How deadly is transformer hummm...

Hello Folks,

I recently collected a lightly used (less than 50 hours) Dennis Had - Inspire - "Fire-Bottle." Within some few days, I noticed a humm emerging from somewhere within the chassis of the unit. As the unit was sold in "perfect" condition, I found the humm startling. Mind you, I've discovered absolutely no evidence confirming the sound is compromised; I mostly hear the sound within a couple feet of the amp, when the surrounding environment is silent.

This amp truly is a work of art. Nevertheless, I am now dealing with this 'humm' sound. I bought an Emotiva CMX-2 as a way to deal with DC offset, and this has not impacted the situation to any detectable improvement. Perhaps there is a slight improvement, but negligible. What to do?? Should I just relax, shake it off, and assume the amp will live well, or a down-the-road transformer replacement will simply become part of my experience with this amp? Should I put pressure on the seller to "right" the situation? He claimed, as I asked him, that it was the quietest amp he's ever owned. His add boasted that the fire-bottle exceeded amps from Pass Labs, a Cherry Amp, and one other that escapes memory. The seller has presented all of his communication in the manner of friendly professional etiquette. 

Your thoughts are appreciated. 
Sounds like DC offset hum, and the CMX-2 isn't quite doing the job. Send it back. You could try the PS Audio Hum Buster (if you can find one) or DIY as per Nelson Pass
By the way, the title of the original post should have included a question mark, and slightly more qualified phrasing:

"How deadly is transformer hummm, to the amp itself...[?]"
Is it a mechanical hum (ie, xformer against chassis) or electronic hum coming from speakers? The former may be as simple as mounting screws needing tightening.
I have a Line-Magnetic LM-218ia that emits an audible transformer buzz, which you can definitely hear anytime you are standing by the amp while it's on. I understand from fellow owners that this is quite common to LM amps, and harmless.  I guess I assumed it was the price of admission for using an SET amp with massive transformers, and since I can't hear it while listening, never bothered me.

As far as this situation, when the seller claimed the amp was the quietest he had owned, I would have assumed he was referring to electronic buzz you can hear from the speakers.  I would assume it's within your right to return it if you wish, since this wasn't disclosed, but it also seems to me to possibly be within the normal operating parameters of the amp?
Naim amps have a reputation for humming too. I’ve had a couple of complete system from them and some transformers have hummed whilst others haven’t. A couple have even stopped humming after a while but it’s never done any of them or the music any harm.
I recently had a hum coming from one of my amps.  The source was a bad tube.  I'd want to rule out other sources of hum before returning the amp.  I was advised to check my tubes for unusual microphonics, which I found to be present.  I quickly identified the offending tube.  Replaced the tube and no more hum.   
I had a humming sound in my system I couldn’t pinpoint.  Turned out my wife was humming along with the music. 😂😂
Since this amp employs an EI core power transformer, DC on the line really won't affect it. But if the cores are not secured properly, it can vibrate.

The four screws on the power transformer at each corner might simply be loose. Its worth it to see if tightening them makes the transformer quieter. This probably can be done fairly easily. Of course the amp should be unplugged from the wall, and to best do this the bottom cover removed. If any of this sounds at all tricky, take it to a qualified technician.
@bdgregory the hum is not audible from the speaker drivers. This is a mechanical event, coming from within the chassis. 
@brownsfan how do I detect tube issues like you describe- microphonics, etc?

@stereo5 I always enjoy the humming of my wife, but it seems her tone is at a much higher frequency.

