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-   -   Heatsink approval needed for lm3886 (http://www.diyaudio.com/forums/chip-amps/105950-heatsink-approval-needed-lm3886.html)

svbear 27th July 2007 05:53 PM

Heatsink approved needed for lm3886
 
2 Attachment(s)
Hi All,

I found someone selling these heatsinks.

The Dimensions are 15 & 1/10 inches long and 7 inches wide and the fins are about 5/8 inch tall.

I was thinking of using BrianGT's pcb boards with it, and having it lay horizontal as a top cover to the amp case.

Any opinions on if it's decent enough, and how many chips could I possibly run on it (with and without fan cooling on top).

Also, does anyone know if Brian's boards can be used with the lm3875 (with minor modifications).


Many Thanks Again,

Adrian

svbear 27th July 2007 05:54 PM

2 Attachment(s)
Different photo.

svbear 27th July 2007 10:07 PM

Heatsink approval needed for lm3886.
 
Sorry Gents,

The title should say approval needed.

That's what I get for typing while on the phone at work.

So, would any of use this car amp heatsink for for chipamps?

Thanks,

Adrian

BWRX 27th July 2007 10:41 PM

You could use that heatsink for at least a couple chip amps.

gtforme00 27th July 2007 11:00 PM

You might want to read National's application note here: http://www.national.com/an/AN/AN-1192.pdf

But that's a lot to read to just say this. Based on AN-1192's suggested heatsink for the Bridged or Parallel LM3886's (see page 19 of AN-1192), I would say that the extrusion you are considering could take 2 chips for every 3 linear inches of heatsink (one on each thick part of the extrusion cross section I recommend). That's about 10 chips for the whole thing! If you are going to be using this in a hot environment or are going to be bridging/paralleling these you might want to err on the conservative side.

I personally have a similar heat sink and similar application and will be using 8 chips on mine. I wouldn't hesitate to add the other two if I needed them though.

Regards,
David

svbear 27th July 2007 11:54 PM

Cool.
Thanks guys. I was worried about the shallow fins, but it was designed for an old school rockford fosgate car amp, so I figured it must be something pretty decent.

He is selling them for $10, I was thinking of getting a couple.

He also has shorter ones, same design, same price.

I was thinking also of hunting down some black plexiglass for the front and back panels.

Adrian

Magura 27th July 2007 11:58 PM

Quote:

Originally posted by svbear
Cool.
Thanks guys. I was worried about the shallow fins, but it was designed for an old school rockford fosgate car amp, so I figured it must be something pretty decent.

He is selling them for $10, I was thinking of getting a couple.

He also has shorter ones, same design, same price.

I was thinking also of hunting down some black plexiglass for the front and back panels.

Adrian


To make a couple of chipamps, all you need is one heatsink and a hack saw :)

I would guess that you could get by with at least cutting it in halves, maybe even in thirds...


Magura :)

gtforme00 28th July 2007 12:22 AM

To answer your other question about the LM3875. I know that the 2876 is pin compatible, but don't have personal experience with the LM3875. A short trip to the National website reveals the following pinouts:
http://www.national.com/images/pf/LM3886/01183302.jpg
http://www.national.com/images/pf/LM3875/01144902.jpg

They don't look pin compatible to me. I would have to assume that it would be not be worth trying to use the LM3875 if you could help it.

Regards,

David

AndrewT 28th July 2007 11:59 AM

Hi,
mute and ground are the incompatible pins.

Magura's hacksaw will do wonders for keeping the chips cooler.

Try cutting that tall heatsink into two shorter halves. It will dissipate about 40% more heat if the two halves are placed side by side.

Similarly if it were cut into 4 equal lengths it's dissipation capacity is just about doubled, compared to mouting all the devices on one giant heatsink.
One 3.7inch tall sink might just be able to cool a pair of chipamps, try fitting one first and see how cool/warm/hot it runs.

pchw 28th July 2007 07:44 PM

Hi Andrew,

Sorry for the stupid question, why cut the heat sink in halves will dissipate 40% more heat?

Thanks!!


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