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Author Topic: Heatsinks for your poweramp  (Read 85031 times)

rowdy_riemer

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Re: Heatsinks for your poweramp
« Reply #45 on: December 13, 2010, 01:20:07 PM »
Not talking about making pennies, but using pennies as a source for zinc to make zamak. :)

rowdy_riemer

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Re: Heatsinks for your poweramp
« Reply #46 on: December 13, 2010, 01:58:26 PM »
Sorry, JM, I might have misread your post.

J M Fahey

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Re: Heatsinks for your poweramp
« Reply #47 on: December 14, 2010, 12:09:39 PM »
You *read* it right, but I think you missed the
 ;)
 ;)
 ;)
 ;)
 ;)

rowdy_riemer

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Re: Heatsinks for your poweramp
« Reply #48 on: December 14, 2010, 12:28:16 PM »
Hehe.

It seems like I figured out one time that using pennies as a source for zinc would cost about twice the market value for zinc. I imagine the negligible amount of copper plating wouldn't hurt anything. I think some Zamak alloys even contain a bit of copper. But it certainly would be cheaper to find scrap zinc.

spud

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Re: Heatsinks for your poweramp
« Reply #49 on: December 15, 2010, 12:45:13 PM »
Hey I'm new here and I'm wanting to build a chip amp but when I started doing some reading and I realized that a heat-sink would be essential if I wanted any real power.  I did some searches and I found these guys:

http://www.heatsinkusa.com/storename/heatsinkusa/ViewDept-269591.aspx

Has anyone used this vendor?  Also, what size would be appropriate for a LM1875 chip amp implementation running about 15 - 20w? Probably 24v or so.  I figure the small 1 inch one would suffice since it's rated at 2.15o C/W/3 or am I not understanding the rating they give? 

Some background: I've built a few pedals (BSIABII, Double D) and have prototyped a few others (Plexi-izer, UBEscreamer, Hot-harmonics), finished 2 tube amps (AX84 HO and a Firefly) and still have 1 on the bench (a 5E3).  I've been considering taking a pedal like the ROG DD  and mating it to a chip-amp for some time but never taken the plunge.  I've got a bunch of parts (Caps, Res, Trans, Op-amps, etc) I've collected (I try to buy in bulk) and I started looking around for amp chips and I realized I needed a heat sink - but most are pretty pricey for what you get (did I mention I'm a cheap) which is a hunk of metal - but I found these guys and was wondering if this was a good source and what size(s) to get.   Optionally, if anyone can help me with doing the calculations to figure it out myself, that would be great.   

BTW - this seems like a real cool site and I'm jazzed that I found it.  Been reading a lot of the threads - great ideas and projects.

Thanks -

Jim

rowdy_riemer

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Re: Heatsinks for your poweramp
« Reply #50 on: December 15, 2010, 01:24:44 PM »
I know this isn't related to the OP, but what did you think of the firefly? I'm kinda considering building one.

spud

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Re: Heatsinks for your poweramp
« Reply #51 on: December 15, 2010, 02:31:22 PM »
Hey - well I like it, here's my implementation of it - called the Small Fry to avoid confusion with the original:

http://s252.photobucket.com/albums/hh7/spudjds/Public/Builds/AMPS/SF/

I added a tone control (By-passable) with a scooped switch.  Also added a switch to allow use of a ECC99 in addition to the 12au7 - rest of it is stock.  I recently re-did the grounds and I have a problem to debug with the boost - no work.  Oh, well - I can't leave well enough alone  ::)

My mods are all documented in the layout and the schematic there. 

Jim

rowdy_riemer

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Re: Heatsinks for your poweramp
« Reply #52 on: December 15, 2010, 03:08:54 PM »
Cool deal. Thx for sharing that.

J M Fahey

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Re: Heatsinks for your poweramp
« Reply #53 on: December 15, 2010, 05:51:56 PM »
Hi.
You somewhat misread the data but no big deal.
That last "3" means that this heatsink provides those 2.5ºC/W for a 3 inch length; they do not state it for a 1" length nor provide the dissipation vs.length table, which amazes me.
Anyway, on experience I cantell you that the actual value will be around 4ºC/W and even more important: it will be enough for a 25W chipamp.
In fact I use a slightly better 20 fin , 2 inch length one for my 100W amps with excellent results.
You will also be able to use a piece of 1/16" flat aluminum sheet, 4" by 6" size, which you may scrounge for even less money.

spud

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Re: Heatsinks for your poweramp
« Reply #54 on: December 15, 2010, 06:50:47 PM »
Hey JM thanks - so I can go to Home Depot and get a 1/16" sheet and cut it to 4 x 6" and use that for the LM1875?  Wow - cool idea.  I like that. With about a thicker piece like 1/8" - would that mean a smaller size?  By what proportion?

WRT to the heatsinkusa product: so I can use a 1" sized one for the LM1875 or does it need to be 3"?   I may go with the 5.x size if it means I can get smaller piece - it's rated at 1.15 vs 2.3 for the 4.x" one I linked. 

So is there a formula to calculate this or some rule of thumb to go by?

Thanks for the info -

Jim

J M Fahey

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Re: Heatsinks for your poweramp
« Reply #55 on: December 15, 2010, 11:38:52 PM »
Basically yes.
Aluminum is a great heat sink material.
I make my own chassis and have always used aluminum, so by just bolting transistors or chips to the chassis (using proper micas, grease, etc. of course), I have "free" heatsinks. WOW !!.
Your 1/16" is fine and still can be bent without heavy machinery.
You may mount a flat sheet with spacers or bolts and nuts "in the air", remember you want free flow of air around it, but being able to bend it in an "L" shape makes mounting easier.
1/8" will work better because heat across it will be more uniform, good, but you still need a certain surface because the last link of the chain is heat transfer to air.
Commercial heatsinks have the added advantage of providing a lot of surface in a smaller size.
There are formulas, which I have not found very accurate for everyday work, or empirical dissipation tables provided by heatsink manufacturers.

rowdy_riemer

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Re: Heatsinks for your poweramp
« Reply #56 on: December 16, 2010, 12:56:00 AM »
The first thing I noticed when I first opened my Crate GFX-212 was that the transistors were mounted to the chassis.

scooperman

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Re: Heatsinks for your poweramp
« Reply #57 on: March 28, 2011, 09:11:11 AM »
for bench testing circuits, an old lawnmower or motorcycle finned cylinder head works fine as a heatsink.  Bob Pease used a VW cylinder head when testing new chips.

joecool85

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Re: Heatsinks for your poweramp
« Reply #58 on: March 28, 2011, 10:12:58 AM »
for bench testing circuits, an old lawnmower or motorcycle finned cylinder head works fine as a heatsink.  Bob Pease used a VW cylinder head when testing new chips.

Great idea.  You could use it as a final product I'm sure as well, albeit much heavier than a more traditional solution.
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spud

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Re: Heatsinks for your poweramp
« Reply #59 on: April 07, 2011, 12:06:38 PM »
How about an old CPU heatsink from a dead computer?  Would that be usable given that you have some thermal goop to put on there.

Jim