Ground loop buzz ???

[Turdus]

Need help understanding this one:

From the sound board, I use a monitor out 1/4" to a 1/4" input on a powered mixer.

If the sound board, and powered mixer are on the same A/C circuit, there is only a small hum/buzz.

If on different A/C circuits, the buzz is very loud.

What causes this?

[HSB0531]

Need help understanding this one:

From the sound board, I use a monitor out 1/4" to a 1/4" input on a powered mixer.

If the sound board, and powered mixer are on the same A/C circuit, there is only a small hum/buzz.

If on different A/C circuits, the buzz is very loud.

What causes this?

It's caused by the two different grounds.

Is the monitor out a balanced line level?

Does the powered mixer have balanced line level inputs?

If so, try running a balanced line first.

If that doesn't work, you'll have to used isolation transformers.

[Turdus]

According to the docs on each, the monitor out is balanced. The 1/4" input on the powered mixer is also balanced.

Does this mean I need to use a tip/ring/sleeve cable, vs standard guitar cable?

[HSB0531]

According to the docs on each, the monitor out is balanced. The 1/4" input on the powered mixer is also balanced.

Does this mean I need to use a tip/ring/sleeve cable, vs standard guitar cable?

Yes a Tip/Ring/Sleeve cable will keep the line balanced.

Also try and keep any audio cables away from the power cables if possible.