Do you need AC Noise Filtering For Your Audio Devices?

[restorer-john]

The tricky thing with analyses of this sort is with how you can be certain that the root cause you've identified is the true root cause, and not something that has happened as a result of something else that you didn't think would be be the root cause, because it didn't occur to you. A younger sister of mine once told me about the engine failure of the car she owned. Apparently there were a bunch of similar failures of the same engine in that particular brand of highly regarded Japanese car. Anyway, as she explained it, the head warped, which caused the engine to overheat. I asked her how she had determined that it wasn't the other way around, i.e., that the reason the head warped was because it got hotter than it was supposed to get, and that the root cause was something else, that had caused (or allowed) the engine to overheat. She insisted that the head warped first and this caused the engine to overheat. This is what some mechanic had told her. She is not a mechanically minded person in the least.

I first ran into these capacitor failures maybe 25-30 years ago. Even unused new old stock capacitors of this type develop micro cracks in the epoxy which, of course, pours cold water on your doubts as to the root cause. The difference of course is they are not subject to 120V/240V AC continuous across the capacitor, with no reactive impedance current flow and zero heating. So they clearly do not explode.

I'll dig out some NOS caps of this type with such cracks if I get a chance (and haven't thrown them out).

 

[MrPeabody]

Stupid question warning.

Is a power strip (or conditioner/filter) likely to limit current such that an amplifier connected to it could get starved of power? I understand its not a great idea to connect multiple high-powered amps to the same power strip, but my question is if these fancy conditioners can get so fancy that they don't pass through all the current that is made available to them by the wall outlet.

If it did, it would have to do so by reducing the voltage seen by the amplifier. The impedance of the strip at 60 Hz would need to be significant in comparison to the amplifier impedance - not the impedance at the audio inputs, rather the impedance to current entering the amplifier via the power cord. It does not seem likely that a power strip or conditioner/filter would have enough impedance at 60 Hz to have this effect. Nor does it seem particularly likely that a power strip or conditional/filter would be unable to tolerate the current that is permitted to flow by the amplifier, however it is prudent to be aware of the current limitation of anything placed between the wall socket and anything that draws a lot of power. In that sentence, current limitation refers to how much current the strip can withstand before it will throw a breaker or waste a fuse or overheat and catch fire. It doesn't mean, in the ordinary sense, a limit to the current it is able to supply, however if a breaker trips or a fused is wasted or the thing catches fire at, say, 10 amps, then obviously it is not going to supply more than 10 amps. It should not limit current unless one of these things happens, and because these things are obvious when they happen, the likelihood seems very low that there would be any limiting of current that would be ongoing and that you wouldn't know about. One way to find out would be to measure the RMS voltage where the power cord enters the amplifier, when the amplifier is pumping current into the speakers. If the voltage is where it is supposed to be, the current will be as Georg Ohm said it will be. But you can't ask him, 'cause he died a long time ago.

 

[MrPeabody]

I first ran into these capacitor failures maybe 25-30 years ago. Even unused new old stock capacitors of this type develop micro cracks in the epoxy which, of course, pours cold water on your doubts as to the root cause. The difference of course is they are not subject to 120V/240V AC continuous across the capacitor, with no reactive impedance current flow and zero heating. So they clearly do not explode.

I'll dig out some NOS caps of this type with such cracks if I get a chance (and haven't thrown them out).

I believe you. If you have seen these cracks develop in unused capacitors of this type that have been in storage a long time, this is a good enough reason to accept your hypothesis. No need to go dig one out and take a picture of it. I was just wanting to say something about how, in general, this is tricky business.

 

[restorer-john]

@MrPeabody So, here's a new old stock cap of the same style and construction.

What you have is a resin potted capacitor. Depending on how centralized the actual metalised (al) capacitor 'roll' is, inside the epoxy/resin encasing, one side will be closer to the surface than the another. The thinner side usually cracks when the resin shrinks.

This particular capacitor, although never used or installed will fail or explode within a short time if installed. Notice the end on view.

See the crack that runs from top edge to the lead out? You can see the exposed aluminium/metallised edge.

 

[MrPeabody]

@MrPeabody So, here's a new old stock cap of the same style and construction.

View attachment 116926

What you have is a resin potted capacitor. Depending on how centralized the actual metalised (al) capacitor 'roll' is, inside the epoxy/resin encasing, one side will be closer to the surface than the another. The thinner side usually cracks when the resin shrinks.

View attachment 116928

This particular capacitor, although never used or installed will fail or explode within a short time if installed. Notice the end on view.

See the crack that runs from top edge to the lead out? You can see the exposed aluminium/metallised edge.