I’m running the amp with a DAC and a CD transport... is it ok to unplug the RCA cables from the system, to rule out those components while this tube amp is on? I hear you don’t want to run a tube amp without connections...
Hum can be caused by DC offset, ground loop, simple transformer mechanicals (loose nuts, etc.), or a poorly wound transformer or one that's degraded.  Google PS Audio + hum + eliminate for a simple guide. Some hums are easily dealt with, and some can drive you up the wall.  Occasionally the only solution is to have a brand new transformer installed. 
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Humming is the obvious choice, when you do not know the truth of all transformers...... they all hum, radiate noise ( Toroids produce less than E-I core ) and exhibit, some amount of vibration, as well. I believe all transformers should be separated / isolated from the chassis, as the older HK Citation power amps ( the model 12, 16 and 19 ) had / have. I have modded hundreds of transformers from various audio products by isolating the transformers, with excellent results in sq ( from the speakers / system ), and lower noise from the chassis. Rubber grommets, Dynamat, roofing repair tape, cork, as well as many other materials, can be used. Be safe, and well. Enjoy !
@atmasphere how tight? I see the four screws from the top, so they are accessible from above the amp. Why remove the bottom panel?
@mrdecibel this is done inside the amp, covering the entire transformer, from inside the chassis, with dynamat? 
Listening99, the easiest way to detect a bad tube is to replace them one at a time, provided you have spare tubes.   Microphonics can be detected by gently touching the tube.  If you get more than just a soft thump, it could be a faulty tube problem.   Reading more on this thread, it seems more likely you have a loose transformer.  Follow atmospheres advice on fixing it.
I see the four screws from the top, so they are accessible from above the amp. Why remove the bottom panel?
If the screws are loose, the nuts on the bottom might spin when you try to tighten them up.
@listening99....I am recommending between the transformer ( where the 4 corners mount ) and the chassis ( the screws will go through the damping material / products ). Transformers do get warm ( in your case, the power transformer, not so much the output transformers ), so covering them " completely " is something I do no recommend, but mounting some material on the outside of the transformer can work. I am not sure how some manufacturers ( generally the higher end products), totally encapsulate the transformers ( for reasons I am talking about ), but....they do it. I recommend you do all 3 of the transformers. Keep in mind, rubber bushings or grommets are easily removable, where Dynamat, is a bitch the remove, once applied.

SET amps can inherently be a bit hummy but should not be to the point you can't enjoy the music. I've read reviews of $20K Air Tight 300b's where the reviewer noted hum from the power supply.  With the Line Magnetic 805ia (for example) there are hum pots in the corners for each channel for the output tubes. The reality is more efficient speakers and SET amps can bring out more noise and the LM amps have been designed to help counter this effectively. Sometimes new SET amps will be a little hummy, and then mysteriously it goes away so you may give it some time to settle.


So, if I open the amp and I'm tightening things, inserting bushings, etc., I will have the amp unplugged, and I'm wondering what I need to do to protect myself from errant charges that might stop my heart... 

My sense is you are pointing to the kinds of bushings that are customarily used along with screws/bolts to aid in keeping them tight...? 

example bushings:
To not get shocked, don't create a circuit. No circuit, no shock.
@listening99....check out Lowes...item # 198831, model # 88577......rubber flat washer...10 pack....I should have stated " washer ". Sorry. These work great. No need to tighten too much, as you want to keep the integrity of the rubber.....
You know crazy simple things can cause DC offset, digital light power supplies are among them.

Turn off everything else in the house and see if your hum goes away.
I had the same hum in my transformers. And as suggested to me at the time, I added some rubber bushings, tightened the screws and 'hum-b-gone'

Make sure to drain the amp before you open it.

Run the amp normally and listen to music. Turn off just the amp, and let the amp "bleed out". (It should get gradually quieter as the caps drain)

After that, you should fine. I would avoid licking anything however...

Turn off just the amp, and let the amp "bleed out".

Then sautee, and serve with fava beans and a nice Chianti.

Unplug the bug zapper in the garage. That made my hum stop 
If you are hearing the hum only when you are physically close to the amp and not thru the speakers, it is the mechanical vibration of the transformer and it is normal but needs "damping".  It is also likely that the chassis is resonating and mechanically amplifying it. 
You should consider tightening its bolts to the chassis and maybe also adding a rubber bushing to damp the vibration. It is like the engine mounts in a car.....

