A simple, cheap bipolar power supply

[Synthaholic AKA sPEW]

Good suggestions...  And sorry to confuse:

I should have caveated that I use this supply for my home lab, which
has been a well behaved electrical environment.  If I were to do gigs
with my equipment, which I do not for lack of time, I would probably
bite the bullet and buy a good supply designed for low noise and wide
variations in AC input and DC output loading.

Since one of the questions was whether a 10 dollar computer supply
would be appropriate, I thought that the asker was interested in a low
dollar solution.

I have used larger transformers and caps when I know that the minimum
load will be significant.  I found 18 volt transformers caused the
regulators to get *hot* with little or no load, even when reasonably
heat sinked (sunk?).  This situation corrects itself as the load
increases.  I have even used power resistors across the DC side to
simulate a heavier load for supplies I have built for projects that
grow.  Once the project's standby load is significant, I remove the
resistor.  For LM340T/LM320T and 78xx/79xx regulators, the ideal (from
my spec book) is to supply 2.5 volts DC above the output regulation
voltage.  Although I have found them to be somewhat rare for some
reason, I have also found 13, 14 and 15 volt wall warts of reasonable
current capacity that work better for medium loads for +/- 15 volt
supplies.  The 12V transformer is better suited for larger loads at
12V regulation.

All in all, though, this has been a very inexpensive solution for me.
80 percent of the cost is in the transformer.

Again, for gig work, I would employ a commercial supply.

- Scott Gravenhorst (Synthaholic)     www.concentric.net/~chordman

Programming: The Ultimate Computer Game. | Windows 95: The Ultimate
Unfortunately, you never win.            |      Pain in the Butt

"I didn't do it."
   -- Bart Simpson