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The Quad II Forty (also styled QII-Forty) is a single-channel, transformer-coupled valve power-amplifier monoblock and a modern descendant of Peter Walker’s classic Quad II. It uses a push-pull KT88 output stage, a 5U4G valve rectifier, and military-specification 6SH7 input valves. Hardwired construction, choke-filtered high-tension supply, automatic output-valve biasing, custom output transformers, and gold-plated terminals are among its design features. Each amplifier delivers 40 watts RMS and provides selectable 4-ohm and 8-ohm loudspeaker taps; stereo systems require two monoblocks. The amplifier is listed on Quad’s current website, although its original production dates to the early 2000s and availability may depend on region and remaining stock.
Amplification power output and characteristics
Analog signal output specifications
Input and output connections
Specifications are community-contributed and may not be accurate or complete. Verify all details with the manufacturer before making purchasing decisions. Terms & Conditions
The closest alternatives on specs, description and the systems they turn up in, with the specs they share set side by side.
The VT100 MkIII's power @ 8ω is 100W against the II Forty's 40W, its signal-to-noise 106 dB against 80 dB, and its damping factor 12 against 20. Both share thd (0.300%).
Both turn up in the same documented systems.
The CAD-120S MkII's power @ 8ω is 120W against the II Forty's 40W, its high-frequency extension 25 kHz against 30 kHz, and its low-frequency extension 17 Hz against 10 Hz. Both share signal-to-noise (80 dB).
The DiaLogue Seven's power @ 8ω is 70W against the II Forty's 40W, its signal-to-noise 84 dB against 80 dB, its thd 0.250% against 0.300%, and its output voltage 1.1V RMS against 1.0V RMS.
The Stereo 60 MkIV KT120/KT150's power @ 8ω is 85W against the II Forty's 40W, its signal-to-noise 90 dB against 80 dB, its high-frequency extension 20 kHz against 30 kHz, and its low-frequency extension 20 Hz against 10 Hz.
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