Hi! I recently got my SE84UFO25 (along with a CSP325 and ZP3), and have been loving them so far. However, I've noticed something super weird: with the SE84UFO25 hooked up to speakers but turned off, with literally nothing else (no inputs or even power cord plugged in), there's a very faint buzz coming from the speakers. I'm assuming something in the amp is picking up some EM in my room, but I don't know enough about how tube amps work to speculate about the actual mechanism (if i just touch the speaker wires to themselves when they're not plugged into the amp, there's nothing, so I don't think it's picking up something off a power cord, but who knows). When the amp is plugged in and turned on (no input hooked up), there's a fairly quiet but audible hum (sounds like a sine wave hum, not the buzzing when it's powered off), so I'm wondering if this is just the amplified version of whatever it's picking up out of the air. Any thoughts on how this might happen/what I can do to mitigate it short of putting it in a faraday cage? Thanks!

Yup! I read through all of those, but I didn't see anything about a buzz specifically when disconnected from power... I'm curious if any of the tubes could be picking something up if my room is electrically noisy (or some other cause) since this seems super weird, and what I might be able to do about it.

Things like this can be really annoying, to say the least. Hope you can find and correct and it's something as easy (if unexpected and mysterious!) as Kahuna Jack's was.

Hmmm so I just tried removing the tubes one by one, and even with all the tubes out, there was still the faint buzzing sound... I hooked up a scope, and it looks like there's about +/- 5mV coming out of the speaker terminals even with everything unplugged... possibly the transformer is picking something up? I'm definitely out of my depth here, just assuming something is acting like an antenna. Maybe I'll try moving it to another location and see if that helps.

FWIW, this buzz doesn't affect me at all, I just have a hunch that whatever is causing the buzz may be related to the hum when the amp is on, which honestly isn't that bad, but, you know how these things go...

Capacitor was my first guess, but it does this after hours/days of not being turned on.

The Zen Triode Amplifiers have a fully floating output stage.  That means that the negative speaker jacks are not connected to ground.  That in turn means that when the amp is off and there is no voltage on the cable, it can become a loop antenna and the buzz you hear is indeed coming from the air - specifically all the wall warts and USB power supplies throughout your home, as well as WIFI and Blutooth.  

The amp is letting you hear the ambient environment it is in.  

You can connect a jumper wire from the negative speaker jacks on the amplifier to one of the transformer bolts, thus grounding it and the noise will stop.

Steve

Just to close the loop here, now that I've had some time to fiddle: Steve - thanks so much, that did the trick, I ran a thin wire from the black terminal to the screw holding down the transformer, and the buzzing when off is gone! There's still a hum through the speakers when things are on (but it's a warm hum and not a buzz like this problem), and the transformers themselves hum a little, but based on the previous issue, likely there's a bunch of noise/bad power in my room. I'll go hunt around the other threads and see if I can eliminate that as well, although it's certainly livable even if I can't fix it. Thanks again!

This post and Steve's suggestion to ground negative speaker terminals to transformer is a revelation! After following this suggestion, my system no longer has the hum described above that has been vexing me for years. A sense of unwanted energy is no longer present when listiening, and this sense is what has made listening to vinyl difficult for long periods. Now, the rests, spaces, within the music are quiet, and I can confidently say that my vinyl system sounds better than listening to digital files streamed from Apple airport to DAC to system  .. . . Digital files sound much better too.  

I'm not sure what benefit of floating output does, or if grounding the speaker terminals diminishes this benefit, but I'm glad I did ground mine!

CSP (upgraded to ii), SE84CS, ZP3, ZMC1, ZDAC