Very faint hum

[Jimb0]

Getting a very faint hum on both channels. Isn't affected by volume. Also getting a ringing like sound when I'm adjusting volume up and down.

[Paul Birkeland]

The ringing sound is completely normal and normal with 6C45P operation.

Does the faint hum change in magnitude when you switch impedances?  If you listen to a 60Hz and a 120Hz tone, does it sound like either?

[Jimb0]

No differences between low and high impedance as far as I can tell

[Jimb0]

Definitely a 60 hz tone

[Paul Birkeland]

If the impedance switch doesn't change anything, what happens if you unplug all your sources?

[Jimb0]

it's still there PB

[Paul Birkeland]

What headphones are you using?  Is this the new Mainline with the universal power transformer? If so what is your wall voltage?  How tight is the hardware on the power transformer?

[Jimb0]

Using HD 650's, older version with 120v. I was missing a screw for the power board but it has been replaced. I will try retightening them and see what happens

[Jimb0]

I've retightened everything but still getting hum

[Paul Birkeland]

Can you double check your voltages to be sure they are all in line?

Have you tried the Mainline in a different room to be sure the source of hum isn't perhaps something close by with a power transformer that just happens to be perfectly aimed?

[Jimb0]

I rechecked the voltages today and they checked out okay. Also tried moving to a different location but the hum is still present

Also I forgot to mention that I had to extend one of the wires from the CAT-5 going to the XLR output. I just used some extra wire and soldered both ends together. Is it possible that this is causing the issue?

[Jimb0]

Pic

[Paul Birkeland]

You could try this modification:

https://forum.bottlehead.com/index.php?topic=11676.0

Extending that wire as you did is unlikely to cause hum issues, but I would cover up the exposed solder joint with some nail polish or RTV.

[Jimb0]

Thanks PB will do

[Jimb0]

Tried the mod but to no avail still getting that hum