Building a DIY amp with NVA amplifier boards

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karatestu
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Building a DIY amp with NVA amplifier boards

Unread post by karatestu » Tue Feb 27, 2018 10:24 am

After my recent experiment with the removal of amplifier components and other keeping it simple measures the Doc kindly offered to supply me with some genuine NVA power amplifier circuit boards so that I can further my journey in learning and the appreciation of all things NVA. I know of one other HFS member who has also been offered these.

I must make it clear that this is a special dispensation, there is no company policy change at NVA and kits or parts will not be supplied on request. The Doc has done it because we seem to keep him entertained with our DIY projects and he will be getting much amusement at my fumbling around in the alternate universe of NVA power amp design.

I also have invested so much in infrastructure (transformers, caps, rectifiers etc etc) that it did not make sense for me to buy NVA product. Instead I would have continued to modify what I already have. I will still do that, but now I have the opportunity to use NVA power amp boards, compare to what I have got already and publish the results here. Should be good publicity for NVA if I am converted (I know what an AP20 can do :dance: ) and the Doc can have his entertainment and watch the magic smoke as it is let out :lol:

At this point I must thank the Doc for giving me this opportunity, helping with my learning and the continuation of my journey to making my own light sabre. :guiness;

So here is what arrived in the package

Image

A couple of amplifier boards ready made with just the output transistors to solder in and mount to a suitable heatsink.

I have all sorts of transformers, rectifier diodes, smoothing caps, bits of wire and other stuff to make these amplifiers. To start with I have chosen these below

Image

A couple of single secondary, centre tapped toroids from Naim amplifiers :naughty: which are 200VA with a secondary voltage of 27.5-0-27.5. Next up are the schottky rectifier diodes (MBR20200CT) which will rectify the AC to DC. The smoothing caps will be 8 Kendeil 6,800uf 63V with no resistors or inductors between them. That will give me 13,600uf per power rail - enough for the time being and the size of the transformer.

Things I need to sort out;

1) Heat sink - I have 2mm copper sheet or various profiles of aluminium at my disposal
2) Wiring - tinned solid copper wire for DC like the Doc uses, ditto with the 0V wiring, silver of some sort for signal
3) Earth - I am going to closely follow the NVA way with the earth arrangement (VERY IMPORTANT)
4) Layout - I will use similar to NVA amps but with as much distance between the transformer and amp boards as possible. This is really important for me as I have listened to things whilst moving transformers around. The results were plain to hear.
5) Wiring layout - as with the other things I think it is important to follow what the Doc does
6) Cases - who needs cases :grin:

These small transformers and parts will get me started and enable me to try things out and make sure everything works. But the thing is I have other bits and bobs to try and dismiss as appropriate.

1) Transformers - I have some 25-0-25 frame transformers, (2) 500vA twin secondary toroids 27.5-0-27.5 and (4) 350VA single secondary toroids 35-0-35. The last ones may be pushing the voltage to the limits. Plus heat sinking needs to be adequate.
2) I can add more smoothing capacitance as the transformers get bigger.
3) Additional psu's for the separate parts of the amp board. I have enough parts to split off the front end and give it an independent psu (like A80's). In fact I could probably stretch to giving the amp boards four psu's each (think statement range)
4) Regulated front end (LTP and VAS stages). Doc does not do this and probably for good reason. Being the inquisitive type I am going to have to find out for myself what this brings / takes away (pray the magic smoke does not appear) :pray:

Should be an interesting ride :epopc: . There will be no changes what so ever to the amplifier boards as therein lies the magic to the NVA sound and I am not clever enough to work it out. Anyway it works brilliantly so why waste time making it worse / blowing it up. I must learn to forget everything I thought I had learnt already. With other projects on the go don't expect this to be a sprint, more of a marathon :grin:

Stu
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Re: Building a DIY amp with NVA amplifier boards

Unread post by _D_S_J_R_ » Tue Feb 27, 2018 10:46 am

Power supplies are a bit of a black art, even 'simple ones' like NVA use. You can play with transformer capacity (my main amp uses two 120VA 30-0-30 transformers and I should have put these in a separate box so I could experiment) as well as capacitor sizes. I'm not an audiophile type any more, but I found increasing the cap size merely made the amp take longer to stop working after switch-off. Someone listening harder to the 'sound' may find more of a difference, especially in the bass. NVA amps don't usually run warm, let alone 'hot,' so I'm wondering if the Kendeils might be overkill here ;) ? I've played with Doc-donated old DNM slit foil caps and again, I'm damned if I can hear a difference from the standard types...basic ones I've used

I can't speak for buzzy old crap Naim transformers, but the basic ones I've used don't buzz unless severely provoked. Align the wire outlets away from the boards not towards them and if the caps come between them as per NVA, I doubt you'll have any hum whatsoever - . You could always make a two-box amp with the transformers, rectification and main smoothing in one box and the amp boards plus anything else in the second, using umbilicals as per the NVA PSU...

