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NVA A70 Power Amplifier capacitor upgrade advice required

Discussion in 'd.i.y.' started by Chaggy78, Apr 12, 2018.

  1. Chaggy78

    Chaggy78 pfm Member

    Hi!
    I have an older model NVA A70 Power amplifer and I want to upgrade the power supply capacitors which are currently 2x ROE (Roederstein) 4700uf 63v and they are big orange can types.
    My question is would I be able to use higher capacitance caps say 2x 10,000uf 63v without any problems?
    I'm not even sure if going larger capacitance will have any benefit though but as they are very old caps I think they need replacing by now.
    Thanks!
     
  2. Chops54

    Chops54 pfm Member

    I'd be tempted to go half way at 6800uf but I don't think 10000uf will cause any issues. I dont know what the supply rail voltage is but if it's anywhere near the 63 volt rating of your original caps I'd be looking at going up to 80 or 100 volts. Caps working close their rated voltage maybe have a shorter life span.
     
    Mike P likes this.
  3. Yomanze

    Yomanze pfm Member

    I'd stick to the actual values. Those caps values would have been chosen for a reason, and through listening. Bigger isn't always better, in fact, NVA like to use the least capacitance they can get away with.
     
  4. Paul R

    Paul R pfm Member

    I'd refer back to the maker. He's an offensive ass but he does know what he intended with his amplifiers. And since NVA amps are deliberately not bullet-proof-take-any-abuse-from-fools designs it may be necessary to take detailed account of component choice to keep the amp safe in use.

    Anyway what makes you think they need replacing other than some impression of age?
     
  5. Pete MB&D

    Pete MB&D Pete Maddex, the one and only!

    And it gives you the biggest profit margin.

    Pete
     
    Mike P likes this.
  6. mega lord

    mega lord Centre tapped

    Well a capacitor is also an inductor and ESL rises as caps get bigger does it not ?
     
  7. Chaggy78

    Chaggy78 pfm Member

    Thanks so much for the advice everyone. I measured the capacitance and it appears that the capacitance has gone up with age they are measuring around 8000uf now instead of 4700uf. They are working fine but as they keep rising surely something may go wrong at some point? I just want to make sure they don't blow or something and cause damage to the circuit boards.
     
  8. mega lord

    mega lord Centre tapped

    Just put some new 4700uf 63V in. Nothing to worry about.:)
     
  9. Dowser

    Dowser Learning to bodge again..

    I’d whack in the 10k items :)
     
  10. audioman

    audioman pfm Member

    Just leave those amps alone. I know the designer doesn't go much on cap change obsession and uses components that don't get overstressed. It's not an old Naim. I expect the caps are fine and are the value chosen for good reason.
     
  11. TheMooN

    TheMooN pfm Member

    I would recommend getting rid of the POS while you still can and look out for an amp that delivers whatever your speakers require in full class A.
     
  12. Pete MB&D

    Pete MB&D Pete Maddex, the one and only!

    Components that don’t get overstretched? What the heck are they?


    Pete
     
  13. DSJR

    DSJR Between us and them

    Wouldn't a Class A amp thermally throttle the caps used, as most pukka Class A amps run very hot?

    The older style amps were sold via dealers I distantly recall, so would have been regarded highly by those who bought them first and certainly weren't regarded as a 'POS!' If the amp is untouched internally, the manufacturer will service if necessary. The fact the OP knows the caps he wishes to replace, means he's been inside though, so who knows...

    Not for me to discuss cap decisions, but the 63V caps should usually be more than fine in this instance.

    P.S. Cap values usually tail off over use I thought.....
     
  14. sq225917

    sq225917 situation engineer

    Why not ask Richard, he built them, he knows why he chose those parts. I'd only swap them if they were leaking or ESR had increased 10x
     
  15. Chaggy78

    Chaggy78 pfm Member

    Richard replaced the boards for me in the amp a few years back and upgraded them with newer versions as the older boards I had inside went faulty. I did ask him about the caps around that time and he said there's nothing wrong with them just leave them in. I was just concerned that the values had changed a lot considering they are meant to be 4700uf and have nearly doubled in capacitance now.
     
  16. thebiglebowski

    thebiglebowski pfm Member

    Be careful think I read somewhere that changing the caps in an NVA amp can cause it to catch fire.

    (or maybe it was switching one on?)
     
  17. YNWOAN

    YNWOAN 100% Analogue

    If you are sure that they have increased in capacity then there is something wrong with them - as you suggest, old age (this is the nature of electrolytic capacitors and not unique to Naim, or amplifiers in general). If you replace them with higher value caps then the amp will still work but likely will sound different - amp designers often balance the size of the mains transformer and reservoir capacitance. I would replace with similar to that originally fitted and, as long as you can solder, should be an easy job.
     
  18. sq225917

    sq225917 situation engineer

    How did you measure them? Did you devolved thrm?
     
  19. Dowser

    Dowser Learning to bodge again..

    And did you also discharge them first, as well as disconnect them? (dishvarg in SQ speak? ;))
     
  20. Dowser

    Dowser Learning to bodge again..

    Slightly off-topic - I'm interested to know why upping smoothing capacitance would cause flames or a degredation in sound quality - I've seen it written often, but my practical experience completely differs - increasing smoothing capacitance can cause a slightly bloaty sound for a few or several hours, but then I assume changing with same values also can, as this is more down to the cap forming?

    From a technical perspective - what can go wrong? Either the inrush current is too high at switch on and either your rectifier diodes or fuse blows, or worst case you could (I assume) burn out the transformer windings at switch on if diodes were high spec and fuse didn't blow? But is that realistic for a transformer? I have done some very silly increasing of smoothing capacitance, especially in my Croft Micro II, with nothing but gains (there's a thread here somewhere from years back when I initially modded it - it's still running fine 8 or so years later!).

    Richard
     

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