Quad 303
Quad 303 stereo power amplifier, designed with a balanced output stage for very low distortion across the entire audio band.
Description
The Quad 303 is a stereo power amplifier intended to complement a preamplifier in a separate hi-fi system. It provides the final amplification of the signal before reproduction through the speakers, with inputs suited to both unbalanced and balanced sources.
Its output stage is based on a balanced architecture known as triple balanced, a principle that greatly reduces distortion and makes the quiescent current independent of the temperature of the output transistors. The input sensitivity is 1.5 Vrms on XLR, with an input impedance of 10 kΩ at line level. The frequency response extends from 20 Hz to 20 kHz, and the harmonic distortion rate remains below 0.002%, a very low level that limits colouration of the amplified signal.
This type of amplifier is intended for a user wishing to build or complement a hi-fi system in separate components, with a dedicated preamplifier upstream. Its balanced XLR and unbalanced RCA connections allow it to fit into demanding installations, particularly where the quality of signal transmission between the components of the system is a priority.
Technical specifications
| Sensitivity | 1.5 Vrms (XLR) |
| Input impedance | 10 kΩ (line level) |
| Frequency response | 20 Hz - 20 kHz |
| THD | < 0.002 % |
| Weight | 6.1 kg |
What to check before buying used
On this power stage, check that the quiescent current remains stable after around thirty minutes of warm-up, as drift may indicate worn output transistors. The filter capacitors, sensitive to ageing, are worth checking: background hum or a loss of dynamics are the first signs of this. Also inspect the condition of the protection relays and the XLR/RCA connectors, whose oxidation can cause cutouts or an unstable channel.
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