Dynaco Dynaquad (1970s)

Name: Dynaco Dynaquad
Brand: Dynaco

The Dynaquad was Dynaco's entry in the early-1970s four-channel race. It was a quadraphonic adaptor based on a circuit concept by David Hafler. Advertised in High Fidelity (April 1971, p.21) and HiFI-Stereo (June 1971, p.17) at $19.95 in kit form or $29.95 factory-assembled, it was pitched as the cheap way into four-channel: just add two more speakers to your existing stereo setup.

The device itself was simple - a few resistors, a volume control for the rear channels, and some connectors. It was passive, so it needed no wall power and had no decoding circuits. You connected it to the speaker outputs of your stereo amplifier. It derived the difference signal (L-R) from the stereo pair and fed it to two rear speakers, creating simulated surround sound. Some recordings responded to this surprisingly well. Others, not so much. As one retrospective notes, the result was not true quadraphonic sound. For authentic four-channel reproduction you needed a discrete format or a matrix decoding system, and the Dynaquad did not really meet that bar.

Many Dynaquad units were sold as kits and wired by hobbyists, so wiring varies from unit to unit. The passive design means most surviving examples are likely still functional, but given the kit-built nature, look inside before trusting one with your speakers.