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NAP160 - what is all the extra stuff inside?

Early Naim amplifiers used BDY55 (very early 120s and 160s) or BDY56 and then moved on to BDY58 before they settled on the Naim branded NA001 & NA002. The NA001 is an uprated BDY58 and NA002 is a selected BDY56.

Several components on the early NAPA boards were SOT (select on test) especially in the compensation networks. When you've seen a number of boards you will realise that this is true and the often-posted schematic contains a number of discrepancies over what is found in practice. Stability was achieved in the factory by using some pretty sophisticated test equipment.

P.S. it is not unusual to find significant differences in compensation components between the two boards fitted in a stereo amplifier.
 
I'm bumping this thread as I would like to know the outcome of this amp and what it sounds like post Witch Hats service work.....
 
I'd be keen to know too, it was one of the most satisfying amps I've ever worked on.
 
Stuart Frazer said:
I'm bumping this thread as I would like to know the outcome of this amp and what it sounds like post Witch Hats service work.....
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MJS said:
I'd be keen to know too, it was one of the most satisfying amps I've ever worked on.
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And me three! Since the work was done, my system has had to go into hiding while we have a move around at home - space is now at a premium with pianos, drum kits, brass instruments and children's paraphernalia cluttering the living accommodation. Hoping this will change soon, and needless to say I will post here once I know.

Mark, I quite enjoyed your tale of how it managed to cause your whole fuse box to trip at one point! I guess just getting the thing to be safe was satisfaction in itself?
 
We ended up re-wiring the entire power supply from input socket to the boards - the quality of the initial conversion wasn't great on the mains side. The switch fell apart and caused some issues with mains not being where it should be but we replaced it all and bought it closer to current safety specifications (something we try and do to all amps where possible, by the way).
 
Here you go:

IMG_3683 by Mark Slade, on Flickr

New Belden mains input socket and lead
New mains switch and wiring, missing earth replaced.
New 4mm/binding speaker posts
New XLR signal socket
Wired for proper dual mono power supplies with star earthing at each pair of capacitors
Rectifiers placed near caps, uprated wiring
Full service on amp boards

All in, a very satisfying project.
 
I was thinking about starting a new thread, but it makes more sense to resurrect this one.
The 160 has finally come out of its extended (over two year! ) lockdown, and was put into the system over the weekend.
Now, I have had the privilege over the last year of having a whole series of CB pre and power amps for company, notably a staff build 90, a long term 110, an old 250 and now the 160. The 90 was quite excellent, almost pristine sound, but sounded as if it was very much kept on the leash, compared to the 110, which was obviously the same sound, but somehow more organic and natural, perhaps something to do with the lack of regulation. Comparing it to the 250, the big amp seemed very forthright, with no messing about, and there seemed to be much more defined lower bass, so that I had to turn the subwoofer level down. What was also interesting is that there must be a difference in input sensitivity between the shoe box amps and the big ones, as I had to turn the volume dial up two notches to level match them, I'm sure someone technical can confirm this.
So to the 160; where the 250 was all muscularity, with a bit of grain, the 160 was incredibly sweet, and the sound stage opened up beyond my speakers (Q Acoustic Concept 20) in a most un-naim like way. I really like the sound it makes, and I'm interested to see how it develops over the coming weeks. I'm guessing this is what mono block 110s might sound like?
Anyway, eventually a much belated thank you to Mark (MJS) and Nic for persisting in getting this amp right, it was most certainly worth it!
 
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MJS said:
I think if I ever reverted to Naim amplification that I would definitely want a bolt-up 160. I love these amps.
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Truly superb amp - I very much regret selling mine on (and the NAC12), both of which I put a lot of effort into restoring.

Lovely work on resurrecting this 160 MKS.
 
Darran refused to touch it, which is only fair within his remit as an approved repair centre. When I bought it, I had no idea as to what lay within! Fair to say the repair bill was not cheap, but it was totally worth it
 
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