Threshold S-500 (c. 1982–1988)
Surviving information on the Threshold S-500 is thin. The archive's record is a handful of trade-press mentions from the 1980s, with no full review or service manual. The S-500 (sometimes written S/500) was Threshold's Stasis power amplifier. A 1982 trade report called it the company's current top-of-the-line Stasis amplifier, rated at 250 watts per channel into 8 ohms with less than 0.1% THD or IM distortion and a −3 dB power bandwidth from 1 Hz to beyond 100 kHz.
Later in its run, the S-500 got the same optical bias control Threshold used across the S-series. HI-Fi-Stereo-Buyers (January 1988, p.16) noted that the new circuitry used optically coupled components to isolate the bias circuitry from the power stages. It sensed idle current directly at the output stage. S-series amps were then biased to run in pure Class A up to about 20 percent of maximum output, roughly 50 watts of the 250-watt rating.
Past that, the record goes quiet. The archive has no confirmed production dates, original pricing, or detailed independent bench tests. The years above show when the S-500 appears in period press, not a verified manufacturing span.
- Output: 250 W/channel into 8 ohms
- Distortion: less than 0.1% THD or IM
- −3 dB power bandwidth: 1 Hz to over 100 kHz
- Stasis topology; later optical bias control, pure Class A to ~50 W
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