So I sat down the other day in front of my speakers and noticed that it was emitting noise. A low level buzz/hum and I thought this very strange as my amp wasn't turned on. so I walked over and proceeded to unplug my amp from the wall and the sound was still thar. It only went away after unplugging one of the speaker wire from the unplugged amp itself!

So my question is, does anyone know what would be causing this? I have used multiple cables and speakers with the same result. Even after the amp is unplugged for many, many hours its still going. The amp in question is the SE34-I. This is not potentially causing damage to anything is it? I have been keeping the speaker wire unplugged until I go to use it, but I have still been using it..

Thanks
Dylan

Weird indeed!

And out of my range of experience, but I will offer some brainstorm thoughts, and hopefully if I am off, someone who knows will correct.

If there is no power to the amp, even with the power cord hooked up, I can't quite feature it being something in the power path of the amp... like internal fuse connections or tubes... but not for sure. I am ignorant about the internal fuses as my amps don't have them. But looking at pics, it seems they are on the rectifier circuit. So if a fuse was bad, wouldn't the rectifier not light up?

Is it possible that it is a strong magnetic field that your amp and/or cables are acting as an antenna to pick up. But to make the sound at the speakers for extended periods without the amp powered up, wouldn't there need to be some power to make noise from the speaker drivers??? Could a strong interference field be enough to activate the drivers???

If you have it happening after many, many hours of being turned off, even if caps were still holding charge, wouldn't the noise at the drivers be draining that power off and eventually be quiet? But also, normally, I have some light hum here, and as soon as I turn off my amps, there is no noise. And doing modifications, I know some caps can stay charged a while without directly discharging them by playing the amp out without power... ie music playing, and power off the amp as a means to drain caps, and by double checking with resistors to ground internally... Anyway, my noise goes away as soon as power is cut, but some caps still have some charge.

Also, seems interesting that it goes away removing the one speaker cable.

Does it go away if you unplug the other speaker cable and leave the one you pulled hooked up?

Could it be some proximity thing that the one cable is closer to a EMF or RFI noise source?

Is this something new?

Just recently noticing it, is it pretty quiet ... like something that you have to have your ear near the speaker to hear?

Did you have anything plugged into the amp after pulling the power cord... Could noise be coming over from your pre or source or source cables?

Have you added some networking or wifi to your setup that might contribute?

Has your power changed in some way?

I have never experienced this, but maybe more trouble shooting thoughts for a talk with Steve if needed. I would not hesitate to call Steve.

Will

Have you disconnected components upstream of the amp?  Noise may be passing through from a CD player or preamp?

Thanks, Crazy,

I would enjoy your dissertation expounded upon.
Wrapping my mind around ways that might be cause.

When you have time.

Thank you

Amp off and the speakers hum sounds like a power supply cap discharging but it would stop after a bit. I suppose a weird synergy between the cables and an external electromagnetic field can't be ruled out but I’ve not encountered anything like that and I’ve exposed electronics to external forces all over the continent.
You've eliminated the speaker by unplugging it. Now attach the cables to the speakers unplugged from the amp and eliminate them as antennae. This sort of vexing problem can only be solved by methodically changing one element at a time until you discover the culprit.

Dylan,

I would call Steve and talk about what’s going on. He can guide you.

If he decides that you need to send it in, you would not be on the new component wait list. Repairs and mods are done separate from those. You should get it back in under a month.

Good luck!

Geno

First I would ask, when you say you plug the power cable or ICs back in... Are they connected to other things, or just plugged into the amp? If on their own in the amp, perhaps antennas, if in the wall of other gear, perhaps ground.

Did you have the amp off when you swapped the EL34s and got a weird sound... I always change tubes with the amp off.

And if it gets noisy when attached to the wall power or ICs connected to other gear, it does sound like it could be ground issues... I have had this happen where my touching a connector, presumably me being another ground connection, makes the ground hum worse.

I am not altogether convinced this needs repair based on your research pointing to ground noise.

The shock thing could be what I was talking about before... Unless fully drained, the power caps can hold charge, and if you go inside and connect ground to the hot side with your finger or whatever, you will get a nasty wakeup zap.

