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NAP-140 Clone Amp Kit on Ebay
NAP-140 Clone Amp Kit on Ebay
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Old 25th September 2018, 03:38 AM   #3241
Ian Finch is offline Ian Finch  Australia
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Originally Posted by maxfrister View Post
........It is fascinating that all but 2 are still active devices and all but 3 are available from my main supplier.

I’ll need to find substitutes for BC239C, ZTX108, ZTX653/753, and a TO-3 output transistor.
See the parts advice and mod. suggestions here: Modifying Naim Audio power amplifiers It's dated but useful for getting the general idea of what's important. Don't substitute ZTX653/753 transistors or any others you can avoid because most of them do matter if you're serious about the particular sound quality. Not everything comes in the mail from Ebay, Mouser or Digikey - in the US, you'll also find these ZTX types at Newark/Element14: https://www.newark.com/c/semiconduct...tors-discretes .Unfortunately, the choice of TO3 output transistors restricts your options severely as the remaining available types are mostly limited to slower switching speeds.
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Last edited by Ian Finch; 25th September 2018 at 03:47 AM.
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Old 25th September 2018, 04:39 PM   #3242
maxfrister is offline maxfrister
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Originally Posted by traderbam View Post
They look like they have some sort of ground plane going on.

Sigh. I wish I had noticed that.


The issue with 2 input grounds is a red herring -- some of the versions of original NAP-140 boards also show that.


For transistor substitutions I am considering:


For BC239C, replace with BC550C


For ZTX108, replace with BC546


For TO-3 output transistors: MJ21194 or MJ15003




I'll try to stick with the ZTX753/ZTX763 pair even if it means ordering 1 transistor from a different supplier.
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Old 25th September 2018, 05:33 PM   #3243
Ian Finch is offline Ian Finch  Australia
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Seems OK for choices but use the MJ21194 as output transistors. It's the lesser of 2 evils but can sound superb in some older designs, particularly those with low distortion designs that are working in class A.
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Old 25th September 2018, 06:59 PM   #3244
traderbam is offline traderbam  Europe
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Originally Posted by Bigun View Post
I believe its well established that this is the case - D. Self has published much on the topic. But even with matched devices, without any emitter degeneration of the LTP or current mirrors you are not going to get great balance because the circuit that includes the VAS is not symmetrical. Secondly, the LTP interacts with the output signal via the low PSRR of the input stage to produce further harmonics. There's no simple approach to viewing the design in terms of it's sound, there are a lot of interactions going on and they are frequency dependent too.
My advice to you if you want to understand how to design an audiophile performance amplifier is to throw your Doug Self book on your gas grill the next time you are having a BBQ. Then, purged of propaganda, examine what Naim have done and enjoy trying to understand why they did it. Otherwise you might make the mistake of thinking Naim made all sorts of basic errors.
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Old 25th September 2018, 10:02 PM   #3245
Bigun is offline Bigun  Canada
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NAP-140 Clone Amp Kit on Ebay
As a book burning person you might like the latest movie rendition of Fahrenheit 451 - I watched it on a place recently. Not as good as the book, but then that's often the case.
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Old 25th September 2018, 10:40 PM   #3246
steveu is offline steveu  United States
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Some dated and/or copied but not understood details:
1. Quasi-comp was a great idea when PNP power transistors were expensive and uncommon But there are compromises that go away when you use complimentary transistors. ie no reason to do this today. The most important is cross coupling, which is a big advantage, very important.
2. There are 3 or 4 unnecessary bias drops that subtract from the output voltage potential, add to the output saturation voltage, reduce the efficiency and max power output. There are reasons for these but there are better ways to accomplish the same thing.
3. The NPN driver is connected to the wrong side of the 27R in the collector of the VBE multiplier.
4. It really needs current limit.
Oh? Suddenly this is an old thread and I see others have already said the same things. I guess I have to check the date.

Last edited by steveu; 25th September 2018 at 10:50 PM.
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Old 26th September 2018, 05:46 AM   #3247
Ian Finch is offline Ian Finch  Australia
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Yes, a lot of dismissive comments and proofs that we can't seriously be enjoying what we prefer to hear, have passed through and around these pages. The central issue is the same whenever heads clash over the merits of subjective assessment v scientific and instrumental proofs. This just amounts to saying that what we will hear through brand X is closer to the original. ergo: must sound better.

'Fact is, the essential Naim electronics and system of connected boxes was not all decided by engineers. Somehow, the demand for the product continues though, decades later and still with prices that remain particularly high. Yes, there are a lot of nits that engineers are wont to pick from Naim products but let them - almost nothing bad has happened as a result in near 50 years, still with many of the same design flaws - more than can be said for the mountain of long forgotten, technically better products.

Regarding the protection system, most designers still resort to mechanical relays, sometimes backed up by muting circuits. Typically, these bring their own failures because of their slow action and breakdown, both mechanical and of the small electrolytics in the control circuits. Even so, the service requirements for Naim products shouldn't be ignored IMV, whether you leave it to authorised agents or DIY.

I've read claims that the VI limiters ruin Naim sound. Considering that we have liked the sound regardless for decades and most claims are just parroted across forums, I think this is exaggerated or applies to amplifiers needing some attention but newer models use a dual slope limiting design that has much less chance of intrusion on signal peaks. If you are using your system within suggested limits, you don't hear any effects but if your speakers are small or otherwise very inefficient, you may well have a problem but attempting to fix it simply by removing the only protection beyond the mains fuse is plainly unwise.
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Old 26th September 2018, 06:26 AM   #3248
johnego is online now johnego  Indonesia
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Originally Posted by steveu View Post
3. The NPN driver is connected to the wrong side of the 27R in the collector of the VBE multiplier.

I just noticed this. But it isn't a mistake. Basically we can spread dummy resistors all over the circuit (at every bases, LTP emitters, along supply lines, in series with Miller cap, etc.). The more the resistors the easier or the more options we have in achieving the design objectives (some Rs will in the end need to be zeros of course).
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Old 26th September 2018, 07:17 AM   #3249
traderbam is offline traderbam  Europe
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As a book burning person you might like the latest movie rendition of Fahrenheit 451 - I watched it on a place recently. Not as good as the book, but then that's often the case.
I’ll check it out. The premise seems impractical with almost evetything widely dispersed indelibly on hard drives these days. I must confess I am guilty of permanently deleting numerous PDF files and Word documents.
Admittedly, my grill suggestion has the drawback of tainting the flavour of your food. You wouldn’t want that. Perhaps a steel bucket and a blowtorch might be better?
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Old 26th September 2018, 07:25 AM   #3250
traderbam is offline traderbam  Europe
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Quote:
Originally Posted by steveu View Post
Some dated and/or copied but not understood details:
1. Quasi-comp was a great idea when PNP power transistors were expensive and uncommon But there are compromises that go away when you use complimentary transistors. ie no reason to do this today. The most important is cross coupling, which is a big advantage, very important.
Naim still uses quasi complementary in all its products except the Statement.

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3. The NPN driver is connected to the wrong side of the 27R in the collector of the VBE multiplier.
What benefit would changing this bring?
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