AC/DC power supply question...

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I want to make a sub amp that could run on 12VDC or 120VAC. It would be nice to have a car sub that I could take out of the car when i wanted to have some extra ghetto-thumping bass. I could just have a regular AC power supply and run it off a power inverter in my car... but that would be a lot of conversion and creaste a lot of heat. How would i make a DC power supply that would output about +-50VDC?
Power supply possibilities

If your amplifier needs 50volt split rails then you are going to need to build an inverter - these are commonplace in commercial car audio equipment as the voltage available in a car is too low to generate the kind of wattage consumers want/expect.

This is not a project to undertake lightly as it will most likely cost you almost as much to build a DIY inverter as to buy a budget readymade subwoofer amplifier, there is also significant complexity to the DIY route to consider as well.

See at Old Colony Lab Sound (Google it!) or Amazon the book "Audio Amateur Power Amplifier Projects" from Audio Amateur. There is a complete Car Audio amp using a switched mode power supply. This supply produces aprox. +/- 45 vdc at output.

It works fine and feeds a 2x70W eff. power amp.


Car Audio Amp project

I have that book right here. The power supply uses a custom transformer which you wind yourself; the author specifies the bobbin (Ferroxcube parts) and gives very detailed instructions on how to wind it. It uses an SG2525 IC from Motorola, which may not be available anymore.
For other sources on DC-DC converters, you may want to check the Linear Technology app notes - if you can find some (apparently no website, how weird). Should be other companies as well.
As you've read, this would be an ambitious project and the economics don't work. However, more power to you.
If you want to sit down and design something instead of building someone else's, the Linear Tech app notes are full of details (thanks for that website Geoff, don't know how I missed it). Try looking at the LT1170 and related parts, they are very versatile.
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