DIY Transistor Amp Using NVA Boards

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Cressy Snr
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Re: DIY Transistor Amp Using NVA Boards

Post by Cressy Snr » Sat Mar 24, 2018 4:07 pm

Dr Bunsen Honeydew wrote:
Sat Mar 24, 2018 3:32 pm

It would be nice to hear from you the benefits or not, strong points v weak points of the valve v solid state amps as I have very little experience of valve work and what I have goes back to the 60's.

Not asking for a winner.
It's a difficult thing to pin down as the technologies are so different. However what I will say, is that with both technologies it appears to be all about the power supplies. Given properly engineered power supplies it is hard to get a fag paper between the two methods, providing your output transformers are up to the job on the valve side of the equation.
At the high power end of the scale, I would personally find valves hard to justify, but again some people swear by huge transmitter triodes carrying over 1KV on their anodes, and they can be truly awesome sounding, but the expense is frightening!

I find it hard to articulate the differences between valves and transistors, and the experience of both hearing and of building your amps, has made it more difficult still. NVA, Nelson Pass, and Nick's amps don't sound like the stereotypical fizzy treble afflicted amplifiers, us valve lovers, love to hate, so in the silky top end stakes, there is little difference with these manufacturers.

There is a certain warmth and humanity about the presentation of some push-pull pentode and ultralinear valve amps that is beguiling and is a selling point for a lot of people, especially those who were burned by the flat earth bullshit. And having built those kinds of amp, and having myself been severely burned by the aforementioned bullshit, I can see perfectly well where they are coming from.

Low power SETs can be built with more of that warmth, extended down to the bass, if your power supply is inadequate and the driver circuitry is less than great, but a top SET, with a proper power supply and good output transformers has none of that artifice. Nick's 300B amps driven by a 5687 cascade and with his trademark top power supplies are a case in point. The bass performance into efficient speakers is as good as a transistor amp and the rest of the frequency range is clear as a bell. I'd also like to think that my own 2A3 SET with its big power supply and power valve drivers to the output stage, is also like that, though the output transformers could stand an upgrade.

I think, with valves, the interface with the speakers is a bit more of a challenge, but someone other than me would have to explain why and how, as I have bit of knowledge, but not enough to be authoritative.
Last edited by Cressy Snr on Sat Mar 24, 2018 4:18 pm, edited 1 time in total.
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Re: DIY Transistor Amp Using NVA Boards

Post by ed » Sat Mar 24, 2018 4:18 pm

Dr Bunsen Honeydew wrote:
Sat Mar 24, 2018 3:32 pm

It would be nice to hear from you the benefits or not, strong points v weak points of the valve v solid state amps as I have very little experience of valve work and what I have goes back to the 60's.

Not asking for a winner.
I have found this akin to chasing smoke.
You also may be asking the wrong people here because emotional investment is present here and it's a trixy little blighter when it gets in the way.

Personally I've found it much easier to differentiate between valves and bjt amps and not so easy between valves and fets....but thats a perfect example of emotional investment......

this one has run for ages, and to my mind will run forever.
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Re: DIY Transistor Amp Using NVA Boards

Post by Nick » Sat Mar 24, 2018 4:33 pm

I think, with valves, the interface with the speakers is a bit more of a challenge, but someone other than me would have to explain why and how, as I have bit of knowledge, but not enough to be authoritative.
Well, simply put valves are high impedance devices, loudspeakers are low impedance ones. It all comes from that.
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Re: DIY Transistor Amp Using NVA Boards

Post by Dave the bass » Sat Mar 24, 2018 7:50 pm

Nick wrote:
Sat Mar 24, 2018 4:33 pm
Well, simply put valves are high impedance devices, loudspeakers are low impedance ones. It all comes from that.
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Transformers..... :)

The path is well trodden yes?
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Re: DIY Transistor Amp Using NVA Boards

Post by Nick » Sat Mar 24, 2018 8:47 pm

Dave the bass wrote:
Sat Mar 24, 2018 7:50 pm
Nick wrote:
Sat Mar 24, 2018 4:33 pm
Well, simply put valves are high impedance devices, loudspeakers are low impedance ones. It all comes from that.
Image

Transformers..... :)

The path is well trodden yes?
Yes, very. The problem is that for a real world transformer, getting the mythical 20Hz to 20kHz at the same time as low output impedance and highish power transfer is far from easy. Any one of those requirements complicates at least one of the remaining ones.

However if we are ok with low power, and not too worried about output impedance ie low power high efficiency single driver speakers, then it all gets a lot simpler.
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Re: DIY Transistor Amp Using NVA Boards

Post by Nick » Sat Mar 24, 2018 8:53 pm

And conversely the things that low power SET's do very well is very hard to get solid state to do unless you start to mimic SET topology in silicon, but you still have non linear input capacitance and memory effects to deal with neither of which exist in the valve world.
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Re: DIY Transistor Amp Using NVA Boards

Post by Nick » Sat Mar 24, 2018 8:58 pm

I am looking forward to hearing these amps at Owston, as I have repeatedly failed to get the sound I am looking for with anywhere near that few components and silicon.
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Re: DIY Transistor Amp Using NVA Boards

Post by Thermionic Idler » Sat Mar 24, 2018 11:58 pm

And then there are insane nutters like me who decided the whole output transformer question was too hard and went down the OTL path, though admittedly one well trodden by people who know what they're doing (Rozenblit).

