I need a little LM3886 help

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That's why I need to use the Single Supply Operation. I'm going to use a DC-DC converter to convert my car battery's 12v up to 24-25v then I'm going to run the LM3886 off of that based on the page 6 schematic. I'll have plenty of current too with the converter I'm buying. That should work, right?

The minimum supply voltage listed is 18VDC, so it should work.

However, according to the spec sheet, you'll only see about 12W of output power with a 4 ohm load (and don't even think about driving 2 ohm woofers).

The good news is, that a such a small voltage yields a low Pd. Meaning that heatsink requirements won't be great, and your DC-DC converter will only need to supply about 25W (1A) of power.

How did *you* calculate the 9W for the 1875?

I calculated 12W by looking at the bottom left graph (Output Power vs. Supply Voltage) on page 14 of the LM3886 spec sheet. That graph is for split supplies, so the X axis point you're looking at is 12V.

As for building power supplies, Brian sells power supply boards and kits, but you need to source your own transformer. Power supplies are easier to build than amplifiers, BTW.

Are you able to cheaply source a 12V->48V DC-DC converter? That would give you +/- 24V rails, IF you isolate yourself from the car's ground. The two converter configuration is probably unnecessary, though, you can probably run a single 48V supply using the traditional voltage-divider ground reference. You'll want to run both those ideas past somebody smarter than me, though.



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Hey, that wasn't a shot at you when I asked how you calculated that voltage. I just wanted to know so I could find out the single supply voltage correcty.

I think the best thing to do is to use my DC-AC power inverter (400 watt peak) and et 2 25v power supplies to power it. and if I can't do that I can always use lead acids to power it.... :p

So does anyone know a good place to get transformers? www.Jameco.com (they're local) doesn't seem to sell any that'll work :/

Your power supply should be nothing more than this:

transformer>bridge rectifier> (4) 4700uF caps (or some variation)... That's it! Well at least how I do it. It works, it's simple.

they have nice boards to get your first amp going, only 2.00USD. I bought about a dozen of them last month. They're supposed to be coming out with a smaller one soon.

pic: http://audioworkshop.com.hk/order/3886_pcb.jpg
Thanks for your help guys. Unfortunately (or fortunately depending on how you look at it), I have decided to completely scrap the idea of making my own car sound system. I was lucky enough to get an Infinity 2 channel 283 watt amp for $56. I also bought two 'Crunch' 250 watt (advertised as 400w) amps for $40 each which had surprisingly good results. It just doesn't make sense to continue working on the LM3886 when I can so much more quality and power for such a smaller price (and less effort of course).

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