Signal coming through ground?

[th!nk]

I'm currently working on a sorta-OCD-based pedal with an active EQ I'm quite fond of. However, I am having serious oscillation issues on certain settings and increasing cap values in feedback loops to cut it requires values that make it sound like butts.

However, I stumbled on a strange thing while trying to diagnose it - even disconnecting the signal from the output jack, connecting only the ground to the ground lug (nothing to the tip lug), I still get signal - very quiet of course, but still there. I can't for the life of me figure out what's doing this and I wonder if it's the source of my troubles. All the ground connections seem fine (output jack is grounded to input jack).

Anyone have any idea what the heck is going on here, and if so any idea of how to fix it?

e: couple more details - signal coming through is actual signal, not just noise. Circuit has the standard noise prevention stuff and the wires from the board to switch and switch to jack are all shielded with one end grounded. No shorts, have tried unshielded output wires too. Happens on battery as well. I know that the OCD is somewhat prone to oscillation, but I'm not sure how it would be getting into the signal when the output wire to the tip is disconnected.

e2: star grounding (going to have to buy a bigger enclosure) and adding a resistor from the inverting input buffer's non-inverting pin to V+ has helped significantly, but it's still there. Still completely baffled as to how it could get through to the amp despite no tip connection though.

[FiveseveN]

Still completely baffled as to how it could get through to the amp despite no tip connection though.

Capacitive coupling.

[GibsonGM]

Bypassing your opamps via the above; search "Miller Effect", "Miller Capacitance", too.   Cool, huh?

[th!nk]

Well, cool might not be the word I feel like using at the moment, but star grounding etc has fixed most of it, and changing the range of the treble control + lowering the maximum gain slightly seems to have dealt with most of the oscillating when it's on. Hopefully when I do up a PCB rather than using veroboard I'll be able to design it well enough to sort this stuff out - I mean, surely it's hard to do much worse than vero for this stuff, right?

[duck_arse]

can we sorta see your sorta circuit? is the ground noise present when the signals are connected all present and correct, and is it objectionable then?

[th!nk]

It is, but it seems mostly sorted now - after doing a bit more reading on capacitive coupling and some other stuff I'm pretty sure it's just a matter of layout for a relatively high-gain circuit (especially as it is increased/reduced by increasing/reducing the gain) - OCD and a Bax EQ, both seem to have issues along those lines.

Anyway, the noise is down to manageable levels (and inaudible while off), so I'd say it's done. Thanks all.