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
@ltmandella There's nothing wrong with that- Elgar did the same thing in some of their conditioners, which could both regulate the AC line and also keep it nice and clean. Elgar made some of the best AC line conditioners ever made. I suspect PS Audio is taking a cue from them. |
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.
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@dtorc An electrician won't be able to help. He'll be out of his league trying to understand why the PS Audio regenerator is able to help. Since it helped only a bit, since you swapped tubes and also sent the unit back, its my surmise that Zesto didn't really test it out completely. You might suggest they use headphones instead of speakers; many headphones are 110 dB efficient so low level noise is easily heard. Is the buzz at the same level in both channels? If one channel has more buzz, it might not be the amp at all. So if the buzz is different between channels, try swapping the interconnect cables left for right at the amplifier inputs and see if the problem moves. If it does, the amp might be off the hook.
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@dtorc What happens when you short the input of the amp? Have you tested the input tubes? They are far more likely to cause any amp to hum, if the amp uses an AC filament connection (and most do). The test that the tubes need to pass in this regard is called the 'leakage test' and it measures resistance between the cathode of the tube and the filaments of the tube. If the measurement is anything less than infinity (no connection at all) then the tube can inject hum or buzz into the amp. How clean your AC power is can affect how much the tubes can cause this problem if they have leakage issues. |
