On Sat, 19 Apr 2008 07:53:25 +0930, a.busker wrote:

Hi. I want to purchase a really nice acoustic amp, for street
performance.
Somebody told me that on some amps you can get technician to bypass the
power supply, so you can run it off batteries. Is that plausible?

Not really unless the amp has a low output or a 1 ohm speaker system.
12 volts isn't enough to produce the power levels you'll need.

Auto subwoofer amps use a step-up power supply. I have one here
extracted from a 400W car subwoofer amp. The power supply MOSFETs
had been blown up by some ignorant modifications to the amp, but
that wasn't hard to fix. It uses a TL494 SMPS chip, as many computer
power supplies used to. Anyhow, the two pairs of output MOSFETs in
the SMPS drive a toroidal transformer in push-pull, with two secondary
windings of 2:1 ratio, which produces an output after rectification
of +-25 volts from a 13.8 volt input.

I suspect that the amp you like differs only from the ones you don't
simply by the quality of the speakers - nothing to do with the amp at
all. Consider buying a speaker you like, and driving it from a car sub
amp on your battery.

Clifford Heath.