Dynaco QD-1

Name: Dynaco QD-1
Brand: Dynaco

The Dynaco QD-1, the "Quadapter," is a passive device. It needs no power supply. A transformer derives rear-channel signals from the difference between the left and right stereo channels. You connect your main stereo amplifier's speaker outputs to the QD-1, then run wires from the QD-1 to four speakers. The catch, noted in Audio (September 1992, p.96), is that you need a second amplifier to drive the rear speakers. The QD-1 only provides the derived signal and doesn't amplify it.

J. Gordon Holt reviewed the QD-1 for Stereophile in 1971 and was impressed. He found the rear hall effect "quite convincing" and noted that the difference-signal approach worked well with most recordings. He was also plain about its limits: it wasn't as good as properly recorded four-channel sound, but it could be "remarkably effective" in some cases. The original price was $69.00.

Surviving documentation on the QD-1 is thin. No numeric specs (frequency response, distortion, impedance) appear in any available source, and production years beyond the 1971 review date aren't confirmed. The classic-audio.com reference mentions a "QD-1A" variant and a "QD-2" in the same Dynaco quadraphonic family, but no specifications for either have surfaced. What is clear is that the QD-1 is a passive, transformer-based decoder that lets you build a surround system from spare speakers and a second amp.

Known specs: