If it was inevitable that sooner or later Bose (of "direct/reflecting" loudspeaker fame) would get into stereo receivers, it also was foregone that the product in this very populous area would be at once "different" and excellent.

To begin with, the requisite equalizer for Bose 901 Series III and Series IV speakers is built in, and there is an added "spatial control" that varies the acoustical focus. However, other types and makes of speakers also can be used, alone or together with the Bose models. The receiver actually has two stereo power amplifiers and selectable output impedance, so that it operates as a 100-watts-per-channel stereo unit or as two 50-watts-per-channel stereo units. When two pairs of speakers are used, the spatial control becomes a balance control between the two pairs.

What is more, the Bose receiver has four "preamp-out; power amp-in" connnections at the rear. With these, you can patch in ancillary devices readily. If any portion of a processed signal requires its own amplification, it may be returned to the same Bose receiver, which would then be used in its "double power amp" mode. This makes hookup of, say, a time-delay device easier. Similarly, a biamplification setup can be created without the need for an extra power amplifier since the separated highs and lows (fed of course from a suitable electronic crossover) can be handled directly by the Bose unit's own extra amplification channels.

In addition, there is yet another lowpowered stereo amplifier built-in, just for driving headphones.

Beyond these unusual features, the receiver offers all the options, and then some, normally expected of a high-quality set. Two tape recorders can be hooked up at the same time, and copies can be dubbed from one to the other. There's a stereo/mono mode switch, the usual input selector switches, low-frequency filter, channel balance, and so on. In place of conventional tone controls, the set uses "source and room compensation sliders. These function as equalizer controls for Bose 901 Series III and IV speakers, and as modified treble and bass adjustments with other speakers.

The phono preamp section is a low-noise, low-distortion circuit with excellent overload characteristics. The FM tuner is highly sensitive, requiring only 3.5 microvolts for 50 dB of quieting. Response is linear across the FM band. There is a muting control, and two meters - one for signal strength, the other for center-of-channel. Besides the usual 300-ohm antenna inputs, a 75-ohm terminal permits direct hookup of cable lead-in.

With all this, the Bose "Spatial Control" receiver, priced at $799, is unlike any other in versatility. As for sound, it is easily among the very best, driving Bose or any other speakers. It strikes me, in fact, as the kind of all-in-one that could appeal to the audiophile who up to now has favored separate preamp, power amp, and tuner. At the same time it is so cleverly designed that the technically uninitiated would find it fun to operate.