Applogise if this is a question which has been asked before but I've scoured this forum, tried all of the suggestions put forward and still have problems. I recently built my 6n6p tube DAC into a steel chassis. Prior to this I had it built in a plastic storage box as a prototype. Since boxing it up I've suffered many problems with hum caused by various ground loops. Initially I made the big mistake of using the chassis as the main signal ground but I have since lifted the signal ground from the earthed chassis via back to back diodes and a parallel resistor/capacitor. I have also decoupled the signal grounds at the RCA output sockets to chassis using 0.1uf discs. I have physically isolated the transformers from the chassis using paxolin board and earthed their metal parts to the chassis. The heaters are smoothed DC and hum remains when their power is removed.
These modifications changed the characteristics of the hum but have not eliminated it. I can however completely stop all hum by disconnecting the screen of either one of the RCA cables.
Can anyone offer any advice based on previous experience of this kind of ground loop.?
Any advice would be appreciated as I'm at that stage where I feel like throwing the damn thing in the bin!
These modifications changed the characteristics of the hum but have not eliminated it. I can however completely stop all hum by disconnecting the screen of either one of the RCA cables.
Can anyone offer any advice based on previous experience of this kind of ground loop.?
Any advice would be appreciated as I'm at that stage where I feel like throwing the damn thing in the bin!