heatsink/chassis question

alizawi · 5th April 2006, 02:38 AM

My search on this forum still left me a little misguided.....is the chassis efficient enough as a heatsink for the lm3875 on its own, or is an additional heatsink required with the chassis....and I'm having trouble finding a chassis that can be delivered FAST to me....anyy suggestions?
Thanks

DcibeL · 5th April 2006, 03:18 AM

It depends on a couple of things. What material is the chassis made of? How thick is the material? How much power will you actually be using (how sensitive are your speakers?)?

I would say that if you are mounting to a steel chassis, then no, you need a heatsink. But an aluminum chassis, maybe. In my opinion your best bet to be heatsinkless is to try and mount the IC's somewhere where you would be able to add a heatsink later. You can then mount the chips without the heatsink and take measurements to see if it will be okay. Many modern multimeters have a thermocouple input that works great for this task. If the temperature measurements are unacceptable, you can then add the heatsink.

When adding a heatsink, it is best to cut a hole in the chassis for the IC to stick through and attach directly to the heatsink (will provide better thermal transfer). That is, instead of:

IC -> thermal paste -> chassis -> thermal paste -> heatsink

you would have:

IC -> thermal paste -> heatsink

alizawi · 5th April 2006, 05:11 AM

I'm tring to find an aluminum chassis...not sure where to find one though, any ideas? I need this kinda fast.......but just to clarify what you said, if I cut the hole in the chassis, its just the size of the chip, and not the heatsink...so the heatsink will stick to the part of the chip that is exposed, and to the outside of the chassis..right?

DcibeL · 5th April 2006, 08:16 PM

What you have explained will work well, in fact it is the same method I have used with my amp. In reality, how you mount the heatsink is completely up to you. Searching this forum you will find many different ideas.

About a chassis, check with your local electronics supply store.Par Metal has some great chassis for their price. ATI also has some excellent chassis, but you would most likely have to wait longer for shipping from them since they are in Thailand.

alizawi · 5th April 2006, 09:40 PM

thanks....yeah the ATI has great stuff, but I don't have that kind of time...I'll check out the other one you mentioned....I'm just gonna stick to that method I explained then, and use heatsink compound

5th April 2006, 02:38 AM	#1
alizawi diyAudio Member Join Date: Feb 2006 Location: California	heatsink/chassis question My search on this forum still left me a little misguided.....is the chassis efficient enough as a heatsink for the lm3875 on its own, or is an additional heatsink required with the chassis....and I'm having trouble finding a chassis that can be delivered FAST to me....anyy suggestions? Thanks

5th April 2006, 03:18 AM	#2
DcibeL diyAudio Member Join Date: May 2003 Location: Saskatchewan	It depends on a couple of things. What material is the chassis made of? How thick is the material? How much power will you actually be using (how sensitive are your speakers?)? I would say that if you are mounting to a steel chassis, then no, you need a heatsink. But an aluminum chassis, maybe. In my opinion your best bet to be heatsinkless is to try and mount the IC's somewhere where you would be able to add a heatsink later. You can then mount the chips without the heatsink and take measurements to see if it will be okay. Many modern multimeters have a thermocouple input that works great for this task. If the temperature measurements are unacceptable, you can then add the heatsink. When adding a heatsink, it is best to cut a hole in the chassis for the IC to stick through and attach directly to the heatsink (will provide better thermal transfer). That is, instead of: IC -> thermal paste -> chassis -> thermal paste -> heatsink you would have: IC -> thermal paste -> heatsink __________________ The power of Science compels you!

5th April 2006, 08:16 PM	#4
DcibeL diyAudio Member Join Date: May 2003 Location: Saskatchewan	What you have explained will work well, in fact it is the same method I have used with my amp. In reality, how you mount the heatsink is completely up to you. Searching this forum you will find many different ideas. About a chassis, check with your local electronics supply store.Par Metal has some great chassis for their price. ATI also has some excellent chassis, but you would most likely have to wait longer for shipping from them since they are in Thailand. __________________ The power of Science compels you!

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5th April 2006, 05:11 AM	#3
alizawi diyAudio Member Join Date: Feb 2006 Location: California	I'm tring to find an aluminum chassis...not sure where to find one though, any ideas? I need this kinda fast.......but just to clarify what you said, if I cut the hole in the chassis, its just the size of the chip, and not the heatsink...so the heatsink will stick to the part of the chip that is exposed, and to the outside of the chassis..right?

5th April 2006, 09:40 PM	#5
alizawi diyAudio Member Join Date: Feb 2006 Location: California	thanks....yeah the ATI has great stuff, but I don't have that kind of time...I'll check out the other one you mentioned....I'm just gonna stick to that method I explained then, and use heatsink compound

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