I have a very quiet Firebottle amp as my main workhorse...I mean really quiet, and although it's plugged into a Humbuster III (2 amps are plugged in to the SS used only rarely for outdoor stuff that had some transformer hum, hence buying the Humbuster) it's quiet without it. I'm seriously sensitive to amp hum and say NO NO NO. Note also that the output transformers do also get hot. I wouldn't put any rubbery thing anywhere near those transformers. If all else fails send Dennis an email via Ebay...he has another guy who works on his amps who is on although his name escapes me.
You should consider tightening its bolts to the chassis and maybe also adding a rubber bushing to damp the vibration. It is like the engine mounts in a car.....

In a Tesla :)
I recently collected a lightly used (less than 50 hours) Dennis Had - Inspire - "Fire-Bottle." Within some few days, I noticed a humm emerging from somewhere within the chassis of the unit.
The power transformer in the amp was quiet when you first hooked up the amp in your system? Only after a few days of playing the amp the transformer started humming/buzzing loudly?

As the unit was sold in "perfect" condition, I found the humm startling.
Did you pick up the amp from the seller or did you have it shipped to your residence?
If shipped did the seller remove the tubes from the amp and well package them for shipping?

I mostly hear the sound within a couple feet of the amp, when the surrounding environment is silent.
Like atmasphere said in his post the power transformer is an EI type transformer. It should not be affected by DC offset on the mains. Toroidal transformers yes, EI transformers no.

Possibly a higher than normal AC THD (Total harmonic Distortion) on the AC mains could cause an EI transformer to hum/buzz louder than normal. But if that was the cause I would think you would be experiencing problems with other electronic items in your home. Not to mention I would think you would hear a hum through the speakers of your audio system. FWIW a distorted 60Hz waveform on the AC mains will pass through the primary winding to the secondary winding(s) of an isolation transformer.


Could a faulty rectifier tube be causing a higher than normal load on the high voltage secondary winding of the transformer and cause the transformer to hum/buzz louder than normal? And still the amp would sound OK? Or maybe a higher than normal filament current draw on the secondary filament winding for the rectifier tube? Could the rectifier tube itself be the humming/buzzing sound the OP is hearing?

If the OP pulled the rectifier tube and then turned on the amp that would remove any load from the high voltage winding. If the OP then turned on the amp and the transformer hum is gone wouldn’t that indicate the problem could be the rectifier tube? Or possibly a problem in the DC power filter section of the amp. The rectifier tube may have been damaged in shipping. Or it just went bad on its own.

If the hum/buzz is still present then it is possible it is somehow AC mains related. But after several days of the amp working ok? What are the odds?


@jea48 A rectifier tube will not cause a power transformer to rattle (humm).

@mrdecibel  If you look at the way this transformer is mounted, using isomerics to secure it is unlikely! Its mounted through a cutout that barely accommodates the transformer core. This type of mounting leaves very little room for using grommets to isolate the chassis from vibration.

IMO/IME tightening the transformer bolts is the best option. If it does not work, replacing the transformer is the next option after that.
@jea48 the amp is entirely quiet at the speaker drivers; the amp was probably humming within the chassis from the start, but I did not hear it until a few days in.

I bought the rubber washers, but further comments seem to indicate that tightening of the transformer screws is the first task. I will unplug the amp, remove the tubes, put on a pair of gloves and remove the bottom plate of the amp this evening, and then I will tighten things. I can look for clearance that might accept the new washers, but I don’t plan on adding those in yet...

@wolf_garcia made an observation about the possibility that the washers will not do well with transformer heat. @atmasphere indicated they likely won’t fit, so the washers will be left out until I’m clear I won’t make things worse in the long run.

