| A Titmus |
Ok, I apologise for asking this very basic question, but I haven't found a simple answer anywhere.
I have a simple MOSFET amp (Maplin kit) using Exicon MOSFETS (I am ordering PCBs for the Aleph-X!). When I run the amp through a dummy load, I can hear the TO3 transistors "singing" to the input, not a resonant mode, but complete reproduction. Is this an example of magnetostriction, are the silicon dies lose or is there a perfectly simple explanation?
Once again, I am sorry if this is a rediculous question.
Andrew |
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| sam9 |
Do you mean the TO3's are mechanically vibrating? If so that's too wierd to think about.
If you just mean that the input network seems to picking up signal from the output, then it is "just" a matter of shielding the input wiring and keeping the small signal stage away from the output stages. This is a common problem with a simple (but not always easy to implement) solution.
Or do you mean something else -- if so try restating a bit more descriptively and precisely. |
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| sully |
I've also heard this..not heard of someone hearing it, but actually hearing it myself.
Within the package is a pair of wirebonds. The source will be anywhere from a 5 to 20 mil thick aluminum wire...the gate can be anything from .7 mil gold up to 5 mil aluminum.
If the source wire is vibrating, I'd be afraid of the reliability of the device, as the wire would tend to fatigue. (But, perhaps that is only an ultrasonic resonance issue, one I've been bitten by.)
My gut feeling is that it's not an internal thing, but the wires connecting the source or drain moving in response to the current within, and the to-3 is larger surface area to radiate it.
Neat, isn't it? who needs speakers??
BTW..if the silicon were loose, it would blow in less than a second as there would be no heat path keeping it from vaporizing.
Cheers, John
PS...it's not a ridiculous question.. |
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| jewilson |
That is totally off in the outer space region of our Galaxy.
You should use IR MOSFET, IR240 or IR244, or IRP244’s in the output.
| quote: | | If the source wire is vibrating, I'd be afraid of the reliability of the device, as the wire would tend to fatigue. (But, perhaps that is only an ultrasonic resonance issue, one I've been bitten by.) |
:hot:
The will sing when music is applied.;) |
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| A Titmus |
thank you for the replies. It would appear that it is not an especially common occurance then. Both of my amp channels exhibit this behaviour, and in both N and P channel devices.
The only thing that I can think of, is that these are "lateral power devices", would this have any bearing on the noise output? I don't have the circuit diagram to hand here, but I have included the details of the tranistor below (the N and P are identical in these figures).
ECF10P16
Ptot(max) 125W
VDSmax 160V
VGSmax ±14V
IDmax 8A
IDdiode 8A
I/P cap 500nF
IDSSmax 10ma
One last thought is that these MOSFETS have some kind of diode inside them, could it be this that is producing the audible noise? It is "quite" loud, in that at about 100W from the amplifier (dummy load) with the lid off, I can hear it about 1m away.
I am not too worried though, a quality amplifier will follw (I hope).
Thank you for all your help,
Andrew |
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| A Titmus |
Oh, and sam9, it is a vibration from inside the TO3. I wasn't going to put my ear on the case because there are a few volts flying around, but you can localise it to them by getting close and shielding the noise with your hand. There is nothing else close enough to produce the noise.
As long as it isn't a normal occurance that simply isn't mentioned because it is so obvious, I am not worried. See no evil, hear only the music!
Andrew |
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| jcx |
| i have read about this phenomena in the past and the given explanation was differential themal expansion, perhaps your mounting pressure/flatness is way off and mechanically distorting the can as this really shouldn't be occuring in well built modern transistors |
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| jewilson |
Andrew,
I have a very hard time believing this, however you can test this out with out putting your ear even close to the device that is making this noise. You need say about a 26mm x 26mm x 400mm about piece of wood and press it against the part, then press the other end against you ear, if you can physically get to the part. The sound energy will conduct vibrations through the wood or some other dense material to your ear.
