Sunday, March 24, 2019

ZenV4, take two

In 2009, Nelson Pass' Penultimate Zen a.k.a. ZenV4 was my first solid state build. I used the parts that were available, did not know much about making it work well, and did not have test instruments beyond a cheap multimeter. Also, I did not have a preamplifier to work with it or speakers sensitive enough to enjoy its 25W. As a result, the amplifier turned out not quite satisfactory and for two years has been gathering dust and my family's complaints. I was thinking about scrapping it and reusing the enclosure for something more useful. Instead, I reworked it.

I removed one of the two power transformers (moving from dual mono to stereo configuration), replaced my original dodgy PSU filter caps with Mundorf M-Lytic HC, replaced internal low voltage wiring with thick speaker wire, reconfigured grounding (so it finally was safe!) and installed balanced inputs with input transformers. What a change in sound! With my Exposure CD player, B1 clone preamp (see a later post) and Heresy III speakers, the amp provided enjoyable listening to Placido Domingo's arias. It also had (some) bass now, which had been sorely missing before. Frankly, I did not expect such a change from apparently minor amendments.

Also, I installed a commercial soft start module, which also provides a pushbutton on/off and works with PTC thermistors to protect the amplifier from overheating.