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Quad 303

Stereo Power Amplifier (1978-84)

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Quad 303


The Quad 303 is a two channel power amplifier primarily designed for high quality domestic installations.

It is ideally suitable for driving loudspeakers in the 4-16 ohm range and will provide an output of up to 45 watts per channel depending upon the load impedance.

The input required for full output is 0.5 Vrms unbalanced.

Transistor triples are employed in an original circuit to provide a completely symmetrical output stage, quiescent current independent of junction temperature and symmetrical current and voltage limiting.

Harmonic and intermodulation distortion products in the audio range are so low that they are difficult to measure in meaningful terms.

The amplifier is unconditionally stable and may be used with any load.

For special applications requiring continuous power into low (less than 8 ohm) or reactive loads such as driving synchronous motors, etc, the maximum power or duty cycle may be limited by the ability of the heat sink to dissipate the heat generated (max heat sink temperature 70 degrees).

The two channels may be used together or independently but the two outputs should not be paralleled without incorporating some form of current sharing network.


Power output: 45 watts per channel into 8Ω (stereo)

Frequency response: 30Hz to 35kHz

Total harmonic distortion: 0.1%

Input sensitivity: 0.5V

Signal to noise ratio: 100dB

Speaker load impedance: 4Ω to 16Ω

Dimensions: 120 x 159 x 324mm

Weight: 8.2kg


service manual   English -

instruction/owners manual   English -

flyer   English -

service data   English -

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Reviewed Feb 21st, 2015 by desertdog

Still I think the best quad made, very close to a good valve sound

Reviewed Feb 16th, 2014 by bwcarter

In my keeper pile...with the 33 preamp. High build quality, compact, funky and different design. But what really sold me was when I A/B compared it to a typical vintage Japanese power unit which I had thought sounded fine - until I switched in the Quad. Dramatically superior sound - way more bottom end and better presence in mids too - playing into my Large Advents at the time. Made the Japanese unit (same power rating) look bad indeed. Have also heard that they can handle low ohm loads, which isn't too surprising since Quad Electrostatic speakers swing quite low, and often were paired with this amp. If you get a chance, buy one and keep it.

Reviewed Oct 26th, 2013 by davjoma

Had mine since new in 1977. Coupled with Spendor BC1 speakers which need a reasonably powerful amp to drive them. Looks the business, does the business - what else is there to say?



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