Building a DIY amp with NVA amplifier boards

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Radio_Free
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Re: Building a DIY amp with NVA amplifier boards

Unread post by Radio_Free »

Yes, I agree with you.
Never my intent to change the original design as I’m already very pleased with the amp as it is. Just exploring simple ways to have small improvement on the PSU whenever possible. Not looking at any reconstruction or whatsoever.
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karatestu (Sun Sep 25, 2022 10:49 am)

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Re: Building a DIY amp with NVA amplifier boards

Unread post by karatestu »

Decoupling the output stage did turn out to be beneficial with the Naim amps I butchered. That may not be the case with nva however. Only you can decide. I once regulated the front end of the nva boards. It didn't sound wrong but I can't remember exactly how it sounded, better or worse.

The 0V (ground) arrangement is the hard bit. Most people believe in star grounding. NVA is a little different.
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Re: Building a DIY amp with NVA amplifier boards

Unread post by karatestu »

Being playing with the amplifiers again :roll: Why can't he leave the bloody things alone ? Well you know how it is. :grin:

When I set up this six channel integrated with remote power supply I did several things that I meant to review and revisit at a later date. Well that date has arrived.

Firstly I routed the speaker returns ( usually referred to negative for some reason) to the head unit where all the amp boards are. I knew that they really should go back close to the centre tap of the transformer. It's one big current loop after all. So this was done and it is has turned out to be sonically superior as I suspected.

Secondly, I had my power amp boards one metre of wire away from the smoothing capacitors. At the time I couldn't be bothered to put a last capacitor near the amp boards. Finally i decided to do it - about bloody time.

I got eight Kendeil 10,000 uf caps from my stash and wired them in as close as I could get them to the power transistors. Two centimeters wire from cap terminal to amp board. Couldn't get that any shorter without soldering them directly to the power rail :grin: . Joined the two caps required for each board and in the centre added a wire to the 0v post. Did this for four of the six amp boards as two aren't required for these speakers.

Image

Now got 40,000uf in line with each power rail, eight of these in total. It's impossible to say what did what as I added local reservoir caps and upped the capacitance on each rail by 10,00uf at the same time. Suffice to say that these two things have made a major improvement. A bit more dirt removed from the musical window.

I need to split the front and back ends again at some point as it has been quite a while since I last did it. That will require another eight psu caps next to the front ends. I have enough 6,800uf kendeils to do that. All bought from Les at Avondale Audio in 2016 and hardly used . I reform them by bringing them up to voltage slowly with my variac.

I seem to be breeding psu's again after simplifying things a while back. Hey ho.

More to come, I've been saving these mods up :grin:
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Re: Building a DIY amp with NVA amplifier boards

Unread post by Latteman »

Let me get this straight
The additional caps wired to the board are supporting those already supplying power to the boards via the +brown & -blue and don’t actually have a direct link to the psu bridge rectifier via cables
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karatestu (Thu Feb 02, 2023 6:56 am)
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Re: Building a DIY amp with NVA amplifier boards

Unread post by karatestu »

Latteman wrote: Wed Feb 01, 2023 8:50 pm Let me get this straight
The additional caps wired to the board are supporting those already supplying power to the boards via the +brown & -blue and don’t actually have a direct link to the psu bridge rectifier via cables
Yes and no. Follow the neg and pos wires back and they do connect directly to the rectifier diodes. All power supply smoothing caps / reservoir caps are essentially decoupling caps - shunting noise to ground and providing current. Coupling caps are different as they are wired in series not shunting to 0V (ground).

Not being an EE it is hard for me to describe. Let's just say the incoming dc from the remote psu does not have to be wired directly to the capacitor terminal.

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Re: Building a DIY amp with NVA amplifier boards

Unread post by karatestu »

Next experiment involves star earthing. Doc did not like star earthing. Not sure why apart from maybe it was too much like what Naim did :lol:

Most 0V returns are referenced to a star point where they meet. In Naim equipment this was done in the preamp .

I will be using this thing which I made years ago. Copper sheet with lines cut into it with a dremell.

Image

Needs some tidying up but provides 14 separate 0V returns. Power amps require four, the three source inputs require six, volume control requires two. I make that 12 in total. When I go back to splitting the front and back end of the power amps then I need another four. So require two more than I have. Might have to drill some more holes .

This star will sit central to all four power amp boards, possibly on top of the volume control. That will give short wires to each apart from the sources of course which are at the other end of an interconnect. Signal 0V is usually joined to mains earth at one point only. I have always done it in the CD player as Naim do but for the last few years I have had it disconnected so essentially floating.
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Re: Building a DIY amp with NVA amplifier boards

Unread post by Geoff.R.G »

karatestu wrote: Thu Feb 02, 2023 2:48 pm Next experiment involves star earthing. Doc did not like star earthing. Not sure why apart from maybe it was too much like what Naim did :lol:

Most 0V returns are referenced to a star point where they meet. In Naim equipment this was done in the preamp .

I will be using this thing which I made years ago. Copper sheet with lines cut into it with a dremell.

Image

Needs some tidying up but provides 14 separate 0V returns. Power amps require four, the three source inputs require six, volume control requires two. I make that 12 in total. When I go back to splitting the front and back end of the power amps then I need another four. So require two more than I have. Might have to drill some more holes .

