Quad 303 Power Amplifier

Function

The remarkable performance of the QUAD 303 is still celebrated today, largely thanks to its unique output circuit developed by QUAD.

In reintroducing the QUAD 303 power amplifier, much like the accompanying 33 preamplifier, QUAD's highly experienced service team collaborated closely with its skilled engineering team to revive the design, charm, and performance of this Hi-Fi legend in a modern format.

As seen with the new QUAD 33, every detail of design and performance has undergone extensive analysis and re-engineering, going far beyond merely updating components and refreshing specifications.

While initially designed for typical home use with moderately efficient loudspeakers, the QUAD 303 also gained popularity in broadcasting and recording studios globally due to its outstanding performance and reliability. This ethos remains intact. The original 33 and its counterpart 303 received the ‘Council of Industrial Design Award in 1969,’ and the original design continues to be celebrated, as evidenced by its inclusion in the Museum of Modern Art in New York. The new 33 and 303 have been engineered to exceed those original standards, showcasing a truly modern appearance and enhanced functionality.

Circuitry

Similar to the original model, the new QUAD 303 adheres to its roots by utilising the renowned QUAD ‘symmetrical triples.’ These facilitate a completely symmetrical output stage, significantly reducing distortion and ensuring that resting current remains independent of output transistor temperature.

This advancement enables the designers to minimize distortion to impressively low levels without compromising stability, maintaining excellence under all dynamic conditions. To put this into perspective, the lowest theoretical distortion in the source material will still be several hundred times greater than that of the QUAD 303, a level that remains inaudible, regardless of how acute the testing.

The use of ‘triples’ allows for effective control of output current while maintaining voltage control, ensuring that output transistors operate within their ratings, thus enhancing reliability under various conditions without requiring complex circuitry.

The original QUAD 303 featured a quasi-complementary output stage due to the absence of complementary transistors (NPN and PNP), while the new version boasts a fully complementary output stage. This enhancement improves linearity, stabilizes static bias, and increases resilience under high voltage and significant current scenarios. Equipped with premium power transistors, the 303 offers excellent gain linearity for precise input signal reproduction and a greater dynamic range.

The amplifier is designed to remain stable even when faced with asymmetrical signals or when loudspeakers are shorted or disconnected.

The new model features a custom-specified, low-noise 200VA toroidal transformer.

The output stage of the discrete power amplifier employs advanced feedback topology to ensure remarkable linearity and exceptional thermal stability. Its Class AB design maintains ideal current levels regardless of output transistor temperature.

The outcome is a compact, cool-running amplifier that delivers dynamic power while preserving rich sonic detail.

Historically known for its consistent power output, the classic QUAD 303 was officially rated at 45W @ 8 ohms—a modest but sincere rating that emphasised performance finesse over sheer power. The new model retains this essence while offering some enhancements, now delivering 50W @ 8 ohms (70W @ 4 ohms) with a maximum current capacity of 10A for challenging loads. Where the original struggled with lower impedance loads, the new 303 excels, making it perfectly suited for the modern audiophile. It can effortlessly drive any speakers, including QUAD’s electrostatic designs.

Connectivity options include single-ended RCA and balanced XLR inputs, a 12V trigger input, and high-quality speaker binding posts. Simple, solid, and authentically crafted inside and out. The power output for 'bridged mode' (used as a mono-block amplifier) reaches 140W @ 8 ohms or 170W @ 4 ohms (bridged mono).

We endeavour to despatch same day for orders placed up to 1pm on available stock items (items with stock message "Usually dispatched within 24 hours"). Please remember to check with us first for a physical stock check if next day delivery is important to you. Any items with stock message "Usually dispatched within 72 hours" are items that we do not hold in stock but order in from the importer or manufacturer as soon as a customer order is received. Occasionally these may be delayed beyond 72 hours due to importer/manufacturer stock levels but we will inform you as soon as we can if this is the case.

UK Orders

We despatch the bulk of our UK mainland items on a 24 hour service – Free of Charge.  Non Mainland locations - Isle of Man, Isle of Wight, the Scilly Isles, the Scottish highlands and Islands, the Channel Islands and Northern Ireland may take a day or so longer and are not Free of Charge. Smaller items are delivered using Royal Mail 24 or special delivery. Larger items are delivered using a courier service such as DPD or UPS.

International Orders:

Due to the nature of our products and brand restrictions we are only able to send certain items internationally. Smaller items are delivered using Royal Mail Small Packets Airmail with International Tracked and/or Signed depending on value of item and availability of the service. Larger International shipments are sent by insured and tracked services using UPS. If there are any delays due to specific customs regulations, etc, you will be contacted by Hifisound or by the courier with a request for any further information required. Customs duties can apply for shipments to any countries outside of the UK depending on where the product you have bought is made. Customers are responsible for all taxes and duties incurred when the items enter their country.

Collect in Store or Home Install

At the request of the manufacturer some items cannot be supplied by mail order but you can click and buy them and then elect to collect them from our store or arrange a home install (if applicable). Applicable items clearly state that they are Collect in store or home install. Once ordered you will receive a message prompting you to contact us by phone or email to arrange for us to deliver and install or to reserve and collect from our store at your convenience, you will also be advised of the delivery time / stock availability as not all Home install / collect in store items are held in stock.