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NAP160 - what is all the extra stuff inside?

The latest is that it may be a butchered early 250 - photos have been sent to Naim for them to comment, so I'll keep you all updated. Shame, as I was rather fancying a dual mono 160 now I know about them.
 
OK, I have access now. The speaker terminals are unusual indeed as are the mains and input connectors. They look more like a 250. The 160s I've seen had three pin Bulgin connectors for the mains and a 4 pin DIN for for input and 24v out.
 
Connection wise, it looks the same as my bolt down 250, so yes, the name plate seems rather at odds with what is presented. The mains connector is called a Cannon type, and though still available, they are only NOS.
 
If it were mine I'd re-route the rectifiers to nearer the caps and get the transformer centre tap right in between the caps. I could have fun with this amp!
 
This appears to be a dual-mono build using a pair of NAP110 transformers

It'll be a stonking amp, believe me.

Whatever you do, don't allow Darran to revert it to 'standard' in the quest
for Naim Audio 'purity'.!
 
Stuart Frazer said:
Is there anything special about the original 160 transformer, or could I get 2 new made up from say Canterbury Windings to make up a pair of mono 160s? Finding an original is proving to be elusive.
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It's a particular design made by Holden and Fisher but like anything else, it's a manufactured item and it can be copied. Any trafo manufacturer will make a faithful copy if you take them the details for the old one, there are no unobtanium parts. H&F trafos are regarded rather like Faberge eggs around here, and they may have something prticular to their design but it's not impossible to rplicate.
 
Going slightly off topic here, H&F were very good at making large flat toroids of the form factor demanded by Naim's case design. They were quite difficult to replicate and get a quiet, hum-free transformer - Les has done a lot of work in this regard with a local manufacturer and is now making them available for the larger Naim amps. If extra height were available, and there is a tad in the bolt-up design, then many more transformers are suitable and Canterbury Windings are great in that regard.
 
trick cyclist said:
Connection wise, it looks the same as my bolt down 250, so yes, the name plate seems rather at odds with what is presented. The mains connector is called a Cannon type, and though still available, they are only NOS.
Click to expand...

I would concur with that. Looks very like the back of a BD 250.
 
Based on knowledge of making my own amps I think a different rectifier/cap layout and grounding scheme would make a big difference to the end result - a star ground at the capacitor 0V and short, thick wires between the rectifier and smoothing caps would be how I would do it.
 
NAP160s were drilled for 4 transistors, the 250s for 8.

The Cannon NLE XLR was unique in that it could be wired for input or output of mains voltage. Suffice to say this isn't allowed any more but there are a few still around on old kit and studios.
 
Thanks for all the ideas about what to do so far. As I'm on holiday, I am not in touch with Darran, so unless he pops up on this thread (which I made him aware of before I went away )it will be a while until I know what he suggests.
 
Update on the next stage for this bit of kit - it was a standard customer 160, which was then unofficially modified by a dealer at some point (I'm not aware who) with additional 160 parts from Naim. It features a questionable wiring layout, along with customized inputs/outputs, and as such is reckoned to be on a knife-edge regarding stability.

It is now winging its way to Mark at Witch Hat, as Darran will (quite rightly) not work on it. This may not be cheap, but I'm trying to keep it dual-mono and preserve its uniqueness, without it potentially causing a fire or damaging my speakers!
 
Which outputs does it use? The family of Naim "clones" use various output transistors, I remember reading that the design is reasonably stable (providing it is loaded at the output correctly).
 
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