Ultimate amps for the ultimate loudspeaker

Upgrading for better sound
I upgraded a 33 preamp by myself. The most difficult part was locating a screwdriver buried under all the stuff on my test bench. I went for the full upgrade: replacing the two main audio output boards, the tape board and the disc amplifier (for LPs) for a total of £156 U.K.  David made sure my upgraded boards included optional, “maximum performance” OPA627AP opamps (miniature amplifier circuitry). The full pre-amp mod also requires a separate, external, plug-in AC power supply. David can suggest a U.S. alternative (120V) to the U.K. version (220V) he lists on his Website.

Updating the 303 power amp was a different story. I changed one of my 303s with a Net Audio power supply board (£50 U.K.). It was easy. But, if you’ve ever seen me wielding a soldering iron you know I shouldn’t try tackling a big job. That’s why I sent my second 303 to Net Audio for a complete overhaul.  He charges £220 U.K. plus shipping.

I wish I could invite all of you to hear how good my hi-fi sounds now. The Net Audio 33 preamp is just plain amazing. Clear, clean and accurate. David has actually improved upon what Quad created 40 years ago by bringing the circuitry into the 21^st century. He was even able to get the old Quad’s disc circuitry to excel using a modern-day moving-coil cartridge (a Reson Aciore sounds fantastic). Overall, to my ears, David's new 33 is one of the best sounding preamplifiers I’ve ever auditioned. 

I also spent a long time listening to both of the modified 303s.  More about that in a minute. First, the power supply-only modded amp. That one had previously been brought up to spec by QS&D, Quad’s U.S. repair agents before I changed anything. 

NET Audio A must for Quad 303 owners.  Net Audio's new power supply board.

I was able to swap-out the original 303 power supply board for the Net Audio replacement. It required un-soldering four wires from the old board and re-soldered them to the new. (For the record, Robin supervised). Total upgrade time was less than five minutes.

The second amp I sent off to David. He performed all the upgraded as listed on his Website and sent it back. Total turnaround time was less than two weeks.

After many extended auditioning sessions I must report that both amps sound great. Different, but great. I agree with David that the simple power supply upgrade is probably the most essential to bring the 303’s sound up to date. The amp with this single board swap is probably one of the best audio bargains on the planet today. It improves upon the 303’s inherent musical qualities and creates an amazingly terrific sounding amp.

NET Audio The beautiful, modern Net Audio faceplate is an optional extra.

The fully modified 303 sounds even more up-to-date and modern.  It greatly improves upon the 303’s high frequency reproduction while maintaining its other good qualities.  After a few months of constant break-in and use, I can happily report that Net Audio’s modifications have been safe and, as far as I can tell, electronically stable.

Here is my recommendation: go for the full upgrade on the 33.  As for the 303, without hesitation, you owe it to yourself to upgrade the power supply board. Do so now.  It makes a huge difference. On the other hand, if you can afford it, the full upgrade will reward you with a detailed, terrific sounding amp.

The value of the dollar is low (when compared to the U.K. pound) so these upgrades are more expensive than they were when I first started on this quest. I figure I spent a little over $1,000 for the modified amplifiers, not including the cost of shipping, which is very reasonable in today's marketplace.

Any way you look at them, the Net Audio upgrades are a comparative bargain. Very, very highly recommended. And music to my ears.

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