SAE Model 4100
A time-delay ambience box that let a late-'70s stereo system fake a rear channel. The front path stays untouched, the rear path is adjustable, and the lab report mostly backed up the claims.
Overview
The SAE Model 4100 is a time-delay ambience system. In the late 1970s it sat between a preamp and a power amp and tried to convince a listening room it had a rear channel. Modern Recording (December 1978, p.76) described it as a device designed to add ambience to amplified sound, connected into a playback system between the preamp and the power amp. One pair of outputs feeds the original power amp, and another pair feeds a second amp for the rear channels. The front channels pass through the unit with no ambient effect applied. Only the rear channels get modified by the circuitry. It's a signal-splitting accessory, not a studio reverb, and it leaves the main stereo path alone.
The physical package is period-typical for better-grade consumer gear. Modern Recording (December 1978, p.77) noted that standard hi-fi jacks at the rear handle all in and out signals, and that the unit is supplied in a metal case with walnut wood side panels. The controls are where the 4100 does its work. Modern Recording (December 1978, p.76) counts six controls governing how the rear channels are treated, including a "short" delay setting that the magazine demonstrated with a tone-burst 'scope photo. The rear-channel processing is adjustable rather than a fixed effect, which sets it apart from the simpler one-knob ambience boxes of the same period.
The lab results are mixed. Modern Recording (December 1978, p.77) measured lower distortion than SAE claimed, and a better signal-to-noise ratio on the rear channel than the spec sheet promised. The front-channel S/N ratio came in a little shy of spec. Measured frequency response of the rear channels came very close to claims. The low end actually bettered the spec, while the high end landed about 1 kHz short.
As for the SAE's standing, it's a period curiosity rather than a collector's grail. It solved a specific problem, adding rear-channel ambience without touching the front path, and did so competently enough that a magazine lab found it met or beat most of its own claims. Whether it's worth chasing today depends on whether the buyer runs a four-channel or ambience setup. On a stereo-only system the 4100 is a box with no job. For someone assembling a late-'70s quad-adjacent playback chain, it's a period-correct piece with documented performance and a clear place in the signal path. Production years are not confirmed in the available documentation. The December 1978 review date is the firmest anchor in the record.
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