I've never experimented with bridge rectifiers over the ones NVA normally use. Is there extra 'foo' (the term is justified here I believe) with fancy ones in 'audio' circuits where you don't need huge wideband response out to hundreds of kHz?

Not sure if I'm allowed to say, but I believe the signal path up to the drivers is even simpler than the amp looks ;)

I'd better push on and finish the next A20X as it's almost done..

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Re: Building a DIY amp with NVA amplifier boards

Unread post by PhilOesophical_1 » Tue Feb 27, 2018 11:02 am

Hi Stu,
This is my first post here so I hope it’s not a stupid one! I should start by saying thank you for introducing me to this forum. I have learned lots already just by reading and I feel I should also publicly thank you for your help, advice and generosity of time. However, you don’t get off that lightly so here is another question for you.

It seems you have been very much favoured with the opportunity to play with some NVA boards. You mention Earthing the NVA way. For the (semi) uninitiated, what exactly is ‘Earthing the NVA way?’

S

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karatestu
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Re: Building a DIY amp with NVA amplifier boards

Unread post by karatestu » Tue Feb 27, 2018 11:42 am

_D_S_J_R_ wrote:
Tue Feb 27, 2018 10:46 am
Power supplies are a bit of a black art, even 'simple ones' like NVA use. You can play with transformer capacity (my main amp uses two 120VA 30-0-30 transformers and I should have put these in a separate box so I could experiment) as well as capacitor sizes. I'm not an audiophile type any more, but I found increasing the cap size merely made the amp take longer to stop working after switch-off. Someone listening harder to the 'sound' may find more of a difference, especially in the bass. NVA amps don't usually run warm, let alone 'hot,' so I'm wondering if the Kendeils might be overkill here ;) ? I've played with Doc-donated old DNM slit foil caps and again, I'm damned if I can hear a difference from the standard types...basic ones I've used

I can't speak for buzzy old crap Naim transformers, but the basic ones I've used don't buzz unless severely provoked. Align the wire outlets away from the boards not towards them and if the caps come between them as per NVA, I doubt you'll have any hum whatsoever - . You could always make a two-box amp with the transformers, rectification and main smoothing in one box and the amp boards plus anything else in the second, using umbilicals as per the NVA PSU...

I've never experimented with bridge rectifiers over the ones NVA normally use. Is there extra 'foo' (the term is justified here I believe) with fancy ones in 'audio' circuits where you don't need huge wideband response out to hundreds of kHz?

Not sure if I'm allowed to say, but I believe the signal path up to the drivers is even simpler than the amp looks ;)

I'd better push on and finish the next A20X as it's almost done..
Yes Dave, get that A20X finished :geek: Thanks for your input, always welcome.

I said earlier that I have to learn to forget everything that I thought I had learnt up to this point :grin: The Doc's own words. This is because I was brought up on bodging all things Naim, with a lot of success I might add. I later moved on to Avondale and thanks to Les (god bless him) I suddenly realised what the rest of the musical notes sounded like :lol: Having no training or knowledge of electronics before embarking on my diy adventure I thought the naim & Avondale ways where the only way to do things. Since joining this forum, reading and experimenting with stuff, my eyes (and ears) have truly been opened.

The transformers, caps and schottky rectifiers are what I have at hand and I would like to use them to their best ability. Naim transformers are well known for buzzing and I have had problems in the past. I am going to try the little NAP140 transformers only as a way to get going with this. They are an adequate size and voltage to get started with and then I can try the other ones I have (not Naim) including some frame transformers and my custom made Canterbury windings 350 VA 35-0-35 jobbies.

I don't know about different rectifiers. I suppose it depends on the PSSR of the amp circuits. Naim and the Doc uses bog standard bridges where as Les supplied me with lots of MBR20200CT schottky. I will just use what I have to hand. The Kendeils are also what Les supplied me with and I might as well use them. I can always drop down to one 6,800uf per rail or I have some 10,000uf somewhere.

I am sure the signal path is very simple as that is what NVA is all about. All those current mirrror transistors make the circuit look more busy than it actually is.
PhilOesophical_1 wrote:
Tue Feb 27, 2018 11:02 am

Hi Stu,
This is my first post here so I hope it’s not a stupid one! I should start by saying thank you for introducing me to this forum. I have learned lots already just by reading and I feel I should also publicly thank you for your help, advice and generosity of time. However, you don’t get off that lightly so here is another question for you.

