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Post by bobbyt on Apr 11, 2021 21:54:22 GMT -5
Quick question for any who've encountered this. I've had a pair of Airmotiv6s for several years and recently noticed the right one has a ground loop/AC-frequency hum, and after being on for a while the ribbon tweeter is warm to the touch.
In a quiet room you can hear it from several feet away, versus the left speaker which only has a very soft static you have to be within a foot to hear. Any idea what would be causing this?
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Post by Gary Cook on Apr 12, 2021 5:47:25 GMT -5
Have you tried swapping them?
Cheers
Gary
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Post by 405x5 on Apr 12, 2021 9:47:58 GMT -5
Quiet before....humming now....not a ground loop in all likelihood
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Post by bobbyt on Apr 12, 2021 19:14:54 GMT -5
Have you tried swapping them? Cheers Gary I tried plugging the right one into another outlet, with the same results. Did not swap interconnects as the hum is there without any input connected. Quiet before....humming now....not a ground loop in all likelihood Sorry I just meant it sounded like one, definitely a hum tied to AC frequency. Noticed the hum a few weeks ago (after years of ownership), but the warmth at the tweeter grill was new, and today when I leaned in close I got a slight burnt smell so I'm thinking a component fried or is slowly frying...capacitor? |
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Post by DavidR on Apr 12, 2021 21:27:44 GMT -5
What is the frequency from the hum?
60Hz
120Hz
etc.
If you have a smart phone you can download a program to ID the frequency of the hum.
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Post by bobbyt on Apr 13, 2021 1:17:23 GMT -5
What is the frequency from the hum? 60Hz 120Hz etc. If you have a smart phone you can download a program to ID the frequency of the hum. Spectrum bounces around 60 & 120, my guess is 60 with a harmonic. Tweeter does not play and is definitely releasing a little heat, not sure if its seeing DC or just from the hum signal. I pulled the circuit board and didn't see any cooked surface mount components, but one of the big capacitors has a stain. Looks like replacement would be straightforward...any thoughts on doing one/both? If voltage/capacitance match, is there any concern of them being 10 years newer or different brand vs. the other speaker?     |
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Post by Gary Cook on Apr 13, 2021 1:42:56 GMT -5
Can't hurt to try a replacement capacitor, match it as close as you can. I use www.mouser.com/ for audio quality components. Cheers Gary |
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Post by bobbyt on Apr 13, 2021 2:01:45 GMT -5
Can't hurt to try a replacement capacitor, match it as close as you can. I use www.mouser.com/ for audio quality components. Cheers Gary Thanks Gary, I've found a couple 50v/10k μF but posted in Keith's forum to see if I'm missing anything before I swap (like potential mismatch in brand/age, etc). |
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Post by DavidR on Apr 13, 2021 8:43:58 GMT -5
What is the frequency from the hum? 60Hz 120Hz etc. If you have a smart phone you can download a program to ID the frequency of the hum. Spectrum bounces around 60 & 120, my guess is 60 with a harmonic. Tweeter does not play and is definitely releasing a little heat, not sure if its seeing DC or just from the hum signal. I pulled the circuit board and didn't see any cooked surface mount components, but one of the big capacitors has a stain. Looks like replacement would be straightforward...any thoughts on doing one/both? If voltage/capacitance match, is there any concern of them being 10 years newer or different brand vs. the other speaker? View Attachment View Attachment View Attachment View AttachmentGround loops are typically 60Hz and component issues (capacitor) 120Hz |
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KeithL
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Post by KeithL on Apr 13, 2021 9:14:46 GMT -5
There are two basic numbers for an electrolytic capacitor - Voltage and Capacitance.
You can replace a capacitor with one of equal or higher voltage rating (generally not lower). (There are also reasonable limits here... for example a 500v capacitor actually may not perform especially well at 5v.)
You should aim for the same capacitance value.
In many cases a significantly lower value won't do the job properly.
In some cases a higher value may improve performance. However, in many cases it doesn't make any difference, and in some it can cause other parts to fail by stressing them. (For example putting much higher valued filter capacitors in a power supply puts more stress on the rectifiers.) In general going to a slightly higher value if you can't find an exact replacement won't hurt anything (in a power supply).
