Do you need AC Noise Filtering For Your Audio Devices?

[Francis Vaughan]

It occurred to me that this video has an unstated observation about modern gear. We have reached the point where a switched mode power supply is the default expectation. I’m not sure when the transition happened. But nobody excepts a big mains frequency transformer in their gear anymore. Even the cheapest thing has one. I guess steam driven stuff with glowing bottles continues with huge lumps of iron. But little else.

 

[Doodski]

It occurred to me that this video has an unstated observation about modern gear. We have reached the point where a switched mode power supply is the default expectation. I’m not sure when the transition happened. But nobody excepts a big mains frequency transformer in their gear anymore. Even the cheapest thing has one. I guess steam driven stuff with glowing bottles continues with huge lumps of iron. But little else.

I saw that in the video too and wondered if linear supplies where being short changed.

 

[respice finem]

My UPS batteries tend to die a few months after the warranty runs out. Many also sit on the shelf and by the time you get them, some of the life is gone from them.

I got 4 identical ones (3 at work and 1 at home), so I've developed a "battery policy": after 4 years (automatic reminder) I buy 4 batteries, so they're fresh, then I wait until all UPSes have the "self test failed" message (there's enough life left in them for a few months), and then I replace all batteries at the same date. Works quite well, the quality of the batteries seem to be very consistent. That said, the UPSes don't have much to do here, so probably that's why the batteries live longer.

 

[respice finem]

...nobody excepts a big mains frequency transformer in their gear anymore. Even the cheapest thing has one.

Especially the cheapest things - and that's probably the answer, these PSUs are cheap to make and they work. I would not want to imagine a linear power supply in my PC, for example. One product line where they still are rare: AV receivers. Probably the manufacturers have long-term agreements with part makers or they can't be bothered to change their designs.

 

[Doodski]

I got 4 identical ones (3 at work and 1 at home), so I've developed a "battery policy": after 4 years (automatic reminder) I buy 4 batteries, so they're fresh, then I wait until all UPSes have the "self test failed" message (there's enough life left in them for a few months), and then I replace all batteries at the same date. Works quite well, the quality of the batteries seem to be very consistent. That said, the UPSes don't have much to do here, so probably that's why the batteries live longer.

I managed a alternative energy and battery shop for a short while and the life expectancy of a SLA (sealed lead acid) battery was not that great. They have lotsa issues. If memory serves me correct it was very thin sulphate deposits on the plates and other recharging issues stuff. I always bought fresh for my own needs like my mountain bike headlamp system that used a halogen bulb system.

 

[Francis Vaughan]

One product line where they still are rare: AV receivers.

Yeah, after I posted above I realised I had forgotten this outlier. Just plain odd. Why AVRs and not other gear? It maybe that they get away with cheaper PS by exploiting on the poorer regulation of a conventional PS, so with the spread across channels and wide dynamics of movies meaning they can get the needed performance out of what would ordinarily be an undersized PS. A SMPS would generally need to be much beefier.

 

[Francis Vaughan]

I saw that in the video too and wondered if linear supplies where being short changed.

Arguably yes.

Switching noise from the rectification can get back out into the world from conventional power supplies. Douglas Self relates how a portable AM radio can be easily used to hear them radiated from mains cords. Use of more modern fast recovery diodes or proper design of a snubbing network on the diodes dramatically reduces the hash. I always put a basic fiter on the input of anyting I build anyway.

 

[Plcamp]

It occurred to me that this video has an unstated observation about modern gear. We have reached the point where a switched mode power supply is the default expectation. I’m not sure when the transition happened. But nobody excepts a big mains frequency transformer in their gear anymore. Even the cheapest thing has one. I guess steam driven stuff with glowing bottles continues with huge lumps of iron. But little else.

We have yet to reach the point where people complain when they don’t get a switched power supply, but that too is coming?

 

[respice finem]

I guess most people (outside of our "bubble" at least) are not interested what type of power supply they have, as long as their stuff works.

