I am a brand new H9000R user, sorry if this is trivial.
I use DB25-Analog connectors going into a patchbay.
From there, I connect the FX Send on my Mesa Mark V-25 guitar amplifer (head only) to Analog 3 input, and I use Analog 3 output to send the signal back to the FX Return of my amp. As far as FX Chain, I simply inserted a Thru (#812) module which does nothing.
The Problem: As soon as I connect the output, the H9K seems to go into a feedback loop with massive digital distortion and the input meter goes way into the red. As soon as I Mute the Thru algo, the problem stop, but then there is no sound.
I tried a few anlaog inputs 1-2-3-4 and outputs 1-3-5 but same result in all cases. To be 100% clear, I must use the FX loop, because I have another preamp (Mesa Triaxis) that i want to use in parallel in a FX chain, so the only way to do that (short of using a SwitchBlade or AxeFX) is to have the power section of my MarkV (the FX return) to be separated from the preamp section of the MarkV (The FX send). I have used this approach with the Switchblade before and I never had a problem.
I used the TriAxis preamp to go through the power amp section of the MarkV, going through the HR9000R as a direct connection and there was no problem. So it must be some feedback loop somehow when using the MarkV pramp through its own FX loop. It’s a bit weird, because I used to do this exact routing with my Switchblade with no problems. I assume it’s solvable, but not worth Eventide support for now unless I re-open this.