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Old 27th September 2004, 10:36 AM   #51
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To sajti : Quite correct .
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Old 28th September 2004, 12:13 AM   #52
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Quote:
Originally posted by Eva
I see some facts that demonstrate that the use of copper in that design is just cosmetical :

- They use copper also in the case of the amplifier, look at the pieces that fix the walls to the floor and the capacitors to the floor . Copper is obviously not expensive for them

- The copper plate appears to be 1mm thich so it spreads essentially nothing. Even a TO-220 output device has a copper plate slighty thicker than 1mm [and featuring 0,5K/W Rth between the junction and the external side of the copper plate ] and the MT-200 Sanken devices feature about 2,5mm thick copper plates

- The cooper plate does not extend above the output devices so half of its heat-spreading capabilities are lost!

- There are no screws nor any means of fixing this copper plate to the heatsink. The copper plate is only guaranteed to make good thermal contact to the heatsink under the transistors. Also think about copper dilatation versus aluminum dilatation. the copper plate must not be continuous, it has to be divided in several pieces with dilatation joints between them since dillatation coefficient for aluminum is 26% higher than for copper

- The ouput devices are placed on the upper side of the heatsink. Shame! the upper side of any heatsink working with natural convection cooling is allways hotter than the lower side. For such a heatsink I would expect 10C difference

- The worst case dissipation for 1400W into 1 ohm resistive with +-65V rails is 1000W and this means about 40W per MT-200 device. Not only such a thin copper plate is ridiculous but also these heatsinks with such a thin heat storage/spreading base without fans are ridiculous for 1400W continuous. If they seriously wanted to reduce operating temperature they would have placed a good quality air blower with speed control. In the other hand, in normal music operation with 4 ohm speakers these MT-200 devices are not supposed to dissipate more than 5W each

Does it make any sense to use copper plates with MT-200 devices dissipating between 5W and 40W ??? How much would junction temperature decrease? Maybe 1C?

I think that kind of gear and bookleets are intended to look attractive to all those audiophiles ready to spend $20.000 or more in an amplifier and knowing nothing about thermal resistances .......
Obviously you know everything about thermal behaviour and putting successful amp design together. At least that's how it seems from your write up. Well, here are few pointers:

1. I can bet that none of the capacitor's clamps is made out of copper, nor the angles and brackets supporting PCB assembly. Clamps are chromated (or whatever the process is called) while brackets are made out of steel an plated with what looks like copper. That's a common practice with Japanese makers.

2 The copper plate is more like 1.5mm thick and it only extents as much as heatsink size allows.

3 I'm not sure how you did come to conclusion that there are no screws holding the plate to the sink. Whatever we can see, there are screws attaching devices (I see at least 22 of them, some of them with 2 screws), the board is attched with 6 screws and each bracket with 3 screws. How many screws all together? And we still don't know if they used any under the PCB.

4 The output devices are placed not only on the upper side of the heatsink, but also on the bottom side, and the same assembly is placed on the other side. I still didn't notice where the actual UHC-MOS devices are placed.

5 The MT200 devices are probably placed on the same heatsink for thermal stability. I did the same when building my A75 amp ( I placed input devices on the main heatsink) as this provided for much less DC offset drift and more steady work conditions (after initial warm up period).

6 I think this type of comments (as yours here) are good for someone who never actually built a high power amp, but again, they bring no positive input and only critism for no actual purpose, unless $20,000 price tag really annoys you.
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Old 22nd July 2005, 05:21 PM   #53
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What about the new SA1 amplifier which has just been introduced?

I recently bought the PMA-S10 Integrated amplifier which is a 50 watt/channel desigh. An amazing amplifier I must say, it also has these uhc mosfets, I tested four different type of speakers on it from 4 Ohms to 15 Ohms and it admirably drove everyone of those without batting an eyelid.
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