View attachment 116927

Interesting. I had hoped to post a response before you went to the trouble. In that last picture you can definitely see the crack. High quality epoxy isn't supposed to do this. From what I recall, all epoxies weaken and soften at several hundred Fahrenheit, but softening should make the resin less likely to crack. (Sorry for the Fahrenheit.) My guess would be that this is some inferior kind of epoxy, and I'd hesitate to extrapolate the flaw to all capacitors of similar construction.

 

[stunta]

Are you talking about a >10KW PA system with 4*18" subs?

I am not well versed in this topic, but a 15 amp outlet caps out at 1800 watts on a 120 v circuit. Where are you getting the 10KW value from?

 

[restorer-john]

My guess would be that this is some inferior kind of epoxy, and I'd hesitate to extrapolate the flaw to all capacitors of similar construction.

Dug into my turntable spares box, as there's always a Rifa brand 250V cap there on a PCB someplace and it didn't disappoint.

This has not exploded, but as you can see, the resin has crazed all over and parts have fallen off. You can see how thin the epoxy/resin really is. This cap would be 30 years old approx.

Pretty much all mains caps are MKP now and they fail less often, but the one pictured in Amir's teardown of the Onkyo AVR is an MKP, set in the same style resin.

The MKPs set in resin inside a plastic moulding (like this Philips style) rarely fail IME. (this is approx 26 years old NOS)

 

[respice finem]

https://www.amazon.de/-/en/Brennens...1615152578&s=network-receiver-speakers&sr=1-4
https://www.amazon.de/-/en/Brennens...21d66&pd_rd_wg=A6y6j&pd_rd_i=B000WKFQJI&psc=1
https://www.amazon.de/-/en/714044-I...615152578&s=network-receiver-speakers&sr=1-19

Not sure if it's really not there or just not stated. I've seen that two times, one was a Brennenstuhl (don't know which model any more), and one of I think Lidl Germany? looking exactly like the other one from Brennenstuhl. In both cases, it was not stated but present anyway. Interestingly, the point of failure in both was the power switch and the insides were identical.

 

[amirm]

Is a power strip (or conditioner/filter) likely to limit current such that an amplifier connected to it could get starved of power?

Depends on the type. There are high-end surge protection devices that operate in series mode. With these you should be careful as they can starve powerful amplifiers for power. They usually have a rating to this effect with some as low as 5 amps and such. I would not plug any power amplifiers into them even if they are rated for 15 amps (if the amp is powerful).

On run of the mill power strip, you are at the mercy of the quality of the outlets, internal bus bar and such. There is likely a bit of a loss but not material unless you run a super powerful amplifier and drive it hard. This may be a reason to shop for a name brand device. I have a special meter that measures this aspect of power devices. Maybe I test a few power strips to see how they do.

 

[amirm]

@amirm : At 5:04 in the video, you tell people to go to the "audio-video review" website while showing how to navigate to the ASR teardown page.

Yeh, I heard it after I recorded. Having to re-record was out of the question as was editing it so I left it in. Laziness is a fixture in what I do.

 

[restorer-john]

There are high-end surge protection devices that operate in series mode. With these you should be careful as they can starve powerful amplifiers for power. They usually have a rating to this effect with some as low as 5 amps and such.

Quite true. I have a 5A unit with full filtering (series/parallel/DC/Surge etc) on my feed to the HiFi. No problems as 5A at 240V (Aus) is >1kW, but yes, I can trip it with two big amps running BTL if I wind it up or plug a 1200W vacuum cleaner into the same feed. The voltage drop is neglible actually- it's circuit breaker (resettable) limited to protect the chokes I'd say.

 

[amirm]

In US we have half your voltage so 5 amp is not much.

 

[Pdxwayne]

@amirm , you mentioned "most" audio devices have built in filter. So, what are the few devices that don't have it? Would external filter help? Thanks!

 

[wwenze]

What does the current rating mean anyway? I'm guessing that's the inductor's saturation current rating?

Below is rated 6A and looking at the wire gauge I doubt thermal is the limiting factor, tho I could be wrong.

Smh I couldn't find the DCR rating in the typical line filters' datasheet so I had to find something more random. DCR is a few tens of milliohms which is around typical for the kind of inductor used. So insertion loss at 60Hz is minimal.

Anyway since I had the pdfs open so might as well post an example of why these filters don't do anything at the audio frequency range. I guess one can intentionally build one that has an effect at the audio frequency range, and then claim (and justifiably so) that it is different from the standard filters meant for EMI. But in this case the designer has to really check the impedances to prevent the "starving of current", although even with that said, anything above 100Hz should be seeing low impedance from the DC side capacitors anyway.

 

[Plcamp]

@amirm , you mentioned "most" audio devices have built in filter. So, what are the few devices that don't have it? Would external filter help? Thanks!

