Another DIY SS Amplifier with NVA Boards

[SteveTheShadow]

The twin carb version then.

[SteveTheShadow]

Anyway, what has been bugging me for a while with this amp is that the output stage has a higher voltage transformer than the input/driver stage, which I’ve realised is a bit pointless as this isn’t a valve amp. The output stage (current amp) can only produce as much current as the swing of the driver stage (voltage amp) will allow it to, so having the output stage at higher voltage is a waste of electricity if the driver is going to bash into its own rails first.

I was going to remove both transformers and install a 30-0-30 for the driver and a 25-0-25 for the output stage, but both the damn’ things together were too big to fit in the case. The compromise was to keep the 120VA, 25-0-25V on the VAS and driver stage and simply fit a 300VA, 25-0-25V to the output stage PSU.

It turns out that both power supplies produce exactly +/- 37V when under load, which is nice, as if the output rails sag under duress, below 37V, the driver rails will stay up courtesy of their own PSU.

[SteveTheShadow]

New 300VA, 25-0-25V toroid at bottom right:

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Whilst I was at it, I removed the crap quality shielded input cables going to the selector and replaced them with simple straight wires.

I find loads of these blue/yellow twisted pairs lying around next to BT street cabinets when I’m out walking. I found a metre of it the other day due to the engineers not cleaning up after themselves. Shame to let it go to waste. The 0.5mm jumper wire makes good signal wire and my old BT Lindstrom long nose pliers strip it perfectly.

[SteveTheShadow]

Revised power supply voltages:

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[SteveTheShadow]

Really pleased with this now. Lovely relaxed, detailed and dynamic presentation and even better now I have my Musical Fidelity M1 DAC in circuit.

The M1 always sounded a bit hi-fi and soulless with my valve amps and the earlier versions of this amp too. However, now the NVA clone (still not sure what to call this thing) has been souped up beyond recognition, the DAC is now being allowed (by the amplification) to give of its best. We now have hi-fi AND all the music. A fine result I'd say.

I can't remember ever pulling off a stunt like this with any of my past systems. I now really do 'get' where Richard was coming from with this circuit. He wasn't going to tell me how to get the best out of the boards, he wanted me to FO, FO and learn something. I've certainly had to embark on a bit of a journey. Fecking brilliant!

[r3xj0hn570n]

Nice. There are technical reasons why the driver stage should be driven from a higher voltage than the output stage. Not sure they apply to a darlington output setup, i'd have to think, and my brain seems to be offline.

[SteveTheShadow]

I think we can now call this project finished.
I tried three power supplies to the boards but it was more trouble than it was worth. However I decided to keep the three supplies and instead, feed the built in NVA Phono1 board with the supply fed by the toroid mounted vertically on the back panel.

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I’ve carried out several more mods to the NVA amplifier circuits themselves but I won’t go into those. Sounds fantastic. Knocks my valve amp into a cocked hat. What a result!

[Daniel Quinn]

There is no difference between a phono 1 and phono 2 board. . The difference is the va of the transformer .

So you can call yours simply NVA inspired phono amp

[SteveTheShadow]

I haven’t modded the phono board. It’s simply an NVA board built into an integrated amp.

[SteveTheShadow]

Power supplies:

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