Are you thinking of turning an audio amplifier into a power supply? Theoretically it can be done.
You can input a weak audio signal of any frequency, and get a strong signal out. You can convert it to DC with diodes.
Of course you are aware something can blow if you attach a load which is a very low ohm value.
And a caution in the other direction: An audio amp is designed to have a load of several ohms attached. If you operate it with little or no load, something can be damaged, with the likelihood being greater the higher the volume is cranked up. I unwittingly did this to my guitar amp with the speaker disconnected, and it blew a tube.