Originally Posted by Biggbass
I recently removed the Whirlwind AB box from my pedal board due to loud ground loop hum. Was wondering if it had anything to do with the battery inside the box, which is supposed to be there just to illuminate the LEDs. But diagnosis pin pointed the AB box as the source of the hum. Could be that it just went kaput and it's time for a new one. Need to open it up and take a look at the guts though.
You got a ground loop because the two amps were on different ground circuits, and the AB box connected their two grounds together. This allows current to flow between the amps and shows up as a loud hum.
To eliminate a ground loop, you need to lift the ground on one amp. This is why DI boxes have a ground lift switch. This can be done at the AB box by using an isolated jack, or with one patch cord having the ground disconnected on one end, or by lifting the amp's ground at the AC outlet be using a 3 to 2 pin ground lift.
This has nothing to do with batteries.