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Old 26th November 2013, 08:38 PM   #1
261jack is offline 261jack  United States
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Default LM3886 Chipamp Project

I am new to this website and the chipamp project world - I am interested in building an amp based on the LM3886T [uninsulated] and have been researching the project on the internet [this site has been very helpful in my research] - I have two questions; #1: Using a hefty power supply, can a transformer with one secondary suffice for both chips? - #2: if fully insulated, can one large heak sink be used for both chips [I understand that the chip's tab is at the same potential as either the + or - supply voltage] - thanks, 261jack

Last edited by 261jack; 26th November 2013 at 10:04 PM. Reason: questions better phrased
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Old 27th November 2013, 03:38 AM   #2
djoffe is offline djoffe  United States
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Take a look at the approach in the GT-101. I think it will answer a lot of your questions.

Akitika GT-101 Audio Power Amplifier Kit

The manual has schematics and wiring instructions...that might help with a lot of the other questions:

http://akitika.com/documents/Assembl...101rev1p37.pdf
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Old 27th November 2013, 07:11 AM   #3
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" #1: Using a hefty power supply, can a transformer with one secondary suffice for both chips?"

Yes

"#2: if fully insulated, can one large heak sink be used for both chips [I understand that the chip's tab is at the same potential as either the + or - supply voltage]"

Yes, one large heak sink be used for both chips. A small fan would also help keep things cool.
BTW the tab is -ve .
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Last edited by availlyrics; 27th November 2013 at 07:18 AM.
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Old 27th November 2013, 11:52 AM   #4
MrBlc is offline MrBlc  Croatia
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For uninsulated version, you should use insulation pad and insulation ring. With insulation pad and ring, one large heak sink be used for both chips.

You don't want to have heatsink on -Ve. It's security risk (you could make short circuit) and it could induce any noise from negative rail to the components conected to input or feedback. As result, amplified noise could appear on output or, in worst case scenario, amplifier could oscilate and burn itself and/or speaker.
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Old 28th November 2013, 12:05 PM   #5
261jack is offline 261jack  United States
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THANKS TO ALL FOR U'R ANSWERS - JUST SEARCHING FOR DESIGN SIMPLICITY [FEWER PARTS] AND AS MUCH HEAT TRANSFER AS POSSIBLE - I KNOW AUDIOPHILES WOULD NOT LIKE MY IDEA - HAVE A GREAT THANKSGIVING OR DAY - 261JACK
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Old 28th November 2013, 01:13 PM   #6
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Another satisfied customer.

Anyway, for me, just reading your replies I am a little more educated. But to extend the question regarding power supplies... I usually use a switchmode power supply for the few chipamp I have made. Is there any advantage in using big iron from Hammond or Edcor and rectifying it instead versus the Meanwell SMPS I have been using?

Or is it more preference?
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Old 28th November 2013, 01:18 PM   #7
djoffe is offline djoffe  United States
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A single supply circuit with a big speaker coupling cap gives you the best possible thermal outcome. The negative rail of the pair is then ground, and you can bolt the uninsulated part directly to the heatsink. The heatsink attaches to the chassis. That minimizes the overall thermal resistance. That's what's done in the GT-101.
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