Yes I know it puzzels me but I will never give up I love problem how are hard to solve.
Besides the power transformer, the EFB board is also in common between channels, something could have gone wrong there.
What happens if you yank out the AC cord from the wall while listening to the hum?
Does the hum immediately stop ( 50Hz induced hum ),
or does it die out over a few seconds ( 100Hz hum from supply rectification )?
It's always possible to wire a board incorrectly to cause a ground loop. If you read my posts, I don't blame the board itself. I build boards like this (and ones more complex) myself...
I’m not a fan of the power transformer core touching both opts. It’s probably not the problem but that alone could be the cause of buzzing
So my friends I have sat all weekend and made every imaginable attempt to tame the pulses that arise. After exhausting all variations and attempts, I have now taken apart the entire amplifier and am starting from the beginning and we will see if it gets better. I will have the mains transformer tested by a friend to see if one 115V or more windings are damaged. But first it must be put together to see if it is I who have made a mistake.
I was thinking about 50Hz from the PT core coupling to the bell covers of the OPTs. A short while ago as I was reorganizing my system, I noticed a low 60hz buzz on the speaker I never heard before, I then realized that the RCA interconnects had worked themselves next to the power transformer core.
Status report, now I have put it back all together after I decided to start over and now the 50Hz is completely gone but what remains is a faint hum which is not heard until very close to the speaker (0.5m) then bear in mind that I have a pair of Altec 604E with high sensitivity.
It's gratifying but still not my preamp has decided not to be in the game so that's the next project to repair and another story. Thanks for all the help and ideas to fix the problem and improvements.
Cheers Anders
It's gratifying but still not my preamp has decided not to be in the game so that's the next project to repair and another story. Thanks for all the help and ideas to fix the problem and improvements.
Cheers Anders