Another DIY SS Amplifier with NVA Boards

[SteveTheShadow]

Thinking yesterday about recently departed Richard Dunn, I decided to bring my NVA A60 clone out of hibernation and tidy up the rat’s nest of an interior.

Parts of the bus bar grounding system were replaced with new, because the existing was so covered in solder blobs and lethal wiry spikes it was frankly a disgrace. The outputs of the supplies to the circuit board power rails were uprated to 17 Amp wire. I also binned the motley collection of cap bypasses and took it all back to basics.

I also took the time to upgrade my P20 passive control unit by fitting a TOCOS 10K log pot and converting it to take 3 inputs, simply by moving the reference washer on the selector switch to number “3” and wiring the “direct” input to the newly created position. So now there is no source direct facility, but the extra input makes more sense and is more valuable to me.

It’s as quiet as the grave when idling, which it ought to be, but the last iteration was not as quiet because I was basically crap at SS power supplies, which gave Richard much amusement. I’m not that clever at SS even now but I’m starting to get there (I think).

[karatestu]

So have you changed your mind Steve and it is more to your liking without psu bypass caps ?

[SteveTheShadow]

No, its better with bypasses, but the ones in there were in a right fecking state; real scrapbox shite. So the plan is to avail myself of some new ones.

[karatestu]

No, its better with bypasses, but the ones in there were in a right fecking state; real scrapbox shite. So the plan is to avail myself of some new ones.

Oh, i see. Carry on up the bypass.

[SteveTheShadow]

No, its better with bypasses, but the ones in there were in a right fecking state; real scrapbox shite. So the plan is to avail myself of some new ones.

Oh, i see. Carry on up the bypass.

Interesting to listen to this alongside the OTL. Pure OTL treble aside the NVA clone is not that far behind in that department but the dynamism is far superior, which it ought to be given the flea power of the OTL. I love both types of presentation, but the NVA has the boogie factor down pat.

[Latteman]

Interesting post- must read it all but a quick question- what are the purpose of the bypass- tanks
I think the wire change is a good start for me on my A60

[karatestu]

Interesting post- must read it all but a quick question- what are the purpose of the bypass- tanks
I think the wire change is a good start for me on my A60

They filter out power supply crap at higher frequencies than the larger caps

[SteveTheShadow]

Tried some new power supply bypass caps, but have removed them as they just didn’t work. Last time I used bypasses, they did work, go figure, but also last time, the busbar and general “dirty end” arrangement was different to what it is now. This time however upon removing the bypasses, I have cleaned up the busbars where the bypasses were rather than simply cutting off the leads. Tidiness doncha know.

Maybe it’s a characteristic of Richard’s circuit, but adding anything other than what is essential to make the things function seems to result in a retrograde step in terms of sound quality. Maybe also, the 10,000uF, SuperTech slit-foil power supply capacitors, I bought from Hi-Fi Collective last year, simply don’t need bypasses on them.

I know Richard was of that opinion as he told me last year, that he’d tried Denis Morecroft’s (DNM) original slit-foil electrolytics back in the late ‘80s and had found them excellent sounding without needing to be bypassed. He had however declined to use them in the end, as they had been too expensive at the time. He’d therefore decided to continue to use “normal” PSU caps with film bypasses as the then new slit-foil types would have pushed up his prices too far.

Anyway, the OTL has been put away for the Summer as it was making the room too hot and the missus was complaining. Mind you I can see her point, it was sweltering in the front room the other night.

It’s nice to have more than one amp.

[SteveTheShadow]

Interesting bit of tweakery to the power supply this afternoon:
The power rail capacitors were made up of 16800uF; each rail consisting of a 10,000uF Supertech slit-foil combined with 6800uF of “normal” Samwaha “Audio Grade” electrolytic.

So this afternoon, I removed the 6800uF Samwahas from each rail, leaving just a single 10000uF slit-foiler per side. The result has been quite lovely. The treble performance of the A60 clone has improved to such an extent, that it rivals my OTL amplifier. I didn’t expect this, but I’ll take it nonetheless.

The Supertech slit-foil caps themselves, are modern versions of Denis Morecroft’s originals and are a joint venture between Morecroft and Supertech. They are the best power supply caps I’ve heard, for transistor amps, but what do I know? This A60 clone is the only transistor amp I’ve ever put a power supply to.

link https://www.hificollective.co.uk/compon ... itors.html

I’m starting to wonder what the four-terminal versions will do.

link https://www.hificollective.co.uk/compon ... itors.html

[karatestu]