Saturday, December 11, 2010

Quad 303 after recapping (2nd unit)

This is the follow-up of my earlier post for my 2nd Quad 303 unit which was purchased to enable bi-amping.

The Quad 303 is actually a well design unit which can sound superb after recapping with better quality components. The resultant sounds like a valve amp, as per many testaments on the web including

The external chassis was rusting. Hence I used AutoSol to clear the rust up before re-spraying. I chose the following colours as it does justice to the unit.
After re-spraying
The original power and audio caps of 2000uF 100V were replaced e.g Rubycon 10,000uF 63V for audio and United Chemicon 4,700uF 100V for power. Was previously using only the United Chemicon for both power and audio reservoir caps - sounded very nice as well. Only changed to the Rubycon for the audio reservoir cap as I have a requirement for both of my 303's to be the same. A 0.027uF Philips BC poly was used as by-pass on the Rubycon reservoir caps.
After large caps were replaced
The capacitors, trimmers and resistors were replaced on the audio and power boards with better quality components.
After recapping with better quality components

In addition I replaced a carbon resistor on each of the audio boards to "open up" the units, as there was still a slight roughness "round the edges" after recapping and re-biasing.  I decide to perform the replacement after some research on the internet.

For the DIY-ers out there, the above were perform according to suggestions by Dada and NetAudio. I choose to use Wima's and Panasonic FC(s). If you decide to revert back to the original Quad sound, it is quite easy. Just replace the big Wima visible on each of the above audio board (next to the 2 caps before the trimmer at bottom of the pix) with a different cap e.g Vishay BC (green) or Evox (grey). And put back the carbon resistor for the "roughness" in the sound quality.


  1. You really tempting me now. Now I'm thinking to get one as well :)

    1. If you do not need a amp with big wattage but require grunt, this is it! The amp was designed to be unconditionally stable as well.

      Once recapped with better quality components, it sounds superb and is a great all rounder.

      I am currently using this particular 303 for my clone Rogers LS 3/5A with AB1 connected in serial. The amp is just slightly warmer than normal after 8hrs!

      The LS 3/5A speakers (even the clone) are known to be difficult to be driven properly - the Quad 303 delivers without any fuss. Sounds even better once I started turning up the volume on the 33!!!

      BTW nice website you have there!!!

    2. Forgot to add - in Asia, the 303's are prized for driving the older ESL(s) as well as Rogers, Harbeth, Spendor, and the alike.