Gain above 60% oscillation issue (clean or distorted)

[Rich C]

I have built the IC based overdrive pedal on the project page. I seem to have one problem with it that I am hoping someone could help me out with.

I have used this stripboard layout and this millenium bypass circuit.


 



The only other deviation I am aware of is a used a 50k linear pot for the gain as I didn't have a log pot.

When I turn the gain up around 60% it starts to create a Hum /  ocsillating sound kind of leaning towards the noisy feedback you get from distortion pedals when they cranked loud.

However when I then turn the pedal to clean that remains and the clean tone sounds quite and wooly (low muffled). Switching between clean / distored the issue remains.

If I don't turn it above 60% gain its works fine clean or distorted.

I think it maybe related to the fact that the input and output grounds are soldered together and then attached to the board rather than separately to the board. I read this link but don't know if I'm barking up the wrong tree!

http://www.diystompboxes.com/smfforum/index.php?topic=63155.0

I am not using a battery either, it is plugged directly into my one spot (i did use a battery when I breadboarded and didn't notice an issue then).

I'd rather get some plausable ideas together before I attack it with the soldering iron again only armed with poorly educated guesses!