Judging from all this, you may even have a semi-"normal" hum, especially if you are using really efficient speakers. In my rooms, until I started modifying things, I alway had some hum from my Decware, though not a lot. And now, almost none with some internal work... but sometimes a small amount.

If this is a hum you have to put your ear to the speaker to hear, I guess I might just proceed to enjoy while trying to set up cables to where they are distanced, and cross each other rather than being parallel and close, and if you can, plug all your stuff into the same receptacle (or strip/conditioner...) These might fix it for the most part.

Re: caps. In normal operation they should drain within seconds of powering off the amp. Steve has said this several times, including just a couple days ago when he posted about fuses. If they still have a change there is a problem. IMO.

I think Steve was talking specifically about amplifiers, with power tubes. ZRock is designed to be always on and may (probably) work differently. But again, IMO.

Kedros - now that the amp is discharged, through you!, hook it back up to your system but don't plug the power cord into 120vac.  Do the speakers buzz?  If not, plug the amp into 120 vac but don't turn it on.  Do the speakers buzz?  If not, the problem is a high voltage capacitor in the amp that is taking a VERY long time to discharge and until it does discharge it causes the speaker buzz.  Many times there is a resistor added to the design to discharge those big capacitors in a reasonable period of time and maybe that part got zapped.

The fact that a capacitor can hold a charge big enough to zap you for minutes or 10's of minutes after being powered off is not unusual.  I found that out at age 13 with a small guitar amp.  I think that was the worst shock I've ever gotten in my entire electronics career.


Dan

Dylan, I had similar thoughts to Dans but haven’t contributed because I was just suspecting. For what it’s worth, ungrounded buildings are fairly common in my area. In my office if I get a cell phone near my computer monitors I get a similar issue as you describe with the hum. It took me a while to figure out it was because none of the outlets are grounded. Likewise, my home has all three prong receptacles but none have a ground attached. I had to physically run my own ground wire from the three prong outside to earth for any outlets I wanted to connect devices to that require it. So, could be a bad resistor or could be your ground. Both are worth checking. Good luck and keep us posted when you find the issue!

This community is great thank you everyone for all the help and advice!

I didn't have much time to do any diagnostics after work yesterday and will be able to do more tonight but just an update.

I had my amp sitting on my work bench for a little over 24 hours completely unplugged, no tubes, power cord, nothing. I proceeded to bring it back into my setup and hooked just the speakers up and nothing else. The noise was gone! At least I couldn't hear anything, however when I touch the amp anywhere, the hum comes back and if I touch the screw that holds one of the transformers underneath directly it gets louder. I would go back and forth with my fingers and the hum would change intensity when I switched between touching the frame and the screw.

So I gotta rule it out as being an issue with the amp right?

Steve, (it's an honour). I tried running a ground wire from the negative speaker jacks to the tops of the bolt on the power transformers and didn't experience any change.

Also when I plugged the power cord back in the hum instantly comes back.

Sorry if its a rushed post I typed it up before work this morning.
More updates asap! Also going to try to post pics.


Thanks
Dylan

I just want to say thanks to everyone for all the help and suggestions it is very much appreciated!!

Well I finally had some time to do some more trouble shooting and Steve, you where right. I had first attached the wire from the negative speaker jack to the top of the transformer bolt with no effect. But when I put it to the bottom bolt of the transformer that went into the chassis the hum immediately went away! It was weird too because its specifically those bolts holding it to the chassis. Well not weird, I just don't really know what the reason behind it is.

So I took it down to the workbench to put a nice wire with a fork spade on it and ended up snapping a bolt

Other than that tho I managed to get the wires on and introduced it back into my system hum free and I am currently listening to it with no issues! I will still be sending it in when I get my UFO25, but that's a different task for a different day. I am just happy I have my amp back and music for the weekend!

Thanks
Dylan

Well at least now we know that if the power grid is hacked and everyone is in darkness for weeks or years, you will be able to receive messages from space just by unhooking your ground wire : ). You can't get a much more zen receiver than that... an antenna connected to a voice coil on a loudspeaker.  See, I really do have your back!

-Steve