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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


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Reviewed Aug 25th, 2018 by Classicfudge

Bought one of these in 1968 still in use today, only change has been all electrolytics replaced and psu caps inverted, a classic .

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?



re: 303

I just received a 303 S today. I'm using a 34 pre-amp with it and a Sherwood turntable. I use the Radio input on the 34 for Broadband TV, the CD input for DVD and the Disc input for the turntable. I use my venerable 4 Ohm Accoustic Research AR-11 loudspeakers with this set. Sheer joy listening to Deutsche Gramafon Archiv "J.S. Bach * Das Wohltempierte Clavier" (The Well Tempered Clavier (in this case a Clavichord - a baroque Harpsichord like instrument and like the Harpsichord one of the precursors of the modern Piano). Far better than I anticipated. Clearly enunciated plucking of the chords as well as a silky smooth crystal clear reproduction of the music itself.

A cool piece of design too - with the cooling fins where they should be, in the front where they will get best access to cooler air.

I don't have sufficient experience of Quad products to agree with Desertdog, but I definitely agree with DWCarter and Davjoma above....

Speaking of other Quad products, my friendly, very patient, local HiFi store owner recently demonstrated the new Quad VA One to me, hooked upto a pair of Graham LS 5/9 loudspeakers, not a recommended match, but one which at least for the purposes of showing off the paces of this cute but gutsy little valve / tube amp worked well.... He played a piece of wind instrument music and with the Quad VA One, one could hear the sound of the lips moving on the reed and the variations in the puffs of air going through the reed of the flute, simply extraordinary sound reproduction....!

For lots more information on the AR-11 Loudspeaker see HiFiEngine:

AR-11 Loudspeaker Specifications:
Type: 3 way, 3 driver loudspeaker system
Frequency Response: 27Hz to 30kHz
Power Handling: 100W
Recommended Amplifier: 25 to 225W
Crossover Frequency: 525, 5000Hz
Impedance: 4Ω
Sensitivity: 86dB
Bass: 1 x 305mm acoustic suspension
Midrange: 1 x 38mm hemispherical dome
Tweeter: 1 x 19mm hemispherical dome
Dimensions: 354 x 635 x 273mm
Weight: 22.6kg

This website is not affiliated with or sponsored by Quad. To purchase 303 spares or accessories, please contact the company via their website or visit an authorised retailer.