I am a little mystified by this situation. I have the L1 Compact and the T4S. I played two guitars through this system. The first is a Martin with a high-end sound hole pickup. The second is a Taylor nylon string with the ESN pickup system built into the guitar.
Our practice room is in an older house and the room does not have grounded outlets so I have to use an adapter to plug my power strip into the two prong outlet. The mixer and PA are plugged into the power strip.
When I connect the Taylor directly to the Compact, I have no hum at all. However, when I run it through the mixer I have aggravating hum but when I use the guitar chord with the metal connector on both ends and I touch either metal connector the hum goes away.
This would indicate to me that there's some kind of a grounding problem when I use the mixer. Why I do not have that when I plug directly into the Compact I am not sure but I clearly do not. Maybe the PA has some kind of a built in grounding system.
The Martin guitar has zero problems connected either directly to the PA or through the mixer nor does my little machine on my microphone.
One additional bit of information. There is a bathroom off of the music room that has a three prong connection. Yesterday I took an extension cord and ran it from the three-pronged connector to the power strip that I have both the mixer and the amplifier connected to and there was no problem with the Taylor guitar connected thru the mixer.
Can anyone explain this? I really don't want to have to run an extension cord from the bathroom to the music room to avoid this hum but will if I have to. Is it something in the Taylor pickup system that would cause this?
It seems to me it would be something related to the mixer because I do not get that hum when I plug the Taylor directly in to the PA even when using the three-pronged to two prong adapter