This is one of the gold standards in analog tuners and has the famed Modafferi modification that takes it to the performance level that the designer had initially intended for it but was held back secondary to cost limitations.
Performance FeaturesMultiple selectivity, normal, narrow and super narrow, switchable from the front panel. An elegant solution to a tough problem. Switching is done by means of diodes using DC switching; an ideal way to handle a difficult RF problem. A two position RF selectivity diode switching circuit for low and high gain antennas adds a useful parameter that is unique. One pair of balanced high level inputs and balanced outputs for all six outputs.
Linear phase (constant delay) IF amplifier for low distortion at even high selectivity and low distortion. Patented two eight pole filters are selectable as well as a four pole multi element crystal in the super narrow position.
A phase linear bridge discriminator provides distortionless conversion from FM to audio and exhibits a capture ratio close to 0dB. No active elements are used, providing a driftless, ideal detector.
Five element tuning capacitor improves RF front end characteristics; more tuned circuits for better selectivity. Silver plated chassis and RF coils for better shielding, lower losses and higher Q circuits.
Highest spurious rejection 100dB (IHF) and highest image rejection 110dB (88 to 108 MHz). This means you receive the stations at only the right place on the dial. You don't receive the same stations, or some mixture, as you tune across the dial.
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 sidebands, then automatically matrixes the recovered information with the L - R carrier signal. This yields the left and right program output with maximum separation.
Modafferi Mod: B- power supply - improved regulation, less hum. RF selectivity improved for better spurious rejection. IF regeneration fixed - better weak signal reception. IF 'tailbiting' fixed - this eliminates degraded reception
at 96.3 and 107.0 Mhz from ninth and tenth IF harmonics. Stereo decoder slew-rate optimized by modifying op-amp
feedback circuits; reduces distortion, improves separation. diode D307 installed (this was left out of MR78 but was
used in MR77); this reduces 'klunk' noises on fixed output
jacks when tuner is turned on and off. IF phase trimming - 'gimmick' capacitors added as needed in
NORMAL IF filter for improved stereo separation. RF oscillator emitter tap re-dressed for minimum leakage
inductance; reduces drift and eliminates oscillator
pulling on strong signals. Jung-Marsh capacitor upgrade in MPX and audio circuits. cardas audio output, midas scope output jacks installed. Muting ground changed - improved muting performance. 19Khz stereo pilot circuit change, reduces stereo distortion. Buffer resistor installed in pointer lamp circuit, prevents
lamp heat from burning red light filter material.
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