power supply ground loop -- multiple fx chains

[PeterJ]

On my board, I use two separate effects chains: one for my lap steel, which goes to my amp, the other for my banjo, which goes to the P.A. I have a Visual Sound One Spot for power, but if I daisy chain the power to everything on the board, I get hum. Can anyone think of a way to use one wall wart to power the two chains? Thanks.

Peter

[smoguzbenjamin]

I think Boss had a good way of preventing ground loops by putting something like a zener diode in series with the -terminal of the DC plug. This prevents current from going 'into' the pedal from the -terminal, thereby stopping ground loops.

Try looking at a boss schematic.

[PeterJ]

That's an interesting thought, Ben. I'll look at some schems. I was thinking that building a simple distribution box (wall wart in, two power chains out) might help, but I don't think that will break the loop.

Peter

[Peter Snowberg]

Hi Peter,

I think your best bet will be to use two adapters. Your other options include an isolation transformer on the signal going to one of the amps which will affect the tone some, or using an AC wall wart with an additional 1:1 transformer to create two isolated AC outs that are then rectified into two isolated DC supplies.

There is one other option I can think of which is to use an opamp to superimpose an "anti-hum" signal on one of the amps, but that approach has severe limitations and it can be somewhat unsafe too.

Sorry, but two wall warts is the best it's going to get I think.

You have to be really careful when dealing with two amps plugged into different line supplies. Depending on the venue, you can often measure HUGE amounts of voltage difference between different grounds. Neil Young's amp tech has written about 150 volt differences between "grounds". I used to do backstage electrical for a big concert promoter and one thing you can always count on is that house power is funky.

Sorry, it's not much of an answer but I don't make the rules of the universe.


Good luck and take care,
-Peter

[smoguzbenjamin]

:shock: 150V ground differences! How's that possible?

[Peter Snowberg]

:shock: 150V ground differences! How's that possible?

I wasn't there for that measurement, but if you have one piece of equipment with a house ground and one with a generator ground, you will see many volts for sure between the "grounds".

Concert power is funny stuff because it is often distributed via loose cables (sets of 4 or 5 thick wires) that can have all kinds of tranformer-like interactions happening. If you have older equipment that doesn't have a ground wire, but takes it's ground via a capacitor on the neutral wire, the neutral may not be well grounded at the main panel, or even grounded at all :shock:.

Take care,
-Peter

[Gearbuilder]

Hi Peter,

First  try supplying  your pedals with 9V battery,if there's no hum ok in this case you should use separate supplies .If there's hum:
it's a ground loop due to common eart with amp and PA.
 Even if you use separate 9V supplies you'll get hum,because the ground is common by the signal pass beetween your pedals ,
it's a ground loop due to common eart with amp and PA.
Solution,
Maybe your banjo signal won't be too much changed if you put a DI box with a ground lift  beetween your last pedal an the PA .Try with Passive model or active .(with line level Active DI Boxes sometimes are  better sounding than passive Box This is  due to the bandwidth of the transformer)
But i'm OK

GROUND  YOUR AMP !



Bruno

[bwanasonic]

I'm pretty sure the Voodoo Labs PSII is protected from ground loops when running into two different amps. I like the one-spot myself, and they are cheap enough that two won't break the bank (Musician's Freind has a $24.95 bundle that includes the daisy chain cable).

Kerry M

[PeterJ]

Thanks, everyone -- I had a feeling that getting a second PS was the simplest answer. I also appreciate that you gave me the reasons behind the answers. That's what I love about this forum. There's all this experience plus a genuine willingness to help. Much obliged, all.

Peter