quieting down a switched power supply

So I have a really sweet bass pedal that I'm just finishing (clone of the acousting 360 head pre section). It requires 24 volts keep run properly so I decided to use a spare Mac powerbook power supply I had lying around to provide the juice. Works great sometimes and looks even better!

My problem is that it will sporadically oscillate at 6.5k and 15.4k. I'm guessing this is because its a switched power supply and I'm not properly loading it. Is there a way to filter this noise out or am I doomed to use an ugly wall wort... I really have my heart set on using this thing so if anybody has any ideas at all I would be happy to entertain.

Thanks!

a massive choke & cap......

how big is massive?

What means "sporadically" and what's the amplitude? Switching PSUs show switching artefacts (repetitive spikes) but if they oscillate something's wrong.

Samuel

By sporadically, I mean that I will switch the power on and 2 out of three times the oscillation with show up and the other 3rd of the time it will be quiet as a mouse. Not sure what the amplitude is on it. I'll have to measure that tonight. FWIW, I hooked up a 24v light bulb (2w) to the rails and it quieted down quite a bit so I think it has to do with loading. Its rated to handle 45watts.

I assume you mean that the audio output has oscillation? Try using a battery to power up the pedal for a while to see if the oscillation goes away.

Beware as well of some switchers that will go into a hiccup mode to conserve power, said hiccups occuring as bursts of normal switcher frequency and with said bursts at often an audio rate.

If it is the switcher doing this, load the output a bit more. It will waste a little energy but big deal (say 17 Hail Gores if that's an issue).

[quote author="SonsOfThunder"]I assume you mean that the audio output has oscillation? Try using a battery to power up the pedal for a while to see if the oscillation goes away.[/quote]

Yeah, its audio output oscilation. I already did that. It's super quiet with batteries so I know its the supply.

[quote author="bcarso"]Beware as well of some switchers that will go into a hiccup mode to conserve power, said hiccups occuring as bursts of normal switcher frequency and with said bursts at often an audio rate.

If it is the switcher doing this, load the output a bit more. It will waste a little energy but big deal (say 17 Hail Gores if that's an issue).[/quote]

Yeah, my experience is that the supply seems to behave if I load it down a bit. I just used a lightbulb but I was hoping for a more elegant solution...

>>>say 17 Hail Gores if that's an issue
:grin: :grin: :grin:

Ya, loading the supply is about the only way to fix it without redesigning the supply. If you don't like the bulb, use a resistor, that way "Al" won't notice the incandescent glow when he comes over to hear you jam.