Can I expect the components are pinned to the top of the chassis, Or affixed to the bottom plate, etc.? I will be careful and slow in removing things, but I’ll take any tips...
@listening99  It would be a good idea to check in with Mr. Had and see if he has any comments. From the outside the amp looks conventional construction. Remove all the tubes before you turn the amp over to prevent damage. Keep in mind though that you are on your own here- if this is at all intimidating, it might be best to bring it to a technician to do the work.
@atmasphere I have not been able to find a close up photo of the transformer mountings of this amp, however, I respect your opinion, and feel, it is quite unfortunate. As I have stated, I have done hundreds of these " mods ", and all for the better, in every way. This is an easy thing to do, with the possibility of using longer mounting bolts. Not all rubber is effected by heat in the same way ( engine hoses, auto tires, as an example, as they last a long time, and the transformers do not get as hot as some engine components....this, ime. @atmasphere ...have you, in your amplifier designs, ever tried decoupling of the power transformers from the chassis ? Remembering now, I also had a Krell amp, a long time ago, that had huge rubber shims between the transformer and the chassis. As far as I am concerned, it should be a part of any design....but, I am not an electrical engineer, nor product designer.....just a tweeker, listening, and looking, to improve things my ear / brain can detect, as improvements is sq. My latest acquisition, and project ( an original Edge M8 power amp, prior to Maker Audio ), was so resonant and vibration prone. I took the amp apart, isolated the huge toroid transformer ( a few layers of Peel and Seal ), isolated and damped the heat sinks ( these heat sinks were the most " ringing " I have ever encountered, not what I would expect from an amplifier that retailed for 5K ), damped the entire chassis, and changed out wiring and binding posts. Now, an incredible, music reproducing amplifier, to these ears. BTW.......looking at many other Dennis Had amplifier designs, it looks as though, these rubber washers, can be used.....based on photos. Anyhoo.......Be well.
Wanted to add, I hear most transformers, when I place my ear, against the chassis of amplifiers ( including this Edge unit ), but, I accept this, as they all make noise, as I indicated. As long as it is not amplified, through the system, out to the speakers ( headphones, if that is your thing ). 
@mrdecibel  We had some very large EI core transformers on our MA-2 amplifier. One of them made a bit of humming. That was fixed by isomeric mounting; after that it was dead silent. The trick is not allowing the transformer or its mounting hardware to contact the chassis directly; that appears to be really difficult to pull off with this particular mounting system.
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If you place your ear near the transformer of a Firebottle you could burn yer face off. 
I've got an email out to the seller of the amp, to see if he can reach out to Mr. Had, for some advice. The amp was made in April and there shouldn't be any transformer degradation of significance by this time. I would open it up with a little clear-firm guidance, but I am recollecting that my last rash of flirtation, soldering gun in hand, was over thirty years ago in a high school classroom. 

Thanks for the new vocabulary word: isomerics

@wolf_garcia has me interested in the heat resilience of the purchased washers and I've discovered that they are more durable than the skin on my face. According to the Home Depot account for DANCO 1/2 flat washer 3/4" O.D.:
  • Can withstand heat between a temperature range of 86°F-248°F (-30°C-120°C)
Would 248F handle the temperatures within the amp @atmasphere ? I'm not convinced, because it's quite hot to the touch, once it been in operation for an hour or more.

Can anyone speak to the expected problems with this kind of symptom? One person claimed it could clear up... I imagine the amp has around 100 hours on it by this time... 
No rubber or BRubber or anything  other than silicone.  I have a few noisy transformers that had mechanical hums. Mounting issues. 

Not all silicones are the same. The super HIGH temp. silicone can be conductive. Silicone washers are OK BUT, read below..

Put your hand on top if it FEELS, mechanical, press down, can you dampen the noise? Turn off, UNPLUG, remove the valves, flip it get a 40 watt bulb with pig tails, discharge the caps. Work.

A little dab will do ya!  LOOSEN the securements. don't remove them.
Get a pin applicator (smaller high pressure needle gun) A small grease gun will work. give it a little shot, not more than a BB amount.  .177-.180
at each securement between the two surfaces. Tighten. Let it dry, and try it.

Still hums

Check the valves, PULL and reseat move them (pencil tap test) around see if the noise changes. BAD VALVE.. Have to check them
Valves are good.

Still hums

Make sure the voltage is 120. I have a few Cary designs, they like 120VAC, not LOW. They will hum. Easy to check and or fix. Voltage maintainer or Variac, will really tell the story. Start at 110v slowly go up, the hum will go away at 118-122VAC

Still hums

????? I'm out of low cost easy fixes, go find a repairman. Everything I offered is under 10.00 silicone an High pressure needle gun.

