Sansui QS-100
Fifty watts of IHF music power and a walnut cabinet, priced to turn a two-channel system into four without buying a new receiver.
Overview
The pitch was blunt: "you don't have to go for broke." Sansui's own advertising billed the QS-100 as a "miracle" available for as little as $214.95 - the figure the company used in its 1972 Electronics Illustrated placements - and sold it as the cheap way into four-channel sound for people who already owned a perfectly good stereo. It was not a receiver. It was a rear-channel amplifier, synthesizer, decoder, and control center in one box, and the buyer only had to add a second pair of speakers.
The QS-100 is easy to misread today. It is not a complete four-channel system and it was never sold as one. Sansui positioned it as a supplement: feed it from the tape sockets of an existing two-channel amplifier, hang two more speakers off the back, and the living room stereo becomes a four-channel rig. The company's Studio Sound advertising (March 1972, p.13) made the same case in a single line - add the QS-100 and a second pair of speakers to a two-channel system and "you have yourself a genuine Sansui 4-channel system."
Total IHF music power is rated at 50 watts. That sounds like very little until you read the fine print: continuous power per channel is 18 watts at 4 ohms and 15 watts at 8 ohms. Those are rear-channel figures, and honest ones - this is ambience and effects duty, not the main event. The QS-100 also carried the same core technology as its bigger sibling, the QS-500: Sansui's own synthesizer/decoder matrix with phase-shifting and the company's exclusive phase modulation circuitry, which the advertising claimed preserves signal location and avoids the cancellation that plagued some competing matrix schemes. Owners could decode compatibly matrixed four-channel broadcasts and recordings, or synthesize rear-channel ambience out of ordinary two-channel material.
Pricing drifted over the model's advertising life. The early 1972 Electronics Illustrated copy lists the QS-100 at $209.95 in its walnut cabinet, while later placements in the same magazine that year quote $214.95. Both figures appear in Sansui's own ads, so call it "around $210-215 depending on when you walked into the dealer." The QS-500, for reference, sat at $279.95 - $289.95 across the same run. That is roughly seventy dollars more for 120 watts of IHF power and a much fuller control set including four VU meters and three balance controls.
What the QS-100 gives up against the QS-500 is mostly ergonomics. The bigger unit had front-rear and left-right balance trims, separate decode and synthesize positions, two- and four-channel tape monitoring, electrical rotation of speaker output, and alternate-pair speaker selection. The QS-100 carried the same synthesizer/decoder brain and the same provisions for connecting discrete four-channel sources — a reel-to-reel or cartridge deck could be plugged straight in — but in a stripped-down chassis aimed at the buyer who wanted in cheaply. Sansui was explicit that the door stayed open: the advertising promised the owner could later "add any adaptor, decoder or whathave-you for any four-channel system" that anyone had hinted at. That was a sales line in 1972 and it reads today as a fairly accurate description of how the quad era actually went.
Audio (July 1972, p.39) surveyed the decoder-amplifier category as the easiest route into quadraphonics — buy a decoder-amplifier and two loudspeakers, feed it from the tape sockets of the main amplifier — which is precisely the architecture Sansui built the QS-100 around. The magazine's own roundup of add-on four-channel converters in its February 1972 issue (p.51) shows how crowded that field was, with power outputs from 15 to 40 watts per channel across the competing units; the QS-100's 18-watt-per-channel 4-ohm rating put it squarely in the middle of that pack rather than at the bottom.
Today the QS-100 is a period piece more than a daily driver. It demonstrates what matrix quad sounded like in 1971-72, and it does that with a minimum of fuss and a maximum of walnut. The rear-channel power is limited - 15 watts into 8 ohms will not wake inefficient speakers - so it wants sensitive ones. The value case is simple: it is the cheapest way to own a genuine Sansui synthesizer/decoder with the phase-modulation circuitry, and it takes up almost no shelf space. It will not replace the main amplifier, and anyone expecting a complete four-channel receiver should look at the QR series instead.
Sansui's advertising in Studio Sound (December 1971, p.15) placed the QS-100 alongside the 120-watt QS-500 as the two ways to build on an existing two-channel system, with the QR-4500, QR-6500, QR-1500, and QR-500 receivers covering the from-scratch crowd.
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