Hey everyone - I hope you are doing well. I somewhat recently incorporated the ps-100 into my studio setup. Since adding it, I’m noticing some microphones issues. My noise floor when I have drive pedals engaged is strange - hollow, tinny noise that starts to squeal. Making sure I’m far enough away from the amps generally helps prevent the squeal (https://youtu.be/BfAgrlIu3Qw).. Adding to my suspicion that something is up with the pa-100, if I lightly tap on the top of the unit, I hear it through my cabinet. Is that normal behavior? I haven’t taken the cover off to do the ole’ tap on the tube with a pencil, but I’m guessing I would hear it.
So, would microphonic tubes cause that strange hollow tinny noise floor and contribute to the high pitch squeal?
Firstly, I’m glad you already found Joe’s first video on mystery squeal (non-musical feedback).
If you have not done so, also check out the second video on ground loops. They can cause many different problems that, annoyingly, manifest in different ways.
The hollow and tinny sounds you are hearing make me think this is a ground loop issue.
He is what I’d suggest.
Disconnect everything from the FX loop.
Make a very simple connection: Guitar → Amp → PS-100 → Speaker with no connections to other equipment.
If you still get these microphonic sounds, then I’d open the unit.
HIGH VOLTAGE INSIDE UNIT
Only ever use one hand when the chassis is open and use something non-conductive to tap the 12AX7 tube.
Replace tube if needed.
Let me know how that goes. If you still need to debug the ground loop afterwards, then we can do that. You might need to use an isolator to break the loop. I typically recommend the Lehle ones
Thanks @dan ! I checked out that second video last night, but haven’t had a chance to tinker. I do have an Ebtech he2 sitting between my drive pedals and my amp switcher. I did the opposite of the video and pulled it out of the mix and did not hear a difference.
One thing I do need to check on is cable ends touching each other. That is almost certainly happening under my board.
I have some things to try out. I’ll report back as soon as I get a chance to tinker. I will definitely be simplifying my setup to try and isolate where the problem is.
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