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Old 3rd June 2005, 01:08 AM   #1
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Default Quick Heatsink question

I want to start building some nicer amps that if they work well I could start selling.

My first model would be a stereo LM3886TF amp. I'm trying to find affordable heatsinks that look nice and work well also. I found these and they look like they meet the requirements for this chip by far, but I just wanted to confirm this. http://www.allelectronics.com/cgi-bi...966&type=store

Another thing is I'd like some suggestions on what these would be worth and what I could get for them assuming they look and sound very good. I plan on, as I said, running two LM3886TF chips so the amp can handle 8 or 4 ohms, or can be bridged with a DRV134 for driving an 8-ohm speaker at 120-130W. The amp would run off of a +/-35VDC torroid-based power supply.

I'm planning on using wood/metal construction for these amps. The heatsinks will be in the front, with a wood center for the LED and volume control (if I build the preamp into it, I'm not sure yet), and the sides will be wood and finally, the top and bottom would be aluminum to match the heatsinks.

That case design is not for sure what I will be doing. I'm just writing what I'm picturing in my head. Who knows-maybe when I draw it or build a prototype it will look bad. I guess I'll just have to find out.

Any ideas would really be appreciated!!

Thanks,
Mike
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Old 3rd June 2005, 07:41 AM   #2
Nuuk is offline Nuuk  United Kingdom
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Mike, as you are probably discovering, the biggest obstacle to building/selling GC's is finding heatsinks/cases at a price that allows you to still make a profit!

IMHO, you would need two of the heatsinks in that link, one per channel, especially for the LM3886.

The other thing that came to mind reading your post, if you want the amps to drive 4 ohm loads, you would be better off with lower voltage rails!
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Old 3rd June 2005, 10:13 AM   #3
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Mike,
one essential value you need to take the fitting heatsink is missing - the K/W - value. This walue gives the heat amount, the heatsink could handle. On your link this value is missing. So it's impossible to make a decision of taking this heatsink or not...
From the physical dimension i would assume this heatsink i too small for both chips. For a single chip - maybe. And: heatsinks without a fan must have bigger gaps between each fin.

BTW: I thought this is a non-profit forum, not for commercial use...?!

Michael
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Old 3rd June 2005, 10:22 AM   #4
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Default Re: Quick Heatsink question

Quote:
Originally posted by soundNERD
I want to start building some nicer amps that if they work well I could start selling.

My first model would be a stereo LM3886TF amp. I'm trying to find affordable heatsinks that look nice and work well also. I found these and they look like they meet the requirements for this chip by far, but I just wanted to confirm this. http://www.allelectronics.com/cgi-bi...966&type=store

Spreadsheet for calculating heatsink and supply requirements:

http://www.national.com/appinfo/audi...gn_Guide15.xls

I don't think the one you're looking at will be sufficient - it's designed for operation with a fan, and the fins are too close together to work well in free air.

The TF package has a higher thermal resistance between die and mounting surface and needs a bigger heatsink than the non-isolated version. Better to use the TA if you can find an insulating kit.

good luck!
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Old 3rd June 2005, 11:50 AM   #5
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Thanks for all of the help so far!

I was planning on using one per chip...but I understand what you are saying about how the fins are too close together. And two huge fans on the front of the amp wouldn't look too good.

I'd like to use these though as I already sort-of have an idea on how I would like to build the amp. The other idea I had was to have both sides with inset heatsinks, all the way across the sides. That may even work better now that I think about it. And, as I picture it in my head, I think it would look pretty nice as well.

So much for the "quick" heatsink question!!! These things are complicated!!!

For me, I think the most expensive part would be the torroid and possibly the case. The heatsinks do not seem badly priced at all (at least those I linked to earlier), and I've got plenty of nice wood sitting around. For the torroid, it seems like the more I look the more I realize how much a chunk of metal wound around a "doughnut" (don't know the exact name ) is!!!

Thanks again for the great suggestions,
Mike
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Old 3rd June 2005, 11:57 AM   #6
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WOW


I wish these were less money and I could think of some way to integrate them into my amp!!!

http://www.electronicsurplus.com/ccp...6-282-3631.htm
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Old 3rd June 2005, 12:07 PM   #7
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Quote:
Originally posted by soundNERD
So much for the "quick" heatsink question!!! These things are complicated!!!
Once you get your hands on the relevant data, calculating heatsink requirements is pretty simple arithmetic. Have a look at the LM3886 datasheet - there's a step-by-step guide. You do need to know the heatsink's K/W rating that Michael mentioned though, or find a way of measuring it if the vendor won't/can't tell you.

Or you could just suck it and see - worst that could happen with the LM3886 is that it'd shut down. Be glad you're not trying to build a class A amp!
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