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Old 16th July 2010, 11:19 AM   #1
Boscoe is offline Boscoe  United Kingdom
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Default I need a PSU for 6 LM3886's

I need a PSU to power two of THESE for a stereo amplifier, it requires -35,0,35 volts so can I just use this

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and use a bigger transformer and bridge rectifiers? And do I bridge the PGND?

Thanks
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Old 16th July 2010, 01:44 PM   #2
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That's a very common power supply design, but it depends on the actual board design.

How much current do you need?
Is there room for heatsinks on the diodes?
Are the traces big enough?

Of course if you put it all together "point to point", with thick wires and heatsinked rectifiers, it's a non-issue. Your ripple will be determined by how much current you draw vs how much capacitance you have, you're going to want quite a bit of capacitance.
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Old 16th July 2010, 01:51 PM   #3
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I can't find anywhere how much it pulls for one or for three on the amp i'm gettin.
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Old 16th July 2010, 01:56 PM   #4
Boscoe is offline Boscoe  United Kingdom
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Found a source I'm going to use a 500VA transformer so could I just up everything in this schematic?
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Old 16th July 2010, 02:02 PM   #5
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If you're interested in getting the best sound, the diodes would benefit from having RC snubbers across each (say 10nF and 100R). And the snubber on the output doesn't need to have a 2W resistor at all. Carlos eventually modified the cap too, to 1.5nF- 3.3nF and the resistor down to 0.47R
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Old 16th July 2010, 02:07 PM   #6
AndrewT is offline AndrewT  Scotland
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the peak current from a 3886 is between 7Apk and 11.5Apk when cold.

6off cold 3886, all at the same maximum peak output, could be ~70Apk current draw from the PSU and decoupling.
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Old 16th July 2010, 02:13 PM   #7
Boscoe is offline Boscoe  United Kingdom
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You sayin to make a ~2000W PSU!????
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Old 16th July 2010, 02:14 PM   #8
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Quote:
Originally Posted by AndrewT View Post
6off cold 3886, all at the same maximum peak output, could be ~70Apk current draw from the PSU and decoupling.
Yes - might be worth investigating making slightly better use of the power supply by running 3 of the chips with an inverted signal (or making them inverting). Peak currents are usually rather asymmetric so by having half the amps running inverted both capacitors get to provide the peak current rather than just one.
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Old 16th July 2010, 02:44 PM   #9
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Quote:
Originally Posted by Boscoe View Post
You sayin to make a ~2000W PSU!????
Not necessarily. Consider making a separate power supply for each channel. While it'll cost a bit more (depending on transformer costs), you won't have to deal with large amounts of power in one place.

Also, what impedance are the speakers you are driving with this amp?
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Old 16th July 2010, 02:58 PM   #10
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Quote:
Originally Posted by Redshift187 View Post
Consider making a separate power supply for each channel.
It will cost quite a bit more than a single unit. Then the inrush current from six power supplies all being switched on together won't be too pretty The advantage I can see from doing all monoblocks is it makes the grounding easier. But I think it won't give such a good bang-for-the-buck as the single higher power supply. The 2kW figure is only extreme peaks, assuming that all channels receive the same peaking signal in phase. Seems jolly unlikely to happen in practice.
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