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Old 27th October 2006, 04:02 AM   #1
john65b is offline john65b  United States
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Default Utilizing a Standard Transformer as Heatsink?

My latest amp is a basic, Dual Mono, minimum component (al la Gaincard) utilizing a LM3886, and all point to point wiring. Trannie is a 24V 0 24V 3A non-toroid type (C Core?)...

Anyway, looking to make this as compact as possible and wondering what I could use as a heatsink...The Tranny has that nice mass of metal, so why not try to use it as a heatsink...so I'm thinking of getting a blob of thermal grease between top of transformer and bottom of a 1" x 1.5" aluminum angle that has the chip attached.

Bad idea?
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Old 27th October 2006, 04:56 AM   #2
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Extremely bad idea. I can hear the hummmmmmmmmmmmmmmming in your speakers now. The transformer radiates 60Hz magnetism that can enter the input of your chip, be amplified, and played on the speakers. Also, when the chip gets hot (as it will from normal use) it dissipates its heat into a heatsink, the heatsink gets hot simply from conducting the heat away from the device. The transformer, on the other hand, actively generates heat both from electrical losses from resistance in the windings and "iron losses." When you mount your power amp IC on the transformer, depending on the transformer's normal temperature rise, it (the IC) could overheat and be damaged. Also, if some kind of fault occurs in the transformer that causes the primary winding to short to the core, you run the risk of putting 120VAC on the speaker outputs. Please save yourself the headaches and get a proper heatsink. Don't forget to put the insulating washer between the IC and the heatsink. I burned one up by forgetting to do that.
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Old 27th October 2006, 02:07 PM   #3
john65b is offline john65b  United States
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Yup, just as I thought. Don't want to chance it...already ruined a perfectly nice tweeter doing something stupid a few months back...

I have seen many designs where the chip is located very close to a tranny, so I thought it would be possible without some major hum or problems...
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Old 27th October 2006, 02:13 PM   #4
Nordic is offline Nordic  South Africa
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The case of the transformer, normaly has a tab to connect it to earth, so if you get it wrong you will force a DC rail to ground against the case...
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Old 28th October 2006, 02:35 PM   #5
Geoff H is offline Geoff H  Australia
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Have a look at fan / heat sink combinations. PC fans can be useful for reducing overal size. Noise can be a problem.

Geoff.
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