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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
ltmandella's avatar
ltmandella
146 posts
 

WHICH PS Audio regenerator do you have?  The reason I ask is that ASR did a disassembly of the newer unit type and found that the mains is still directly connected to the outputs.  All the newer units do is run a filter/regenerator that  contributes a small fraction of the total, in parallel.  No real isolation.

puptent's avatar
puptent
174 posts
 

I just recently purchased a new, to me, amp and had a persistent hum. I used my fluke to test the shield on all the interconnects, all good. The new amp was a 2 conductor wall plug, didn't matter if it was plugged in 180 degrees or not (which sometimes cures TT issues). Finally used a meter test lead to go between a cover screw on the new amp and my reference ground at my power conditioner. Instant cure. It was a failure of a ground point inside my preamp.I have ordered a 3 conductor IEC socket. ALL of my other equipment grounded through 3 conductor power cables, so never knew there was an issue...

That darned 60 cycle humm  :?

atmasphere's avatar
atmasphere
11,753 posts
 

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.

@dtorc

If I can point out something, it seems as if you are using hum and buzz interchangeably. They are not. A buzz can be heard in the midrange and tweeter. A hum is only audible in the woofer.

So which is it? Since you say ’buzz’ in the quote above, I’m led to believe ’buzz’. If this is the case, you might ask Zesto if "the rectifiers in the power supplies have been properly snubbed." I put that in quotes so you know what to ask.

With certain kinds of noise on the AC line, you can get a phenomena of buzz that is an interaction between the transformer and the power rectifiers known as a ’swept resonance’ which is an interaction between the inductance of the power transformer and the capacitance in the junctions of the rectifiers in the power supplies. A mechanically audible buzz can result, as well as one that can be heard in the speakers.

But if the AC line is clean, the noise might go away entirely, which would explain why Zesto does not get it in the shop.

 

 

 

dtorc OP
21 posts
 

Thank you for that distinction. I can hear the buzz in all three drivers. The pitch changes a little, of course, but it is about equally loud. And, as I mentioned earlier, there is a buzz at the transformer itself.

 

This gives me something to talk to Zesto about. Thanks for that.

 

Inspired by tales of Glade air fresheners and coffee makers, I started to go through my house. I removed all of the Xfinity "pods" that are -lugged directly into a socket, and meant to distribute the wifi signal over the house more evenly. No luck. I also took off all LED nightlites. No luck there, either. I'll keep trying, and talking to Zesto.

 

Thanks again

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