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.
The OP asks how deadly is transformer hum. With only a little bit of exaggeration, I feel transformer hum might have significantly lowered risks to my life:
I have a class A tube amp. A little bit of transformer noise when up close, but nothing to annoy or out of the ordinary IME. Earlier this year, I moved out of the new-ish apartment building I was living in when I bought the amp into an old house. Now the transformers were humming loudly. I tried new tubes I had in reserve. I tried tightening the transformer mounting bolts. I tried a couple of DC blockers. No improvement. I checked voltage — consistently within a half volt of 123v at different times and at different outlets.
A clue that the house wiring might be an issue came from noticing that the equally-annoying hum from the speakers was reduced after switching off all other circuits (but still no reduction in mechanical transformer hum).
I gave a call to the owner of a local audio shop from whom I had bought speakers and sources. To his credit, he referred me to his electrician, rather than different amps or power treatments. Long story short, the electrician replaced the corroded meter box and exterior wire, the ancient and miswired electrical panel, the grounding rod (with two), all of the outlets and switches (removing a bunch of dimmer switches), and some old interior wiring (where it appeared that high current draw had nearly started a fire). In the course of that, he removed some weird junction boxes in between the meter box and before the electrical panel, fixed phase miswiring and shorts in a few outlets I had not yet used, and redistributed load at the electrical panel.
The result? Not exactly silence, but the same faint mechanical hum as when I bought the amp, and equally low noise at the speakers.
So, despite what you are told by some (@cakyol), mechanical transformer hum is not always because of mechanical issues. An amp that works fine at the factory bench can misbehave when fed AC with loads (literally) of harmonics on the line. I would recommend trying all the nearly-free options I tried above. If you can, I would highly recommend following @jea48’s advice to see how your amp behaves connected to a couple of different mains power sources. (A techie’s would be ideal if you don’t mind paying the inspection fee, but a friend’s in a newer house in a different neighborhood would also be useful.)
How did the hum improve my odds of survival? About a week after the electrical work was done, we had several nights of intense thunderstorms and strike lightening. I sure felt more secure knowing that I had new grounding rods and a whole-house surge protector, and that several wiring faults had been rectified — which I probably would not have had done were it not for going all out to fix the transformer hum. Best of luck in your quest for (good) silence.
Also if the amp only has 50 hrs on it it's possible the hum may go away to some extent with further run-in. My Line Magnetic amp hummed slightly at first but after 60 hrs or so it pretty much went away except during the initial 10 minutes of start up. Once it gets warm and presumably the transformers expand a bit everything becomes dead quiet.
I want to update this thread, bring it full-circle, so to speak.
I was able to finally develop a conversation with Dennis Had, who built the amp. He asked for a picture of the amp, which has been sitting on a thick slab small side-table type of stand, or pseudo-stand... He then asked me to put the amp on my kitchen counter and plug it in... he said the Inspired design is stable, doesn't need speakers, so I didn't have to haul any other equipment into the kitchen.
The amp was noticeably more quiet in the kitchen.
He then suggested I buy some sound coat, or similar product, claimed that the wood stand acted as a wood resonator, much like a piano.
This is great news, because it's a wonderful piece of equipment and I've got some new open baffle speakers on order, which should complement the amp nicely. The speakers are based on the F-15 Lii Audio driver and boast 97db efficiency.
This will be a single-driver setup - I'm thirsting for a vast soundstage!
Thank you all, for participating in this discussion...
As long as your home AC is within reasonable spec I dont think it would be the cause of tranny hum. The type of hum from home AC would likely be most evident at the speaker. Although good to check your AC voltage although that tool is just to check the circuit and wont give you an actual reading. I suspect that the 110 volt will light up even if your at 120 or so--probably even at 130 ...because at times that is what home ac is. Thats what it was at my previous home and I had utility company come over and even he had to comment . well the AC is a bit high here and he went to the sub station to lower it for the neighborhood I guess.
Its in your amp for any number of reasons. As Atmasphere mentioned be sure to check the bolt down for the PT and put rubber washer in there as well if you can.
@wolf_garcia My wife thinks I'm being too sensitive about the hum, which doesn't show up at the speakers, as I've already described. Given the sellers description of the "quietest amp he's ever owned" I figured it should be literally dead silent, but now I'm hearing that there may be some small sound issuing from some of these amps, and perhaps the old circuitry of my dwelling is going to place the amp under different forces/conditions than what the seller experienced. As I've also described, it's definitely not impacting the sound, for the system is presenting, along with the speakers, the most beautiful music I've heard in this space. My main concern is longterm difficulty and having just picked up the amp I wanted to address it right away.
Hum is my number one bugaboo. I can not stand it .. Often when asking a seller if there is any hum in the unit and being really specific that Im referring to the amp itself they will respond with --oh, its very quiet from the speakers. thereupon now comes a lengthy explanation from me. I have never held onto anything long that had hum. It often can be in the power supply design but also being directly coming from a transformer Ive been told that it is the plates vibrating. On new transformer in a new unit like the one you got I cant imagine -either p.s. design or cheap transformers .. Im not a tech so cant identify exactly but pass along my experience. I had a custom 2a3 SET built once and it had a hum and the builder used a recycled power transformer ---how old was that thing ? I sent it back,, and he didnt do a thing about it. I sold it. Really had good sound but the hum was so obvious it could be heard from 5 feet away even with music on low. Send it back to Had or at least complain. ruins the experience.
I had a 80's Sony STJ75 tuner that is well known how black the noise floor is but it had a hum ... Sent it to ASL Absolute Sound Labs and he actually had the transformer re-potted . fixed the hum.
@jea48 This two-story single family dwelling was constructed in 1986. I have not checked the mains voltage. I imagine this requires a volt meter, which I do not possess. I see a number of them for sale at the Home Depot, which is the closest such facility to my home. Is there a special type I should be using for this test?
There is a sense that the amp is on if you listen very close to the transformers, but any hum is at such a low lever as to be virtually inaudible unless maybe you listened to it with a heat resisting stethoscope. Note that relative to any other amp I've owned, either transistor or tube, there is nearly zero noise even if you put your ear on a driver...the the Firebottle is by far the quietest amp I've ever owned.
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. @listening.....you 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.
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.
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."
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 )...lol....I will stay tuned to your progress.
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.
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.
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...
@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.
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 ).
@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.
@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.
@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...
@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.
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 thing...one 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 AudioAficianado.org although his name escapes me.
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.....
@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.....
@mrdecibel 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...?
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.
@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.
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.
Humming is the obvious choice, when you do not know the words....lol.....Seriously......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 !
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