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McIntosh MR-78 (1972–1977)

Richard Modafferi's RIMO filter let this tuner pull a weak station out from under a strong neighbor. Forty years on, collectors still argue it was the finest FM front end McIntosh ever shipped.

Overview

The MR-78 is an FM/stereo FM tuner. No amplifier, no speakers, just a front end built to do one job. McIntosh introduced it in 1972 as the flagship of its tuner lineup and kept it in production through 1977. What sets it apart is selectivity. The IF strip is specified at 210 kHz wide at 60 dB down, and the design's reputation rests on that number. Stations that ordinary tuners smear into each other come through clean on an MR-78, which is why it keeps turning up in talk about the best analog FM tuners ever built.

The published sensitivity figures are strong but not freakish on their own: IHF usable sensitivity of 2.5 µV (13.15 dBf), 2.0 µV for 35 dB quieting, a 75 dB mono signal-to-noise ratio, and 100 dB of image rejection. McIntosh noted that those numbers were taken in the "normal" selectivity position, the wide setting. Audio (February 1977, p.66) carried the full manufacturer's spec sheet in its review of the tuner, which is more documentation than most McIntosh tuners of the period ever got in print. Intermodulation distortion was rated at 0.2% for any combination of frequencies.

It's a wide, shallow chassis, 406 x 140 x 330 mm, with the black solid glass front panel that defines the McIntosh look of the period. The face carries meters for multipath/signal strength and tuning, plus switches for Selectivity (Normal, Narrow, Super Narrow), Filter, Muting, and Mode (Stereo Only, Mono, Stereo Auto). The three-position selectivity switch is the heart of the thing, more on that below.

Key Features

The RIMO Filter and Three-Position Selectivity

The MR-78's defining circuit is the RIMO filter, a patented IF passband filter designed by Richard Modafferi. It gives the tuner user-selectable passbands and, according to the design literature, remarkable adjacent-channel rejection, meaning it can reject a strong station sitting right next to a weak one. RIMO is also credited with improving channel separation and lowering distortion. That matters because you want narrow when the band is crowded, but narrow filters usually cost you separation and add distortion. The MR-78's answer is a switchable system rather than one fixed compromise. An Audio tuner-design survey (January 1979, p.40) illustrated the arrangement as a two-position IF system with a main filter and a switchable narrow filter. The front panel offers three selectivity settings - Normal, Narrow, and Super Narrow - so the user can trade bandwidth for rejection as the dial demands.

Phase-Locked-Loop Multiplex Demodulation

The MR-78 was McIntosh's first tuner to use a phase-locked-loop multiplex demodulator circuit. The PLL recovers the stereo subcarrier and separates left from right, and it does so more stably than the older approaches. It doesn't announce itself on the spec sheet but shows up in how solid the stereo image feels on a marginal signal. The tuner relies completely on transistor technology, with no tubes anywhere in the signal path, which places it firmly in McIntosh's solid-state era.

Four-Gang Tuning Capacitor and Crystal IF Filter

The front end uses a four-gang tuning capacitor paired with a crystal filter in the IF stage. Four gangs is serious RF hardware. Combined with the crystal filter, it gives the tuner the tracking consistency and selectivity that the RIMO stage then refines. This tuner is built around its RF and IF sections first.

Rear Panel and Antenna Flexibility

The rear panel, as described in the 1977 Audio review (p.67), includes test points for the optional McIntosh Maximum Performance Indicator, a rear-accessible 0.5 A slow-blow line fuse, and both push terminals for 300-ohm antenna line and a 75-ohm coaxial connector. The tuner can be fed from either a classic folded dipole or a modern coax downlead without an adapter.

Panloc Mounting and Optional Wood Case

Like other McIntosh components of the era, the MR-78 uses the Panloc mounting system, with shelves and shelf brackets and the necessary hardware supplied, so it can be installed in a cabinet or rack cleanly. An optional wooden case was offered for free-standing use, and the analog dial is the traditional McIntosh slide-rule type.

Historical Context

The MR-78 arrived in 1972 as McIntosh's flagship tuner, the top of the line at a moment when FM broadcasting was the serious listening medium and a tuner was a component worth designing around. The RIMO filter was not an overnight development. Modafferi had begun the underlying design work as a graduate student at the Newark College of Engineering (now part of the New Jersey Institute of Technology) in the mid-1960s, and the MR-78 was where that work reached production. The result was a tuner precise enough to pull in the weaker of two stations broadcasting on very close frequencies, which was a genuine advance.

By the time Audio reviewed it in February 1977, the MR-78 was near the end of its production run, which closed that same year. The review preserved the manufacturer's full specification set in print - the sensitivity, quieting, S/N, image rejection, and IM distortion figures quoted above - at a time when independent lab numbers for tuners were not always easy to come by.

Collectibility & Value

The MR-78 sits in the top tier of collectible analog tuners, and prices reflect it. A "Used - Mint" example was listed on Reverb at $2,600, and an eBay listing for a tested working unit carried a $1,695 asking price. That's a single data point each, so treat both as asking prices rather than settled market values. Enthusiasts and at least one dealer describe the MR-78 as among the finest FM tuners ever made, with one specialist outfit ranking it "unquestionably among the top five."

Buyers should expect service. Alignment is a standard maintenance item on any tuner of this age, and dealers routinely advertise MR-78s as "fully serviced and aligned by our in-house tech," a phrase worth looking for in a listing. At least one buyer reported receiving a pre-owned unit that "needs a lot of repairs," so condition and service history matter more than cosmetics. Original service manuals, schematics, and brochures for the MR-78 circulate in the collector market and are worth having if you plan to keep one running. The tuner's construction is frequently cited as a high-water mark for classic tuner build quality, named in the same breath as the Accuphase T-100 and Pioneer Series 20 F-26.

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VINTAGE TECHNOLOGY ARCHIVE / 10-20-2026 / FEEDBACK