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? 






@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.

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Sorry - in the list of things I said that I tried, the cheater plug should have been first. No luck there.


I have changed the inout tubes a few times, and that doesn't seem to affect it. I don't know whether there are quieter versions out there ( I used JJ 12 Au7's). 


I think the that the power, which comes from the PS Audio Power Regenerator is pretty clean, at least according to the scope built in to the unit. But something is off, clearly...


Thanks for thinking with me...



That is the danger of running tubes with high efficiency speakers, Hum is usually inevitable.  Have you checked with the manufacturer to see if the amount of hum you are getting is normal?

Yes - I sent the amp out to the manufacturer/designer, and he said he didn't get any hum at all. Of course, i don't know what speakers he uses, and you are right - the efficiency of the speakers certainly exacerbates any hum problem the amp has.

I think I may need an electrician who is mindful of audio needs. Most are not, I'm finding.

@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.



Hi OP!

I think the place to start it to understand if the hum is inherent to the amp, or perhaps a ground loop issue.

Disconnect all inputs and listen.  If you still hear a humm its an amp issue, and as I think you suspect, may only be noticeable because of your high efficiency speakers.  OTOH, if the hum vanishes with no inputs, it's a ground loop or upstream problem.

I had a hum problem once, although mine did not involve tube amplification nor high efficiency speakers.  I found isolation units from Jensen Transformers were effective when all else failed.  Of course, I had to get comfortable with the idea of inserting an isolation unit in the signal path, but I couldn't hear any sound quality degradation and the hum was eliminated.


So, on my (so far) futile diagnostic journey, I disconnected all input to the amp. and then unplugged them. The amp, with nothing plugged into it, or even sharing the same wall plug, continues to hum. I have to say the builder, George Counnas of Zesto, has been very accessible and involved with my process. Besides taking the amp back and checking it out, he has called me more than once to check on my progress. I think he has made an honest effort to help. 

I"m not a technical person, so trusting my gut is not really a substitute for process, but my suspicion is that the culprit is somewhere in my house. 


I really appreciate that a number of you have tried to think with me.



Interesting. Leaving the speakers attached, with the inputs disconnected I’d put a multimeter on the outputs, set it to AC and see how many AC volts you are getting. It may be that your few millivolts of AC (humm) are "normal" but also too much for your high efficiency speakers.

 I know very little about this, but Vandersteen suggested I try touching a wire (any old hookup wire) to the various chassis of the system and to the 3rd ground wire of a wallplug (just take the stripped wire and shove it into the round (not spade) hole.....one component was the culprit...gone now.

@dtorc I can commiserate.I,m trying to solve this exact problem right now. My system (on profile) has been running dead silent for years, I had this problem when I first built the system but after struggling with it for I can’t remember how long ,it disappeared. System is running on a single 20 amp home run straight into a plastic box with an Audiquest receptacle. 200 amp service has two 8 foot ground rods one in front and one under the panel which are bonded together,I’ve completely broken down and rerouted all the interconnects and AC cables which are name brand, Ive changed all tubes since I had a complete set of extras ,I’ve moved components around and done all the same ruling out procedures discussed in this thread, no joy! It’s driving me crazy, its a buzz and a hum combined if that makes any sense,audible thru all drivers and tweeters. Anyone? Thanks in advance!

I had a weird buzz coming through my Forte / Quicksilver combo in my last home.  It was a plug in air freshener.   It was on a different circuit but still cause noise.  Took a long time to figure that out.  

I had a Zesto preamp and i can honestly say it is the quietest , blackest , free of noise component I've ever owned.   I am not surprised George said it checked out OK.   

In my new place I had a different kind of buzz / noise.   That was rooted out quickly.  It was an ethernet cable running alongside and touching a speaker wire behind the rack. 

Good luck.  


Have a new Hi Fi Rose streamer, hooked up last night. Sounds pretty good but for the first time-hum. Can't handle hum so here I go as well. 

@OP. That kind of hum problem can be very difficult to diagnose. As you have found out by using two different valve amplifiers, tube amps are inherently more susceptible to low frequency hum - often at the frequency of the mains - 60Hz in the US. Tubes aside, I have known situations where certain amplifiers hum in certain installations and do not do it anywhere else, with no apparent reason. Though it would be a bit of a pain, you could move the amp and speakers to another room to check if there anything in the listening room that is inducing the hum. But before that, I would disconnect all electronic appliances in the house and see if the hum disappears. Then you can reconnect the one by one to see if you can identify a cause. It's a long shot because the PS Audio regenerator should deal with that, but in the circumstances, every option has to be explored.

Has the amp ever been quiet or did it have this hum from the first time you used it?

I’ve had hum from tube amps associated with noisy tubes. Atmasphere already confirmed you swapped the input tubes whch are more likely to be the problem. I’ve had full boxes of tubes that were noisy so it is possible the replacement tubes are just as noisy.

Have you used any connection improvement products? These are dangerous as they can create a path to ground.



I had a similar experience with a horn/tube combo. Do you have any dimmer switches nearby that can transmit RF? Also, a dedicated home run to the panel is recommended. Since you live in the “Boston” area, do you have an old house? Some electrical panel updates can cause ground loop issues with old BX wiring. 

I had that issue years ago. I started unplugging everything in the house until I found the culprit. A coffee machine. 

I can sympathize. A hum can get into your head until the whole musical experience is ruined. I too have a hot tube amp and my speakers boast of a 104 db efficiency rating. (Asking for trouble but I owned speakers before I discovered the amp) No matter what (and I mean, no matter what) the hum, though minimized, could still be heard from my chair between songs and even during songs if they ever took a breath. This forced me to stay on a certain type of music that maintained a clatter while I was trying to forget about the hum. Nearly ruined the whole experience forever UNTIL....I rearranged my room to be able to move 4 feet further away from my speakers. (Kilpsch Lascala II) Problem solved!! I can lean forward and put my head back in the "hum zone" but back 3-4 feet nearly zero hum. Why is this? I have many theories but no real 'scientific' answer. AND of course, very few can rearrange their listening room so as to gain both width and depth. I removed 10 bookshelves around and behind my listening areas to gain that extra space. This comes after a million other attempts. Yes. I had an electrician run two dedicated lines directly from outside power box to my listening area, Changed in and out tubes incessantly. Sent back to manufacturer to install grounding harness and new improved everything. And while everything helped a little, moving back has made it so weak I finally don't even think about it any more. A side benefit to all this isolation etc is that the quality of reproduction has also improved,  

@mashif Were you hearing mechanical hum, or was it coming from the speakers?? On the same circuit?

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...


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

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.

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  :?

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.


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.




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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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.


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.

@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.

Could it be a DC offset issue? Maybe Class D amps are less susceptible to DC? Perhaps this could help from Amazon: Fi SilentPower | DC Blocker - Blocks Any DC Offset, IEC Connector. Good luck!

I recently experienced a slight hum and a slight intermittent bacon popping sound from my recently rebuilt Adcom GFA-565’s into my Polk SDA SRS 1.2tl’s.

Turns out that I’d also placed a Bluesound Vault 2i in the room, which connects to my network downstairs via a Ethernet over Powerline adapter.

First thinking it was my closet florescent ballasts, I changed to LED.  Partial problem solved. No more popping when the closet light was turned on or off.

Took everything out of all wall outlets one at a time. When I got to the Netgear Powerline adapter my hum and pops went away.

Now I  have to figure out an Ethernet run through the walls to go directly to the Bluesound Vault.

induced my own problem. But problem solved. Good luck with yours.