Strange problem? Bad ground?

[biotron345]

Hi all!
I've built a simple LFO for my modular synth based on an LM741. Works well except when I move my hand near it the LFO speed rises very slightly. I assume the is a bad ground? Any advice would be great!

[voltz]

The circuit is such that the impedance at the 741 inputs will be quite high, therefor sensitive to external fields.
Without wanting to change the design, i would make sure the Pot case is earthed. Failing that, put the whole thing in a metal box.

[biotron345]

Thanks Voltz! Are the any minor changes I could make?

[voltz]

Well, by decreasing both resistor values while increasing the capacitor value to keep the time constant right while at the same time reducing input impedance. But try the earthing first.

[biotron345]

Will do, many thanks!!!! 

[biotron345]

Redesigned!!!!