Ampex Micro 85
A compact stereo cassette system with hi-fi convenience that measured better than its own spec sheet.
Overview
The Micro 85 landed when the cassette was still viewed with suspicion by serious listeners. The complete system - deck, stereo microphone, table stand, patch cords, and a pair of speaker systems - carried a list price of $199.95. It came in a walnut-grain body barely wider than a shoebox: 14¾ inches across, 8½ deep, and 4¼ high over the knobs. For a household that wanted to make and play tapes without learning a reel-to-reel threading diagram, that footprint was the whole pitch.
The controls are simple. There are four knobs (recording level, balance, volume/on-off, and tone) and seven piano keys: record, cassette, play, rewind, fast forward, pause, and stop. The record key is red and must be pressed together with play to engage recording. The cassette key releases the holder for loading. The pause key lets you set levels without committing tape, and it also works as a momentary stop for interruptions. A digital counter with a push-button reset sits at the upper left of the panel, with the record-level meter at the lower right.
The claimed numbers were modest by component standards, but fair for a 1⅞-ips cassette deck of the period. Overall frequency response is held to an 8-dB envelope from 100 Hz to 8000 Hz, signal-to-noise ratio is 40 dB minimum, flutter is 0.4%, and speed accuracy is 5%. Mic input sensitivity is 1 mV minimum at 1000 ohms. Line input is 200 mV minimum into 1 megohm, and line output is 500 mV minimum into a 100k-ohm load. The built-in speaker outputs are rated 800 mW minimum. Crosstalk is specified at 50 dB minimum in mono at 100 Hz side-to-side, but only 20 dB minimum in stereo at 1000 Hz. That reflects the difficulty of fitting two tracks into a cassette shell, and Audio (March 1968, p.64) called it "adequate for stereo."
The Micro 85 beat its own published specifications when a reviewer put it on the bench. Audio (March 1968, p.66) measured the line output within a 6-dB envelope from 45 Hz to 9500 Hz, well beyond the claimed 100 Hz to 8500 Hz. The speaker output, at the claimed 8-dB envelope, extended from 50 to 8200 Hz with the tone control at mid-position, or out to 9100 Hz at maximum highs. Signal-to-noise came in at 54 dB against the 40-dB minimum, and the line output measured 1.7 V at 400 Hz at the 3% distortion point. Flutter measured "a shade over 0.3%," which the same review considered about normal for 1⅞-ips machines of any type. Reviewers expected the worst from the 0.4% flutter claim and heard nothing disturbing in a piano comparison.
The engineering inside is more serious than the price suggests. There is as much circuitry here as in a full reel-to-reel: preamps, equalized stages, controls, an output amplifier, a power supply, a bias/erase oscillator, and a record-level indicator, all squeezed around the transport. The signal path uses BC 109 transistors in the preamp and equalized stages, a BC 108 driver, and a complementary-symmetry output stage built around an AC 187 and an AC 188. All are NPN except the AC 188. Both channels are identical. A BC 107 runs the bias/erase oscillator at roughly 55 kHz. The power supply is unusual because there is no conventional transformer at all. The four-pole motor carries four sets of coils, two acting as primary and two as secondary. They feed a bridge rectifier for 19.4 V and 16.4 V to the output stages, and a pair of diodes wired as a voltage doubler supplies 28.6 V to the preamp, recording stages, and meter driver. The motor has a two-step pulley for 50- and 60-Hz line operation, and the primary coils are tapped for 110, 127, 220, or 245 volts.
The supplied speakers are conventional and sized to match the system. Each measures 14½ by 9 by 7⅛ inches, with a single 6×9-inch cone and an 8-ohm impedance, so any reasonably efficient 8-ohm speaker can be substituted. The speaker output jacks carry a shorting contact that places a 15-ohm terminating resistor across the output when a plug is pulled. Audio (March 1968, p.66) judged the speakers satisfactory and the system as a whole foremost convenient and attractive, with audio performance that was "satisfying if you're not too picky."
For buyers who already owned a stereo, Ampex offered the same transport without the speakers as the Micro 50, at $139.95 — sixty dollars less than the complete system. The reviewer's honest note was that the cheaper configuration, played through a real hi-fi, would of course sound better. That is the tension the Micro 85 lives with: it is a convenience machine, and it knows it.
The unit can also serve as a public-address amplifier, though at 800 mW it won't cover much of a room. The record-level meter and the single set of level and balance controls — no separate right/left trims — are part of the same philosophy: the machine is designed for the person who wants to press record and get a tape, not the person who wants to calibrate one. HiFi-Stereo (July 1972, p.72) photographed one installed in a Mediterranean-style walnut cabinet alongside a Dual 1009 SK turntable and a Kenwood TK-66, which is exactly the kind of domestic role the Micro 85 was built for.
Collectors should treat the Micro 85 as a period piece rather than a serious recording tool. The format's limitations are baked in, and the crosstalk and response figures are what they are. It still came with a microphone, speakers, and a walnut-grain case, and it outperformed its own spec sheet in the 1968 review.
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