Ok, so I have finished my build of the EAR834p clone but have a hum problem and would like some help with resolving it from kind souls. I am not experienced. This is my first amp build. :)
The hum is on both channels and increases with the volume. I have two inputs going trough a switch. One for MM, the other for MC routed trough a SUT. Hum is present from both inputs so it is not related to the SUT. I do have an aluminum plate between PSU and amp board. I have twisted all wires except for input and output. For output I have a shielded wire.
I have followed this grounding scheme from LencoHeaven forum (picture below).
This is what I have tried so far:
If I do not have the turntable connected I still have hum (a little bit lower tough).
If I remove ground on ICE I still have hum.
I desoldered the input wire from board. Still hum, but lower.
With three Brimar CV4004 tubes the hum is 50hz. If I change to JJ ECC83S (in particular the middle tube) hum is somewhat lower (around 4db) but now have I both a 50hz peak and a 100hz peak. If I increase the volume 50hz hum increases the most.
If I touch the first tube (closest to input) hum increases.
I have tried to change the wire from SUT to shielded also (but not to SUT). No difference.
I have tried to move around the amp. Still hum. Hum changed a little with movement.
Can you see any obvious ground loops?
Could this be a transformer issue?
Have you tried moving the long ground wire from the main preamp board around in different positions? Maybe get it away from the relatively high current choke sitting down by the power supply board?
I managed to reduce hum a bit yesterday. This transformer has a center tap for the 6.3V that I was told should go to ground for less hum. I had it installed to my star point. When I removed this entirely, the hum was reduced a bit. Still there but definitely better.
Try viewing Jonathan Krogh’s YouTube: “Tube Phono preamp build ear834 clone kit.” Towards the end he talks about a hum and his solution.