Loaded VRef?

[karbomusic]

So to follow up... I etched and built the changes above making it a completely different layout (previous was Vero) and a slightly different circuit. Boxed it up..... Wait for it...

Still squeals like a pig when the input is floating (bypassed). Due to the number of differences in the newer design (not to mention a laundry list of changes and failed attempts on the Vero which was also the second Vero layout), I've come to the conclusion it must simply be the amount of gain + the gain boost bump on top of that in the blend circuit + possible alignment of the stars with op amp combinations. There simply isn't much, if anything else left to eliminate. Though I'm not ecstatic that I lost this battle, it's OK, what was learned along the way was invaluable.

To bring this saga to a close... I was using a JFET for the LED switching, I removed the DPDT, replaced with a 3PDT and used the extra poles to ground the FX input when bypassed. I also finally chose to do this for another reason... Had I solved it, the problem may have only been dropped just below the surface, meaning it could potentially rear it's ugly head again in the wild, in someone else's rig/psu/environment. Grounding it feels like safer long-term fix from that perspective.

And most importantly.... thanks for all the help!