The bonding wires being so short could only vibrate at some high frequency. In addition, if were doing such a crazy thing the bond would loosen over time causing a failure. |
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| Mark A. Gulbrandsen |
Actually this is a pretty common phenomonon and I used to hear this noise all the time when I used to repair Phase Linears, ESS, and Crown amplifiers back in the mid 70's. The higher power the amp the more you would hear it sing. I believe the noise is caused by current induction in the wiring itself... somewhat similar to the buzzing noise that is heard in a power transformer. I've found that almost all high power amps sing to some extent...what they sing just depends on what you feed them. I've even been able to feed an amp from an FM tuner and actually hear dialog eminating from amplifiers by running an amp near wide open into a static 8 ohm load.
Perhaps someone like Nelson Pass would be able to better explain it.
Mark |
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| jewilson |
Mark Gulbrandsen,
What have you been smoking, send me some. I've worked on a truck load of amps even some of those crapy Phase Linears, MAC's Crown DC300 to Ampzillas and never hear this. Maybe its the amps crying not singing, I could understand a Carver amp doing that.
Do you hear this under load or no load? |
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| sam9 |
| From inside the TO3. It sounds wierd but since I used to broadcast AM and CB on my turntable (*HONEST!*) back when I still had one I shouldn't be sketical. Anyway, if I was getting sound out of my TO3s I would soon consider goint to TO-247s if I couldn't find the cause. After fighting ground loop hums, buzzing transformers and some other annoyances in the past I'd be inclined to go to work on the TO3s with a hammer! |
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| sam9 |
" I am sorry if this is a rediculous question."
The question isn't rediculous, the situation is rediculous. I'm persuded that its really happening. Just don't panic when the Men in Black knock on your door. Tell them you will only talk to Scully and Mulder. |
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| phase_accurate |
I can confirm this phenomenon as well, though I did never bother to find out where it comes from (even though I was wondering).
AFAIK I even heard it without load connected on a receiver. We just turned the volume up with inter-station noise and one yould clearly hear the sound emerging from the area of the output stages. And it wasn't restricted to amps with TO3 devices.
Regards
Charles |
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| Nick |
| Piezo Electric effect on silicon? |
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| mrfeedback |
Hi Andrew, your question is not even slightly ridiculous, and top marks to you for being observant.
A couple of posters have stated they have heard this effect, as have I also.
The first time I encountered this was in the first amplifier that I built - a bridging output 13.8V powered IC amplifier.
The thin U-shaped heatsink mounted on top the IC's sang in sympathy to the music with the amplifier unloaded.
The sound was thin and tizzy, but was recognisable as music.
Damping the heatsinks by squeezing them reduced the level, but did not eliminate this sonic emission.
I did not get around to finding the root cause, but I don't think that it is related to bonding wires - these IC's were fully encapsulated so there was no internal room for the bonding wires to move.
I also regularly observe this effect in standard domestic amplifiers driven into dummy loads or unloaded, and the level and nature of this sonic emission substantially changes when the amp is driven into clipping.
Perhaps there is a differential themal expansion or piezo electric effect in the device chips at work here - at present time I do not know the mechanism responsible but be comforted that you are not the only one to observe this effect.
Eric.
"That is totally off in the outer space region of our Galaxy. "
Jim W. - And you call yourself an engineer ?????. |
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| phase_accurate |
I just wonder how long it takes until someone makes the "most important development in audio ever...." in order to cure this effect that is so damaging to the flow of the music !!! :devilr:
Regards
Charles |
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| Tube_Dude |
Hi
Me to !! I also have observed this "singing" that become louder as the load impedance become lower...that means that is a current dependent issue.!!
The some happen with output transformers in valve amplifiers when conected to dummy loads...
The vibrational hum of a mains transformer is also the "singing" of the transformer...in this case with a only "note" 50 Hz here in Europe.;)
Cheers |
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| gfle |
Yes, I've noticed that in TO3 bjts.
The "phenomena" is really noticable during clipping! |
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| Richard C |
I've also heard this effect but never investigated its exact origin.
