Original Website © Amplabs 2009 This new site created February 2024
Quad 303 Full Left & Right PCB upgrade with high performance circuits (Q303HPUG)
Amplabs
The Quad 303 has a warm, valve like sound when correctly serviced. It is well known for its sound quality and robustness.
Despite this, we receive lots of requests from enthusiasts and audiophiles alike, to ‘improve’ the 303’s performance.
Electronic devices have advanced a lot over the years and today’s well designed amplifiers offer low, harmonic and
modulation distortion, as well as improved safety measures. With a well produced recording, these amplifiers can separate
out the individual instruments and voices across the sound arena more readily than the 303. But the difference can be quite
minimal unless you have a decent pre-amplifier and of course good quality source material and speakers.
If you want your 303 to sound a little fresher and perform safely, at least have your 303 serviced and properly checked-out
electrically. Our standard 303 service adds extra fusing and the upgrade options including adding RCA sockets and fused
IEC mains inlet and ON-OFF switch. If you want to go a step further, our 303HPUG service option will add an extra boost to
its performance and safety. The new PCBs contain new circuits which are designed and configured by ‘Rob’ our engineer.
He named the new boards ‘Sufi’. For the technically minded, each Sufi circuit is based on discrete high performance
transistors, with a long-tail-pair front end utilising, current mirrors and constant current sources. These drive a fully
complementary output stage. On good quality recordings, the result is a noticeably uncluttered ‘sound stage’ with a good
bass response and beautifully clean mids and highs. The sensitivity is similar to the original 303, so you won’t have to
change your pre-amplifier settings. The output power capability is increased slightly too. We have purposely used ‘the old
way,’ (through hole components), rather than modern SMD technology, to make parts procurement and replacement easier
in the unlikely event of a component failure.
What we do to your 303 to bring about this transformation:
The L & R PCBs are removed from your Quad 303 and new high performance plated through hole, double sided FR4
boards are fitted. The four smoothing/output caps are replaced and fitted using our fused, PCB capacitor board. The heat
sink transistors are replaced with fully symmetrical MJ15003/4 matched pairs. (4 off) We also fit our front panel upgrade
which incorporates an on-off switch. gold plated, RCA sockets and professional 4mm LS binding posts. This improves the
overall connectivity and electrical safety. The 303’s original regulator PCB is removed and replaced with 10 second
loudspeaker-connection delay circuit. This helps to prevent power surges and on-off switch transients, from damaging your
loudspeakers and the amplifier. If the mains momentarily turns off and back on, e.g. during sudden power surge, the circuit
will repeat the 10 second cycle.
Full component replacement with new, Amplabs SUFI circuits, output transistors and capacitor PCB
For ure listening pleasure