Devices absent of digital interfaces and control might not have filters, vintage stuff commonly does not. Reasons are multiple, but if you are not marketing a product with a clock higher than (I’ve forgotten the exact frequency) no regulations apply to emissions.

As to whether such equipment might benefit, I would say possibly* with the warning that dealing with EMI and RF Interference is generally like squeezing a balloon, unless you deal with all the cable interfaces at the same time.

* if you can detect a real problem to start with

 

[Pdxwayne]

Devices absent of digital interfaces and control might not have filters, vintage stuff commonly does not. Reasons are multiple, but if you are not marketing a product with a clock higher than (I’ve forgotten the exact frequency) no regulations apply to emissions.

As to whether such equipment might benefit, I would say possibly* with the warning that dealing with EMI and RF Interference is generally like squeezing a balloon, unless you deal with all the cable interfaces at the same time.

* if you can detect a real problem to start with

Let's say we have vintage stereo power amp with no digital interface nor control. In what kind of scenarios would a power strip with AC filter help? Thanks!

For example, in the same circuit, there are other non audio devices plugged in. Would refrigerator, freezer, lights, etc. cause any issues?

 

[Plcamp]

Let's say we have vintage stereo power amp with no digital interface nor control. In what kind of scenarios would a power strip with AC filter help? Thanks!

For example, in the same circuit, there are other non audio devices plugged in. Refrigerator, freezer, lights, etc.

I think you would need something pretty severe for a power amp to be upset, an electrically nearby commutating ac motor might be an example where enough noise is present to be detectable. I have personally never had the problem with such audio equipment.

Devices with higher gains stages, like microphone or phono preamps would be somewhat more likely to detect power noise problems first.

I will bet that most people have experienced a temporary noise burst and/or disruption of even their filtered products in the presence of a nearby static discharge.

Know that everything is susceptible, and filtering is one tool to maximize immunity. Unfortunately, it is often added to products as an afterthought barnacle as they struggle to match compliance requirements.

The best designs have immunity built into the PCB design, by using advanced signal integrity layout support and by doing thorough timing analysis to maximize internal margins.

...I used to manage signal integrity, timing and connectivity analysis services for digital products.

 

[Pdxwayne]

I think you would need something pretty severe for a power amp to be upset, an electrically nearby commutating ac motor might be an example where enough noise is present to be detectable. I have personally never had the problem with such audio equipment.

Devices with higher gains stages, like microphone or phono preamps would be somewhat more likely to detect power noise problems first.

I will bet that most people have experienced a temporary noise burst and/or disruption of even their filtered products in the presence of a nearby static discharge.

Know that everything is susceptible, and filtering is one tool to maximize immunity. Unfortunately, it is often added to products as an afterthought barnacle as they struggle to match compliance requirements.

The best designs have immunity built into the PCB design, by using advanced signal integrity layout support and by doing thorough timing analysis to maximize internal margins.

...I used to manage signal integrity, timing and connectivity analysis services for digital products.

Thanks!

Would video like this one show why some modern audio equipments are still not designed well enough to stop interference?

Or is it a totally different issue?

 

[Plcamp]

Heh, fun video.

Sure looks like there are some energetic switching transients within those LED modules

As for the susceptibility of the tuner...that could be either noise conducted into in, or (I guess more likely) noise broadcasting over the air into it from the cables.

Not sure what kind of fan that is, but if it commutates, it might also be a source.

Those clamp on beads are most effective when all wires to the suspected module go through the same bead.

The major observation is that crap is best dealt with inside the source design, and if it is not then it will be expensive and difficult to add the protection back in later.

I wouldn’t locate similar LED modules near my stereos.

Edit: It does appear that LED headlights are driven by a switched mode current source...a great source for broadband noise generation that would disrupt a tuner.

so no, this does not show that some products are deficient.

 

[Pdxwayne]

Heh, fun video.

Sure looks like there are some energetic switching transients within those LED modules

As for the susceptibility of the tuner...that could be either noise conducted into in, or (I guess more likely) noise broadcasting over the air into it from the cables.

Not sure what kind of fan that is, but if it commutates, it might also be a source.

Those clamp on beads are most effective when all wires to the suspected module go through the same bead.

The major observation is that crap is best dealt with inside the source design, and if it is not then it will be expensive and difficult to add the protection back in later.

I wouldn’t locate similar LED modules near my stereos.

Edit: It does appear that LED headlights are driven by a switched mode current source...a great source for broadband noise generation that would disrupt a tuner.

so no, this does not show that some products are deficient.

I have seen another interesting one a while back regarding common mode noise.

Common mode noise relevant at all for audio quality?

If relevant, in those cases the author shown us, anything audible possible for music setup?

Thanks!