Building a DIY amp with NVA amplifier boards
Posted: 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 ) and the Doc can have his entertainment and watch the magic smoke as it is let out
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.
So here is what arrived in the package
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
A couple of single secondary, centre tapped toroids from Naim amplifiers 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
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)
Should be an interesting ride . 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
Stu
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 ) and the Doc can have his entertainment and watch the magic smoke as it is let out
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.
So here is what arrived in the package
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
A couple of single secondary, centre tapped toroids from Naim amplifiers 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
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)
Should be an interesting ride . 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
Stu