LM4780 insulators

BrianGT · 17th April 2009, 10:00 PM

I haven't built up an LM4780 amp in a while, and was wondering what people are currently using to isolate the chip.

Previously, I bought some big sheets of insulator material and cut them for the strange sized package, but would rather find something made for this task, vs buying a big sheet.

What are others using?

--
Brian

taj · 17th April 2009, 10:06 PM

I bought a sheet of non-pressure sensitive Kapton (polyimide) on eBay for about $5 and I cut out appropriate-sized pieces and use it like mica insulators, with grease. It's nice to work with since it just cuts like a thin plastic (which it is) with scissors.

..Todd

MJL21193 · 17th April 2009, 10:15 PM

Quote:

Originally posted by taj
I bought a sheet of non-pressure sensitive Kapton (polyimide) on eBay

I've got similar stuff but I'm flummoxed as to how to make a hole in it. Cutting is easy - the hole is not.

What are you using?

pacificblue · 17th April 2009, 11:14 PM

http://www.campbell-bosworth.com/han...es/punch2.html

sangram · 18th April 2009, 07:13 AM

I go bare onto the heatsink for open chassis amps.

For closed chassis, I use Mica insulators used for TO3 transistors. There is no other option available here. Scissors are used to shape the pads, and a small needle makes enough of an ingress for the bolt to spear through. I also divide the insulator: One can easily yield three. Thermal transfer is excellent this way.

We have suppliers who deliver custom shapes for bulk orders, and of good Indian Mica. They tend to be very thick however. I am sure other grades exist, but those are not commercially available. Splitting the mica works fine, but requires a new insulators if taken apart, as it is pretty fragile like that.

sakis · 18th April 2009, 10:59 AM

Quote:

Originally posted by MJL21193

I've got similar stuff but I'm flummoxed as to how to make a hole in it. Cutting is easy - the hole is not.

What are you using?

aaa this is very very easy ....the only thing you need to do is to go in a belt shop there you can see the tool they use to make holes in leather belts .... you may buy one of them and they are really nice to use ...( comes with a various holes ) and also very very cheap

regards
sakis

Peter Daniel · 18th April 2009, 02:00 PM

That tool does not always work well, a lot depends on quality and sharpness of the tubes:

You can make aluminum template and drill the holes through (a wooden base required); that produces most accurate and clean holes.

Ted205 · 20th April 2009, 10:42 AM

i have to admit this is one of the reasons i've moved away from lm4780s'

AndrewT · 21st April 2009, 07:28 AM

If the IC is clamped to the heatsink then an insulator without a hole is perfectly adequate.

chipco3434 · 21st April 2009, 11:55 AM

If I had one of those hole punches, I couldn't find it in any case.

Here's a simple scheme... Find a piece of tubing who's ID matches the size of the hole you want. Grind the edges so it's sharp on one end... bevel them to form a knife edge. Add a hammer to the equation.

Can't find a piece of tube? Drill a hole axially into a piece of steel... doesn't have to be very deep. Sharpen.

Can't find a drill or piece of steel?

Consider golf or horseback riding.

17th April 2009, 10:00 PM	#1
BrianGT diyAudio Moderator Emeritus Join Date: Jan 2002 Location: near Atlanta, GA	LM4780 insulators I haven't built up an LM4780 amp in a while, and was wondering what people are currently using to isolate the chip. Previously, I bought some big sheets of insulator material and cut them for the strange sized package, but would rather find something made for this task, vs buying a big sheet. What are others using? -- Brian

17th April 2009, 11:14 PM	#4
pacificblue diyAudio Member Join Date: May 2008	http://www.campbell-bosworth.com/han...es/punch2.html __________________ If you've always done it like that, then it's probably wrong. (Henry Ford)

18th April 2009, 02:00 PM	#7
Peter Daniel diyAudio Member Join Date: Jul 2002 Location: Toronto, Canada	That tool does not always work well, a lot depends on quality and sharpness of the tubes: You can make aluminum template and drill the holes through (a wooden base required); that produces most accurate and clean holes. __________________ www.audiosector.com “Do something really well. See how much time it takes. It might be a product, a work of art, who knows? Then give it away cheaply, just because you feel that it should not cost so much, even if it took a lot of time and expensive materials to make it.” - JC

21st April 2009, 07:28 AM	#9
AndrewT diyAudio Member Join Date: Jul 2004 Location: Scottish Borders	If the IC is clamped to the heatsink then an insulator without a hole is perfectly adequate. __________________ regards Andrew T.

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17th April 2009, 10:06 PM	#2
taj diyAudio Member Join Date: Feb 2005	I bought a sheet of non-pressure sensitive Kapton (polyimide) on eBay for about $5 and I cut out appropriate-sized pieces and use it like mica insulators, with grease. It's nice to work with since it just cuts like a thin plastic (which it is) with scissors. ..Todd

18th April 2009, 07:13 AM	#5
sangram diyAudio Member Join Date: Sep 2002 Location: India	I go bare onto the heatsink for open chassis amps. For closed chassis, I use Mica insulators used for TO3 transistors. There is no other option available here. Scissors are used to shape the pads, and a small needle makes enough of an ingress for the bolt to spear through. I also divide the insulator: One can easily yield three. Thermal transfer is excellent this way. We have suppliers who deliver custom shapes for bulk orders, and of good Indian Mica. They tend to be very thick however. I am sure other grades exist, but those are not commercially available. Splitting the mica works fine, but requires a new insulators if taken apart, as it is pretty fragile like that.

20th April 2009, 10:42 AM	#8
Ted205 diyAudio Member Join Date: Jun 2008	i have to admit this is one of the reasons i've moved away from lm4780s'

21st April 2009, 11:55 AM	#10
chipco3434 diyAudio Member Join Date: Feb 2004 Location: Racine, Wisconsin	If I had one of those hole punches, I couldn't find it in any case. Here's a simple scheme... Find a piece of tubing who's ID matches the size of the hole you want. Grind the edges so it's sharp on one end... bevel them to form a knife edge. Add a hammer to the equation. Can't find a piece of tube? Drill a hole axially into a piece of steel... doesn't have to be very deep. Sharpen. Can't find a drill or piece of steel? Consider golf or horseback riding.

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