Question about Impedances

[oguinn]

I get the same noise irrespective of whether anything’s connected to the RCAs. I poked around with the chopstick without a source connected earlier and heard it.

[Paul Birkeland]

Have you performed the diode mod to provide some ground isolation?  It's possible that what your hearing is ground pollution.

[oguinn]

I have, yes.

[oguinn]

God this is dumb.

I pulled the amp off my desk and reheated some of the joints on the 6080 socket. I plugged it in over at my workstation and noticed that there was still some background hum and whine, but nothing nearly so bad as it was before - probably outside of the range worth worrying about. Take it back to my desk and plug it in - hum is back. Ok, that's a power line problem then.

I have two power strips on one outlet. The strip the Crack is on is behind some furniture so I turned the other strip off first. Noise drastically reduced. After a process of elimination, it seems like it's the wireless headset on the opposite side of my desk plugged into the non-Crack strip. I'd moved it farther away when there was noise pollution noticeable on the HD 6XX and it solved the issue. Then I added the diode mod. Then I switched to higher sensitivity headphones and noticed it again.

Long story short:

• Noise pollution strikes again, and I should have started there.
• There's still some low-level noise that I think is probably just to be expected on this amp with the more sensitive headphones.
• Seems like the diode mod does a good job cleaning up these sorts of issues, but there are still limits.

[oguinn]

To tie off here - I replaced the 6AS7G I was using with a GE 6080 (branded Telefunken, but produced by GE) and the issue's resolved itself. I'd be more apt to think it's really a cold solder joint except that it only seems to go away with the new 6080.