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Naim NAP160 help

AdeBlackpool

AdeBlackpool

My favourite power amp - Alchemist Forseti SS
Hi everyone.

Hope you are all keeping well.

I have been working on a NAIM NAP160 with 1 working channel. Initially I noticed that the neg. speaker post on the dead channel was broken and shorted to the chassis. Both BDY56 shorted along with one small diode, a few cooked resistors, a shorted A06 tranny, etc.
My question is regarding some tant values and resistors.
It has had previous work done. The 10uf tantalums were all 25v, so I fitted the usual 10uf 35v Kemets. C2 was 47uf and C3 was 10uf. I'm thinking someone saved some money on cheaper tants as the circuit diagram shows 68uf in these positions. Can anyone shed any light?

I have not powered up the amp yet, so I'm planning to first unplug the new BDY56'S as they are on the rear panel, then set basic bias.

Power supply reads 37.5 v and has been re capped.
 
I have a fully recapped 160 bolt down and I took some pictures before and after.
I am too dummy to post some pictures here but if you send me a pm with an email address I can send you these.
A tantalum capacitor usually fail short when they get out of life and this causes damage on surrounding components so a full review has to be performed when that happens.
In my unit, I also replaced the large resistors near the output transistors as they were slightly brownish probably due to overheating so I would recommend replacing these upfront.
I took care to install them with a gap of at least 1/4 inch from the board to allow air circulation around it to help getting rid of the heat.
My favorites for this are the Mill resistors with close tolerance.
 
Hi,
Thanks for the pics. I can't figure how to upload pics. Anyway, your amp is in much better condition than the one I'm working on. So, you have 3 x 10uf tantalums, 1 at the input and 2 back to back in the protection circuit area at the output end. So what values do you have for the other 2? 47uf/68uf
 
They are 47 uf in my amp but I know that some 160 came with some 68 uf.
Not 100% sure but I think the bolt down version like mine uses 47 uf and the sleeve/chrome bumper version of the 160 uses 68 uf but I never came across a sleeve one so I can’t confirm.
 
Thanks. I have fitted 68uf 16v in both positions, so hopefully this will be ok and matches the circuit diagram.

Best wishes.
 
I just powered it up. I have a bias adjustment range of 2 to 4 mV on the pot with the BDY56's disconnected. Supply rails are 38.3v and 38.1v
 
There's no bias to set if the output devices aren't fitted ;). But set it to minimum before you put them back in and turn it on again.
 
Thanks for that MJS. Obviously not, but the fact that I get 2 to 4 without them connected is a good sign that the rebuilt pcb is good and is similar to the other channel pcb. That was my point.:D
 
Re: a NAP160:
Please can somebody confirm if a NAP160 indicator bulb is either a 24 or a 48volt 'slide' style incandescent bulb?
Thank you.
 
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Brilliant, thank you! You don't happen to have an original schematic of a NAP160 do you? I can't locate one that seems genuine, anywhere. It's the power and power supply section, rather than the amp boards themselves that I am interested in. Thank you!
 
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Do you have the bolt down or chrome bumper version? I don't have a diagram of either, but what information are you after?
 
hififansince1965 said:
Brilliant, thank you! You don't happen to have an original schematic of a NAP160 do you? I can't locate one that seems genuine, anywhere. It's the power and power supply section, rather than the amp boards themselves that I am interested in. Thank you!
Click to expand...
Think you’ll probably find it’s the same as all other NAP circuits. Differences were in the power supply - bigger/more caps, regulator boards or not, mono or stereo. Have a look at the acoustica site http://www.acoustica.org.uk/
 
The NAP amplifier circuit is 99% the same between most of them. Input and SoA caps are all 10uF/35v Tantalums, the feedback is 47uF or 100uF (or two 47s in parallel), and there was a 47uF across the bias transistor. Early 160s used two separate transformer windings to create two positive rails, and these were placed in series to create a dual polarity supply. Later ones were probably converted to use bridge rectifiers and wired conventionally.
 
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