Battery Power Supply whine

[Chris S]

Hey all I have a Jamman looper than needs to be run on it's own isolated power supply otherwise you can hear a digital whine. The AC power supply I have works fine. After the transformer and rectifier it has a 0.1uf and 2200uf caps before the 9v regulators and 0.1uf and 220uf caps after the regulators. The problem is that I have 12v 7.2amp rechargeable battery that I am powering an amp with and it is also powering two effects pedals. I have used the same cap configuration as my silent AC power supply but I get a whine (just like if I was daisy chaining by the 2 pedals together). Any suggestions on what might be going on and what I can do to fix greatly appreciated. thanks.

[anotherjim]

I have used the same cap configuration as my silent AC power supply...

I suggest you fit a hum-break in the negative battery supply to that 9v regulator.
The hum-break is a low-value resistor in series with the negative supply with a film or ceramic capacitor of at least 100nF across it to provide a lower impedance path for RF noise. The resistor can be 10R to 100R depending on how much voltage drop you can get away with, and must have sufficient power rating. Ideally, the hum-break goes before the regulator so it doesn't drop the 9v supply, but if the regulator chip 0v must be attached to chassis ground for heatsinking, then the hum-break needs to go after the regulator in the 0v wire to the pedal, or arrange an insulated heatsink.

While your problem isn't a ground hum as such, whine can be caused by ultrasonic currents mixing in the power supply common connections.

Another possible solution is to wind the power cable to the pedal in a Ferrite ring. This makes an inductive filter, and you will notice many commercial digital products have a ferrite slug moulded in the cables near a connector which are the same idea.

[Chris S]

Thanks heaps Jim. A 100ohm resistor prooved a bit too much, stopping the looper getting enough power, but managed to carefully dial in the right amount with a 1k pot. Whine reduced by about 95%.