Laptop Power supply for pedalboard

[tempus]

Hey all;

I've been experimenting with an old laptop PS to power my pedalboard. It actually works quite well - it's compact and has a ton of current available. It is, however, slightly noisier than the bench supply I'm comparing it to (some higher end hash - almost like a fluorescent or neon light kind of interference). The increase in noise is minimal and only detectable at all in a quiet room with the amp at high volume. Still, it'd be nice to get it cleaner if possible.

Does anyone have any ideas on how to filter the noise out?

Thanks

[artifus]

http://www.beavisaudio.com/projects/Huminator/index.htm

[tempus]

Thanks for your reply Art.

I've tried using some caps after my voltage regulator to filter out the noise, but to no avail. I haven't tried the resistor yet, but I need to have nearly 1A available for my board, so I'll need a pretty high wattage and low resistance resistor for that job. Looking at the Huminator schem, I think he should've spec'd his isolation resistor at 1W instead of 1/2W. By my calculations, there will be 90mA passing through the resistor. 9v*90mA = 810mW.

[PRR]

> By my calculations, there will be 90mA passing through the resistor.

Only if the output were dead-nuts ZERO voltage. Dead short.

I do agree that it would be "wise" to spec stage-gear to survive dead shorts. But....

A happy small pedal may be several 10K stages, say 5mA total. 5mA*100r= 0.5V drop, small; and 0.0025 Watt dissipation.

> I need to have nearly 1A available

9V at 1A, <<9V drop at 1A.... that would be a heroic RC filter. The switcher hash should be mostly HF/ultrasonic. You want a choke. The hash-choke sold for car-sound filtering is worth a try. Or a purpose-made pedal supply instead of a trashy flaptop supply. (Even the laptop does not run on that stuff; there's additional filtering inside the laptop.)

[Perrow]

Most laptop supplies I've seen are something like 18-19V or ever higher. Would it help to have two regulators to step down the voltage? First a 7815 or 7812 then the 7809 with filtering before, in the middle and after.

[Perrow]

http://www.beavisaudio.com/projects/Huminator/index.htm

Note the consistency issue on that page. On the schematic the resistor (R1) is between the led and the caps, on the wiring diagram it's between the diode and the led, and finally on the photo it's before the diode

[arawn]

god love dano but he's an uberspazz and just misses things sometimes

[runmikeyrun]

that's weird, the laptop supplies i've used are extremely stable and quiet, way more so than any wall wart.

[tempus]

that's weird, the laptop supplies i've used are extremely stable and quiet, way more so than any wall wart.

That's the thing - it actually is very quiet, much moreso than I was expecting, but it's noisier than the PS I'm currently using to power it (only slightly, mind you - and in the higher range). I figure there's gotta be a way to get it as clean.