Post by godathunder on Jun 10, 2020 7:25:20 GMT -5
I picked up a used umc-1 last year to replace my old teufel decoder and am having issues with a 100hz buzz through all channels
the problem is present with all inputs etc disconnected from both the umc-1 and the mains supply.
the umc-1 has what I believe to be the latest firmware (w7.04.00.19)
my hifi has its own dedicated circuit from the board. my amp rack (5x samson servo 170s) is located in my attic but is also directly connected to this circuit. continuity testing and loop impedence testing of the power outlets shows a resistance difference of 0.02ohms between the two outlets, and is confirmed by loop impedences of 0.67 and 0.65ohms. I have tried isolated all other power everywhere in the house, leaving only the hifi supply powered. this makes no difference to the problem. i have also checked continuity of all mains and signal cables with no issues. the signal cables are screened and of decent quality
with the amplifiers disconnected from the umc-1 they are silent. when they are connected to the umc-1 (with the umc-1 completely isolated from the mains supply) there is a barely audible 50hz hum. when the umc-1 is connected to the mains earth but unpowered this hum becomes very slightly more audible. when the umc-1 is powered but in standby there is an easily audible 100hz buzz, that is loud enough to be very annoying.
the problem is the same regardless of whether all amplifiers or just one are connected. I have also tried transformer isolating 1 channel and only connecting this. the buzz persists
the old teufel decoder didnt exhibit this problem but was powered by an external supply and didnt have an earth connection.
with thanks
ger
before I mark this down as a problem with the umc-1, is there any flaw to my methodology I should investigate first
edit: Im based in ireland, nominal 50hz 230v supply, neutral and earth bonded at service head