Buzzing with the power turned off.

[StivVid]

Hi, all.  Just finished my first S.E.X. 3.0 build.  Had a listen last night before the C4S upgrade and everything sounded great.  I heard a short hum through headphones when powering up.  Assumed that was the transformers?  Anyway... as soon as everything warmed up it was nice and quiet and sounded great.  Today, I installed the C4S upgrade and am experiencing an issue.  I hear a constant buzz through headphones when the power is turned off.  As soon as the power is turned on, I hear the hum of the transformers then the tubes warming up, then it's nice and quiet and seems to behave normally.  I'm guessing there's some kind of grounding issue if I hear buzzing before the amp is even turned on.  Any thoughts?

[Paul Birkeland]

How were your voltage checks?

[StivVid]

All checked out.  C4S voltages were 66 at both terminals.

[Paul Joppa]

I have seen that happen from electro/magnetic fields - it can be from electric fiends (lights, dimmers, etc) or from magnetic fields (nearby transformers, electric heaters, etc.)

[StivVid]

You may be right.  Just checked it again and no buzzing.  Certainly appears to be intermittent.  I'll have to do some trouble-shooting.  Thanks, Paul.

[Paul Joppa]

No problem. I had that with my first 300B amp - my speakers are efficient (101dB) and I heard a buzzy hum when the amps were off; I even pulled the power cord and input cables, made no difference. As you have found, once the amp is on, it greatly reduces. I have a theory why, but it's too long for a post. :^)

[MD1200]

i get some noise when i have the fluorescent tube lights on in my room from time to time, But i hardly use them anymore since i added a lamp at my desk.

[StivVid]

Well... I haven't heard the buzzing again since my original post. We'll consider the issue solved.for.now. Thanks as always for your help and suggestions.