Another important characteristic is the temperature rating (for example 85c means that the capacitor is rated for 85 degrees centigrade). It's OK to replace an 85c capacitor with a 105c one... but usually not the other way around...
Most electrolytic capacitors have a relatively short rated life expectancy if operated at full temperature.
However their life expectancy increases dramatically for every ten degrees or so they stay below their maximum rated temperature. So, again, it would be fine to replace an 85c capacitor with a 105c capacitor, but usually NOT the opposite.
There are other factors...
If the capacitor is exposed to a lot of AC ripple current you should choose one rated for that. This can be a factor in power supply decoupling capacitors...
But it's probably not an issue in a small linear power supply like in the Airmotiv speakers.
And, if the capacitor is exposed to power at HIGH FREQUENCIES, then you usually need a "low ESR" capacitor rated for high frequencies. This is quite common at certain circuit locations in switch mode power supplies. You MUST use a low ESR capacitor at those locations in the circuit.
If you replace a low ESR capacitor with an ordinary one in those locations the power supply may not work at all... And, if it does work, it will tend to overheat and die very quickly... (We may be talking smoke and ultimate failure in minutes or days.)
Note that putting a low ESR cap where it isn't necessary doesn't specifically improve anything...
But failing to use a low ESR capacitor where one is required may result in an immediate and dramatic failure... (Low ESR capacitors cost a bit more more so designers tend to only use them where it matters... )
(But, if you're replacing a capacitor, and you're not sure, using a low ESR capacitor will almost never hurt anything. )
Can't hurt to try a replacement capacitor, match it as close as you can. I use www.mouser.com/ for audio quality components. Cheers Gary Thanks Gary, I've found a couple 50v/10k μF but posted in Keith's forum to see if I'm missing anything before I swap (like potential mismatch in brand/age, etc). |
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DYohn
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Post by DYohn on Apr 13, 2021 10:11:11 GMT -5
Just to add to Keith's excellent post above, if it was me I'd look for a cap with a higher temperature rating, if one is available. Not because I think the design needs it, but because higher temp caps have a longer expected life and I only want to replace it once. If the cap in the system is rated for 85C, replace with one rated at 105C. If it is a 105C cap already, see if you can find one the same size rated to 125C. And pay attention to polarity when you install the replacement.
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cawgijoe
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Post by cawgijoe on Apr 13, 2021 10:55:51 GMT -5
Just to add to Keith's excellent post above, if it was me I'd look for a cap with a higher temperature rating, if one is available. Not because I think the design needs it, but because higher temp caps have a longer expected life and I only want to replace it once. If the cap in the system is rated for 85C, replace with one rated at 105C. If it is a 105C cap already, see if you can find one the same size rated to 125C. And pay attention to polarity when you install the replacement. DYohn makes a very good point on the polarity....I have found that taking pics prior to removing anything as well as making notes really helps. |
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Post by bobbyt on Apr 13, 2021 11:31:05 GMT -5
Just to add to Keith's excellent post above, if it was me I'd look for a cap with a higher temperature rating, if one is available. Not because I think the design needs it, but because higher temp caps have a longer expected life and I only want to replace it once. If the cap in the system is rated for 85C, replace with one rated at 105C. If it is a 105C cap already, see if you can find one the same size rated to 125C. And pay attention to polarity when you install the replacement. Just to add to Keith's excellent post above, if it was me I'd look for a cap with a higher temperature rating, if one is available. Not because I think the design needs it, but because higher temp caps have a longer expected life and I only want to replace it once. If the cap in the system is rated for 85C, replace with one rated at 105C. If it is a 105C cap already, see if you can find one the same size rated to 125C. And pay attention to polarity when you install the replacement. DYohn makes a very good point on the polarity....I have found that taking pics prior to removing anything as well as making notes really helps. Existing cap is rated -40 to 105C...can't imagine they're anywhere near even 85C with my use, but I'm sure whatever temp they do see would be lower stress on a higher rated cap. And yes I will double check polarity. Thanks for the help everyone. |
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Deleted
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Post by Deleted on Apr 13, 2021 11:46:36 GMT -5
