NAP-140 Clone Amp Kit on Ebay - Page 73 - diyAudio
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Old 3rd January 2012, 09:02 PM   #721
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For me sound is important it must create a smile on my face.The fact is I bought the boards of Hoka but he had problems with this amp did the needed changes but never did come around to test them.That's one of the main reasons to create a new layout.
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Old 3rd January 2012, 10:46 PM   #722
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Quote:
Originally Posted by meanman1964 View Post
Planning to make a new layout of the NAP140 and NCC200.Who can provide me the latest schematic and suggestions regarding the best output and pre driver trannies etc.
Hi meanman1964,

Here's my interpretation of a NAP140/NAP140 Clone/NCC200. Untested, and transistors may not be optimal.

If you PM me your email address I can email you all the documentation I have collected from the web.

regards
Attached Files
File Type: pdf ANC340 schematic.pdf (29.9 KB, 363 views)
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Old 16th January 2012, 02:07 PM   #723
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Will it be OK if I use BC550 for all the NPN transistors and BC560 for the PNP transistors? Thanks.
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Old 19th January 2012, 04:01 AM   #724
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BC550/560 are only 50V Vceo small signal transistors. As the schematic specifies, you can use these at the input, TR1/2. Originals elsewhere are 80V MPSA 06/56 or similar BC546/56 can be used. These suit the general voltage levels. However, you can't just use the cheapest available parts if you want good sound and for the amplifier to work without failure. TR4/5 must be fast, higher voltage and Ft types for the VAS. If you can't buy any type covered in this thread (many different types are supplied in kits) then you could use the old BD139/40 for VAS or drivers but there is always a compromise with such part swapping.

IMHO, many parts will work as you suggest, if you pay attention to the transistor specifications but "to work" and "to be best suited" are not the same.
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Old 19th January 2012, 04:49 AM   #725
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Default DC offset in Naim 140 C

Hello everyone. I am having trouble getting DC offset on one board down to the same level as the other one. The good one is measuring 30mv with no speaker that seems acceptable to me. The other one measures 300mv which is way too much. I tried all measurements possible, both boards have the same parts and measure the same at all critical checkpoints except at the input LTP. At the bases of the two transistors I measure 350mv and 360mv in one board and 25mv e 35mv in the other (the good one!). All transistors checked and resistirs checked and rechecked. The same ~300mv higher reading shows of course the collector of Q3 (tail) and then flows through to the output. Any clues where I should look at? Could just be poor LTP transistors matching? I am using B550 for LTP and Q5, ZTX for VAS, MJ15032/3 drivers, MJL3281 output biased at 30ma. Current across R 15 and R 18 is 9.75ma and 10.75ma in both boards (I thought they should measure the same, is this close enough?)

Thanks a lot for any help, it is driving me crazy
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Old 19th January 2012, 05:41 AM   #726
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Thanks Ian. I've read up more after I've posted. Found the Avondale NCC schematic and I'll build the amp based on it. BC546 for TR1/2/3, ZTX753 for TR4, 2N5551 for TR5 and ZTX653 for TR6.

This project was supposed to be a quick and easy build with available parts on hand but as always after reading and research I'll be making it a dual mono with the right parts.

Quote:
Originally Posted by Ian Finch View Post
BC550/560 are only 50V Vceo small signal transistors. As the schematic specifies, you can use these at the input, TR1/2. Originals elsewhere are 80V MPSA 06/56 or similar BC546/56 can be used. These suit the general voltage levels. However, you can't just use the cheapest available parts if you want good sound and for the amplifier to work without failure. TR4/5 must be fast, higher voltage and Ft types for the VAS. If you can't buy any type covered in this thread (many different types are supplied in kits) then you could use the old BD139/40 for VAS or drivers but there is always a compromise with such part swapping.

