During rip out today I managed to have a little play in a 'real world' environment, the system in use last night was 3 bluecom belt packs, one on the end of about 30m of FST from the 721 and the 2nd on a 20m mic cable then 6m link to the 3rd. All nicely zero'd on circuit 'A'. Moved the beltpacks to the location of the 721 by adding 2 20m mic cables which made no difference. Changing to circuit 'B' meant all 3 packs had obviously more side tone and loads with my home made PSU. Each time I could easily re-zero them. I repeated with 2 BP1's and a BP2, zero'd them on circuit 'A' then moved to 'B' with no apparent change. On my home made PSU there was just a little more side tone. Exactly the same results happened with a second 721. From this, my conclusion is the bluecom's are more sensitive to variations than Techpro. This is observation/feedback, not critisism. I'm really didn't understand what is you problem, but let me tell you that I made my Bluecom's following both beltpacks and psu schematics. I has been using my bluecoms in the last 3 years, in different "real world" indoor and outdoor conditions, in "real world" productions, even with 50 or 60m wires, and I've had zero problems or faults. Zero. The system is solid as rock Having said that, a quick question: is this system compatible with our comm's? https://fccid.io/BYMBH80074/User-Manual/manual-221208.pdf Best regards!