Bose 901 Compatible Receiversby Joe Murray
The Bose 901 Direct/Reflecting speaker system, a high-end piece of audio equipment, possesses several features. Introduced in 1968, each of the two active matrix enclosures houses nine individual 4.5-inch speakers. A separate active equalizer provides the speakers with a balanced tonal output in nearly any enclosed environment, which allows for a stereo effect regardless of where the listener is located in the room. In six iterations over 42 years, the Bose 901s have added more than 350 improvements and modifications, yet maintain the same overall basic design, components and appearance.
To accommodate the additional active equalizer hardware, the stereo receiver used to drive the 901s requires an open connection between the preamplifier output and the amplifier input. This is generally found on the input/output panel on the rear of the receiver. The connectors are a pair of standard audio (RCA) type of female sockets labeled "Preamp out" above a pair of standard audio (RCA) type of female sockets labeled "Amp input." These connect left to left and right to right channel with a pair of dual male standard audio plugs.
The stereo receiver used to drive the 901s should have a minimum of 100 watts RMS per channel output. This is especially important among the earlier 901 series l, ll and lll. In later models, including the current series Vl, higher wattage is not so much demanded as recommended. The reason for high wattage amplifiers becomes clear when it is pointed out that each 901 enclosure contains nine individual speakers. On the upper end, 901s can be driven by amps with 400 to 500 watts per channel of RMS power without concern of overtaxing the speakers.
An adequate but somewhat primitive workaround for the inclusion of the Bose active equalizer in nearly any receiver can be used when the preamp out/amp input type is unavailable. Using the tape inputs and outputs in the same manner as the amp and preamp inputs and outputs will work. However, the tape monitor switch must be kept in the "on" position in order to listen to the speakers, and all audio signals must be run through the tape preamp, which in some configurations is separate from and inferior to the main preamp reproduction capabilities.