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.