amp in 2 boxes - grounding scheme?


2007-07-18 7:06 am
I built recently a headphone amp where I packed the transformer in a one box and the PSU and amp boards in the other.

In the first box I packed a bit of a filtering before and aftere the trafo, a fuse and connected the central tap of the trafo to the mains ground by using a ground breaker. Box is also connected to the other side of the breaker (mains side). The output voltage ~25AC was taken by a cable to the second box. There, the ground from the trafo box was connected directly to the PSU ground pin and I linked PSU ground to the chassis over another ground breaker (this time only a 100ohm resistor in parallel to a filter cap 0.1uF).

I cannot say that I have any hum issues. A bit of a barely audible hum is present on the maximum volume. I wonder if the connection to the 2nd box is relevant at all or should I leave the second box floating without any ground connection?

To expand my question - what is the proper way of grounding devices that have PSU and/or transformer in a separate box.