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Bradford336 14th October 2012 03:11 AM

help with LM3886 amp project
I purchased this diy guitar amp kit and the instructions are direct translation and are horrible. The instructions say it needs a 15-0-15 to 25-0-25 5Amp power source. They say VAC but everything I have read including their sales ad says VDC. Any Ideas? Here is a link to the kit pic Chip Amplifier Sales, LM3886 Audio Chip Amplifiers Representatives, Sound System Supplies I can e-mail a copy of the schematic. My second question is where can I get a schematic for a power supply for it? I hope to add volume, tone and such on a separate board later so a flexible power supply would be nice. Would a simple rail splitter be best or should I stick to a toroidal transformer and filter board like this one?

ByronInPortland 14th October 2012 04:44 AM

Hi Bradford.
My first amplifier was an LM3886 too. The learning curve is, indeed, steep on your first build.
Check out Texas Instrument's data sheet here
On the very first page is specifies +/-28V (that's DC) to get a max of 68watts into a 4ohm load, and +/-35V (again, DC) to get 50watts into an 8ohm load. These are maximum values, and assume excellent cooling, so don't skimp on the heatsink and thermal paste. If you're going to put this in a chassis, use one that's ventilated. Of course there's no harm is using lower voltages.

Linear, unregulated power supplies can be a bit confusing, because the VDC (rail voltages) you get out of the rectifier is actually 1.41 times more than the VAC (secondaries of your transformer) going into them, minus a little for inefficiencies. This means you'll want at most, a transformer with 20VAC secondaries for a 4 ohm, and 25VAC secondaries for an 8 ohm speaker. For a single LM3886, you only need about a 100VA to 150VA transformer. Keep in mind that a larger transformer will give you a little better sound. The power supply you linked seems just fine. Another good one is here: Chipamp Power Supply Kit |
Here is a nice beginner's guide: Building a Gainclone chip amp power supply.
Good luck!

Bradford336 14th October 2012 02:12 PM

Thank you very much! You were a lot of help.

Bradford336 15th October 2012 02:45 AM

So for a transformer with 25 VAC secondaries and 150 VA would I use the 63V Caps and 100Vdiodes? Using the filter board that I posted.

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