Jolida JD-9A Phono Stage Hum Problem

Well, all the ground wires end at a bolt in the middle of the bottom of the chassis. I took the nut off and removed the "O" lugs and found that there was only a small amount of powder coating removed and the bare metal had some surface rust. I removed the rust and created a larger, powder coat free diameter for an improved connection. This did reduce the hum by about half, but it is still there. Funny thing is, grabbing the chassis near the transformer no longer has any effect at all, no reduction of hum. Does anyone else have this problem?

Thanks for your responses. I am in the USA and it is not ambient, amplified thru the speakers. I have tried weighting the top of the unit and surrounding the case with metal, nothing stops the hum but my bare hand grasp. As I recall, the (4) transformer bolts, attaching the it to the case have rubber washers to isolate it from the case. I'll pop the top and look for loose connections ....

If you can touch it and the hum more or less goes away, it's probably a grounding issue near the transformer. It might be a loose ground wire or lug. As mentioned above, try locating the transformer inside the unit and tightening everything around it.

Try some weight on top of the case in combination with some type of rubber material above where the transformer is located. See if that improves things. As an example, I use 40 durometer rubber squares on top of the transformer cover of my amps, then place VPI bricks on top of that.