Happy hunting

...and now I have email out to Dennis Had...
What you purchased, that I recommended, should be fine with temperature, as the mounting area, does not get as warm as other areas of the transformer. Additionally, heat rises. I would like to see a close up of the transformer mounting area, as I am curious to see what atmasphere is speaking of. I have not run into a transformer that could not be isolated, but obviously, I have not seen them all. I am sure Dennis Had will respond, will treat you with professionalism and respect, and, will look to help you. Maybe he will suggest sending him, or his servicer, the amp.
I believe I found a picture, that allows me to understand what atmasphere was speaking about. The power transformer, seems to be " sunken ", into the chassis, but imo, can still be isolated from the chassis, but likely, not with these that I recommended ( I am sorry ). You can use them on the output transformers, with access through the underside, which is necessary with all transformers, as atmasphere pointed out. I would wait to hear from Mr. Had. I am not surprised you hear the transformer in that thing, close up to the chassis, as it is MASSIVE, for that design. As I said, I hear most power transformers in amplifiers, when close up ( with being careful not to burn myself, as pointed out by wolfie ) will stay tuned to your progress.
Mr. Had has already responded, making an impression and stands firmly by his product. He's given me a test of sorts, to remove all of the tubes in the amp, to then see whether the amp hums. This I will address in the morning... more thereafter... 

Oh, I will include this marvelous detail about the amp's design: "The transformers are made with grain orientated steel and impregnated with a special anti vibration varnish. Also the chassis of all Inspire products is non-ferrous aluminum."
Tubes have been removed and the hum persists. Second email out to Had. 
Atmosphere is there any reason why manufacturers don't use nyloc nuts to mount these transformers. They wouldn't come loose with a nyloc nut.
listening99 OP112 posts 


Tubes have been removed and the hum persists. Second email out to Had.

Someone suggested you check the mains voltage at the wall outlet. Did you check the voltage?

What type of residence do you live in? Single family dwelling, house? Multi-story building dwelling? Older or newer structure?

To rule out the problem is caused by the AC mains power in your home take the amp to some one else’s home and check the amp out. Not a home in your building or neighborhood.
Would 248F handle the temperatures within the amp
No worries.
Oh, I will include this marvelous detail about the amp's design: "The transformers are made with grain orientated steel and impregnated with a special anti vibration varnish. Also the chassis of all Inspire products is non-ferrous aluminum."
FWIW, the transformers are 'EI' cores, and all EI cores should be constructed as described above and usually are (often are what is called 'double dipped' in the varnish, which is very helpful in the anti-vibration department). The chassis material will not affect whether a transformer makes noise or not.
Atmosphere is there any reason why manufacturers don't use nyloc nuts to mount these transformers. They wouldn't come loose with a nyloc nut.
Actually they could come loose, since what happens here is that with a enough heating and cooling cycles the varnish can relax a bit. So this might require tightening the end bells down so they don't rattle. Transformers have been made for over 100 years without the need for locking nuts.

I have an amp in my collection, a Smart Theater Systems TA 242, which is based on a Hafler design, nicely built power supply, toroid transformer, highly biased in class A, roughly 120 X 2. I acquired this years ago from a movie theater updating it’s gear. A wonderful sounding amp. When I use my otr microwave while this amp is powering a system, the transformer of this beast, starts getting pretty loud, even though the microwave is on it’s own circuit. So, there is some truth to what many are saying here about the effects of ac. might want to try moving the amp to other electrical outlets throughout the home, just to see ( hear ) if the transformer still hums loudly. Again, I feel it might be normal. @wolf_garcia , without burning that beautiful face of yours, lol, do you hear the transformer of your Had chassis ? @atmasphere, are the transformers you use, completely silent, when close up ?Again, hum, from a transformer, is typical, and to some extent, normal, when close up to it. As long as it does not interfere with the music listening.