erik2A3 Posted January 2, 2015 Share Posted January 2, 2015 (edited) Mark I'm always working on something of some sort. I recently put together the Transcendent Sound phono stage for one of of my systems, and have been simultaneously rebuilding a fully direct-coupled single ended 2a3 stereo amp designed by Craig Uthus of Moth Audio (reformed under a new name, Eddie Current). It's an extraordinarily simple circuit that uses paralled 6SL7s for voltage gain, direct coupled to the output triode. His design incorporated regulated DC on both input and output stage filaments, however, after some experimentation, continue to prefer AC heating over DC despite its unavoidable but mild 60hz hum from the 2a3's directly heated cathode/filament. Despite these changes, which includes some alteration in the power supply, the actual signal circuitry is totally by Uthus. The amp sounds enormous for a low power triode. Some Of that is the result of heavy cathode resistor bypassing on the input stage, as in the range of 470uf, but I am using very low impedance Panasonic electrolytics in those positions. The Transcendent Sound phono stage (MM) is so good I want to scratch build another, with some small changes in the power supply just to take advantage of parts I already have on hand -- all of which will be installed in a common Bud box or cake tin like the old days! Edited for spelling/typo errors...I found my glasses! Edited January 2, 2015 by erik2A3 Quote Link to comment Share on other sites More sharing options...
Wardsweb Posted January 2, 2015 Author Share Posted January 2, 2015 Mark I'm always working on something of some sort. I recently put together the Transcendent Sound phono stage for one of of my systems, and have been simultaneously rebuilding a fully direct-coupled single ended 2a3 stereo amp designed by Craig Uthus of Moth Audi (reformed under a new name, Eddie Current). It's an extraordinarily simple circuit that uses paralled 6SL7s for voltage gain, direct coupled to the output triode. His design incorporated regulated DC on both inout and output stage filaments, however, after some experimentation, continue to prefer AC heating over DC despite its a unavoidable but mild 60hz hum from the 2a3's directly heated cathode/filament. Despite these changes, which includes some alteration in the power supply, the actual signal circuitry is totally by Uthus. The amp sounds enormous for a low power triode. Somemof that is the result of heavy cathode resistor bypassing on theninput stage, as in something 470uf, but I am using very low impedance Panasonic electrolytics in those positions. The Transcendent Sound phono stage (MM) is so good I want to scratch build another, with some small changes in the power supply just to take advantage of parts I already have on hand -- all of which will be installed in a common Bud box or cake tin like the old days! Erik care to share some info on your phono stage build? I'm in the market for a phono stage project now that I have the linestage and amp done. Quote Link to comment Share on other sites More sharing options...
erik2A3 Posted January 3, 2015 Share Posted January 3, 2015 (edited) Mark, I had to smile while reading about your thoughts on class D amps. I say this because several months ago I bought one from a guy locally -- very cheap, $25 I think. I don't remember the brand, but was one of the Chinese offerings. It was not much bigger than a pack of cards, and was good for about 20 watts into 8 ohms. I went from our squeezebox Touch straight into the amp and from there to La Scalas .... And was simply floored. Honestly. No gigantic OPTs and power trannies, no mega-buck boutique coupling capacitors, and for $25 could not believe what I was hearing. I told an audio friend the thing was so good I was tempted to dig a whole in the back yard and bury it so I might just forget the whole thing. Terrifically efficient compared to some of the class A valve amps I've built, particulaly one OTL I can think of that becomes too hot to touch (literally) all for 1.5 watts (they are very good sounding 1.5 watts though!). I sent my friend the amp to try, and he adored it....until one day it stopped working. I told him to just throw it away LOL! I completely understand your interest in this! One could put a small monoblock module inside a la scala, heresy, Cornwall, whatever, and have a very decent active system. Edit: thinking back on this, I got that little amp more than a year ago. Too much going on, time going by too quickly. I've since purchased another from Parts Express. Great sounding little thing, but has an inherent POP from an arcing power switch. Small cap across contacts should help that. Edited January 3, 2015 by erik2A3 Quote Link to comment Share on other sites More sharing options...
Wardsweb Posted January 3, 2015 Author Share Posted January 3, 2015 We all seem to be venturing into the world of digital. I now have four of my systems that have streaming digital as a source. XP machine running JRiver pulling from an internal 2T drive with USB out to a M1DAC, a laptop running Windows Media pulling from a 1T USB drive with 3.5 out to my new linestage, XP machine running Foobar2000 pulling from an internal 500G drive feeding a Winesome Labs Mouse tri-path amp and a Olive Opus 3HD server feeding a Vincent integrated. Quote Link to comment Share on other sites More sharing options...
erik2A3 Posted January 3, 2015 Share Posted January 3, 2015 Streaming is convenient; we use it regulalrly for informal background music. Under good conditions, as you outlined, it can be great as a primary source too. BTW, please know my comment about really expensive capacitors (I have some in a few amps too!) was not at all in reference to the Jupiter output capacitors in your beautiful new preamp. What I said was just to help illustrate how this tiny digital amplifier could sound so ridiculously good at its price point. TS phono stage: a 6 tube kit product complete with all parts and chassis from OTL designer Bruce Rozenblit. See at: www.transcendentsound.com 1 Quote Link to comment Share on other sites More sharing options...
Wardsweb Posted January 4, 2015 Author Share Posted January 4, 2015 Thanks for the info. I am still in research mode for a tube phono I can scratch build or worse case boards I can fit in a custom chassis but P2P is my preference. Thanks again. Quote Link to comment Share on other sites More sharing options...
erik2A3 Posted January 4, 2015 Share Posted January 4, 2015 Absolutely point to point. Better still, sans separate terminal strips for passive parts. Wire resistors and caps directly to tube pins, even though it may not look as clean and orderly. One gets the benefit of shorter lengths of wire. Quote Link to comment Share on other sites More sharing options...
Wardsweb Posted January 5, 2015 Author Share Posted January 5, 2015 (edited) Absolutely point to point. Better still, sans separate terminal strips for passive parts. Wire resistors and caps directly to tube pins, even though it may not look as clean and orderly. One gets the benefit of shorter lengths of wire. I totally get that. The 2A3 in this system I built that exact way. It isn't as clean as the linestage, but then, I've learned a few things in the 12 years since I built it. Edited January 5, 2015 by Wardsweb Quote Link to comment Share on other sites More sharing options...
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