Power supply floating ground

[vockleya]

I have recently acquired an old hammond organ. This organ only has a 2-prong power plug. It has an internal ground that I measured at 0VDC, but 60VAC. I believe it is causing a large amount of hum in the speaker. The thing I am confused about is that the ground bus is connected to the center tap of a transformer. So shouldn't it be at 0VAC? Is there something I should do? Can I connect the internal ground to earth somehow? I have attached the schematic of the power supply section if you need it.

 

[KJ6EAD]

Have you checked the polarity of the mains input? Sometimes that causes hum if it's reversed but the condition of your filter capacitors is probably to blame. You don't want to connect your floating DC ground to any earth ground.

 

[vockleya]

One direction I get 60 VAC from internal ground to earth. The other way I get 20VAC.

---------- Post added at 00:33 ---------- Previous post was at 00:28 ----------

Just to clarify, the floating ground is not DC, it's AC.

---------- Post added at 01:07 ---------- Previous post was at 00:33 ----------

And now that I think about it, this AC voltage is present on a lot of other wires in the organ. Even the DC supplies have this 60 or 20 VAC voltage present on them (only relative to earth, obviously not internal ground).

 

[KJ6EAD]

The chassis ground may be used for AC and DC but it must be isolated from the incoming AC line. Other than a safety check to that incoming AC line, no other measurements to the incoming line are relevant. All circuit measurements should be referenced to the chassis ground. Replace your dried out electrolytic capacitors.