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Help please - NAP 160

H

hollamby

Active Member
Posted in the Audio section, but I've been advised it maybe the wrong place.

Please, can anyone help with the repair of a Bolt Down Nap 160 or tell me where I can send it.

The amp is working, and all capacitors have recently been replaced.

However, one channel is louder than the other.

Could someone have a look at it for me please - I'll cross your palms with silver.

Avondale won't touch bolt-downs btw.

Many thanks, Kim
 
Shhh! If we don't post any more, nobody'll ever look at this thread...

PS If you do decide to send it to Darren at Class A, make sure that you extract an agreement from him first that he does not post photos or comments about my 'work' (aka 'bodge'). If I'd known anyone else was ever going to see that amp, I'd never have undertaken the task in the first place! I shall have to fall on my sword...
 
From the pictures on the other thread I thought it had been bodged before Johnny Blue got hold of it?
 
You're right, but I really bodged it getting in the big caps: they had screw connectors and so I had to solder some solid-core copper wire to the existing (soldered) connections to get enough to fasten them to the new caps.

It wasn't pretty...
 
Johnny Blue said:
You're right, but I really bodged it getting in the big caps: they had screw connectors and so I had to solder some solid-core copper wire to the existing (soldered) connections to get enough to fasten them to the new caps.

It wasn't pretty...
Click to expand...

When my Kendeils arrive I'll be doing the same, they also have screw terminals.

From the original photo I note that one of the big 8R2 resistors appears to have been changed; some of the 0R22 resistors seem slightly burnt or swollen and several of the smaller resistors have been chopped out and replacements soldered to the old legs.

I hope the buyer of this got some recompense from the seller who described it as 'untouched' :eek:

malcolm

p.s. there is a way to delete your duplicate post from the 'edit' button
 
misterc6 said:
When my Kendeils arrive I'll be doing the same, they also have screw terminals.

From the original photo I note that one of the big 8R2 resistors appears to have been changed; some of the 0R22 resistors seem slightly burnt or swollen and several of the smaller resistors have been chopped out and replacements soldered to the old legs.

I hope the buyer of this got some recompense from the seller who described it as 'untouched' :eek:

malcolm
Click to expand...

Gawd almighty! People are noticing things in these pictures that I haven't noticed with the real thing!

I understand '0R22' but not '8R2' in terms of resistors. Where are these?

misterc6 said:
p.s. there is a way to delete your duplicate post from the 'edit' button
Click to expand...

Thanks! Done!
 
Looking at the photo that was posted and concentrating on the left hand board. At the top left there are four wirewound resistors (three green and one black).

Working from left to right the first one is a 0R22 which connects the output of the amplifier to the speaker through the white wire just above it. This resistor looks swollen at the top and slightly burnt at the bottom.

BTW it would be interesting to know which of the two channels is down. Is it this one with the white wire or the right hand board with the blue wire? In the great, confused, Naim scheme of things the left hand (white wire) board is the right hand channel (channel 2) and vice versa.

Anyway the next resistor is the 0R22 emitter resistor on the positive side of the board.

This is followed by the 8R2 which is part of the Zobel network. Note that this one is black and more modern looking than the one on the other channel suggesting that it may have been changed although Naim at this date didn't really try to use components from the same source in order to match up the appearance of the two channels.

The final resistor is the 0R22 emitter resistor on the negative side of the board.

I can also see three smaller resistors that have been chopped out and replacements soldered to the legs that remain. They are to the right and just below the trimmer potentiometers, there are two on the left hand board and one on the right hand board.

Someone else commented that the small (1N4148) diodes are blue on the left hand board and multi-coloured on the right. I also note that the mounting nuts on the driver transistors (small heat sinks) are different and seem much newer on the right hand board. My 160 is of the same sort of vintage and doesn't have any rust on the mounting nuts and bolts like yours has.

Darren is the best man to sort this out but my money would be on one or possibly two of the BDY56 output transistors on the rear panel having blown possibly taking an emitter resistor with it.

malcolm
 
Crikey! Spot on! How observant you are!

It is indeed the board to the left in the picture (white wire) that is playing up (IIRC).

Naim NAP 160 Kim amp3n.jpg


Now that you've drawn my attention to it, I can see there are lots of anomalies with the two boards, although CJ posted a photo where his coloured/blue diodes were the reverse of Kim's. Could CJ's amp and Kim's have been twins separated at birth?
 
I've no idea how relevant this is, but now that Malcolm has drawn my attention to it, I can see many differences between the 2 boards:

Naim NAP 160 Kim amp3n2.jpg


Is it really just a matter of which component(s) came to hand during assembly and that there's no real difference, or is it an indication that this amp has been meddled with previously?

misterc6 said:
...although Naim at this date didn't really try to use components from the same source in order to match up the appearance of the two channels.
Click to expand...
 
If the 'bottom' leg of the feedback network were open circuit then the channel's gain would drop to 1 and therefore be very quiet.

This is the rightmost red tantalum and the resistor directly above. On the left board the resistor at least is incredibly bodged. That's where I would look first in fault finding.

Paul
 
Paul Ranson said:
If the 'bottom' leg of the feedback network were open circuit then the channel's gain would drop to 1 and therefore be very quiet.

This is the rightmost red tantalum and the resistor directly above. On the left board the resistor at least is incredibly bodged. That's where I would look first in fault finding.

Paul
Click to expand...

Good spot Paul!
 
Paul

That's very useful. I have replaced all the tants (as per the earlier thread) and may well have disturbed that dodgy resistor. I'll have a look when Kim gets his amp back from Les (if he lets me!).
 
hollamby said:
He won't answer phone calls or emails.
100% feedback as well.
Click to expand...

Send Doug and Dinsdale round... :)

but seriously - which card id it that gives out the reduced volume? I think we all suspect the one on the left in the pic but...assume nothing, check everything.
 
Don't assume that the resistors on legs are bodged. They are quite likely to have been tweaked in value during testing or the last service to keep the amp stable under all loads.

When you say the volume is low - is it actually a full bandwidth but quiet signal or are you hearing just the top-end? If the latter it suggests a dodgy contact somewhere and you're hearing capacitive coupled signal breakthrough, possibly in the pre-amp relay.

Mark.
 
misterc6 said:
That gives your age away :D
Click to expand...

And his nationality, I'd always assumed Neil was a Yank!

Can't confirm which board (until Kim gets it back from Les), but I'm pretty certain it's the one on the left (in the photos above, as opposed to stereo channel).

The duff channel is full bandwidth, but very, very quiet, which is why I like Paul's suggestion of the feedback circuit playing up...
 
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