2. amps-preamps
  3. 188545-177823

A persistent hummmm...

I have a Zesto Bia 120 all tube, Class A amplifier. I am currently using it with a pair of Volti Razz speakers - pretty efficient horn speakers. My problem is a hum that is audible from the listening chair. Most music masks the sound, but in the quieter passages, there it is. It hums the same way when nothing else is connected to it - just amp to speakers, or when the preamp is hooked up. I have had an electrician out to the house to check the ground. It was good, but he put two more 8 ft. copper bars in the earth - no difference. I had sent it out to George Counnas, the designer/owner of Zesto. He checked it out (and upgraded it while it was there). He couldn't make it hum. 

I have tried using an extension cord to other power outlets in the house, and the hum was no different. I have changed speaker wire in case my regular wire (no shielding or conventional insulation) was acting like an antenna. I have used a iFi DC filter. Obviously, I have changed over the tubes (KT88's). I use a PS Audio Power Regenerator, and it hums less when the amp is plugged into that device than when it is plugged directly into the wall.

 

When I use a high powered Class D amp, I do not get hum. When I use an old Scott 299A all-tube integrated, I do. That makes me think something is making the transformers hum, and the Class D doesn't have them in the same way.  

 

I remember reading that Michael Fremer had a persistent hum with his gear, and finally changed out a lot of his house electrical set up. My two electricians can't see a problem, but clearly, there is one. Anyone have any suggestions for other things I could try?

 

I live in the Boston area of Massachusetts - does anyone know electricians or audio experts who specializes in these kinds of problems? 

 

Thanks,

 

David

dtorc

Showing 1 response by snilf

snilf's avatar
snilf
194 posts
 

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.

More to discover