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 2 responses by ltmandella

ltmandella's avatar
ltmandella
118 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.

ltmandella's avatar
ltmandella
118 posts
 

Measure AC voltage across the + - speaker connections at the speaker, with the amp powered up but no signal input.

This gives you emperical measurement that you can discuss with ZESTO.  You might also ask him to do the same with one or more of his in stock units.  If your measurements are reasonably close to ZESTO's in stock units, well, it's inherent to the amp.

If your unit measures more than about 20% higher than the average of ZESTO's units, you know it is something special to your unit or envrionment.

You might also measure when powered up throught the PS Audio regen.  And compare that measurement with ZESTO's.

Also, the newer PS Audio are not really.  Try an oiriginal model PS 300 that totally regenerates the AC, as opposed to current models which allow much of the original mains to be included in the output.

 

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