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Old 24th September 2003, 11:01 AM   #21
tcpip is offline tcpip  India
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Default How do you fix chip to heatsink?

Quote:
Originally posted by Peter Daniel
Just to let you understand this better, the non insulated version has copper tab exposed, while the insulated is covered with plastic, which is not the best heat transfer material.
Thanks, everyone. Got it. I hadn't realised that in order to isolate the back plate, NS was actually putting a layer which was a poor heat conductor. This seems silly, but I guess they have their reasons.

Okay, now that I know I'll need to look for the non-isolated version, can you tell me what you consider the best inexpensive way to insulate heatsink from chip? I am told mica washers are better conductors (because of their thinness?) than Sil-pads. Also, I feel that Sil-pads will inherently be a worse approach because they are soft and compressible, and the chip comes with a hole for just one screw, right at the top. That way, the bottom of the chip will tend to rise off the heatsink, because the Sil-pad will act as a spring-cushion. I've seen this happen, visually, though I don't know how much this reduces heat conduction.

Also, I presume I'll need a non-conducting shoulder washer to isolate the bolt from the chip? I have drill, drill bits, and taps to tap a threaded hole in the heatsink for a bolt of appropriate size. If I need to fit a shoulder washer, I am using a bolt of thread size 9BA. If I can do away with the washer, I can use a bolt of tap size 3mm. Any comments/recommendations on these?

I ask because I've seen 2SA1943/2SC5200 transistors, and their back plate (metallic) has a fairly wide (2mm radius?) annular gap near the bolt-hole, thus making it very unlikely that the bolt will touch the conducting metal surface. In those cases, I guess I can just use a Sil-pad or mica sheet, but do away with the shoulder washer.

What do you guys recommend?

Thanks once again for all the help. I know I'm asking for micro-guidance, but it's the details which screw up my DIY.

Tarun

PS: I don't know whether the author of the Gainclone FAQ in Decibel Dungeon is reading this. I wish we could ask him to add one little piece on T versus TF chips, and another about the ways of fixing the chip to heatsink.
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Old 24th September 2003, 01:17 PM   #22
ronc is offline ronc  United States
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I like the idea of lapping.I am building a new design amp with a tda1524a active pre (batt powered) which i call a " buffer" LOL.I have designed in a hold down bar so i can adjust the loading pressure and without even thermal grease the conductance will be greater, sadly the case(hammond) wont allow me to have my vortex cooling tubes as the height is too short.
ron
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Old 24th September 2003, 02:21 PM   #23
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Here's how I attached the chip in my latest amp. I didn't really notice any ill effect on sound from squeezing (although didn't compare), but I also think that comparing to my previous mounting method, this one is definitely more efficient in heat transfer. Although the chassis frame is quite big, it gets pretty warm and I think it's warmer than the previous amps. This could only mean better heat disipation.

Sil-pad was used here.
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Old 24th September 2003, 02:55 PM   #24
Bricolo is offline Bricolo  France
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Quote:
Originally posted by Peter Daniel
This could only mean better heat disipation.
On mine, It meant oscillation
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Old 24th September 2003, 03:01 PM   #25
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Quote:
Originally posted by Bricolo


On mine, It meant oscillation
On mine, it gets warm only when music is playing
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Old 24th September 2003, 03:10 PM   #26
UrSv is offline UrSv  Sweden
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Getting warm only when playing music does not mean it is NOT oscillating...
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Old 24th September 2003, 03:38 PM   #27
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I just suspect that by attaching chip almost directly to a big chunk of copper improves heat spreading and that's why the temp is higher. I wouldn't really expect the amp to oscillate, although I didn't scope it yet.
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Old 24th September 2003, 04:01 PM   #28
BTW is offline BTW
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Default Clamping method

Quote:
Originally posted by Peter Daniel
Here's how I attached the chip in my latest amp. I didn't really notice any ill effect on sound from squeezing (although didn't compare), but I also think that comparing to my previous mounting method, this one is definitely more efficient in heat transfer. Although the chassis frame is quite big, it gets pretty warm and I think it's warmer than the previous amps. This could only mean better heat disipation.

Sil-pad was used here.
Yes, clamping method will result in better heat transfer, don't forget the clamping bar on top actually behaves as an additional heat sink because the additional surface area of the clamping bar will further aid in heat transfer via convection also the screws coupling the clamping bar and the chunky heat sink below will allow a certain amount of heat transfer via conduction as well. So actually the clamping method is great from a heat transfer point of view. I think a certain amount of tuning is possible as well, anyone still remembers the Michael Green
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Old 24th September 2003, 04:04 PM   #29
Bricolo is offline Bricolo  France
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Quote:
Originally posted by Peter Daniel


On mine, it gets warm only when music is playing

OK, you win
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Old 24th September 2003, 04:28 PM   #30
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very nice peter, and close to 100 % optimal too.....
with copper bolts your soundstage will turn full cirkel....
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