 

[Count Arthur]

It looks like I've been wasting my time: https://www.audiosciencereview.com/...ne-noise-emi-filtering.976/page-2#post-554128

Looking at the Class D amp modules in my speakers and subwoofer, it looks to me like there's a mains filter right on the board:

Ah well, it was fun building the DIY filters and the sale of the ISOL-8 filter, and the collection of Russ Andrews power cables I had, paid for the parts with a significant amount of change left over.

 

[Hutch]

I have a Naim Mu-So that had an annoying hum and I put it on a (relatively) inexpensive Furmam 2 outlet AC filter. Fixed the hum, thank goodness. Moved to a new house and didn't really need the filter.

 

[Xulonn]

LOL!!!

@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.

That calls for a look at my pre-pandemic avatar...

 

[stunta]

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.

 

[Lambda]

: One can hardly buy a power strip (at least here in Germany) with 8-10 sockets without a "filter"/surge protector,

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

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

No!

I understand its not a great idea to connect multiple high-powered amps to the same power strip,

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

Having to many filters can increase ground current and at some point trip the GFCI.

 

[ksip2021]

If multiple class d amplifier modules are being used, some salient points should be addressed, such as if spread spectrum clocking were being used and non-sync between modules, complex beat frequencies emission might occur both on far field radiation and conducted on the mains supply. Adding extra mains filter may sometimes increase the radiated emission. Therefore measurements may be required on both radiated and conducted emission at the same time.

 

[Lambda]

http://rundsteuerfrequenz.de/
We have a very strong signal from 400-2000Hz modulated with up to 10% amplitude a view time a day.
As far as i know its to control some street lights and energy meters.
But even this is not causing any problems with my audio gear / but it is measurable

 

[milosz]

http://rundsteuerfrequenz.de/
We have a very strong signal from 400-2000Hz modulated with up to 10% amplitude a view time a day.
As far as i know its to control some street lights and energy meters.
But even this is not causing any problems with my audio gear / but it is measurable

That is very interesting. Here in Chicago, the electric utility can turn service on or off for a premises that is using a Smart Meter remotely by pumping some signal through the power distribution network. And there was once a scheme to provide Internet service over some carrier modulated onto the power lines. As far as I know none of these systems interfere with audio gear, but amateur radio operators did become upset because the powerline internet system carrier radiated from the lines and caused interference in one of the bands they use to communicate - I think it was the 80 meter band.

In fact there are a whole range of systems that use the power line for communication - such as X10 home automation and so on. To the best of my knowledge none of this causes any issues with audio playback systems. See https://en.wikipedia.org/wiki/Power-line_communication

 

[milosz]

Most domestic AC lines are not horrible. They are not wonderful but they are not disasters either, so in general some kind of line filtering isn't going to have a positive audible impact. But- there are probably some scenarios where a line filter would be useful. Running off a small portable generator maybe, or sharing a power line with a welding shop. But for most domestic audio gear I've ever bought, if the manufacturer didn't put enough into the design of the power supply to keep line noise out of the audio, I would return the thing as defective and ask for my money back.

 

[wwenze]

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.

This is not a stupid question... judging from how often this question pops up on the "non-science" forums.

tl;dr A good filter will appear as high impedance to the source (mains) while appearing as a low impedance to the load. The capacitors added after the inductors do that job, in the same way the big electrolytic capacitors do theirs.

 

[MrPeabody]

The thing is, they are beautifully sealed/potted when new, and even for many years. Then I think the epoxy/resin- whatever it is, crazes (like perspex). Tiny cracks appear, air gets in, the aluminium reacts and the cap start dissipating more than it would. It gets warm, the aluminium 'roll' expands, cracks the epoxy more and the process accelerates until the dielectric is compromised, it shorts and goes bang.



They call me CSI John.

First it was the common problem back in the day with turntables where they don't turn off (shorted cap over the arm microswitch) or they make a loud pop through the system (open suppression cap) was where I first saw it. Virtually every vintage table had a bad Rifa (or other similar style) brand cap from all the major manufacturers. Then I realized they were on practically every power switch on Japanese gear made in the 70s-90s. Inside kitchen appliances, over power drill switches, even hair dryer switches.

@amirm often has some really cool details buried in his pictures and videos and I can't help myself.

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.