Buzzing in passive circuit

[lilolfunnyboy]

My first post and I'm sure this has been covered a thousand times but I've not been able to find anything helpful so far...
I built a simple volume cut to go in the amp's fx loop:
input jack > DPDT switch > 100k pot > output jack
Idiot-simple and worked great. Now I've decided to swap the DPDT for a 3PDT switch and add a status LED with dc adaptor jack.
With the DC supply plugged in I'm getting LOTS of buzzing - the level of buzzing you get when you un-jack the guitar.

Any ideas how I can solve this?

[artifus]

hi. and welcome. there are some really easy to digest diagrams and articles over at:http://www.beavisaudio.com/

search the forum for power supply filtering. good luck.

[lilolfunnyboy]

Thank you. It's actually the Beavis Audio true bypass loopers that I used as a guide.
Anyho... I have solved the problem by connecting the LED and jack to ground on the case (rather than the discreet cuircuit in the Beavis diagrams). Is this a sensible solution and why does it work?!

Thanks again.

[artifus]

congratulations! you created a faraday cage! you have defended your circuit from external emf and radio waves by persuading them to go to ground instead of your output. sometimes a small pf cap is used to ground to case too. rg has an article over at geofx - go have a read.

[lilolfunnyboy]

I will have a read thanks!
I know just about enough to put something simple together (like this volume selector or a buffer) but how it all works is a bit of a mystery to me

[artifus]

that's all you need! and keep that mystery alive!