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12AX7 Tube Preamplifier Kit

Mark Houston    Australia Flag     To email Mark, type out the email address.

Page 1: Introduction, 12AX7 Valve Preamp, Kit Assembly
Page 2: Enclosure, Sound
Page 3: Measurements
Page 4: More Photographs


Enclosure Construction

Pure silver wire was used from the RCA jacks and potentiometer into the preamp. The black material in Photograph 04 is vinyl dampening material glued in and under the case to get it as quiet as possible. I also added a ferrite choke around the power supply leads to the preamp section.

Inside the 12AX7 Preamp Enclosure
Photograph 04 - Inside the Enclosure


Sound - 12AX7 Tube Preamp Kit

I have built a small handful of these kits and I got a number of listening sessions in along the way. Prior to building the enclosure, I tried the preamp with the NAD C542 and the LM3875 monoblocks. It was evident on the first listening that this was exactly what was required to restore the full passion of the performance. This made for a very nice combination, beautiful valve tones, a more convincing performance and the power, speed and clarity of the LM3875 chip amps. I knew I was on the right track.

I promptly took the uncased preamp to a friend's house for another listening test with his gear. He has a Harman Kardon CD player, English design Classic 80W amp and large bookshelf speakers. We played a number of tracks with and without the preamp in place and both agreed his whole system sounded stacks better with the preamp. He like the preamp so much, he ordered one on the spot!

I'm convinced now about the benefits of a preamp, but it must be chosen to fit with the rest of the system.

Finished 12AX7 Preamplifier Enclosure
Photograph 05 - Finished 12AX7 Preamplifier Enclosure


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Introduction, 12AX7 Valve Preamp, Kit Assembly
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Measurements