Flea Market Bargain -- Enclosure for my LM3886

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AndrewT

R.I.P.
Joined 2004
your 300VA on a 110/120Vac supply would normally need a T3A fuse, but may run on a T2.5A fuse because you will not be drawing much power. It might even run on a T2A fuse, but I think that would be unreliable.

Read all about soft starts on this Forum. And use a proper timer. Not an RC that may, or may not, trigger on very variable mains supply.
 
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Jennifer G

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Joined 2015
Are any of the following good locations for speaker terminals? Does it matter how close they are to AC main? IF not, I prefer the first one, to allow more room for taller and wider heatsink later on. EDIT: Actually the third one would work fine as well becasue I don't think I need taller.. I just might add 3/8" thick aluminum bar to the heat sink between the chip and the heatsink.

An externally hosted image should be here but it was not working when we last tested it.


An externally hosted image should be here but it was not working when we last tested it.


An externally hosted image should be here but it was not working when we last tested it.
 
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Jennifer G

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Joined 2015
AndrewT said:
I recommend you twist EVERY signal pair without exception.
Well there is one exception: the 3wires from a dual polarity PSU has +ve , zerovolts and -ve. Twist these as a triplet.
Ensure the loops at the terminals are kept as small as possible. This is all about LOW LOOP AREA.
Loop Area increases interference.
Click to expand...

I actually have 4 wires coming from dc supply board:
+ve, -ve, ground for +ve and ground for -ve.

Should I braid the 4 of them together as one?

or since they each have thier own ground, twist them in pairs and run in parallel?
 
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Jennifer G

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Joined 2015
My brother had a scrap piece of aluminum bar and machined it to the dimensions of the heatsink. The heatsink is plenty thick enough now :)

ilk2e0.jpg
 
A

AndrewT

R.I.P.
Joined 2004
Jennifer G said:
I actually have 4 wires coming from dc supply board:
+ve, -ve, ground for +ve and ground for -ve.

Should I braid the 4 of them together as one?

or since they each have thier own ground, twist them in pairs and run in parallel?
Click to expand...
Don't braid them.
Twist them for smallest loop area.

Consider one supply.
If it has +ve , Zero Volts and -ve, then twist all three as a triplet.
Minimise the loop area at the terminal connections.
Repeat for the other supply.
 
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Kjeldsen

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Joined 2003
kjeldsensforbindelser.dk
Jennifer G said:
My brother had a scrap piece of aluminum bar and machined it to the dimensions of the heatsink. The heatsink is plenty thick enough now :)

An externally hosted image should be here but it was not working when we last tested it.
Click to expand...

It's all about surface area not thickness. It will probably cool a bit worse than without the extra aluminum. It depends on how efficient the heat transfer is between the joints
 
A

AndrewT

R.I.P.
Joined 2004
Kjeldsen said:
It's all about surface area not thickness. It will probably cool a bit worse than without the extra aluminum. It depends on how efficient the heat transfer is between the joints
Click to expand...
I agree, there is a risk this solution will be worse than without.
I explained that in an earlier post and gave amethod that is more likley to improve on the added plate.

But she has ignored that advice.
 
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Jennifer G

Member
Joined 2015
AndrewT said:
I agree, there is a risk this solution will be worse than without.
I explained that in an earlier post and gave amethod that is more likley to improve on the added plate.

But she has ignored that advice.
Click to expand...

I didn't ignore it. You said yourself it would be a bit tricky to implement yourself.. the bar over the top of the chips. I agreed and didn't do that.

The transfer between the heatsink and the bar is actually quite good. They were both machined perfectlly flat and there is thermal compound between them, with six bolts holding them together! BriantGT from chipamp.com said that aluminum bar itself was enough for these chips. Now it has fins as well AND ventiliation from the bottom and top with airflow between the vent and bar. I think it'll cool quite sufficiently./

I'll find out tomorrow how well it works, will have it up and running by then.
 
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