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Quad 405 rear panel and associated PSU sub-chassis parts, sold as-is for spares or repairs. Fully disassembled; not a complete amplifier. Specifications
Country of Origin: United Kingdom
Year Manufactured: 1970s
Type: Two-channel solid-state power amplifier
Amplifier Topology: Current-dumping (Class A front-end + Class B output stage with feedforward error correction)
Power Output: 100 W per channel into 8 ohms
Speaker Load Impedance: 4 Ω to 16 Ω
Frequency Response: −1 dB at 20 Hz (12 dB/octave subsonic filter); −0.5 dB at 20 kHz; −3 dB at 50 kHz
Power Bandwidth: 10 Hz – 20 kHz
Input Sensitivity: 500 mV for 100 W output
Input Connector: 4-pin DIN socket (RCA adaptor cable supplied)
Total Harmonic Distortion (THD): 0.05%
Signal-to-Noise Ratio: 95 dB
Damping Factor: 80
Channel Separation: 85 dB at 1 kHz
Dimensions (W × H × D): 340 mm × 115 mm × 195 mm (13.4" × 4.5" × 7.7")
Weight: 9 kg (20 lbs)
Years of Production: 1975 – 1982 (Quad 405); succeeded by Quad 405-2 (1983–1993)
Manufacturer: Acoustical Manufacturing Co. Ltd. (later Quad Electroacoustics), Huntingdon, England
Generating expert take…
Quad, the venerable British hi-fi brand, traces its origins to 1936 in London, when engineer Peter J. Walker founded S.P. Fidelity Sound Systems, soon renamed the Acoustical Manufacturing Company. Relocating to Huntingdon in 1941 after wartime bombing, the firm shifted from public address gear to domestic audio amid post-war demand for superior sound reproduction. Walker's pioneering ethos—prioritizing "the closest approach to the original sound"—defined Quad from its early QA12 amplifiers, adopted by the BBC, to the iconic Quad I of 1953.
The brand excels in amplifiers and electrostatic loudspeakers, revolutionizing both categories. The Quad II power amplifier of 1953 introduced cathode coupling for vanishingly low distortion, while the 1956 ESL 57 delivered the world's first full-range electrostatic speaker, employing a massless film diaphragm for unparalleled transparency and transient speed. Quad advanced into solid-state with the 1967 303 and transistor designs featuring innovative "Triples" output stages, later expanding to integrated amps like the 99 series, moving-coil speakers, and modern electrostatic models such as the ESL 988 and 989.
Today, under the International Audio Group since 1997, Quad holds a prestigious position in the high-end market, revered by audiophiles for its unyielding pursuit of accuracy over trends. Its heritage components command vintage collector status, yet contemporary offerings maintain a niche boutique appeal among discerning buyers seeking refined, distortion-free reproduction that honors Walker's legacy.
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