Pedal Supply Hum. Using WPDLXFMR-2 Transformer

[Chris S]

Hey All I've build a power supply using a weber wpdlxfmr-2 transformer http://www.tedweber.com/wpdlxfmr-2. I have used this schematic... (basically this repeated 6 times and a two outputs stacked together to produce one 12 volt output). Works except that it has a hum which gets noticeably worse as I move my guitar pickup towards the unit. Any ideas or a hit list of what might be causing this appreciated. The unit is in a large heavy duty plastic box.

Edit: Also just discovered if i move it about 20cm away from my valvecastor and out from under a couple of other pedals it goes quiet. Still, I would like to have the power supply nice and close to the pedals.

Thanks!

[R.G.]

The transformer is leaking magnetic field. All transformers leak some of their magnetic field out into space, and some are worse than others. Toroids are best (i.e., least leakage) E-I types are worse than toroids.

You can move the transformer away from sensitive things to lower the amount of field, as you've discovered. The field/hum decreases as the square of the separation, so as you've also discovered, even a little distance makes a big difference. You can try to shield the transformer, with conductive bands and steel enclosures. Shielding is harder to do well than separation.

[Chris S]

Thanks RG! Will try this. Thanks too for sharing all your extensive knowledge on this forum you rock!

[R.G.]

My friend the amp tech was asked down to the new site of Antone's in Austin. They had finished the electrical wiring and were trying the stage, but all guitars produced horrible hum, with all amps and all cords, all the usual suspected. The stage was unplayable.

He took a strat with a long cord and walked around, looking for where the hum was better and worse. It was worst along a line across the stage. Turns out there was a large steel I-beam under there that held up things like the stage, and the beam was emitting magnetic field, probably because it was carrying ground return current for the refrigeration units in the building, something like that.

Guitar pickups, wah inductors, and other transformers make great pickups for radiated magnetic hum fields.

[PRR]

> the beam was emitting magnetic field, probably because it was carrying ground return current for the refrigeration units...

...which shouldn't leak to ground.

_I_ have that (but in dirt), because my power line is so very long.

It shouldn't be happening in a new building. I fear they won't find anybody who can find the fault.

First step is flashlights, battery amp, start turning off *everything*. With luck, breaker #13 kills it silent. What's on #13? Is it really wired right? Without luck, ALL circuits contribute hum, bad feeder connections.

60Hz notch-filter guitar cords?