Vactrol grounding // mains hum

[CHRISKELLY]

Hi guys

I've recently built analog drum voices on perfboard.

Parts of the circuits are controlled by DIY vactrols, and up til now I've used separate grounds for the analog components and the vactrol LED's. My reasoning for this is that the vactrols will draw larger currents. Is this the correct approach?

Also - there is an inherent mains hum in the circuits at the minute. I use a DC 12V single power supply from a wall wart with no earth pin (just a plastic pin) The audio goes to an ipod docking station again powered by a wall wart with no earth pin.

When I connect circuit ground to my oscilloscope earth (which does have an earth pin on the power plug) the hum vanishes. Or if I connect circuit ground to earth via a rod in the ground in my garage the hum vanishes.

Since I'll be powering this thing via a wall-wart there will never be a physical connection to an earth pin unless I introduce it externally. My question is whether this is a normal issue with diy builds, or is this indicative of a problem with my power supply?

Cheers
Chris