When you are really making a Feedback Simulator for the H90 which is really great news then I would recommend you as a little inspiration the following two song for very nice use of a Feedback Effect. (If you don’t already know them.)
First Joe Satrianis Flying in a Blue Dream. The intro with the Feedback tone is magical. I think he is playing a lower C note and you hear as feedback the octave, the fifth (G) and maybe also I am not sure the second (D). I tried this with the freqout, but never got really satisfying results. So this is one of the most iconic examples of a diatonic feedback.
Second Frank Zappas Zoot Allures. Very interesting because here we have the combination of a rather Clean Tone (out of phase Neck+Middle Pickup would be my guess) with Feedback. I tried that with the freqout playing the fifth as feedback and it doesn’t nail it perfectly, but let’s say anyway what you get is pretty pleasing to the ear. My ears are not so trained so my guess would be that for the Zoot Allures Feedback tones the fifth is involved, whereas the octave not so much and I think it is more a mixture of a diatonic and a non diatonic natural feedback.
