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NAP-140 Clone Amp Kit on Ebay
NAP-140 Clone Amp Kit on Ebay
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Old 15th September 2018, 12:07 AM   #3211
pattox is offline pattox  Australia
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Originally Posted by traderbam View Post
I've marked up the amplifier schematic with what I would do.
--> No warranty implied <--

You may get conflicting advice here (very rare in DiyAudio) and I am not always going to explain things because I am secretive. But you may want to assemble one board this way as a comparison.

Also, your transistors are not the Naim choices and not matched so this will cause an unpredictably worse result. Unless you use Naim's build process it will not sound as good as a Naim. It is up to you whether you decide to spend extra money on these parts.

Schematic changes
- Remove crossed out parts. Replace with wire as appropriate.
- Use 35V tantalums for C7 & C10. DOn't use lower voltage ones as they may not like being reverse biased during half the music signal. IF YOU ARE NOT EXPERIENCED building these then use electrolytics for power-on and once you are sure the dc offsets are ok then change to tantalums.
- the base networks on the darlingtons will not be correct for these transistors. I am not going to explain how to correct them but you stand a better chance if you use MJE243/253 drivers like Naim does.
- Inputs better with BC550C low noise.
- Adjust R26 (Q8 emitter resistor) to get the dc offset small. The BC546 is ok but it is different from the ZTX part Naim uses and the Vbe will be different.
- Remove output coil, replace 15ohm with 0.22.

Power Supply
The supply should be transformer with separate winding for each rail, two bridges & two smoothing caps per channel. Use good caps as I mentioned earlier. Don't wire lots of caps together. You need to be careful with your grounding paths. This is very important and there is lots of advice around here about that already.

I can't comment on the regulated supply yet. I need to find time to study it. But use the board unregulated to start with anyway. See how it sounds.
I'm not sure if I'm missing something but even with the suggested changes there seem to be quite a few resistors the values of which are wildly different from those in many schematics of the NAP140/200/250 /ncc200 that I've seen.

eg R001 71R Should be 100k ?
R026 92R " " 620R ?
R28 51R " " 8R2 ?
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Old 15th September 2018, 03:01 AM   #3212
Ian Finch is online now Ian Finch  Australia
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Originally Posted by traderbam View Post
......
May I ask what caps you recapped the psu with?
The most recently fitted electrolytics are standard Kemet ALT22A type, if I recall correctly. For a very short period I fitted Kendeil KO5 but I was uneasy about it - probably because of the idea as much as the perception of change from a past audio experience.
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Old 15th September 2018, 10:22 AM   #3213
traderbam is offline traderbam  Europe
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Quote:
Originally Posted by pattox View Post
I'm not sure if I'm missing something but even with the suggested changes there seem to be quite a few resistors the values of which are wildly different from those in many schematics of the NAP140/200/250 /ncc200 that I've seen.

eg R001 71R Should be 100k ?
R026 92R " " 620R ?
R28 51R " " 8R2 ?
You are quite right. Some of the resistor values are backwards. So the 100R is shown as R001 and the 620R is R026 and the 8.2R is R2.8.
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Last edited by traderbam; 15th September 2018 at 10:28 AM.
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Old 15th September 2018, 10:27 AM   #3214
traderbam is offline traderbam  Europe
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Originally Posted by Bigun View Post
I do believe the earlier DACs that were expensive were far better than the lower cost ones. There have been a lot of advances in DAC chip engineering since then and some companies have done much to take advantage of this e.g. Schitt. Their stuff looks good although I haven't auditioned it.
I'm sure you are right. It goes beyond the DAC chip of course...clock quality, noise, component quality, power supply.
But I am willing to follow your advice and modernize; would you please buy me one of these for my birthday this month? Alpha DAC Reference Series 2 MQA — Berkeley Audio Design
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Old 15th September 2018, 01:12 PM   #3215
Bigun is offline Bigun  Canada
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NAP-140 Clone Amp Kit on Ebay
I didn’t see any mention of the price but judging by it’s appearance I’m afraid to ask!
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Old 15th September 2018, 10:49 PM   #3216
coresta is offline coresta  France
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Originally Posted by Ian Finch View Post
Do we know just how many individual amplifiers are used to make up the 1450W/4R rating?
I spent an hour looking at detailed pictures of that beast ... IMHO each channel is a stereo bridged 200W : 4 cells are + and - (2 NPN and 2 PNP) output branchs, 2 cells are the drivers ... So : 800W @ 8ohms , i.e. theoritically 1600W 4 ohms, 3200W 2 ohms and 6400 at 1 ohm
...if power cord is bigger than the genuine one
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Old 16th September 2018, 12:51 AM   #3217
Bigun is offline Bigun  Canada
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NAP-140 Clone Amp Kit on Ebay
with this kind of beast, the 'sound' is going to be dictated by the pre-amp not the power amp.
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Old 16th September 2018, 07:19 AM   #3218
coresta is offline coresta  France
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yes , and the line preamp seems to contain 18 paralled ones ..
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Old 16th September 2018, 10:22 AM   #3219
traderbam is offline traderbam  Europe
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Quote:
Originally Posted by coresta View Post
I spent an hour looking at detailed pictures of that beast ... IMHO each channel is a stereo bridged 200W : 4 cells are + and - (2 NPN and 2 PNP) output branchs, 2 cells are the drivers ... So : 800W @ 8ohms , i.e. theoritically 1600W 4 ohms, 3200W 2 ohms and 6400 at 1 ohm
...if power cord is bigger than the genuine one
Yes each of the four power amp boards contain the same type of transistor. 2 boards are NPN and two are PNP. Steve Sells states they use "positive feedback error cancellation" and there is no global NFB around the voltage gain stage.
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Last edited by traderbam; 16th September 2018 at 10:24 AM.
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Old 16th September 2018, 01:57 PM   #3220
Vrystaat is offline Vrystaat  South Africa
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But is it not about in every amp that the front end( make) the big difference in sound character ?
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