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Naim NAP250 Advice

Well done!

And thanks for the great write-up with photo - very helpful for anyone else in future who searches for this, and esp your point of view and findings.

Now just enjoy it some more :)
 
To take the sleeve off is it a simple matter of unscrewing the 4 feet and the six allen head bolts on the bottom of the amp and sliding the inards out?

I get the impression that you are better at this than me :) but the first time I did this I managed to damage the fascia which is quite fragile. Luckily I was able to replace it with a genuine part but that was a while back.

Tim
 
Well done! So the golden caps don't need to be replaced...?
If this was my amp and these caps were electrolytic, I would replace them all upfront. No need to be an axial type, many radial ones can be used, you just have to bend the leads to fit in place.
 
That's a good point, but for all the things 'wrong' with the regulator design* - a quick look at the schematic shows it is not sensitive to the status/quality of that 47uF axial cap.

That cap, one per rail, is used to pre-filter the feed to the zener reference: and even if the axial cap at , say ESR >+10ohms and cooked in old age - ripple at say 0.5Vrms at the reservoir caps only (nominally) rises to c. 100uV on the reg ( - based on simple approximation at 100Hz.)

So - fortunately - it's much less critical than the axial 10uF parts for sure :)



* @PigletsDad has posted detailed analysis on this, in last 3-5yrs. tl;dr: the whole regulator design is 'upside down' and that gives up 20-30dB of potential performance - but to gain that margin requires homebrew & testing of something entirely different. You cannot get there by simple parts mod on the original PCB.

So when the factory layout works well-enough to please most people, most of the time - and is as demonstrated above , easy enough to service even by people new to opening-up their power amp - I'd suggest ...don't worry about it. If you love your NAP250 / NAP135 as it is - it is very, very easy for you to keep things that way.

:)
 
Jeff did that, see this thread. I built his regulator board and can confirm it sounds very good and clean:

XFz1JDp.jpg


As today mains are more polluted (than in the 70s) the improved rejection of his version is welcome.
 
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