Quad 50 (c. 1975)
Little is documented about the Quad 50. The best surviving source is a short description in Studio Sound (August 1975, p.39), where it appeared as the "Quad 50E Amplifier." The "E" presumably marks a variant or export version. The review treated it as a versatile, fixed-installation power amp, and every known specification comes from that single mention.
Here is what the record shows. The Quad 50E could bridge 600-ohm lines to drive speakers directly. It could also deliver 50 watts into a 100-volt line from a 0.5-volt unbalanced source, with no internal modification. A pre-set level control was adjustable from the front panel. The review quoted a frequency response of −1 dB (no range stated), 0.1% distortion at 1 kHz at all power levels, and a noise floor better than −83 dB referred to full output.
Past that listing, almost nothing survives. No production years, original price or circuit details are recorded. The 50 appears to have been aimed at commercial or institutional use - monitoring, paging, line distribution - rather than the domestic hi-fi market of Quad's better-known models. Whether it shares any lineage with the contemporaneous Quad 405 or the earlier Quad II is unknown.
Known specifications (from Studio Sound, August 1975):
- Power output: 50 watts into 100-volt line
- Input: 0.5 V unbalanced (also accepts 600 Ω balanced bridging)
- Frequency response: within −1 dB (range not specified)
- Distortion: 0.1% at 1 kHz at all power levels
- Noise: better than −83 dB referred to full output
- Controls: pre-set level adjustment on front panel
- Versatility: no internal changes needed between bridging and line-drive applications
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