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Author Topic: LM 3886 current feedback poweramp  (Read 852 times)

phatt

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Re: LM 3886 current feedback poweramp
« Reply #15 on: October 01, 2017, 08:53:53 AM »

Agree,,, a Very good effort, thanks for the pictures. :dbtu: :dbtu:
Obviously a lot of thought went into that project.
I take it you cut and bent the metal out by hand?
I know how hard that is,, because I've done it many times. :duh

Just note, You might need a bigger heat sink if you run it at full power for a long time. ;)
Phil.
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sajy_ho

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Re: LM 3886 current feedback poweramp
« Reply #16 on: October 01, 2017, 09:20:38 AM »

Cool project, congratulations  :tu:

By the way, nice carpets, where are you from?

Always fill Country/City information in your user profile ... sometimes we are surprised :)
Thanks man, glad you liked it.
I'm actually from Iran; here carpets are pretty common and can be found on every house's ceiling... :cheesy:
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sajy_ho

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Re: LM 3886 current feedback poweramp
« Reply #17 on: October 01, 2017, 09:28:04 AM »

 :duh
Agree,,, a Very good effort, thanks for the pictures. :dbtu: :dbtu:
Obviously a lot of thought went into that project.
I take it you cut and bent the metal out by hand?
I know how hard that is,, because I've done it many times. :duh

Just note, You might need a bigger heat sink if you run it at full power for a long time. ;)
Phil.
Thank you Phil, Unfortunately that's the biggest heatsink I could find in stores here! Anyway I have a CPU heatsink laying around and I might give it a shot.Untill then I have to keep the volume down :cheesy:
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J M Fahey

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Re: LM 3886 current feedback poweramp
« Reply #18 on: October 01, 2017, 02:14:28 PM »

You have 2 options:

1) get a nice thick aluminum extrusion, some which is available normally anywwhere for "normal"  uses by "normal"  people ... not us crazy experimenters  :duh
You can always find somebody who makes aluminum doors and windows who will have surplus odds and ends who he will sell cheap "by the kilo" or even free.
Some will make a nice, (if odd) heatsink.


2) add a small computer type fan blowing into the current heatsink.
Best is a standard 80x80mm PC supply fan, followed by two mini CPU fans in series.

Both will need a series resistor to drop from your supply (25/28V?) to 12V or 24V needed there.

Measure *actual*  fan motor current consumption using a 12V supply, then calculate needed resistor using Ohm´s Law.
Also calculate resistor dissipation, you might need a 2W to 5W resistor.
Bypass fans with a 1000uF capacitor, both to improve running speed and to minimize motor noise.

« Last Edit: October 01, 2017, 02:16:25 PM by J M Fahey »
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sajy_ho

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Re: LM 3886 current feedback poweramp
« Reply #19 on: October 01, 2017, 04:17:52 PM »

Thank you so much J M Fahey, the aluminium extrusion seems a pretty cool idea :dbtu: I'm heading to local aluminium maker next weekend.

Thanks again...
Sajad
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phatt

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Re: LM 3886 current feedback poweramp
« Reply #20 on: October 04, 2017, 09:54:23 AM »

Even a thick angle of alloy will be better than nothing. The chip needs to dump heat instantly under heavy load and *Mass* is the key. Obviously many fins on the edge of a large mass is ideal (look at CPU heat sinks for clues) but in a pinch 6mm alloy angle is better than flimsy thin bits with no mass.
Here is a pic of a biamp monitor from Behringer,, 3 LM3886 chips on one chunk of alloy angle. The thick angle is also using the outer case to help dissipate heat. Working on the limit I'd say but hey it ran for ~10 years before the tweeter drive blew.
Phil.
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J M Fahey

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Re: LM 3886 current feedback poweramp
« Reply #21 on: October 04, 2017, 12:24:47 PM »

Fully agree.

If you go the surplus/leftover route, you can bolt 2 L or U aluminum profiles back to back to increase thickness, at least where the chipamp sits.
You can (should) add a little thermal grease between mating surfaces.
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