Does this add more weight to arguments in favour of mechanical damping and the sonic effects of heatsink and casework materials? |
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| A Titmus |
Richard,
thant is exactly what I have been wondering. I have always dismissed the possibility of microphony in modern solid state electronics, and still regard it with some suspicion ("I tried this £10,000 stand and it made my system sound twice as clear" sort of comments I doubt, but then, I have never listened to a decent commercial system and am willing to be proved wrong).
I was going to put the sound down to magentostriction with the package, but if it also occurs in IC amps, and plastic devices, I don't know. Purely out of interest, I wonder if it would occur with a couplig material (to the heatsink) that wasn't metallic. For instance would using a Peltier, or TE, device reduce this noise? Not something I can try with TO3's. When I have my equipment back at home over the summer I will try experimenting. I am at university at the moment, without the tools or space! |
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| mrfeedback |
I think Yamaha or something made a feature about puttting rubber blocks between heatsink fins to stop ringing decades ago.
They did not distinguish whether this was acoustic feedback caused HS fin ringing, or transistor/current caused.
I don't think they made actual claims about this being a benefit, except for saying that these rubber blocks stopped the HS fins ringing.
Just like a phono stylus sending direct audio into the room, so does a heatsink - I prefer not to have these sounds in the room alongside the speakers sound.
Eric. |
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| Richard C |
Pioneer used a heatsinks formed from a 'honeycomb' extrusion on their M90 amplifier to reduce ringing.
I really hadn't considered the potential significance of this effect until reading this thread:eek: |
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| peufeu |
put a line of bathtub style transparent silicon putty (available in those lare syringes) on the end of yoru fins...
Also, isn't it the output inductor singing ? |
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| wintermute |
Yeah my T03 Mosfet amp does it too, although I hadn't narrowed it down to the mosfets.
http://www.diyaudio.com/forums/show...4415#post284415
Above was a post where I mentioned it...... Was driving into a dummy load of about 7.5 Ohms, also amp would have been close to clipping, got much louder if I drove it into clipping.
The weird thing was it also started doing it when I was doing tests using rmaa (but only when there was no input signal.... I put my multimeter (in freq mode) on the speaker output and it was registering 56Khz. If I unpluged the sound card from the amp the sound went away and so did the 56Khz..... All very weird :xeye:
Tony. |
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| jewilson |
MR FEEBACK
Obviously, you have not read all the responses I have made. So obviously you are just another shoot from the hip jerk with nothing to contribute, so bit me. :drool: :crazy: |
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| Mark A. Gulbrandsen |
"What have you been smoking, send me some."
Jim W.
I really don't appreciate your comments here on this site!
Since you made that rather insulting post its pretty obvious that alot of other people have also heard this same effect. I heard the effect loaded but some amps would also sing somewhat if unloaded. Though usually not as loud.
Mark Gulbrandsen |
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| sully |
It is not a thermal effect. It is not due to the devices being lateral or vertical. The conduction paths of the silicon differ in each case by mils..
Thermal: the thermal time constant of the junction is 10 to 100 usec..through the die is 1 mS..to the case..10 to 100 ms..to the heatsink..10ms to 2-3 seconds depending on the isolator.
Bonding wires will move from lorentz forces at all frequencies...amplitude based on current..when the freq gets up into the tens of kilohertz, the wires can resonate, which will lead to fatigue failure( this can be seen on autopsy by slip deformation on the surface of the wire, you will see the clean surface of the wire become rough in a crystalline fashion near the break.
I would have a hard time believing the bonding wire movement would be heard outside the case..and, noise from an encapsulated IC certainly does eliminate that.
Leaving movement of the wires leading to the device, or movement of the actual device on it's isolation mount.
Cheers, John |
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| phase_accurate |
| quote: | | Thermal: the thermal time constant of the junction is 10 to 100 usec..through the die is 1 mS..to the case..10 to 100 ms..to the heatsink..10ms to 2-3 seconds depending on the isolator. |
That does still not fully rule out thermal causes. If the sound is generated thermally on the die then it just has to find a way out of the package.