Just to add to Keith's excellent post above, if it was me I'd look for a cap with a higher temperature rating, if one is available. Not because I think the design needs it, but because higher temp caps have a longer expected life and I only want to replace it once. If the cap in the system is rated for 85C, replace with one rated at 105C. If it is a 105C cap already, see if you can find one the same size rated to 125C. And pay attention to polarity when you install the replacement. DYohn makes a very good point on the polarity....I have found that taking pics prior to removing anything as well as making notes really helps. Existing cap is rated -40 to 105C...can't imagine they're anywhere near even 85C with my use, but I'm sure whatever temp they do see would be lower stress on a higher rated cap. And yes I will double check polarity. Thanks for the help everyone. At highest ambient temp and listening volume that your gear is subjected to you could always use a thermal infrared laser thermometer in order to not leave things up to imagination  Of course, if your gear is stacked in an oven of a entertainment stand you'll want to take the reading in it. |
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DYohn
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Post by DYohn on Apr 13, 2021 11:49:01 GMT -5
If it's a 105C cap that's good. Again replace it with at least the same or with a 125C cap if you can find one. This has nothing to do with the actual temps in the amp, it has to do with the materials the cap is made from which enables a longer life.
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Post by Deleted on Apr 13, 2021 11:57:56 GMT -5
If it's a 105C cap that's good. Again replace it with at least the same or with a 125C cap if you can find one. This has nothing to do with the actual temps in the amp, it has to do with the materials the cap is made from which enables a longer life. How would the thermal rating not be pertinent to operating thermal temperatures? I mean in my brief time experimenting w/ overclocking devices utilizing peltiers and water cooling the object was to keep a device such as a processor below a certain temperature while increasing voltage in order to reduce the effects of thermal resistance and expansion within the processor so that transistors didn't "butt" up against one another and cause error. If you don't mind DYohn I see articles such as this: atceramics.com/userFiles/uploads/pdfs/thermal_resist.pdfThermal resistance is specified - what are the undesirable effects of a component operating outside its' thermal specifications? I'd think resistance etc would be affected? If thermal resistance is affected wouldn't that affect the thermal emissions from such parts and thereby affect surrounding parts - and their operationality at said temps ..... ? I'm just dumbfounded as to how a superconductor below x Celsius for example wouldn't be affected by raising temps to ambient air temps? |
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KeithL
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Post by KeithL on Apr 13, 2021 12:18:26 GMT -5
DYohn is correct...
What YOU are talking about is the actual structure of the processor performing differently at different temperatures. This is true and relevant for semiconductors - especially of the sort used in microprocessors.
A polypropylene capacitor is comprised of layers of metal foil and plastic sheeting. And both of those materials last a very long time under normal conditions. Likewise for various other types - like metal plates or foils with mica or teflon dielectrics.
But the working part of an electrolytic capacitor is made up of a chemical liquid or paste (similar to a battery). And the actual chemicals and materials an electrolytic capacitor is made up of break down and deteriorate over time. This deterioration may occur very slowly at normal or low temperatures...
However it occurs much more quickly at elevated temperatures... (And this will happen whether the higher temperature is due to internal resistance or environmental conditions.) (And, yes, higher internal resistance may contribute to more internal heating, which may certainly contribute to this.)
But an electrolytic capacitor is in fact more similar internally to a rechargeable battery than to most other electronic components. If it's a 105C cap that's good. Again replace it with at least the same or with a 125C cap if you can find one. This has nothing to do with the actual temps in the amp, it has to do with the materials the cap is made from which enables a longer life. How would the thermal rating not be pertinent to operating thermal temperatures? I mean in my brief time experimenting w/ overclocking devices utilizing peltiers and water cooling the object was to keep a device such as a processor below a certain temperature while increasing voltage in order to reduce the effects of thermal resistance and expansion within the processor so that transistors didn't "butt" up against one another and cause error. If you don't mind DYohn I see articles such as this: atceramics.com/userFiles/uploads/pdfs/thermal_resist.pdfThermal resistance is specified - what are the undesirable effects of a component operating outside its' thermal specifications? I'd think resistance etc would be affected? If thermal resistance is affected wouldn't that affect the thermal emissions from such parts and surround parts within and their operationality at said temps ..... ? |
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KeithL
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Post by KeithL on Apr 13, 2021 12:23:56 GMT -5
You also need to distinguish where the heat is coming from.
