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Help please - NAP 160

I'd say thats actually been made out of 2 160's of slightly different age.

Note the diodes on one are all different to the diodes on the other, and some of the polystyrene caps on one are different to the other, but actually consistent within the board.

I reckon a previous bodger has tred to identify and harmonise any differences in resistor values in an ugly hack sort of a way.

If the feedback loop isn't the problem then I'd initially be looking for dry joints and to identify any differences between resistor values that remain.

I'd also re work all those badly bodged components.

I can fully see why Les didn't want to even touch it! His labour cost for getting that anywhere near respectable would exceed its value. It virtually needs a complete ground up rebuild in my opinion.
 
colasblue said:
I'd say thats actually been made out of 2 160's of slightly different age.

Note the diodes on one are all different to the diodes on the other, and some of the polystyrene caps on one are different to the other, but actually consistent within the board.

I reckon a previous bodger has tred to identify and harmonise any differences in resistor values in an ugly hack sort of a way.
Click to expand...

I'd agree with you, except that CJ1045 (? not sure if that's the right 'handle', from memory!) posted a picture on the other thread which had almost exactly the opposite diode colour arrangement, and, as was mentioned by Malcolm here earlier, Naim might not have been so picky on colour co-ordination back in the day.

colasblue said:
I can fully see why Les didn't want to even touch it! His labour cost for getting that anywhere near respectable would exceed its value. It virtually needs a complete ground up rebuild in my opinion.
Click to expand...

As regards Les not working on this particular NAP160: I got the impression from the amp's owner that Les told him he doesn't fix bolt-down Naims (whether it's because Les knows they must be ancient, or just that they're physically more awkward to get at, I don't know).
 
Here's a picture of the boards in mine exactly as received from CJ:

http://picasaweb.google.com/lh/photo/EsCSlbMZD2byUJc5HE4IJw?feat=directlink

I visited the Naim factory on many occasions in the mid to late 70s around the time that my amp (s/n 2006) and the amp in question were being built. Naim were frequently let down by suppliers and, to be honest, used whatever components they could lay their hands on. The two boards in your amp could have been made by different assembly workers at the opposite ends of the bench from whatever happened to be in their parts bins.

From the photo of mine you'll note that in several places the resistors on the two boards are the same value but from different manufacturers. Two examples are the 4K7s at top left and the 27Rs to the left of TR2.

You can also see that all the small diodes are blue apart from the two at the bottom right of the left hand board where you can also see just one resistor that has been adjusted in value by cutting the legs of the old and soldering the new from the top of the board. The circuit calls for a 620R here but the right hand board has 680R and the substitute on the left hand board is 750R.

In some ways these are easier to work on than the later models where the heat sink and power transistors are attached to the board and you have to mess around with heat sink compound when you take them in and out.

Many of the Naim boards I've seen have had component values far removed from the circuit diagram. The best sounding Naim boards I've heard were a pair of faulty 110 NAPA 5/2 or maybe 5/3 that I stripped and re-built with modern components exactly to the circuit diagram. They are also 100% stable.

malcolm
 
Interestinger and interestinger...

The photo of Malcolm's (ex-CJ) NAP160 is indeed almost the mirror image of Kim's I posted earlier on this thread (at least in respect of the diode colours, at bottom right on each board). I wonder if the assemblers thought for a moment that their random choice of components (in terms of appearance, if not values) would drive us all to distraction nearly 25 years later?
 
The circuit calls for a 620R here but the right hand board has 680R and the substitute on the left hand board is 750R.
Click to expand...
This will be tuning the tail current, which will be dependent on the particular transistor and diode in the constant current source.

Interesting forensics. I have an early NAP250 waiting for some love and affection, I think I'll have a close look at the details of the circuitry.

Paul
 
Malcolm

I'll reply partially to your question by referring you to the last page of another thread, where this same NAP160 was the subject of much discussion previously.

I'm not sure that Kim thinks his first experience of upgrading his hi-fi via eBay was a total success!
 
Hi Malcom,

The amp sounds fine now thanks, and better every day. Thanks to Darran for fixing it and the less said about the other clown the better.

Beware buying anything like that from ebay, as I got stung. Amp owes me over £550 now and me and Johnny Blue got lots of grey hairs in the process.

Thank you all again for your help.
 
It won't make you feel any better but I recently bought a Chrome Bumper 160 on eBay for a bargain price. One of the tantalum beads was fried and one of the main power supply capacitors was leaking very slightly. I replaced the tant bead and removed the old power supply replacing it with a pair of DIY MiniCAP6s. It's currently taking pride of place in my main system and sounding very good indeed.

There's definitely life in these old dogs! The amps, not us!

malcollm
 
Doesn't make me feel any better, but I'm pleased for you.
As for the dogs, there's more life in them than me and Johnny Blue.

But we'll solder on, won't we John.
 
I think my soldering days might be over, especially as I was practicing on your 160 before I got round to doing all my 135s. I can't afford to send them all to the Darren, but, on the other hand, after my experience with the 160...

(I used to be indecisive, now I'm not so sure.)

...perhaps I'd better not lend you the NAC32.5 to try instead of the 92?
 
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