XPost: alt.guitar.amplifiers, aus.electronics   
   From: no.spam@please.net   
      
   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.   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)