NAP-140 Clone Amp Kit on Ebay - Page 33 - diyAudio
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Old 11th June 2009, 03:36 AM   #321
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Quote:
Originally posted by thanh1973
I think you can use BC546 instead of BC550 which is rated for a higher voltage (ie 80V)
I used 2sc2240, but I had to twist the legs around. No big deal realy.

Thanks! I solved the problem by replacing new transformers (2x monoblock)


By modern standard, this amp is noisy. Is there audible noise improvement using 2sc2240?

Cheers!
C
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Old 11th June 2009, 03:58 AM   #322
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Default Re: Nap 140-C Amp clone

Quote:
Originally posted by marcel5996
Hi all, I'm a newbie who got "bit by the bug". Enjoyed so much this thread that decided to purchase Nap 140-C clone bare boards on ebay (the longer ones) and build my first amp. Parts were selected separately picking from this thread suggestions. Did my homework studying and reading carefully other diyers' experiences on this thread. I'm at my third board and still can't get it to work!! Was hoping someone could help me troubleshoot, maybe posting some of the approximate readings that I should expect at the different stages. I have a 250 VA 30-0-30 toroid, dual rectification with 8x4700uf (4 each rail) smoothing caps. Don't have variable bench power so I set lamp bulb in series with mains (only lights up briefly at power up), have 2x10 ohm 10 watt resistor at main supply and 2x100ohm at +/- pcb supply terminals to make sure I get warned if there is a short. Input ground, speaker, pcb ground all go to the common point on the caps. With no input/no output load everything seems fine at power up, current set to suggested minimum of 10ma (2.2mv across emitter resistor r29), negative rail showing the same reading. Output DC offset around 12mv, trimpot works, resistance across r17 is around 650ohm. All transistors/caps checked for proper forward bias and correct alignment. Have MJL3281A output transistors mated with MJE15032/3 drivers (as per Neil McBride). What happens is that when I finally attach a speaker (no input yet), the "warning" 100ohm resistor on the negative supply side overheats with smoke, forcing me to power off (no time to check music). Also tried with quiescent current set at minimum level, 1.4mv across r29, or 6.4ma (275mv across base/emitter 100ohm resistor r26) which should give hardly no current at all to power transistor with the same result. Any idea what is going on? Thank you very much for any help/suggestion.

I supposed that you did a good check at Q5? The transistor outline is wrong...
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Old 11th June 2009, 08:47 AM   #323
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Hi Skyraider if you have noise it is most likely due to poor layout or inadequate capacitance smoothing, or faulty components.

Could you describe what you mean by noisy?
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Old 12th June 2009, 03:06 AM   #324
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Hi Thanh,

Its white noise thats audible for about 4-5 feet away. Its not really noisy, just that I have experience with amps that is 'pitch black'.

If i touch the input wires, oscillation/buzzing happens. Is this normal for this amp, or can be improved?

Thanks! Colin
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Old 12th June 2009, 07:15 AM   #325
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How efficient are your speakers?
What sort of speakers do you have?
It sounds like an earhing/grounding issue. Have you star earthed?
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Old 14th June 2009, 10:12 PM   #326
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Smile Re: Re: Nap 140-C Amp clone

Quote:
Originally posted by skyraider



I supposed that you did a good check at Q5? The transistor outline is wrong...
Hi skyraider, thanks. Yes, after reading the posts on wrong transistors outline I double checked all transistors with boards schematics.
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Old 27th June 2009, 05:59 PM   #327
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Quote:
Originally posted by DreadPirate
I compared this schematic with the one posted by Carlos, some slightly different values, those are highlighted with an asterisk.
Sorry to revive a rather old thread - but I bought this same kit about a year ago (maybe 18 months!) and have just got around to looking at building it.

I wasn't supplied with a schematic, and I was happy to find the copy you had posted. Mine differs slightly ffrom yours, in that it has two additional components in the feedback loop.

My board also has all component values on the silk screen layer.

I preapred the attached schematic, based on your poseted schematic, and comparing that with my PCB.

Tony.

EDIT: I can't seem to get the schematic clear here..

EDIT: Embed image.

Click the image to open in full size.
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File Type: png naim-clone-schematic-small.png (43.0 KB, 1432 views)
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Old 27th June 2009, 07:10 PM   #328
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I've also noticed some people have been having problems with the transistor orientation.

I scanned the silk screen side of the board, and marked out (in orange text) the Base / Emitter and Collector pins.

This hopefully will help others who might be constructing this kit.

All the transistors supplied with my kit appear to be exact matches for the layout.

Click the image to open in full size.
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Old 27th June 2009, 11:46 PM   #329
Ruwe is offline Ruwe  Europe
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Hi marcel5996

I may be a little late, I don't read the forum very often, but the first thing to check is where you attach your speaker. Of what you're saying it looks to me that you have connected the speaker between the negative power rail of your board and the ground (or from negative power rail and the speaker output). This way you're shorting through the speaker the negative rail.

If your amp is stable without load then your load is the problem. Check where are your terminals attached on board.
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Old 28th June 2009, 04:41 PM   #330
807 is offline 807  Netherlands
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Quote:
Originally posted by audio_tony


I preapred the attached schematic, based on your poseted schematic, and comparing that with my PCB.
Hi Tony

I think there is a small error in your schematic. The upper driver base is connected through a 470pF capacitor only. Probably this network has to be the same as for the lower driver. I hope the PCB is Ok.

Hans
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