QUAD 303 Amplifier Owner’s Manual

QUAD 303 Amplifier

Amplifier

Very few hi-fi components are as instantly recognisable as the QUAD 33 and 303, and for that, we make no apologies!
Still one of the most popular models in the history of one of the world’s most poignant hi-fi brands, the QUAD 33 and 303 are benchmarks in almost every angle of desirable audio equipment – performance, reliability, industrial design, value and musical romance.

By revisiting the QUAD 33 and 303 components, QUAD demonstrates its authenticity, pedigree and excellence as a juggernaut of the British hi-fi world – past and present.
In listing the names involved in the development of this stunning iteration of an icon, you’ll find a calculation of close to 200 years of engineering experience and 100+ years of QUAD-exclusive design and service.

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A dream team of Rob Flain & Paul McConville (the world’s most experienced QUAD service engineers), Jan Ertner (30 years of experience in QUAD design), Peter Comeau (the acoustic director behind some of QUAD’s most successful loudspeakers) and David McNeill (the industrial designer responsible for two decades of QUAD innovations) were all a part of this labour of love, making no compromise in the demand for a product that could be the name of 33 and 303.
The QUAD 303 power amplifier was intended for normal domestic use with loudspeakers of moderate efficiency, but was also used by broadcasting and recording studios, worldwide, who appreciate its excellent performance and dependability. The ethos hasn’t deviated.

Function

The outstanding performance of the QUAD 303 is still celebrated to this day, and is largely due to the unique output circuit developed by QUAD.
In reissuing the QUAD 303 power amplifier concept, exactly like the matching 33 preamplifer, QUAD’s incomparably experienced service team was matched with the equally adept engineering team to reinvoke the design, romance and performance in a thoroughly modern iteration of a hi-fi legend.
As with the new QUAD 33, every aspect of design and performance has been analysed and re-engineered way beyond simply modernising components and refreshing of specifications.

Circuitry

However, much like the original, the new QUAD 303 maintains its faithfulness to the original by employing the famous QUAD ‘symmetrical triples’. Employed to provide a completely symmetrical output stage, greatly reducing distortion and rendering the resting current independent of output transistor temperature.
This development enables the designers to reduce distortion to emphatically low levels without sacrificing stability and to maintain this excellence under all dynamic conditions.
To put this in perspective, the lowest theoretical distortion present on the very source material will still be some hundred times greater than that the QUAD 303!
Such a level is, of course, completely inaudible no matter how refined the test.
The use of ‘triples’ permits simple and effective control of the output current and since the voltage is also controlled, the output transistors are completely protected and must always operate within their ratings with the obvious advantages of greatly improved reliability under all conditions, without the use of elaborate and expensive circuitry.

The amplifier cannot be upset even when overdriven by an asymmetrical signal or by shorting or disconnecting the loudspeakers.
A brand new 200VA, custom specified low-noise toroidal transformer has been developed for the new 303.
The output stage of the discrete power amplifier circuit employs an advanced feedback topology to ensure superior linearity and exceptional thermal stability. Through its Class AB design, the ideal current is maintained independently of the temperature of the output transistors.
The result is a compact, cool-running power amplifier that possesses the capacity to deliver dynamic power and maintain a firm hold on the music while providing rich sonic detail.

Always respected for its conservative but consistent power-output, the classic QUAD 303 was officially rated at 45W @ 8 ohms. A modest but honest output, the 303’s venerability is in the finesse of the performance, not just the raw power. The new model is thoroughly the same.
However, with some tweaking and enhancements, the 303 is loaded with a little extra power – offering 50W @ ohms (70W @ 4 ohms) with a maximum current delivery of 10A into difficult loads. Perfectly suited to the more demanding requirements of the modern audiophile, it ensures any speakers – even including QUAD’s electrostatic designs – can be driven with ease.
Connectivity options comprise single-ended RCA and balanced XLR inputs, a 12V trigger input and high-quality speaker binding posts. Simple, solid and thoroughly authentic, inside and out.
The power output for ‘bridged mode’ (for use as a mono-block power amplifier) reaches 140W @ 8 ohms or 170W @ 4 ohms (bridged mono).
The industrial design of the new QUAD 303 is instantly recognisable and is ‘true QUAD’. The anodised chassis CNC-routed heat sinks on either side offer enduring quality which the tankhousing also provides a rugged structure that resists interference from external vibrations.

Versatile Application

Originally intended for domestic use, the QUAD 303 power amplifier found popularity in broadcasting and recording studios globally due to its exceptional performance and reliability. This versatility remains a hallmark of the QUAD brand.

Innovative Output Circuit

The QUAD 303 features a unique output circuit developed by QUAD, known as the ‘symmetrical triples’. This circuit ensures a completely symmetrical output stage, reducing distortion and maintaining stability under all dynamic conditions.

Intelligent Feedback Topology

Further to the QUAD ‘Triples’ circuitry, the 303 utilises advanced feedback topology to ensure superior linearity and exceptional thermal stability.

Enhanced Power and Connectivity

While maintaining its venerable performance, the new QUAD 303 boasts enhancements, including increased power output to meet modern demands. Connectivity options include single-ended RCA and balanced XLR inputs, a 12V trigger input, and high-quality speaker binding posts.

Iconic Design

The industrial design of the new QUAD 303 remains true to its heritage, with instantly recognisable aesthetics and durable construction. CNC-routed heat sinks and a rugged chassis ensure enduring quality and resistance to external vibrations.

Specifications

Customer Support

www.quad-hifi.co.uk
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QUAD Official
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IAG House, 13/14 Glebe Road, Huntingdon,
Cambridgeshire, PE29 7DL, UK