The whole concept of OTL is wrong on so many levels but I've yet to hear anything I like better. I've had the lowish power OTL working reliably in my system for years. One day I might get the higher powered behemoths finished...
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Re: DIY Transistor Amp Using NVA Boards

Post by Nick » Sun Mar 25, 2018 2:04 am

Thermionic Idler wrote:
Sat Mar 24, 2018 11:58 pm
And then there are insane nutters like me who decided the whole output transformer question was too hard and went down the OTL path, though admittedly one well trodden by people who know what they're doing (Rozenblit).

The whole concept of OTL is wrong on so many levels but I've yet to hear anything I like better. I've had the lowish power OTL working reliably in my system for years. One day I might get the higher powered behemoths finished...
Yes, agreed, I have head some good sounds from OTL's
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Re: DIY Transistor Amp Using NVA Boards

Post by Mike H » Sun Mar 25, 2018 3:48 pm

Dave the bass wrote:
Sat Mar 24, 2018 7:50 pm
Nick wrote:
Sat Mar 24, 2018 4:33 pm
Well, simply put valves are high impedance devices, loudspeakers are low impedance ones. It all comes from that.
Image

Transformers..... :)

The path is well trodden yes?
Image
 
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Re: DIY Transistor Amp Using NVA Boards

Post by ed » Sun Mar 25, 2018 5:47 pm

Dr Bunsen Honeydew wrote:
Sat Mar 24, 2018 3:32 pm

It would be nice to hear from you the benefits or not, strong points v weak points of the valve v solid state amps as I have very little experience of valve work and what I have goes back to the 60's.

Not asking for a winner.
A point which I missed in my earlier reply is the cost factor, firmly in favour of solid state.

Having lost my entire pension fund in 2012(oh waily), the cost of transformers, chokes and replacement valves scares the pants off me. The valve parts and kit that I have doesn't impress me any more than the SS stuff I have so I would have to embark on new/different valve projects to improve the balance. That doesn't seem likely, so all future investigations/projects are likely to be solid state...

Anyway, as most of you know, my recent preferences have been in that direction anyway

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Re: DIY Transistor Amp Using NVA Boards

Post by Cressy Snr » Sun Mar 25, 2018 7:42 pm

ed wrote:
Sun Mar 25, 2018 5:47 pm
A point which I missed in my earlier reply is the cost factor, firmly in favour of solid state.
You're right there Ed.
Having built with the Doc's boards, even taking in the cost of cases and heatsinks, which will come in again when I upgrade the things to a higher power regime sometime in the future, the cost/performance ratio is still very much in favour of the solid state option.

My 2A3 SET is plenty good enough for me as it, in conjunction with my speakers, has hit the sound that is in my head. I doubt very much whether I'll be building anything else of a hollow state nature, as I'm now on a budget, and speakers, omni and conventional, using good value drivers will be my main focus going forward.

The Doc's amps are the other half of my listening pleasure equation, giving more power whilst retaining the sweetness of the SET. There's nothing not to like and as Stu knows how to go about getting the best possible sound out of the boards, there's more performance to be had for not a lot of dosh in comparison to what it would cost to obtain a similar jump in performance from valves. All I need to do is ask Stu, or Richard if he's not busy about how to get more out of the boards.

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Re: DIY Transistor Amp Using NVA Boards

Post by karatestu » Mon Mar 26, 2018 7:52 pm

Hi Steve, glad you are as happy as a pig in......

Getting more from the boards? I think the way to go is add a dedicated psu for the front end. Oh and the biggest transformers (VA) you can manage. I like to keep the transformers as far away from the boards as is practical without making the charging loop too big (from transformer to rectifier to caps and back to transformer).

The tinned solid copper wire is obviously good stuff as Richard would not use it and I cant be bothered to try anything else. I have used 2mm for everything apart from the signal in which is solid silver. Getting the 0V configuration right is important although I am new to this bus bar type approach. Bodging Naim for a lot of years has not helped and I need to forget the star earthing style that they used :roll: Spacing wires apart instead of running in looms or twisting is also new to me but I am doing it automatically all the time now. Cant put tinned wire in a loom or twist anyway :lol:

I am just about to swap out my 200VA 28-0-28 transformers on the output stages for a couple of 340VA 35-0-35 custom made jobs that I use on my other amps. I have EI transformers on the input stages at the moment and I am really enjoying what they are doing. The Doc prefers toroids and I am sure he will be rolling his eyes at the thought. I have only 6,600 uf on the output stages at the moment (three 2,200 uf in parallel) and they have very low value inductors in between. I will be swapping them out for MBR20200CT schottky rectifier diodes and two 6,800uf caps per rail (because I already have them). See what difference that makes.

Stu
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Re: DIY Transistor Amp Using NVA Boards

Post by Cressy Snr » Mon Mar 26, 2018 9:49 pm

Cheers Stu.
I've got a 300VA 30V transformer coming, so will remove the existing 25V TX I pressed into service, to get the amp going, and replace it with the new one this week.
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Re: DIY Transistor Amp Using NVA Boards

Post by Neal » Wed Mar 28, 2018 4:02 pm

Good Job Steve!
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