This star will sit central to all four power amp boards, possibly on top of the volume control. That will give short wires to each apart from the sources of course which are at the other end of an interconnect. Signal 0V is usually joined to mains earth at one point only. I have always done it in the CD player as Naim do but for the last few years I have had it disconnected so essentially floating.
Stu, what you are doing is trying to solve what in professional audio is known as “the pin 1 problem”. It relates to the resistance between a supposed ground and actual ground potential. In mixers a resistance between a channel ground and the 0V point causes cross talk. In aircraft audio select systems a high resistance can become a significant problem. In both pro-audio and aircraft the distance between the ground point and true earth (0V) can be sufficient that a usable (measurable) and audible signal can be developed. In a domestic amplifier simply using thicker wire should be sufficient to get the resistance down to a value that prevents an audible signal.
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karatestu (Sat Feb 04, 2023 8:21 am)

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Re: Building a DIY amp with NVA amplifier boards

Unread post by karatestu »

Geoff.R.G wrote: Fri Feb 03, 2023 11:38 pm
Stu, what you are doing is trying to solve what in professional audio is known as “the pin 1 problem”. It relates to the resistance between a supposed ground and actual ground potential. In mixers a resistance between a channel ground and the 0V point causes cross talk. In aircraft audio select systems a high resistance can become a significant problem. In both pro-audio and aircraft the distance between the ground point and true earth (0V) can be sufficient that a usable (measurable) and audible signal can be developed. In a domestic amplifier simply using thicker wire should be sufficient to get the resistance down to a value that prevents an audible signal.
Hello Geoff. I'm glad we have somebody here (and Rex) who actually knows what they are talking about :grin: I'm one of those dreaded diy audio electronics bodger monkeys. No formal education in electrons and at first learn by the means of "monkey see monkey do". This develops over time into a confidence to try out all sorts of things without actually knowing what they are doing. :grin:

I was aware of what you say but grounding is still a bit of a black art as far as I'm concerned. Current flows in loops and usually the aim is to keep that loop as short and closed as possible. Twisting wires together comes in here but then you find people like RD who never did any of that and still produced hum free product .

You've got to know where these loops are to be able reference the earth in the right place. Don't want to induce a voltage thaf shouldn't be there.,Then you have signal grounds and power grounds which should be kept separate for as long as possible . I suppose the main star is where they all come together.

No star ground in NVA gear and the grounding arrangement is very different to the ways I learned bodging Naim and Avondale equipment back in the late 2000's. Every day is a school day.
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TheRealAleman (Sat Feb 04, 2023 9:14 am)
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Re: Building a DIY amp with NVA amplifier boards

Unread post by r3xj0hn570n »

No-one is perfect, let alone me. I think of the layouts in a typical amp this way, and let me be clear, i could be wrong.

Input. That first transistor is amplifying the difference between it's base and however it's emitter is connected to ground. The input ground should be shielding (or twisted around) the signal wire all the way to that point, not the bus bar or any star ground point.

Output. Current is coming from the PSU caps. They should be the central point of any star ground or the middle of your bus-bar.
How you connect each stage to this star point probably won't make much difference, as long as the impedance is low enough.

Seeing as you've got capacitance all over the place (you should have bleeders in each group BTW), choose whichever is closest to the output transistors.

Cheers, Rex
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karatestu (Mon Feb 06, 2023 6:09 am)

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Re: Building a DIY amp with NVA amplifier boards

Unread post by karatestu »

r3xj0hn570n wrote: Mon Feb 06, 2023 3:24 am No-one is perfect, let alone me. I think of the layouts in a typical amp this way, and let me be clear, i could be wrong.

Input. That first transistor is amplifying the difference between it's base and however it's emitter is connected to ground. The input ground should be shielding (or twisted around) the signal wire all the way to that point, not the bus bar or any star ground point.

Output. Current is coming from the PSU caps. They should be the central point of any star ground or the middle of your bus-bar.
How you connect each stage to this star point probably won't make much difference, as long as the impedance is low enough.

Seeing as you've got capacitance all over the place (you should have bleeders in each group BTW), choose whichever is closest to the output transistors.

Cheers, Rex
Thanks for your thoughts Rex.

"you've got capacitance all over the place" :grin: - just 30,000uf next to the transformer and rectifier then one metre of wire then another 10,000 uf as close to the board as possible. I have now split the input and output stages so the input stages have big ass caps right at the side of the board .

Same pic as before....

Image

For the input and output stages I now have a curved tinned wire going over the top of the board and connecting thd two caps. I do worry this is not optimal and that the bus bar between them should be as short as possible. You mostly see psu caps very close together with a short link between. Do you have any thoughts on that Rex ?

You mention bleeders (discharge resistor to ground) in each group :grin: - do you recommend this just for safety reasons ? What resistance and wattage do you suggest ? I believe that the value shouldn't be too low as it wastes power during normal use but obviously the higher the resistance the longed it takes to discharge the caps. By the way, I always discharge them with a 60w lamp before messing about with them. With the speakers connected (4 ohm load) I always find they have all discharged apart from the output stage positive rail overnight.

Thanks, Stu
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