[sdiy] multiple dc from a single ac supply

[Paul Schreiber]

I used that technique in 1979 on the Radio Shack 300-baud modem. Hey, don't
laugh, we sold 300,000 of them.

Paul S.

----- Original Message -----
From: "Lincoln Fong" <Linc at christeld.freeserve.co.uk>
To: "Synth-Diy" <synth-diy at dropmix.xs4all.nl>
Sent: Friday, October 12, 2001 3:35 AM
Subject: [sdiy] multiple dc from a single ac supply


> While looking inside a broken Alesis Midiverb 3 yesterday I noticed that
> from a single 9V ac wallwart (probably no more than 500mA) they had
produced
> plus/minus 12V dc reg (just for the audio I presume) as well as 5V
regulated
> driving all the logic and 3X  7 segment LED displays. The highest DC
voltage
> I measured was nearly 20V unregulated! I guess by voltage doubling and cap
> isolation. Why don't people use these methods more often? It seems
sensible.
>
> Having said that can anyone point me to a schematic? The power is fine but
> all the LEDs/displays are dead and it phuts on the output.
>
> Lincoln
>