Huge shout out to The Fractal Wiki - its a gold Mine !!!
Close to finishing dialling in my FM3 Pre-sets, and very unexpectedly, I was having trouble with both the Dirty Shirley models.
The tone and drive was great ..... but no matter what I did - pre-amp-block-eq-cuts or post-amp-block-eq-cuts .... it had this really subtle but very unpleasant "thud" ..... really noticeable when palm-muting.
As a last go, I went to the Fractal Wiki for this Amp and found the following from Cliff:-
" .... If you want more clarity in the low mids ..... reduce Negative Feedback. Friedman's designs are a bit odd in that he takes the feedback off the speaker jack rather than off a transformer tap ..... the amp will sound tighter and clearer in the low mids .... "
Go figure ... dropping the NFB from the stock ~ 4.8 to ~3.0 ..... totally solved my problem.
Anyway ... just highlighting how good and useful the F/Wiki is.
All the best,
Ben