Though I also opt for magnetic or piezoelectric effects. This would in turn also mean that it might be good to pay a little attention on mechanical resonant behaviour of an amp's construction.
So maybe we should even copy the "Spruce amp" ?! ;)
Regards
Charles |
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| jewilson |
Mark,
I was just kidding with you, just because I never heard the effect does not mean it does not exist in some form. It seems that some people are talking about TO3 cans and others are talking about heat sinks, which could be two different issue or maybe not. This could be something like a sympathetic oscillation caused by the inductance in the DC power leads with the TO3’s and coupled with the transformer when under load.
Some one that has experienced the problem and can repeat it should look at the issue. I just have never heard or experienced this. Having said, I believe this is real but is not caused solely by the bonding in the TO3’s.
;) |
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| Fred Dieckmann |
| Finally............. someone to teach the words to the transformer. |
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| sully |
| quote: | Originally posted by phase_accurate
That does still not fully rule out thermal causes. If the sound is generated thermally on the die then it just has to find a way out of the package.
Though I also opt for magnetic or piezoelectric effects. This would in turn also mean that it might be good to pay a little attention on mechanical resonant behaviour of an amp's construction.
So maybe we should even copy the "Spruce amp" ?! ;)
Regards
Charles |
The die has a TCE of 3.3 ppm/degree C. A reasonable sized power die will undergo temp excursions in the 10 C or so range maximum at the surface of the die for frequencies that are faster than the die to header time constant.
A reasonable die is 250 mils by 250 mils.
.25 inches * 3.3parts *10 e-6 (per million) * 10 degrees C =
.25 *3.3 *10e-5 = .825 *10e-5 = 8.25 microinches.
Hmmm..that seems pretty small.
Also, don't forget..that movement is lateral..the die width and length is moving 8 millionths of an inch sideways, not up and down. Since that movement is symmetrical about the center of the die, there is no coupled vibration which is going through the die attach material (solder or braze).
I'd personally discount the die thermal as the possibility..
For a to-3, it's possible that the lead pins are make of kovar, which is a magnetic matched expansion material used for going through glass seals, but mrf said he heard it on a plastic encapsulated IC, which is purely copper based construction.
Cheers, John
PS...Boy, do I love this ****...
:D :D :D |
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| sully |
Oh, almost forgot this calc of vertical movement.
Since the die temp excursion is 33 ppm (assuming 10 C), the vertical movement (assuming even HALF the die thickness is being used) would be 10 mils times 33ppm, or .33 microinches.
And to consider the silicon as a reaction mass against which the die size change can push, a quarter inch square of 10 mil silicon VS a 60 mil thick copper nine times the area, 54 times the volume, about 100 times the mass..the case of the package will move about .0033 microinches, or 3.3 billionths of an inch as a result of silicon thermal expansion mass reaction.
Still think it's the external reactions...but I may be wrong..
Cheers, John:angel: |
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| millwood |
first of all, I have been using mosfets for over two decades and have never heard it.
2ndly, is it possible that other parts of the amp are singing?
3rdly, the construction of the mosfet is very much like a capacitor. so if capacitors can sing (which I have herad), maybe mosfets can sing too. |
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| SY |
| :cop: jewilson: I understand you have some strong feelings here, but the personal insults are totally out of bounds and against forum rules. |
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| Fred Dieckmann |
"3rdly, the construction of the mosfet is very much like a capacitor."
