Has anyone experienced this?

[Fletcher Munson]

I had my new build on the bench, plugged into a dummy load. I injected a signal (150mV) from my signal generator and could hear the sound coming from somewhere in the chassis. I can move the frequency up and down and clearly hear the change in pitch. So I thought, well something must be vibrating, and tried touching/damping every component in the chassis with a chopstick... to no effect.

The sound level is pretty faint (you'd never notice it with a speaker connected) and changes with the volume knob: loudest with volume full up, and disappears with the volume at zero. Can anyone explain what's happening here?

[The Dude]

It could be lots of things, but I'll bet on OT resonance. If the amp works as it should, I wouldn't sweat it.

[nsubulysses]

You can hear it in the power tube too right ?

I would guess this is not a loud amp? I think with amps that are 100 or hundreds of watts it's pretty easy to hear the sound in the OT and (I thought) the power tubes as well.

Classic example of this is people being weirded out when they record at a studio and their amp is in the control room with them and 4x12 (or whatever) is in another room. A cranked amp and you can only hear the sound from the OT............. it sounds like the amp is in pain

[Fletcher Munson]

It's really hard to localize the sound, but I don't think I can hear it from the power tubes. It just seems to come from somewhere inside the chassis.

This is a low powered amp; about 15 watts, based off a blackface Princeton.

The sound is definitely not a problem. Once you're plugged into a speaker, whatever noise it's making is a just fart in a hurricane. I'm just trying to understand how the sound is produced.

[Leo_Gnardo]

Sometimes the windings in an OT "sing along." Sometimes the metal on the transformer cover does the same. One of my fave amps in the world, THD's Flexi 50, has power transformers that whistle at a midrange pitch. Some multiple of 120 Hz no doubt. Touch the cover and it it goes away. All in all, nothing to worry about, but yes sometimes it does freak people out.

[Dave H]

I can hear it on my amps with a dummy load. I've always thought it was the OT. I can hear the tone change as the amp just starts to clip.

[Enzo]

Lots and lots of OTs sing, and some power tubes do as well. Quite normal.


Want to localize it? Roll up a magazine or a cardboard tube from a paper towel roll. Hold it to your ear and use it for a stethoscope.

[drewl]

Hear it all the time using a dummy load.

[SoulFetish]

^^^What everybody else here said. When I first plugged a build into a dummy load and ran signal into it, I shut my amp off almost intermediately because I heard what we're all describing and thought my amp was about to blow. I was not expecting that (as I guess you weren't either), and thought something must be wrong. But, it's totally normal and you're going to hear it all the time now. In fact, now I get nervous when I don't hear it.

[DrGonz78]

I remember the first time I heard the chiming ring sound running a Peavey classic while connected to a dummy load. Posted about the ringing in a thread while working on the amp. Nobody seemed to say anything bad about it so I assumed it was a normal type occurrence. Doesn't happen with every amp though so at first I was a bit alarmed. I can tell ya the noise seemed to be coming through the tubes.