A persistent hummmm...

Since Erik asked, I’ll ask it, too. The OP doesn’t say whether or not the hum is coming from his speakers, or just audible at the listening spot.

I ask for this clarification because I, too, have had a problem with a persistent hum—but, evidently, it’s due to "lamination rattle" in a toroidal transformer. The problematic amp is old, and the varnish that the transformer was "dipped and baked" in has become brittle over time. Vibrations can cause this brittle varnish to break, allowing the laminations in the transformer to rattle at 60 Hz.

FWIW, I tried most of the fixes suggested here, including even a PSAudio power regenerator a friend owns. Nothing did more than slightly help. But, my hum is mechanical, NOT in the speakers. It does not vary with the volume setting, and is audible even with nothing connected to the amp (not even the speakers). In fact, it’s audible in the transformer when it’s removed from the amp and connected, all by itself, to power.

Of course, the OP says this hum occurs with TWO different amps (both tubed): his Zesto, and a Scott. But NOT with his "high powered Class D amp." It could be that both of the tube units have lamination rattles in their transformers. That would be a coincidence, but not all that unlikely, if both units are old. I have two identical amps, both from the late 1990s, and both of them have problems with the same lamination rattle in their transformers.

In any case, Erik’s question needs an answer for any further diagnostic advice.

Hi all,

My Zesto amp is pretty new - a couple of years old. The hum was there from the start, but my previous speakers didn't emphasize it as much as my new speakers do. As a few folks have said, the efficiency of horn speakers has a down side.

The sound comes out of the speakers, AND if you put your ear to toe back left of the amp (where the toroidal transformer is), you can hear it buzzing there, too. 

I like (well, at least as a path) the notion of unplugging many things in the house - I've already done so in the listening room itself. My listening room was a "found" space - it was an old three sided porch on the side of the house I enclosed and made into my room. It lives on top of the boiler room in the basement. That room has an oil burner (with a pump for the oil), and since it is baseboard hot water heat, it has multiple pumps to circulate the heated water throughout the house. I wonder if those pumps are throwing junk into the line?

Anyway, you have inspired me to search for the equivalent of the coffee maker that a poster found in his house. The source is out there...

@erik_squires 

Yes, from the speakers. Hum and buzz caused by coffee machine plugged in. Adjacent room, but IDK about circuit. Many years ago.

We have multiple dimmers in our house. Noise is reduced by not turning them on or running them in bright. They are not even on the same circuit. Something to think about. 

Seems like it's the Amp

I feel for you

A hum in my system turned out to be a bad preamp 

Latest hum from subs was solved by grounding to my amp chasis