If the tweeter itself is becoming warm that would suggest DC current leaking through it and heating the printed voice coil. This in turn would suggest a DC offset on the output of the internal tweeter amplifier. This is the sort of situation that is bad, and will tend to get worse, resulting in a fried tweeter. It's also unlikely to be caused by a bad power supply capacitor alone - although not impossible.
However, the tweeter is a thin part, with a shell and insides made up of plastic and metal. It's possible that the heat is coming from the electronics inside... And is simply warming up the tweeter from behind.
(The tweeter will conduct heat and will also feel warmer to the touch than the surrounding wood cabinet.)
What is the frequency from the hum? 60Hz 120Hz etc. If you have a smart phone you can download a program to ID the frequency of the hum. Spectrum bounces around 60 & 120, my guess is 60 with a harmonic. Tweeter does not play and is definitely releasing a little heat, not sure if its seeing DC or just from the hum signal. I pulled the circuit board and didn't see any cooked surface mount components, but one of the big capacitors has a stain. Looks like replacement would be straightforward...any thoughts on doing one/both? If voltage/capacitance match, is there any concern of them being 10 years newer or different brand vs. the other speaker? View Attachment View Attachment View Attachment View Attachment |
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Deleted
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Post by Deleted on Apr 13, 2021 12:25:39 GMT -5
DYohn is correct...
What YOU are talking about is the actual structure of the processor performing differently at different temperatures. This is true and relevant for semiconductors - especially of the sort used in microprocessors.
A polypropylene capacitor is comprised of layers of metal foil and plastic sheeting. And both of those materials last a very long time under normal conditions. Likewise for various other types - like metal plates or foils with mica or teflon dielectrics.
But the working part of an electrolytic capacitor is made up of a chemical liquid or paste (similar to a battery). And the actual chemicals and materials an electrolytic capacitor is made up of break down and deteriorate over time. This deterioration may occur very slowly at normal or low temperatures...
However it occurs much more quickly at elevated temperatures... (And this will happen whether the higher temperature is due to internal resistance or environmental conditions.) (And, yes, higher internal resistance may contribute to more internal heating, which may certainly contribute to this.)
But an electrolytic capacitor is in fact more similar internally to a rechargeable battery than to most other electronic components. How would the thermal rating not be pertinent to operating thermal temperatures? I mean in my brief time experimenting w/ overclocking devices utilizing peltiers and water cooling the object was to keep a device such as a processor below a certain temperature while increasing voltage in order to reduce the effects of thermal resistance and expansion within the processor so that transistors didn't "butt" up against one another and cause error. If you don't mind DYohn I see articles such as this: atceramics.com/userFiles/uploads/pdfs/thermal_resist.pdfThermal resistance is specified - what are the undesirable effects of a component operating outside its' thermal specifications? I'd think resistance etc would be affected? If thermal resistance is affected wouldn't that affect the thermal emissions from such parts and surround parts within and their operationality at said temps ..... ? Thank you once again gent! But I am still confused, seems like you're saying operating temperatures do affect the part in question at least longevity and reliability? Lemme ask this plainly, are the thermal ratings of capacitance affected by temperatures not only in resistance but in long term longevity? As you can tell I do not have an electrical engineering degree. I only have electrical engineering in an applied field and never studied this deeply - at such time I'd call a specialist. |
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DYohn
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Post by DYohn on Apr 13, 2021 15:25:13 GMT -5
The thermal rating of a capacitor is determined BY the materials it is made from and has no impact on the voltage or capacitance rating. The thermal rating impacts lifespan depending on the actual temperature the unit is exposed TO, but the capacitance values are not affected. There is no such thing as "thermal rating of capacitance," it is simply a steady-state exposure rating for the component materials, with lifespan increasing the farther away from the limit you operate.
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