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Old 25th September 2004, 07:58 PM   #21
Magura is offline Magura  Denmark
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Quote:
Originally posted by Peter Daniel
Here it is. Worth noticing is additional shielding plate between channels, something you never see on Elma's.

Thanks. Have you ever seen such a switch IRL??

Magura
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Old 25th September 2004, 08:06 PM   #22
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Regarding the copper plate, the thinner gauge allows also for better flexibility and contact is improved if the flatness isn't perfect. That would be much harder to achieve with thicker plate.
Well yes, but doing so would counteract the very reason for putting it there in the first place!

/Magnus
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Old 25th September 2004, 08:16 PM   #23
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Quote:
Originally posted by Swedish Chef


Well yes, but doing so would counteract the very reason for putting it there in the first place!

/Magnus
How do you know that? Did you do any tests and have a proof for your claim?
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Old 25th September 2004, 08:18 PM   #24
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Quote:
Originally posted by Magura



Thanks. Have you ever seen such a switch IRL??

Magura
I didn't see the exact ones, nor lates Shallco, but I have some other, similar switchers.
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Old 25th September 2004, 08:59 PM   #25
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Quote:
How do you know that? Did you do any tests and have a proof for your claim?
No. But let's look at what is happening here.

First, lets view the case where the junction resistance between the alu heat sink and the copper plate is infinite. No matter how low the thermal resistance of the copper plate (or any other material for that matter) is or how thick it is, the total resistance will be much larger (infinite) than just using an alu heat sink.

On the other end we have the case where the junction resistance is zero, i.e. a perfect thermal junction. In this case putting any material that has a lower thermal resistance than aluminium (copper has about one-half of that of aluminium) would be beneficial, regardless of thickness.

Now, in practice we will end up with a junction thermal resistance that is between those extremes, that is with a finite value. For any such given value there will be a corresponding thickness of the copper plate (i.e. a reduction in thermal resistance compared to aluminium) that cancels the resistance of the junction, that is the net effect compared to just using aluminium is zero. Increasing the plate thickness above that value (lowering resistance in the plane paralell to the plate) will improve heat transfer compared to aluminium. Decreasing it will make heat transfer worse.

Now, neither you nor I know the exact values here, we just have gut feelings about the thickness. Only careful modeling and real world experiments would tell.
My point is that you seem to believe that just putting copper there regardless of thickness would be beneficial. I say that that is not the case.

Then there are other factors for a practical implementation. Getting a low-resistance junction is difficult. And the different thermal expansion coefficients of copper and aluminium can create great mechanical stresses on a tight junction. There are numerous other complications although not all of them are significant for audio. Total weight is one of them - critical in pro audio but a non-issue in home audio.

Cheers
/Magnus
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Old 25th September 2004, 09:05 PM   #26
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Quote:
Originally posted by Swedish Chef

My point is that you seem to believe that just putting copper there regardless of thickness would be beneficial. I say that that is not the case.
If I believe in anything here, it would be the ingenuity of Denon engineers. I don't have any precized POV on that matter as I didn't perform any tests. However, it seems to me that thinner plate is better as it doesn't store the heat, but rather spreads it and quickly release it to aluminum heatsink.

As to the thickness of that plate, it's pretty easy to figure it out from a picture; it's definitely less than 2mm.
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Old 25th September 2004, 09:36 PM   #27
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I only believe in ingenuity of Denon engineers.
Well, for purely technical issues I don't. For financial and marketing issues I do.

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As to the thickness of that plate, it's pretty easy to figure it out from a picture; it's definitely less than 2mm.
For the first time we seem to agree! That plate looks to me to be something in the vicinity of 1mm. That's what made me skeptic in the first place! But maybe that's enough, I don't know.

/Magnus
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Old 25th September 2004, 10:05 PM   #28
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Yes, my guess would be around 1.5mm.

I also don't think that this is much of a marketing issue, as people who can afford such stuff usually don't have much clue about mechanical/materials concepts, so this wouldn't impress them, especially if nothing is printed about it. Also, financially it wouldn't be worth to introduce it just for the looks.

Those who like to build equipment, definitely look at this as something interesting and worth consideration.

Well, if I decide to build one more real man's amp, I might give it a try.

PS: As an interesting insight, most of you must have seen those copper looking angles, plates and screws in some upper level Japanese stereos. Well those are not made out of copper, but a regular magnetic material is plated in this color. Makes me wonder why, maybe for corosion protection?
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Old 25th September 2004, 10:17 PM   #29
jcarr is offline jcarr  United States
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Peter's "switch 1" photo from the Denon is a Seiden. Luxman also uses these in some of their upper preamp models. The resistors are Riken RMGs (likewise used by Luxman), and found inside some Sony products.

The Seiden has a better tactile feel than a Tech-Lab or even Shallco (and is far more dependable than a Tech-Lab), but is quite large and heavy. The main reason why I don't use the Seidens is that in recent years the company has been unwilling to manufacture customized switches (I believe that they have lost key engineering staff).

BTW, the power supply of the Denon power amp (at least the PS for the output stage) utilized synchronous rectification (also using those UHC MOSFETs), which is unusual in audio amplifiers.

regards, jonathan carr
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Old 26th September 2004, 02:38 AM   #30
Magura is offline Magura  Denmark
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Quote:
Originally posted by Swedish Chef



Now, neither you nor I know the exact values here, we just have gut feelings about the thickness. Only careful modeling and real world experiments would tell.
My point is that you seem to believe that just putting copper there regardless of thickness would be beneficial. I say that that is not the case.

For a TO-247 the "magic" number is a 10*50*100mm copper bar, with those dimensions the benefit is obvious. This is proven by real life setups. I usually go for more than that, but that's only because most heatsinks are so incredibly skimpy that you can benefit from it, if not for that there would not be any significant benefit, as the heat would never reach the edges of the copper.

As for the other drawbacks you mention, I have never seen any of them in real life applications, though theoretically you're right.

Magura
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