Post by Owen Y on Jun 22, 2020 20:23:44 GMT 12
In 2007, I built these 2A3 triode Push Pull amps - & have been using them ever since. Around 6 years earlier, after discovering & then building Single Ended Triode (SET) amps (300B, 2A3, 46), I settled on the 2A3 SET used in a Push-Pull topology, as suiting my set-up & tastes well. Output is around 10 Wpc at ~0.4V input sensitivity. They suit my very sensitive horn speakers well, I think & to me, it's combining a lot of the sound qualities 'directly heated' triodes, with the extra power output & better damping factor (bass control) of Push-Pull. However, you never stop learning in this game  & there are a number of things that I'd do differently now.... 
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Post by Owen Y on Jun 23, 2020 16:36:11 GMT 12
Firstly, instead of 2 x 'monoblock' L + R ch amps, I should have built these as 1 x stereo amp + 1 x PSU chassis. It is common audiophile 'wisdom', to separate L & R ch's at all costs, everything should be built 'dual-mono'. But it makes more engineering sense to physically separate the noisy AC components from the signal circuit. Especially. with v high sensitivity loudspeakers & high voltage/high impedance tube circuitry, noise is hard to eliminate. Presently, I have the PSU AC components (power transformer, filament transformers, rectifier, smoothing chokes, all housed inside each amp chassis. What I will try to co-configure now, is to re-house all the AC power components into an outboard chassis (or two), with umbilicals supplying the existing amp signal circuit boxes.  (The extraneous loose white wires, around the bottom/rear OPT, are a Negative Feedback experimental connection.)
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Post by sadface on Jun 23, 2020 18:47:49 GMT 12
Cool stuff!
I will admit that I am very much all about that dual mono stuff....
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Post by colinf on Jun 23, 2020 18:49:22 GMT 12
Dual mono separates the grounds and chassis of the two channels and makes the sound more open in a way that integrated channel grounding and enclosures can’t. I always prefer dual grounding to stereo grounding if you can afford to do it, over the extra expense of a separate power supply, if cost is a concern. But to separate the power supply physically is good as well, but watch for extra RF ingress via the power supply cable. So both dual mono and separate power supplies is good, have fun!
AMR-iFi R&D
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Post by cartridgeguyonline on Jun 24, 2020 7:13:36 GMT 12
Plus it keeps the box count up !
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Post by snewt on Jun 24, 2020 7:29:01 GMT 12
Just what I was thinking! And your boxes are nicer than mine 😉 
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Post by cartridgeguyonline on Jun 24, 2020 8:20:57 GMT 12
Go on: That looks like a proper enthusiasts set up doesnt it! Bet that scares away the women and children....
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Post by Owen Y on Jun 24, 2020 11:40:05 GMT 12
colinf - I usually build with a separate Gnd bus for ea signal cct, connected at input socket. A downside with outboard PSU, I found, is that the signal Gnd needs to go back to the PSU chassis (via the umbilical). snewt - that pic of my amp above, was taken by your Dad I think 
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Post by Owen Y on Jun 24, 2020 17:07:52 GMT 12
The above amp was designed by a remarkable Japanese builder Valve's World (Tossie), who appears to have designed & made (& sold) many, many valve amps. This is the schematic (with my notes): 
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Post by Owen Y on Jun 24, 2020 17:30:48 GMT 12
Another error I made initially, was to use a 'traditional' high value input load resistance of 510k ohms (as in my Leak Stereo 20 amplier). This, together with the interconnect cable capacitance (~50pF) results in HF roll-off, way down at 6kHz (-3dB). After loading down 91k ohms, HF bandwidth should be up at 35kHz (-3dB). And indeed, much improved HF tone, 'shine', 'leading edges' & faster transients - also, improved bass 'power' (a phenomenon that often occurs, improved HF level seems to also enhance bass impact, bass harmonics).
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Post by snewt on Jun 24, 2020 18:36:11 GMT 12
Go on: That looks like a proper enthusiasts set up doesnt it! Bet that scares away the women and children.... Can't say my wife loves it.🙄 But she loves me so I get away with it 😉
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Post by snewt on Jun 24, 2020 18:42:35 GMT 12
snewt - that pic of my amp above, was taken by your Dad I think That's nice to know, Owen, thanks. I love following your diy projects by the way; you do such a nice job.
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& there are a number of things that I'd do differently now....
