Schematics Ivor's Quad 33 revision PCB | Electronic Circuits

Schematics Ivor's Quad 33 revision PCB

Circuit Quad 33 Revision. A beginners tale.

I am a professional violinist who also has a small recording studio, and In the past couple of years I have built a small collection of Quad amps. This currently includes a 33/303, 405-2 and grey 44/606mk2. I realised after years of trying different equipment, both for domestic listening and in my studio that the Quad power amps are perfect for my needs. They are fairly cheap, built fantastically well, and sound great. I use the 303 with Quad Esl 57's , 405-2 with Harbeth P3ESR (In the studio) and the 44/606 await Harbeth Super Hl5's. The big problem I have experienced is with the Pre-amps. The 33 just sounded dull to my ears, and I could not enjoy using it even after a Quad service. I still have a large record collection so need a phono stage, and I like the look of the Quad preamps, but needed to try to improve the sound to the point where I felt I could use them whilst keeping as much originality as possible.

Dada kits seemed like a sensible proposition without costing too much. The down side for me was I have had absolutely no previous electronics experience except for a couple of poor attempts at soldering broken mic leads. Here are some perceptions I experienced whilst doing the work.
I had to do some basic web searches to work out the values of resistors, and youtube provided me with tuition on soldering and the use of solder pumps. Initially I just wanted to do the power supply modifications, and although there was a picture provided of the modified board, I did manage to put a couple of capacitors in the wrong way round. (Negative to positive) . I experienced some issues then when trying the preamp as my mistake had damaged the two new capacitors. A couple of emails to Stefaan in Dada support sorted that confusion out, and when I refitted the new Capacitors (which I re-ordered from Dada) the preamp worked like a dream and that “dull” sound was replaced with much more transparency.

Success lead me to want to do all the 33 modifications in the kit (except the reduction in input sensitivity since I use an Fm3 Tuner). The biggest problem I then experienced was coming across slight variations in board layout of the Disc Pre Amplifier Board M12019 (issue 4) and Tape Adapter Board M12027. Since I cannot read a circuit diagram yet or don't actually really know what the components even do yet, I was stuck.

The instructions from Dada are very good, but a few colour photographs of finished boards would have helped me. I found a site online where someone had completed the Dada mods on his 33/303, and using his pictures of finished boards that had the same layout as mine, I was able to work out the placement of a couple of components. I then took photos of my completed boards and sent them to Stefaan at Dada to make sure I had not made any silly mistakes. (I enclose my pictures of those two boards after modification)

The end result is that I now have an extremely good sounding preamp that cost relatively little, and looks perfectly in keeping with the rest of my equipment. It took the 33 from not really usable to very good, and I do trust my ears! At the same time I am learning more about electronics, and feeling more confident that I can service my own Quad amps in future. That saves me money, gets me a better sound, and gives me a feeling of personal contentment. I will do more Dada mods to my other amps, why not, it was rewarding, not too expensive and sounds great.
Ivor

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