IMHO, many parts will work as you suggest, if you pay attention to the transistor specifications but "to work" and "to be best suited" are not the same.
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Old 20th January 2012, 03:02 AM   #727
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Quote:
Originally Posted by marcel5996 View Post
At the bases of the two transistors I measure 350mv and 360mv in one board and 25mv e 35mv in the other (the good one!). All transistors checked and resistirs checked and rechecked. The same ~300mv higher reading shows of course the collector of Q3 (tail) and then flows through to the output.
Hi,
If the base voltages at the LTP are similar then the feedback is working as supposed to. Assuming that the resistor values are OK I would troubleshoot in this order (following the eBay circuit):
1. Make sure that input capacitor C1 is OK and not a leaky one.
2. Do the same for feedback capacitor C5.
If fault is still there:
3. Check the voltage across the current source resistor R21. The working channel is big advantage, because you can compare. Current of 0.8-1.2 mA through R21 is OK and should be similar for both channels. If it's not,
check LTP transistors base to emitter. You should see ~0.5-0.6Vdc. If close to 0V or higher than, say 0.75V, transistor is faulty.
If OK:
4. Do same check for the current source transistor.
If current source is fine as well, then I would say the problem is something silly like solder drop shorting somewhere, or cold solder joint, or ground not attached to the right place, or input connected on the wrong side of the input capacitor etc. in this line of thoughts...
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Old 21st January 2012, 08:27 PM   #728
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Ruwe, thank you for our precious input as always. I checked everything that you mentioned, current source is okay, all transistors drop 0.6v, capacitors orientation is okay, no continuity between capacitors ends, the boards are a bit beat up because of experimentation but could not find obvious faults. Current source is constant at ~1.2ma and approximately equal to the sum of the measured through the 2 top resistors in the LTP. The ~300mv appear at the base of both LTP trannies. Q5 emitter measures 1.4V, collector ~0.4v, it seems reasonable. I have no protection circuit. Need to let it cool and think it through. Anything else you can think of?
Troubleshooting is frustrating but very informative
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Old 21st January 2012, 11:19 PM   #729
Ruwe is offline Ruwe  Europe
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Quote:
Originally Posted by marcel5996 View Post
Anything else you can think of?
Hi,
LTPs following each other is OK, they are supposed to do so. The question is which base is leading the change from 0mV to 300mV (the other base is just following). At first I thought it should be the input (e.g. leaky cap), but you say it is OK. LTP transistors sharing current equally means they're OK as well. The feedback cap is also not leaky, right? ... By the way, caps may be leaky and still measure as high enough resistance. If you're out of useful ideas, why don't you swap them with the other board and see whether the fault moves with them.

Something very important: make sure that the input ground is connected to the feedback ground, i.e. the feedback capacitor. They should be on the same path on board.
In this circuit ground is the reference point, if ground is not the same on both sides of the LTP the circuit will balance itself somewhere where it finds it most comfortable, between two different "references". Also make sure that the output ground (Zobel and speaker out) is connected together with the input ground to the power supply common. I remember the eBay circuit had two separate grounds (input and output) and they should be linked or both must be soldered to the power supply common. I'm sure you know that, but check that's valid for this particular channel. Sometimes when all wires are spaghetti like, one can omit something ... Check that nothing is touching the case, if not supposed to ... like speaker terminals or input jacks with missing plastic insulators ... stuff like that.

Did you try this channel with music? Is it working at all? You can try it with some cheap speaker connected through a big cap (like in a single-ended amp), thus isolating the DC component during the listening test. It's important to know whether the amp works without distortion.
If it's playing music nicely, the only thing left to unbalance the DC offset are the resistors, you know the rule: R2+R3=R8+R9 (ref. eBay schematic).

Troubleshooting can be frustrating First rule is "check the obvious and the easiest".
In general, circuits with feedback loops are the most difficult to troubleshoot, because it's never clear what's causing the fault, everything is affected through the feedback, sort of "the chicken or the egg" dilemma. Luckily, in this circuit, there is only one feedback loop!
If you're out of reasonable ideas, try something practical. Swapping suspicious parts is big helping tool, comparing with working circuit is another one.

Last edited by Ruwe; 21st January 2012 at 11:23 PM.
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Old 22nd January 2012, 08:45 PM   #730
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hi all
ım try to complate my nap140,ı complated my pcb and heatsink,at the last making psu is rest.

now ım wondering that is nap140 class b or ab? its biased to 40 ma if no signal at input.

40ma is enough for the class ab, if not how much bias is needed for class ab?

thanx inadvance to one who will replay.
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