Yes I'm connecting unbalanced (Denon AVR as source) into balanced (a bunch of pro audio amps with XLR in). I don't know why they say disconnecting rca shield is bad and/or bridging 1 and 3 pins at XLR side (as seen in minidsp documentation) is good, but you see that everywhere.That’s interesting that you mention that. I will try that later this week. Just haven’t got to it yet.
I bought an Ifi gnd defender and the hum went away completely on my center but only lowered the hum level on my fronts.
I still wonder why both Hypex and Purifi (and others) consider disconnecting the shield on RCA side to be the incorrect way of fixing hum.
Also are you connecting an unbalanced source to a balanced input? Actually a RCA-XLR cable? Not the opposite? XLR-RCA.
Consider this minidsp diagram:
I made that jumper from S to Negative for the input. When I touch it to the terminal with all components powered up and idle I'm blasted with maybe 80 db of 60hz+harmonics background hum. It's better with the jumper off but by no means silent. I've been living with this for years but finally achieved silence today with the above-mentioned cable. I plan to do my LCR next and have the monoprice cables on order, but I think I might actually need plain XLRs + solder on my own RCA ends. If the monoprice cables don't have a twisted pair *inside* the shield that then gets grounded to the XLR side I think it might defeat the purpose.
For further reading, this paper by Bill Whitlock from Jensen is great and they show proper transformer-based solutions, but they are super expensive. Do I really need to buy four Jensen boxes to filter 8 channels at ~$300 a piece???
https://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.305.873
sample: