Background

This project started its life as a simple voltage regulator that I used between a cheapo wall-wart DC adapter to get a nice flat 9VDC. I packed it inside an aluminum promo cigarette box.

New version

I made the new version with an integrated transformer and both 9V and 12V outputs. Some pedals like to see 12V for increased headroom.

The xame schematic can also be used to build other power regulators but make sure that you have at least 3VDC more on input than regulated output voltage. This circuit can easily be modified to do just filtering and regulation for usual unregulated AC-DC adaptors. Also, you can omit one of regulators if you need only one voltage. This schematic shows only one 12V and one 9V output jack, but you can daisy-chain as many as you need with no modification. You can calculate DC voltage that comes out bridge rectifier with this formula:

Vdc ~ 1.41 * Vac

This means that 12V transformer I used gives about 12VAC * 1.41 = 16.92VDC which is more then enough to feed 12V regulator. LED is optional but it’s nice to know when device is on. In addition to that you can install SPST switch between bridge rectifier and + lead of 220uF cap to enable turning supply box off without pulling cable from the wall.

Parts

• 7809 +9VDC 1A regulator
• 7812 +12VDC 1A regulator
• 2x 100uF 25V electrolytic caps
• 1x 220uF 25V electrolytic caps
• 1x 0.1uF mylar cap
• resistor for LED, any value between 470ohm and 4.7K will work, but with lower resistance you get brighter LED and more power consumption
• LED
• Enclosure, wire, perfboard, vero board or PCB, DC jacks and plugs
• 4x 1N4007 rectifier diodes or bridge rectifier

Transformer is 12V@800mA and came from toy car power supply. For outputs I used two cables salvaged from old crappy chinese wall-wart AC/DC adaptors. They have universal output connectors, which makes them usable for all types of pedals. I placed components on sides of enclosure because they already had some ventilation holes there so there’s no need for additional drilling and it gives maximum available distance between transformer and output. I got the PC power supply from flea market for about 1$. Removed “unnecessary” stuff which left me with enclosure, 3 prong connector and on/off switch.

Pictorial

Click on an image to see more details.

HIGH VOLTAGE WARNING!
Be extremely careful when working with high voltages. While messing with this project I got zapped by 220VAC directly from wall. I forgot to plug cable out from wall before touching inside and it could cost me a life. That’s the stupidiest thing I’ve ever done, so try not to do it yourself.