The Quad Electroacoustics 33 preamplifier, FM tuner (like the FM3/FM2), and 405 power amplifier represent a landmark era of British hi-fi engineering from The Acoustical Manufacturing Company.

Timeline and History

1967: Quad launched the Quad 33 preamplifier and 303 power amplifier as their first solid-state (transistor) domestic separates, alongside matching tuners.

Late 1960s/Early 1970s: The companion FM3 tuner was introduced to complement the 33/303 aesthetic and compact styling.

1975: Founder Peter Walker introduced the revolutionary "current dumping" amplifier topology, leading to the release of the iconic Quad 405 stereo power amplifier, which was often paired with the 33 preamp or later control units.

1978: The Quad 405 won the Queen's Award for Technological Achievement for its innovative current-dumping circuit.

1982: Production of the Quad 33 ended after an impressive run of roughly 120,000 units, while the 405 transitioned into the updated 405-2 version.

Key Components

Quad 33 Preamp: A compact, modular control unit featuring distinct push-buttons, filters, and plug-in internal audio boards.

FM Tuners: Designed for high-fidelity analog radio reception with minimalist styling matching the control units.

Quad 405 Power Amp: Used current-dumping technology—using a low-power, high-quality class-A amplifier to provide signal accuracy while a heavy-duty current amplifier supplied the muscle.

These units are fully restored and (partially) recapped, More specifically, all brown Roederstein caps were replaced with modern ones. The speaker protection board of the 405 ('clamp circuit') was completely rebuilt. The 405 got cinch inputs (din input still present, but inactive). Casing has minor blemishes, congruent with their age. Available as set only. Complete with all necessary cables.

Quad 405-I power amp, FM tuner & 33 pre amp set

€500.00

Quad 33 Preamplifier
The Quad 33 is an all-transistor stereo control unit featuring distinct modular plugin boards.
Frequency Response: 30 Hz to 20,000 Hz (±0.5 dB)
Total Harmonic Distortion (THD):0.02% at 0.5V RMS output (30 Hz–10,000 Hz)
Input Sensitivity: 2 mV (Phono MM), 100 mV (Line / Aux / Radio)
Signal-to-Noise Ratio (SNR): 70 dB (Phono MM), 85 dB (Line)
Outputs: 100 mV (Line/Tape out), 0.5V (Pre-out to power amp)
Tone Controls: Bass (±16 dB at 40 Hz); Treble (+14 dB to -13 dB at 10,000 Hz)
Filter Options: High-frequency cut filters at 5 kHz, 7 kHz, and 10 kHz
Dimensions & Weight: 260 x 92 x 165 mm; approximately 3 kg
Quad FM3 Tuner
The companion Quad FM3 is a solid-state, self-powered, analog FM-only broadcast tuner.
Tuning Range: 88 MHz to 108 MHz
Sensitivity: 2 μV for 30 dB quieting (Mono)
Frequency Response: 20 Hz to 15,000 Hz (±1 dB)
Total Harmonic Distortion (THD): Less than 0.3% in stereo (at 1 kHz, 30% modulation)
Channel Separation: 40 dB at 1 kHz
Aerial Inputs: 75-ohm coaxial and 300-ohm balanced
Output Level: 100 mV into a matching Quad amplifier load
Dimensions & Weight: 260 x 92 x 165 mm; approximately 2.7 kg
Quad 405 Power Amplifier
The Quad 405 stereo amplifier employs Peter Walker's specialized "current dumping" circuit design.
Power Output: 100 Watts per channel into an 8-ohm load
Frequency Response: 20 Hz to 20,000 Hz (-1 dB at 20 Hz subsonic filter; -0.5 dB at 20 kHz)
Total Harmonic Distortion (THD): Less than 0.01% at 1 kHz; less than 0.05% at 10 kHz
Input Sensitivity: 0.5V RMS for full 100W rated output
Signal-to-Noise Ratio (SNR): 95 dB (A-weighted, relative to full power)
Damping Factor: 80 at 1 kHz (into an 8-ohm load)
Speaker Load Impedance: Suitable for speakers ranging from 4 ohms to 16 ohms
Dimensions & Weight: 340.5 x 115 x 195 mm; approximately 9 kg

Quad 405-I power amp, FM tuner & 33 pre amp set

Technical specifications