What would cause noise (ground noise?) when touching the volume control and tone controls?

I have a new preamp that I recently hooked up and I'm getting some interference or what may be ground noise but I only hear it when I'm physically touching the metal volume knob and tone controls.  When I touch the metal top of the case in addition to the knobs, the noise will subside.  Just looking for ideas to help isolate the cause.  I think the case itself just isn't grounded sufficiently.

I have tried new power cables, RCA cables and plugging into different outlets with no change.


@audio-union  I just checked my outlet ground with my checker and it doesn't show any ground faults with the wiring. 


@imhififan  I did a continuity check with my Fluke and it does beep when touching the center ground pin of the power cord and then touching ground points on the preamp chassis.  It beeps when I touch the grub screws holding the knobs on the pots as well.  I opened the preamp and all the grounding/shielding is in place and looks to be well done.  Otherwise the chassis is wood with metal top, front and back plates.

It could just be the nature of the beast.  Tube quality is unknown so I'll try some new ones before going further.

So I tried a few more things but I'm still getting the buzz/hum.  When I touch the ground stud on the back of the preamp (for the phono stage), it goes silent.  Maybe I can run an external ground wire?

Does this happen when no sources are connected to the preamp? If not, try an optical cable between your streamer and dac. I had a similar problem years ago that just couldn't be resolved until I did that. Very strange but it worked. 

So I tried a few more things but I'm still getting the buzz/hum. 


If you did so without talking to the manufacturer then you were wasting your time. This is a problem that has a very specific cause and I suspect that manufacturer, if a good one, would like to know about it.

I've encountered this problem before- as I mentioned in my prior post, its most likely a grounding problem, such as the controls themselves are insulated from the chassis since the chassis is finished with either paint or anodizing (both of which insulate). If the control bodies are not grounded they can pick up noise; when you touch them that noise pickup will be more obvious.

If the chassis is not properly grounded it can have the same effect. The chassis is supposed to be a safe harbor in which the audio circuit resides. If its not grounded, it can instead inject noise. Its worth getting this fixed.

Call the manufacturer (or dealer, if you can't contact the manufacturer)!


@tubeguy76   Since you confirmed that your preamp is a tube preamp, it would be instructive to know what make and model and also the tube compliment that it uses. While a grounding problem is likely, my suggestion about a tube issue is also possible. 

IMHO,It is a little crazy in this day and age that manufacturer's still have problems with grounding issues!