I suddenly have a weird buzz issue; can someone help me solve the problem?

Hi all,


To provide some background, My system is as follows:


A “headless” Mac Mini as Roon core (my hands are tied with respect to using the MacMini, as I use Theoretica Physics BACCH4Mac cross-channel cancellation software/filtering to achieve "true" 3D sound, and this requires the player/streamer be a Mac device), outputting USB to a BelCanto RefLink USB-to-SPDIF converter, outputting SPDIF to a Mojo Audio Mystique v3+ DAC, which feeds a custom-built Dennis Had LP-2030 preamp, which outputs to a custom-built Dennis Had Inspire KT88 FireBottle SEP amplifier (max output, depending on tubes, is 12 WPC). Speakers are Coherent Audio GR-15 Neo Signatures.


All components are plugged into a Puritan PSM156 conditioner. I also have a GoldenEar Forcefield powered sub (amp is like 1200 watts) that is plugged directly into a dedicated outlet.


About a week ago, I became intrigued with the idea of powering my system completely off the grid, as even with the Puritan, I still noticed my system sounded markedly better on certain days and at certain times of day than others.  Also, there was some hum/buzz from the system, which I assumed was still AC-related, as it seemed worse at certain times of day than others.


I followed the guide from Ric Schultz here:



All necessary components arrived, and I got them all hooked up.  Everything except the powered sub is plugged into the Puritan, which is now being fed by the Giandel inverter.


Interestingly, when I powered everything up, the previous hum noise is gone (yay!), and the sound is glorious when music is playing, but I now have a buzzing sound coming from my speakers (when nothing playing) that increases as I turn up the volume on my preamp. I tried installing cheater plugs on all components, lifting everything from ground, as I thought it could have something to do with the sub being plugged into the wall and the other components all going though the Puritan and the Giandel inverter, but this made no difference at all.


I would be very grateful for any advice/suggestions on what I can try.


One thing I noted is that the inverter is putting out 122 volts. I am wondering if the preamp is “unhappy” with this slightly high voltage and would prefer something closer to 115-118 volts, as read on another forum that this may be an issue and that one can test this by using a Variac, but I don’t know enough about electrical things to know whether it is a valid point or not, and I don’t know if I can plug a Variac into the inverter or not to test this possibility.


Thanks so much,



 Looks like some of your tubes not doing great and need to be checked/replaced. Custom built tube components are the most probable contributors. No further information is necessary. 


Thanks czarivey,

Given Dennis' longtime success while he owned and ran Cary Audi and designed everything they made and sold amps, I'm sure he knows how to design and build a tube component without any issue.  At least I would certainly hope so.

However, your suggestion about the tubes would certainly be an easy fix.  Do you have any suggestion which tubes would be the likely culprits, i.e., signal tubes, rectifiers, voltage regulators?  Would it likely be tubes in the preamp or power amp?  I'm just trying to narrow down the options so I don't have to swap everything one-at-a-time.

Thanks so much,


Cary Audio, obviously, not Cary Audi, which would be a very different skillset 🙃

Laptop and PC power supplies are notoriously bad sources of noise in the AC line, as well as introducing ground loops including via USB. I’d pull the power out of your "clean" power section and use a USB isolator, like this one between your Mac and the audio unless you were 100% sure your USB to S/PDIF converter was already galvanically isolated.

Hi Erik,

Thanks; I had also thought it might be the USB, so I checked on the BelCanto - it does, in fact, include galvanic isolation.

What do you mean by "pull the power out of your "clean" power section"?




So if you imagine a power conditioner, it has a dirty side (the source) and a clean side, which is after the conditioner has cleaned up the noise. Putting a polluting power supply on the "clean" side can contaminate it. So, assuming you have an ideal battery solution putting a PC power supply on it may in fact make it dirty again.

If you know you have galvanic isolation there’s no reason to keep the Mac on the clean side of your power supply. Go ahead and put it on your wall outlet. The galvanic isolation will ensure there’s no weird lifted interactions between your battery power and your audio circuit and the wall outlet.

This way any possible noise introduced by the Mac can't inject itself into the AC again.




In my experience, preamp tubes is most-likely culprit no matter who designed components. They're also a lot cheaper to swap-check than power tubes. Then you test power tubes. I must assume that you have an extra set just in case and if you don't -- plan to have it.


BTW, kudos to Bel Canto for having that feature, sadly not every USB input for audio has this and they 100% should.

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Oh, also try disconnecting the sub. 

The different AC potentials between your power generator and outside devices may be causing a ground loop.  If this fixes your problem you'll need a line level isolator.

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Tubes are consummables.  You should always have a complete spare set of tubes and when you hear something wierd, the first thing you should do is tube swapping.


Thank you all for your suggestions.

So, I tried leaving everything connected as-is with the battery and inverter powering the Puritan, into which all components are plugged, as I'd really like to get this to work), but I powered on only the power amp with no ICs from the preamp. Silence (with subwoofer still plugged to wall socket and connected). So this rules out subwoofer and power amp, as well as all tubes in power amp.

I then connected and powered up the preamp and power amp, with nothing connected to the preamp's inputs - the buzzing returned. This rules out the Mac Mini, the BelCanto, and the DAC, as well as differing ground potentials between the components, as they were not connected (at least I think it rules these all out; please correct me if I am mistaken).

I swapped new signal tubes into the preamp - buzzing continues. I tried a new rectifier - buzzing continues. I did not try swapping the voltage regulator tubes, as I can't see why they would be the problem, but I could swap those if someone thinks they could be the issue. The preamp uses 01A tubes which, by definition, have to be from the 1920s or 1930s, because that is when that tube type was popular. I have read they can often be microphonic, but I am not sure if that could the issue and, if so, why swapping through 3 pairs of tubes made no difference.

