Wall Warts Power Supplies: Switching vs. linear - Ground Loops

[BrianJ]

I have a Wah project that is moving along well.  I have decided that I like the sound better when I run the circuit off of 18-30 volts DC.  The problem here is the 24v DC Electro harmonix power supply I am using injects a lot of hum.  When I use my 9v  pedal board supply (of the switching supply) the noise is gone.  I increased the the power supply bypassing from 100uF to 2200uf with only a slight improvement.  I suspect there is a ground loop.

Are switching supplies known to inject less ground noise?  Are power adaptors and inductor based Wahs known to interact this way?

[Processaurus]

I don't think it is a ground loop, as there is no new path to ground through the EH transformer.  More likely what it is is that they use cheapo power supplies that let a lot of 60hz ripple through.  They get away with this because their big pedals have voltage regulation inside.  You could follow and put an 18v regulator inside your wah. 

If the upping the big bypass cap in your pedal didn't help, you could also try putting a resistor (say, 100 ohm to 470 ohm) in series with the + coming in, before the bypass cap.  That forms a better lp filter than the cap alone.  The regulator would be dead quiet though.

[BrianJ]

Thanks

I failed miserably at perfboarding and mounting a regulator inside so  I tried a 1k ohm resistor in series with my supply.  Worked like a charm.  I lose only about 2 volts so there's still plenty of headrooom.

The only draw back is it takes few second for the supply voltage to come up but I don't see an issue.

I recommend to any wah fan that they experiment with higher supply voltages as well.

[jakenold]

Hi Brian,

The EHX PSU is unregulated! I recently fixed an Electric Mistress for a friend, and I installed a 7824-regulator inside the effect, and suddently the noise was all gone. It's really worth it!

I've had mixed experiences with switching adaptors... High gain effects really let the noise shine through, so a high gain pedal is a pretty good tool for finding out whether or not your power supply is noisy.

Hope this helps.