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Old Yesterday, 07:53 PM   #3601
johnego is online now johnego  Indonesia
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Originally Posted by Ian Finch View Post
it took Naim decades to get around to improving the thermal design of their amplifiers so that they settled faster
Theoretically it is easy just to do a good thermal tracking of an amplifier. But to do this without changing the known optimal operation of the circuit is the issue. It is obvious (to me at least) that amplifiers of this bandwidth and topology have narrow window for good sounding operating points.
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Old Yesterday, 08:50 PM   #3602
lohk is offline lohk  Europe
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As far as.I know in early stages of the NAP110 the bias tracking transistor was actually thermally connected to one of the drivers heatsinks. But I am not at home right now to look up that fact in my archive.
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Old Yesterday, 09:00 PM   #3603
Bigun is offline Bigun  Canada
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NAP-140 Clone Amp Kit on Ebay
Ian - I don't think the transistor type has that much influence on the speed of the thermal feedback control - just to nit pick - the real issue in my opinion is the one you mention - dangling the Vbe device in thin air inside the enclosure is the real issue in the original design. It's simply poor engineering. I fixed that in my clone with the benefit of Spice simulations to allow a first-time-right solution.
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Old Yesterday, 09:01 PM   #3604
huggygood is offline huggygood  France
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to my knowledge,no and that was never the case for the chrome bumper and olive generation

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Old Yesterday, 09:07 PM   #3605
johnego is online now johnego  Indonesia
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Originally Posted by lohk View Post
As far as.I know in early stages of the NAP110 the bias tracking transistor was actually thermally connected to one of the drivers heatsinks. But I am not at home right now to look up that fact in my archive.
Just observe that the negative part of a quasi is a CFP, then you will remember.
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Old Yesterday, 09:19 PM   #3606
johnego is online now johnego  Indonesia
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Originally Posted by Bigun View Post
dangling the Vbe device in thin air inside the enclosure is the real issue in the original design. It's simply poor engineering. I fixed that in my clone with the benefit of Spice simulations to allow a first-time-right solution.
Design is about making compromises. That's especially true in amplifiers with NAP's bandwidth and topology. You can make small change to the circuit (eg to make the thermal tracking better) but will the sound be similar? Try it with the original/commercial NAP!

I don't think that the speed to reach optimal bias is not part of the compromises to make. Ime, it is part of the compromise. An out of the box solution is to design a dedicated cct that will sense the cold heatsink then QUICKLY heat up the heatsink and stop when a certain temperature (or time) is reached. Poor engineering, huh?
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Old Today, 12:08 AM   #3607
Bigun is offline Bigun  Canada
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I'm at a loss to identify any compromise that could explain the choice of thermal management of the original design other than not having the cost associated with mounting a Vbe multiplier device onto a solid surface where it can properly 'measure' the temperature of the output stage and also, no longer being able to tell customers that they need their amp to warm up for half an hour before it's stable just like fancy Class A amplifiers.

The 'speed' of the thermal control loop need not be super fast because the heatsink acts like a low pass filter for temperature changes.

Still, it's also no big deal. It's part of the charm and character of the original design. I decided to 'fix' it because I wasn't trying to clone the amplifier exactly - for starters I used a different pcb layout and I used modern components that I was able to buy new and these for sure are different from the original production units. I accept the clone is not 100% but my experience of the sound is an uncanny match to published reviews for the Naim and that's good enough for me to enjoy myself making it. If I was to insist on an exact copy I'd just go out and buy a real Naim amp on the used market - they keep their value well so it would not cost me anything that I'd worry about. I have thought that as my interest in firing up the soldering iron wanes over the years I might switch to collecting the originals but I wouldn't learn much that way.
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Old Today, 01:21 AM   #3608
Ian Finch is offline Ian Finch  Australia
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Quote:
Originally Posted by Bigun View Post
Ian - I don't think the transistor type has that much influence on the speed of the thermal feedback control - just to nit pick - the real issue in my opinion is the one you mention - dangling the Vbe device in thin air inside the enclosure is the real issue in the original design. It's simply poor engineering....
I thought that was exactly the point I was making. The NAP 200 and probably other models in that series and maybe some in the olive series that preceded it, were finally reducing the thermal delay problem to a tolerable one by closer proximity to the heatsink.

It was a stubborn acceptance of the long delay and lame excuses by both the manufacturer and defensive owners that turned me off Naim products long ago. DIY experiments and fun here in recent times have been a great education in what could have easily been done 30 or more years ago, just by examining what the competition was already achieving at little extra cost.
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Old Today, 01:46 AM   #3609
Bigun is offline Bigun  Canada
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sorry, missed your point then, my bad!
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Old Today, 02:06 AM   #3610
johnego is online now johnego  Indonesia
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Originally Posted by Bigun View Post
I'm at a loss to identify any compromise that could explain the choice of thermal management of the original design other than not having the cost associated with mounting a Vbe multiplier device onto a solid surface where it can properly 'measure' the temperature of the output stage.

Let's talk about the real NAP design. I don't know about the amps but if you really think that mounting the Vbe transistor to an aluminum plate that is connected to either the driver or the output will solve the problem (without changing anything else), then you are right. Do you think any amp manufacturer might need decades to think about such solution?


I can say tho there are cases where you cannot just do like the above. Look at the driver-output pair of the negative part (CFP). The bias window is so narrow. There is one short-range optimum bias where below this the sound is horrible and above this the sound is not so good either. In other words the bias is sensitive. Then combine that situation with another where you are not allowed to speed up the bias by increasing the Vbe of the driver...
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