It seems you have been very much favoured with the opportunity to play with some NVA boards. You mention Earthing the NVA way. For the (semi) uninitiated, what exactly is ‘Earthing the NVA way?’

S
Hi Phil,

No problem, others have taken time to help me in the past and i am happy to continue the cycle. Great to see you here and posting . There is lots to read and learn, i agree :grin:

Earthing the NVA way - i am sure i can say this as it is not a secret and there are pictures showing it on here. Forget the star earthing of Naim et al. The NVA uses a tinned solid copper bus bar which runs around the inside of the case by a specific route. Some components are soldered to it directly and others have their 0V connection by means of a tinned solid copper wire between it and the bus bar. Everything that ought to have a 0V connection has one. I think the art is the route the bus bar takes and the location (relative to other connections) each connection to it is made. Hope that makes sense and i hope i have got it right :think:

Stu
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Re: Building a DIY amp with NVA amplifier boards

Unread post by _D_S_J_R_ » Tue Feb 27, 2018 12:30 pm

I'm sure star-earthing has a definite place in low level circuits such as active preamps, but I believe it was a re-reaction to the casual way that earthing planes on circuit boards were being done in the 70's. Another DNM thing taken up by others. My old Croft preamp had a combination - metal case with single common earth point, but all the phono sockets as supplied, had a ground plane on them with a single wire going back to the main earth point. NVA with Perspex cases doesn't seem to need this and the amp boards have a solid ground plane down half their centre line if you look ;)

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karatestu
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Re: Building a DIY amp with NVA amplifier boards

Unread post by karatestu » Tue Feb 27, 2018 12:50 pm

_D_S_J_R_ wrote:
Tue Feb 27, 2018 12:30 pm
I'm sure star-earthing has a definite place in low level circuits such as active preamps, but I believe it was a re-reaction to the casual way that earthing planes on circuit boards were being done in the 70's. Another DNM thing taken up by others. My old Croft preamp had a combination - metal case with single common earth point, but all the phono sockets as supplied, had a ground plane on them with a single wire going back to the main earth point. NVA with Perspex cases doesn't seem to need this and the amp boards have a solid ground plane down half their centre line if you look ;)
Cheers Dave,

Star earthing gone mad - I remember a preamplifier from PFM called the starfish that was well regarded by those who used them. Everything was star earthed.

No metal cases for me. Wood all the way except the heat sinks of course. Acrylic is too expensive for the likes of me to be cutting with my chainsaws :lol: My music centre would look very cool in black acrylic though. I have seen the ground plane running under the resistors - clever.

I will not be using the Loctite thermal glue for the output transistors though. Sill pads and nylon bolts will have to do. Still deciding on whether to use my 60cm square sheet of 2mm copper for heatsinking or some aluminium profiles I have. The way I have designed things none of the heat sink will be seen from the outside. I will try my best to stick to class II construction if possible.

Stu
Naim, Linn & Harbeth fanboy

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karatestu
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Re: Building a DIY amp with NVA amplifier boards

Unread post by karatestu » Tue Feb 27, 2018 9:00 pm

The psu arrangement i will be using at first. Probably not the correct way to draw it.
Image

Nothing spectacular about this. No snubbing, no soft starts, no film bypass. Trying not to ferk with the music. All hardwired with tinned solid core copper wire, not a pcb in sight.

Stu
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SteveTheShadow
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Re: Building a DIY amp with NVA amplifier boards

Unread post by SteveTheShadow » Tue Feb 27, 2018 9:11 pm

Might seem a daft question, but where do you get tinned solid core wire from Stu?
I've never had to use it until now.
DIY NVA amplification ( roughly equivalent to NVA A60) BTE Designs passive preamp, BTE Designs Lenco L75 turntable, Rega R200 arm, Goldring E3 cartridge, NVA Phono 1
Musical Fidelity M1 DAC, AppleTV4 with Apple Music subscription, ripped CDs streamed via WD MyCloud Home Duo NAS, with PLEX media server.
Speakers - Large sealed cabs, with Fane 12-250-TC 12" full range drivers.


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Re: Building a DIY amp with NVA amplifier boards

Unread post by SteveTheShadow » Tue Feb 27, 2018 9:27 pm

Thanks Doc.
DIY NVA amplification ( roughly equivalent to NVA A60) BTE Designs passive preamp, BTE Designs Lenco L75 turntable, Rega R200 arm, Goldring E3 cartridge, NVA Phono 1
Musical Fidelity M1 DAC, AppleTV4 with Apple Music subscription, ripped CDs streamed via WD MyCloud Home Duo NAS, with PLEX media server.
Speakers - Large sealed cabs, with Fane 12-250-TC 12" full range drivers.

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