Not sure that I can, but I’ll try. In Pre/Post, one output channel carries the effect, the other carries a dry signal (unless KILLDRY). This signal will be delayed about a millisecond from its input (due to A/D and D/A transition times).
If this delayed “dry” signal is mixed with either input, you will get a “comb-filtered” sound, much like a flanger (this is how a flanger works). You can tell whether it is the effect input or the through input by seeing whether it has the effect on it. If you mix it with the through input you may get some feedback, as you describe.
Now over to you to see how they are getting mixed.
Thanks, now I understand. Well, we found the problem finally!
So: first of all the pedal must be in Relay bypass. The Dsp buffer keeps the flanging always on.
Then: if I use the h9 in Pre with the parallel FXloop turned off the flanging disappears (and the feedback noise with it 🙂 ), while if I keep the parallel fx loop active the dry signal from output 2 goes into the fxloop and gives the flanging sound, as you mentioned. So I need to keep always the killdry On…
This way I have 2 solutions,which I don’t like.
1) turn the fx loop on only when I use the h9 in Post with the killdry activated (but it’s boring and I need tap dancing )
2) keep the killdry On when using any algorithm in Pre ( so Bye Bye blending wet and dry for any fx in the Input of the amp) and some algorithms sound strange..
Honestly I don’t like any of these 2 possibilities…
If you could make an option to set the killdry off/on for any of the 2 IN/OUT I think the problem could be solved!
Uh, and a “master Pre/post” for any kind of fx could be useful… buy I already read this request from another user!