Does anyone have any other thoughts?

Thanks so much to all of you for your help,


On a serious note, I kind of remember I once stumbled on a thread (here on A'gon) related to tube amps making a hum or buzz, and I thought I remembered someone posting that either a failing transformer or failing electrolytic caps (the large power caps) could create a hum.  But I cannot remember which.

I would send everything back and put the system back the way it was.  Life is too short to be chasing noises. 

I have a similar problem with buzzing in the left speaker only, I switched everything around ( short story) and narrowed the cause down to the tube preamp. It was not the tubes and I suspect caps or left channel transformer as the problem source. However as I can't hear the buzz from the listening position I have chosen to do nothing for the time being, Have to grit my teeth at times to ignore it as I know it's there but at least it's not costing me money.

...down w/ @immatthewj on the Pquat part....

....Put that roach to rest and slink away....;)

Try a spare solid amp and pre

if there is no hum it’s your tube stuff 

if there is a hum you have dc on the line and need to install a dc blocker in your house power box 

This may or may not be useful… I recently demoed a new preamp. I’ve had a silent system for years and years, with many component changes but the new preamp brought a hum with it like you describe. The culprit ended up being the Puritan 156 or so it seemed. Tried one balanced transformer power conditioner and tried a passive Furutech power filter strip. Both had not issues. Went back to the Puritan and there was the hum again. BUT a cheater plug on the DAC solved the issue. 
Both the preamp and the Puritan have ‘special’ builds so they say, with a quite different and powerful, U.S. patented, power supply on the preamp (called GreenForce) and the multiple filtering stages of the Puritan, evidently being ‘special’ and not seen from any other company, made us feel there was simply a mismatch somehow between the 156 and the new preamp’s power supply. 

Thanks all, for the additional suggestions. @pennfootball71: I don't think it should be DC, because the Puritan has a DC blocker and because I'm running the system off a battery and pure sinew wave inverter. I have an old SS preamp that I can try, though, since the buzz/hum does not appear with just my tube power amp - that's a great idea!

@vinylshadow and @jriggy - I will try cheater plugs. I don't think it's a ground loop, as I installed cheater plugs on all components and the buzz/hum remained, but I did not try installing the cheater plug on one component at a time, so I will give that a try.

@jriggy: that's quite interesting about the weird interaction of your preamp and the Puritan, but that putting a cheater plug on your DAC solved it. I will do some testing with the cheater plugs one at a time. I'll also try plugging everything into just a piece of junk power strip in lieu of the Puritan and see what that yields.



Longshot reply here. Had persistent buzz/hum. Called Steve at Decware. Thought it might be the amp. I started listing the numerous components in the system. He told me to shut up. He asked if there was a WiFi router near the components. I said yes. He said move it. I did that. Noise gone.

I recommend the song, "I'm through with Buzz" by Steely Dan. That should fix it.

I eant thru this issue a few years back. 
Comcast/Xfinity cable boxes are famous for this issue. 
My fix was a cable ground isolated - $15. 
goes between the cable coming in and the box. 

fixed the issue totally. 

So, I reconnected the system to the wall outlet; buzz/hum continues, even with nothing attached to the inputs of the preamp. What's even weirder, the hum/buzz changes as I turn the volume knob, even when the input selector is set to "mute", so there should be no output.  Does this help indicate what may be going on?


So, I reconnected the system to the wall outlet; buzz/hum continues, even with nothing attached to the inputs of the preamp. What’s even weirder, the hum/buzz changes as I turn the volume knob, even when the input selector is set to "mute"

You could try a ground cheater on the preamp but I doubt the problem is a ground loop.

Buzzing could be caused by a bad tube. Especially from this statement of yours.

What’s even weirder, the hum/buzz changes as I turn the volume knob, even when the input selector is set to "mute"

You don’t say if the volume level of the buzz increases and decreases as you turn the volume control knob up and down. Just a guess it doesn’t. A bad signal tube can cause a buzzing sound heard through the speakers. Two things to try. Tap quickly, firmly, on the chassis near each signal tube with your index or middle finger. Does the buzzing sound change with each tap of your finger? Another test is to use a wood pencil with an eraser and lightly tap on the glass envelope of each signal tube. Does the buzzing sound change with each tap on the tube?



Hi BB,

Sorry for not better clarifying.  The volume of the hum increases as I increase the volume knob, i.e., turn it clockwise, even if the selector knob is set to "mute". if I get to about 2 o'clock, the hum is easily audible from across the room. If I turn the volume knob all the way down, there is no audible hum through the speakers.

Tapping my finger near the signal tube certainly produces some interesting results that are easily audible through the speakers, almost like the tubes are resonating with the tap of my finger on the chassis. Is this normal?

I tried three pairs of signal tubes, and the hum persists with all three pairs, so I am assuming it's not the tubes themselves causing the hum, unless all the signal tubes I bought are bad (which I suppose is possible, given the age of the 01A tubes). I have not yet tried the "tapping test" with the other sets of signal tubes, however.

I did try a cheater plug on the preamp, but as you predicted, this had no effect.

Any other tests I can do to figure out what's amiss?

Thanks so much,



Just amp turned on, preamp not connected to inputs on amp, no buzz.

Only preamp and amp are connected together by interconnects. Nothing connected to any of the inputs on the preamp. Buzz.

Amp and preamp are fed from your home’s AC mains power. Inverter is turned off. Not used. No powered-on routers or any such items located near the preamp. Buzz.

Ground cheater installed on preamp. Made no difference. Buzz

You replaced tubes in preamp. Made no difference. Buzz.

There has to be a problem with the preamp. Have it looked at by a service tech.