NAP-140 Clone Amp Kit on Ebay - Page 109 - diyAudio
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Old 22nd January 2013, 04:09 PM   #1081
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Quote:
Originally Posted by Ian Finch View Post
is the board signed LJM as in the the pic?
It says, "NAP 140 CLONE" and below that shows "LJM". It doesn't say "140C" like other pictures I see on ebay and prints are little different. For example, Q3, 7 and 8 don't show E B C on my board. Also, C1 and C5 are printed reverse on my board.
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Old 22nd January 2013, 05:00 PM   #1082
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OK, thanks. It seems to be another, probably newer revision than I've seen, since I haven't yet seen the word "clone" printed on any. It doesn't help you much but at least there is a reason for the confusion.
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Old 2nd February 2013, 07:41 PM   #1083
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Well, I replaced all transistors that didn't pass DMM test and checked and rechecked all the leads but still no change in bias voltage and -34vdc at output. Unfortunately, this board I purchased isn't the same as others. I haven't gotten to light bulb test because I maxed out my allotted time given by my girlfriend. I'm done (for at least 6 months).

Thank you Ian and Ruwe.
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Old 18th February 2013, 12:45 AM   #1084
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Slowly I rebuild my Naim clone.
Actually the schematic based on the NCC200 kit. It sound so much better in any way compare to the Ebay Naim kit not even can mentioned in the same league.
I had two Ebay clone, the first I purchased many years back from Tubes hunter that time he sold his kit expensive and with original transistors (not counterfeit)
At first I did like the amp sound I did listen the amp over 6-8 months.
I ordered other kit for the PC board so I can start to test different transistors and capacitors in each place.
Later I found the NCC200 clone so I took the McBride PC board layout and I modded after the NCC200 circuit.
I built the new amp with the same component like my first Ebay kit.
Sound wise Heaven and earth between the amplifier to favour of the NCC200.
After I spent several (4-5) moths testing each place different transistors and capacitors until I get a really great amp.
Now I did not had chance to compare my clone with the orig NCC200 since that way to expensive just to get it for comparison.
All I can say I did listen my clone few mouths and I went back to the Ebay kit to compare it again after burn in.
I could not listening the Ebay kit any more the difference was so huge.
So I sold both Ebay kit..
Now after all those test I have to rebuild my clone because I soldered and re-soldered that PC board over 4-5 month it became a junk..
Now the new PC board was designed so I can test the Greg Ball modification to.
I hope soon I ca report back the result.
I kept one side the orig and another side with the mode.
I do believe it is important to burn in the components so when I test a amplifier I give min. 50hours to the new component to burn in.
Also important to match the components to each-other. Not enough to pick the best components and build.
My experience that often do not gave the best result sound wise!

Greetings Gabor
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Old 25th May 2013, 07:47 AM   #1085
caowei is offline caowei  China
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Hello everyone, I am from China, I also recently DIY NAP140, Ó¢¹śNAIM-NAP-140 ??? - Powered by Discuz! ,
do not know the original NAP140 quiescent current is how much? My hands have a genuine NAIM 3R, 0.22 resistor bias is 2.8MV, now I'm the DIY NAP140 is transferred 2.8MV, sounds okay, but I would like to further optimize the use of the power transistor MJ15003.
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Old 25th May 2013, 07:51 AM   #1086
caowei is offline caowei  China
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I had just arrived forum, do not know how to upload photos?
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Old 25th May 2013, 12:43 PM   #1087
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Quote:
Originally Posted by caowei View Post
...... My hands have a genuine NAIM 3R, 0.22 resistor bias is 2.8MV, now I'm the DIY NAP140 is transferred 2.8MV, sounds okay, but I would like to further optimize the use of the power transistor MJ15003.
The bias current for NAP 140 and most similar NAIM designs is already discussed several times in this thread. The current is in a range of 25-38mV maximum before instability becomes likely in the original Naim design with its small case etc. It will vary for individual DIY ideas.

Remember, the time for bias to stabilise is dependent on the size and type of case because there is no thermal connection to the output stage other than by air transfer or direct radiation. In some installations it may never stabilise and this is part of Naim amplifiers' typical long, >20 min. "warm-up" time.

The voltage is measured across one or preferably both 0.22R "emitter" resistors to determine the bias current. 11mV across 0.44R obviously means 25 mA current. This is a good starting point after first testing with zero bias when building. I hope this answers your question but don't forget to check out other posts discussing the bias setting. Other guys have different ideas and some may be OK if the current is still below the advised maximum.
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Last edited by Ian Finch; 25th May 2013 at 12:50 PM.
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Old 25th May 2013, 01:16 PM   #1088
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Quote:
Originally Posted by gaborbela View Post
....... Now the new PC board was designed so I can test the Greg Ball modification to.
I hope soon I ca report back the result.....
No result? Perhaps you found a very different sound with Greg's engineering approach having both LTP collector resistors equal. That usually kills the even harmonic distortion, and for this reason, NAP and NCC200 both have intentional gross LTP imbalance.

When heard a quickly converted trial version of the modification, I have to say I was really unimpressed. Perhaps if the clone sounded typically poor already, it might have been an improvement but this improved clone originally did sound close to genuine Naim.
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Old 25th May 2013, 01:33 PM   #1089
caowei is offline caowei  China
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Quote:
Originally Posted by Ian Finch View Post
The bias current for NAP 140 and most similar NAIM designs is already discussed several times in this thread. The current is in a range of 25-38mV maximum before instability becomes likely in the original Naim design with its small case etc. It will vary for individual DIY ideas.

Remember, the time for bias to stabilise is dependent on the size and type of case because there is no thermal connection to the output stage other than by air transfer or direct radiation. In some installations it may never stabilise and this is part of Naim amplifiers' typical long, >20 min. "warm-up" time.

The voltage is measured across one or preferably both 0.22R "emitter" resistors to determine the bias current. 11mV across 0.44R obviously means 25 mA current. This is a good starting point after first testing with zero bias when building. I hope this answers your question but don't forget to check out other posts discussing the bias setting. Other guys have different ideas and some may be OK if the current is still below the advised maximum.
Thank you for your reply, I try late.
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Old 26th May 2013, 03:06 AM   #1090
caowei is offline caowei  China
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Hello iam finch, I just do the experiment and found that the quiescent current or in the 11MA (a 0.22R across the resistor 2.8MV) when listening to sound better, specifically natural sound more clear, 25MA, I felt some noisy ear . ^ _ ^
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