power supply?

[Stopp,Gene]

I just did such a thing for a little portable amp for my Etherwave
theremin. It's not finished yet, but the electronics are working.....

A car stereo amp will draw quite a bit of current, since the total
voltage of the supply is limited to 12-15 volts and the speaker wattage
needs to be in the 15-100W range. For this, it's not good enough just to
use a raw DC supply, since the rectifier ripple will be way too high
under load - you need a regulated supply. I used a 24 VAC 3 amp
transformer powered by 110VAC, into a fullwave bridge (one of those 1"
square high-current things) into a 2900 uF 75V electrolytic cap. For
regulation I used an LM338 5-amp adjustable regulator in a TO-3 can on a
heatsink, with the programming resistor divider set for 15VDC regulator
output. When a 5 ohm power resistor is placed across the 15V, the raw DC
side (which sits at around 35VDC quiescent) gets some ripple on it, but
the 15V side is solid at 3 amps. Good enough for my 16W amplifier.

The LM338 is a bit expensive, probably close to 10 bucks, but it works
well here.

 - Gene

 ----------
From: ganglion at utxvms.cc.utexas.edu
To: synth-diy at mailhost.bpa.nl
Subject: power supply?
Date: Monday, April 20, 1998 4:07PM

How much current would a fairly beefy car stereo amplifier such down
at 12 V?  Is there a cost effective power supply solution for using a
car stereo amp in your living room?