That is not even close to accurate. First off you would have to specify the type of capacitor since electrolytic, metalized film, and film and foil capacitors have different construction even among similar types. Winding tension, outer tape, and whether or not the cap is round or oval in cross section. Different monolithic ceramic capacitors have greatly different piezo electric characteristics. Which type of cap in particular do mosfets resemble? None of them would be my answer. I have heard audible noise from amplifiers when driving high currents into resistive test loads. There are a variety of mechanisms that can cause this noise. This is not that rare an occurrence as most people who have run high current test into resistive loads. What is all the controversy? This is high school physics stuff and is not that complicated or mysterious. |
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| millwood |
| quote: | Originally posted by Fred Dieckmann
[BThis is high school physics stuff and is not that complicated or mysterious. [/B] |
that's why I wasn't surprised that you couldn't find the right answer.
Usually, the more "rudimentory", the more difficult to understand.
the world's mathematians are still trying to prove 1+1? I bet you that most of us have no idea what that means. |
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| SY |
| sully, if the heating starts at a surface region, the time contants don't enter into it. You can heat and cool a surface region pretty fast, and that can couple to the surrounding air (look up Rosencwaig's work on the photoacoustic effect, for example). I'm not saying this is the mechanism- I think some sort of effect like what you speculate or similar is more likely- but surface effects can be funny and they don't depend on heating up the entire chip or even the entire junction. |
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| sully |
| quote: | Originally posted by SY
sully, if the heating starts at a surface region, the time contants don't enter into it. You can heat and cool a surface region pretty fast, and that can couple to the surrounding air (look up Rosenzwaig's work on the photoacoustic effect, for example). I'm not saying this is the mechanism- I think some sort of effect like what you speculate or similar is more likely- but surface effects can be funny and they don't depend on heating up the entire chip or even the entire junction. |
Agreed in principle..but only for the top of the chip.
On the bottom of the case, the heat pulses (no cooling pulses here) will have been low pass filtered out the wazoo..with a time constant in the tens to hundreds of milliseconds, the filtering is strong.
But I will admit...pulses of hot air pinging the underside of the to-3 case like an ink jet printer would be pretty neat...the to-247 case of course, does not have that air..
Cheers, John |
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| SY |
| Well, the top of the chip is where they attach the wires! |
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| Christer |
| quote: | Originally posted by A Titmus
Ok, I apologise for asking this very basic question, but I haven't found a simple answer anywhere.
...
Once again, I am sorry if this is a rediculous question.
Andrew |
And some 40 posts later the discussion is still going on and
no definitive answer as to what causes the effect has been
agreed upon. That is how elementary and ridiculous the
question was. :)
As some earlier poster said, there is no need to apologize
or assume a question is ridiculous. Some of the seemingly
most stupid and elementary questions (where I would not
include your question) are actually not trivial at all, but rather
so elementary that almost nobody has bothered to think
about them. |
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| SY |
| Here's a simple answer- replace the output devices and see if the singing goes away. If it does, demand an explanation from the devices' manufacturer. |
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| Fred Dieckmann |
"that's why I wasn't surprised that you couldn't find the right answer."
It's responses like this that make me so eager to get in the middle of nonsense like this. Why try to discuss anything just to argue with idiots with a chip on their shoulder. Why try and educate someone who has no desire to learn anything. maybe I should just Email answers to people with questions to avoid having to deal with moronic post like this.
http://hyperphysics.phy-astr.gsu.ed.../forwir.html#c1
http://hyperphysics.phy-astr.gsu.ed.../wirfor.html#c1 |
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| millwood |
| quote: | Originally posted by Fred Dieckmann
[BWhy try to discuss anything just to argue with idiots with a chip on their shoulder. Why try and educate someone who has no desire to learn anything. [/B] |
my thoughts exactly when I was replying to your posts.
Who said different minds don't think the same?
:) |
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| Peter Daniel |
| quote: | Originally posted by A Titmus
Ok, I apologise for asking this very basic question, but I haven't found a simple answer anywhere.
...
Once again, I am sorry if this is a rediculous question.
Andrew |
Seems like this guy here was also hearing things: http://www.diyaudio.com/forums/show...86978#post86978 |
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| SY |
| Fred: In a word... no. |
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| A Titmus |
Just for fun, I took the lid off of my amp and drove it with a highish input signal and no load. The input signal was just audible from the MOSFETS with my ear up close. Without a load it is not particularly loud. The only interesting thing is that I replaced two of the transistors a couple of months ago. All four of them are producing the noise.
