTIPLEX SECTION

Mclntosh has developed a special detecting circuit used in the multiplex section. A particular advantage of this circuit is the elimination of the critical adjustments necessary with commonly used matrixing circuits. The circuit detects the L - R sidebands, then automatically matrixes the recovered information with the L + R carrier signal. This yields the left and right program output with maximum separation. ...

 AM SECTION

The AM-RF amplifier circuit includes a three section variable tuning capacitor in the metal enclosed shielded RF module which also houses the FM-RF front end. A three section variable capacitor is used for greater spurious rejection. The RF amplifier is unique. The circuit has constant sensitivity, constant selectivity, high image rejection across the complete AM band. Ordinary AM-RF circuits cannot do all of these simultaneously. This circuit design achieves equal sensitivity even at the low end of the band. Spurious, image, and intermediate frequency rejection are all superior. The same circuit delivers equal selectivity across the entire band. The Mclntosh circuit is unique in a superheterodyne AM receiver ...

...The AVC (automatic volume control) system was designed to prevent bursting or thumps when the AM is tuned through a strong signal. Distortion at low audio frequencies is minimized by using two AVC filter sections instead of the conventional one.

PHONO PREAMPLIFIER

There are three transistors in each channel of the phono preamplifier. The output of the third transistor is connected by a negative feedback loop to the emitter of the input transistor. The feedback loop reduces noise and distortion. It also provides precision RIAA frequency compenation required for magnetic phonograph cartridges. Feedback remains in effect even at 20 Hz, where gain is highest. The negative feedback also provides a low output impedance for the tape output. ...

L + R AMPLIFIER

The L + R amplifier consists of a single transistor connected as a voltage amplifier. Negative feedback is used around the summing amplifier to maintain low distortion and provide a low impedance for the center channel output.

POWER SUPPLY

The power supply of the MX 113 has received very special attention.

Three separate rectifier circuits are used. First, a fullwave rectifier supplies DC to all audio circuits. The second full-wave rectifier supplied DC to all tuner and multiplexdecoder circuits. The third supply provides DC to the AM circuit. The power supplies are elaborate in design. They use electronic filtering to insure the lowest possible background hum level, maximum stability, and extremely good regulation.

Specifications

FM Section

Useable Sensitivity:  2.5 microvolts at 100% modulation (± 75 kHz deviation) for less than 3% total noise and harmonic distortion,

Signal to noise ratio: 70 dB at 100% modulation,

Harmonic Distortion:

Mono : Will not exceed 0.3% at 100% modulation ±75 kHz deviation.

Stereo : Will not exceed 0.5% at 100% modulation ±75 kHz deviation.

Frequency Response:  ±1dB from 20 Hz to 15,000 Hz with standard de-emphasis

Capture Ratio:  1.5 dB

Spurious Rejection:  90 dB

Image Rejection:  95 dB at 88 to 108 MHz (IHF)

Stereo Separation:  Exceeds 35 dB at 1,000 Hz

Selectivity: 

Switch Setting : OUT /IN

Adjacent Channel : 6 dB /15 dB

Alternate Channel : 58 dB /88 dB

Tuning Indicator:  D'Arsonval movement meter with increased sensitivity

Stereo Indicator: Stereo light activated by 19,000 Hz pilot signal only

AM Section

Sensitivity:  75 microvolts at 1,000 kHz (using external antenna input).

Signal To Noise Ratio:  45 dB

Harmonic Distortion:  1% at 30% modulation

Frequency Response: Down 6 dB at 3,500 Hz

Selectivity:

Switch Setting : OUT/ IN

Adjacent Channel : 35 dB/45 dB

Image Rejection: 65 dB; 540 kHz to 1600 kHz

Preamplifier Section 

Frequency Response:  ±0.5 dB, 20 to 20,000 Hz.

Distortion:  Will not exceed 0.1% at 2.5 volts output, 20 to 20,000 Hz.

Input Sensitivity & Impedance:

Phono 1 and Phono 2: 2 millivolts for 2.5 volts output at 1,000 Hz, 47,000 ohms;

Auxiliary and Tape: 0.25 volts for 2.5 volts output; 250,000 ohms.

Voltage Amplification:

Phono 1, Phono 2 to Main output: 62 dB,  to Tape output: 42 dB.

Auxiliary, Tape to Main output: 20 dB,  to Tape output: 0 dB.

Output:

Main: 2.5 volts with rated input. Up to 10 volts can be developed without increase in distortion. FM will produce 10 volts output at 100% modulation.

Tape: 0.25 volts with rated input. Phono signal to 10 millivolts produces 1.2 volts output. FM will produce 1 volt output at 100% modulation. L + R 2 volts with rated input

Hum & Noise: 

Phono 1 and Phono 2: 72 dB below 10 millivolt input; (equivalent to less than 3 microvolts at the input terminals)

Aux-Tape: 85 dB below 2.5 volts output, (unweighted)

Bass Control:  -18 dB to + 16 dB at 20 Hz

Treble Control:  ±20 dB at 20,000 Hz

LF Filter:  Flat or roll off below 50 Hz, down 12 dB at 20 Hz

HF Filter:  Flat or roll off above 5,000 Hz, down 12 dB at 20,000 Hz.

Power Requirements:  120 volts, 50/60 Hz, 30 watts

Transistor Complement: 

2 - JFET

3 - MOSFET

30 - Silicon Planar

31 - Diodes

2 - Integrated Circuits (each contains the equivalent of 16 transistors and 8 diodes)

Mechanical 

SIZE:

Front panel :  16 inches wide (40.64 cm) by 5-7/16 inches high (13.81 cm);

Chassis :  15 inches wide (38.1 cm) by 13 inches deep (33.02 cm), including PANLOC shelf and back panel connectors;

Knob Clearance :  1½ inches (3.81 cm) in front of mounting panel.

WEIGHT:  26 pounds (11.79 kg) net, 38 pounds (17.24 kg) in shipping carton.

FINISH:  Front panel: Anodized gold and black with special gold/teal panel nomenclature illumination.

CHASSIS:  Chrome and black.

MOUNTING:  Mclntosh developed professional PANLOC

Features & Facilities  

Volume Control:  Precision "tracked" at al l listening levels. (0 to —65 dB). Does not change stereo balance as loudness is changed. The AC power ON/OFF switch is coupled with this control.

Balance Control:  Natural balance at center position, attenuation of left or right channel by rotating control.

Loudness:  Loudness compensated or flat response—Loud- ness position boosts low frequencies for low level listening. Operates as a function of volume control position. Full compensation is obtained at lower volume levels and flat response is obtained at full volume.

Selectivity:  Increases the ability of the tuner to separate a weak (distant) station from a strong (local) station on adjacent channels.

Mode:  Selects either stereo or mono operation

Phase Control:  Electronically reverses phase in the left channel to correct "out of phase" program sources. MUTING: Suppresses the background noise and hiss normally heard between FM stations.

Tape Monitor:  Pushbutton; compares recorded tape with program source while recording.

Muting Adjust:  Modifies the noise rejection threshold on

FM Dial Scale Intensity:  Modifies the brightness of the illumination of the front panel