I did get someone else to listen to it as well, they found it difficult to identify the tune (tinny, high and very quiet), but it was there. I wouldn't expect it to replace my speakers!
I would also like to thank everyone for their opinions so far, I never dreamt that this would attract so much attention.
Andrew |
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| Peter Daniel |
| quote: | Originally posted by millwood
the world's mathematians are still trying to prove 1+1? I bet you that most of us have no idea what that means. |
I wasn't aware of your deeper. philosophical side. |
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| SY |
| quote: | Originally posted by Peter Daniel
I wasn't aware of your deeper. philosophical side. |
Russell and Whitehead showed that, indeed, this is a deep philosophical issue. It's amplified a bit in Courant's "World of Mathematics."
Remember the line in Videodrome: "They have something much more dangerous than that. They have a philosophy." |
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| millwood |
| quote: | Originally posted by Peter Daniel
I wasn't aware of your deeper. philosophical side. |
not terribly surprised. awareness is an acquired taste and not everyone is gifted to have it, as you have proven it personally. |
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| Peter Daniel |
| quote: | Originally posted by millwood
not terribly surprised. awareness is an acquired taste and not everyone is gifted to have it, as you have proven it personally. |
This is my first post I'm reporting to moderators. |
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| millwood |
| quote: | Originally posted by Peter Daniel
This is my first post I'm reporting to moderators. |
what are you reporting it for?
your having no awareness? well, you said that yourself. :) |
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| Fred Dieckmann |
| Which particular guys did you have in mind.............. |
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| Christer |
| quote: | Originally posted by Peter Daniel
I wasn't aware of your deeper. philosophical side. |
I am not so sure there was anything philosphical in there,
unless millwood made a typo. You cannot prove whether
"1+1" since this is not a statement. You can calculate it,
but you cannot prove it. Perhaps he meant
proving whether "1+1 = 2", which is or isn't true depending
on our choice of algebraic system. For the usual algebraic
system it is elementary and follows from the Peano axioms. |
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| Christer |
| quote: | Originally posted by Peter Daniel
This is my first post I'm reporting to moderators. |
Are you reporting it to yourself? :) |
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| Peter Daniel |
| quote: | Originally posted by Christer
Are you reporting it to yourself? :) |
I'm looking for a third party opinion, as I don't believe what I see. |
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| Christer |
| quote: | Originally posted by Peter Daniel
I'm looking for a third party opinion, as I don't believe what I see. |
Yes, I didn't mean there was something wrong with it. You
report it as a member, not as a moderator, to the moderators.
I just thought is sounded a bit fun that a moderator reports
to the moderators, but it's late and I'm tired, so it probably
wasn't as funny as I thought. |
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| SY |
| quote: | Originally posted by Fred Dieckmann
Which particular guys did you have in mind.............. |
How recently? ;)
Christer, it IS funny, at least to a third party. |
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| Peter Daniel |
Funny, are the other members posts. Especially the ones dealing with awarness prerception.;)
Funny was also fact that I didn't know how to do it, but I did it anyway. |
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| millwood |
| quote: | Originally posted by Christer
You cannot prove whether "1+1" since this is not a statement. |
sure you can. both 1+1 and 1+2 come from a very old mathematical conjecture. and 1+2 has been proven (partially) but 1+1 remains.
Again, awareness is an acquired taste and not everyone is gifted with it. |
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| sam9 |
| My "awarness prerception" is strongly influenced by the quality of beer in the fridge. I suggest all parties kick back and modify their perceptions. As Miss Scarlet said "Tomorrow is another day." |
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| SY |
| :cop: We've exhausted the actual topic at hand and gotten way off track. I'm closing the thread. If anyone has any further data, experiments, or conjectures regarding the singing FETs, feel free to start a new thread and I'll merge it with this one. |
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