Impact of AC Distortion & Noise on Audio Equipment

[mac]

@amirm should try powering his AP analyzer with the PS Audio P300 to see how much the residual noise floor drops.

 

[b4nt]

Cable shield capacitive current will remain an issue.

Do you think that is an option? Maybe keeping probe cables short? https://teledynelecroy.com/doc/build-your-own-power-rail-probe-appnote

At least, I'd like to better see what is going on or not there.

 

[wjc]

@amirm
I'm looking at the AC waveform for the dimmer simulation with the Topping A90, and it doesn't look to be the same distorted waveform that you've shown earlier. Can you verify whether or not the correct input AC source was used.

 

[1audio]

I see some limitation using the B&K. Its good for lower frequency stuff and checking for sensitivity to a variety of power source issues, like dropouts etc. But its bandlimit is too low. Power lines can move significant energy up to 30 MHz, which is what PLC uses with peak currents of over 1A. And once that energy is moving though the power it also radiates. Many other household devices have broadband radiation. One of the worst I ever tested was a cheap phone charger.
I was shown years ago a prototype of an interesting gadget that injected a swept sine into the power and measured how much came through the audio. it was surprising how much did come through. The project got lost in other priorities but still is interesting. I think I have enough stuff to recreate it. However no motivation now.
Measuring and quantifying power line noise is an undertaking needing a wide band spectrum analyzer and an interface to prevent the junk on the power line from frying your expensive analyzer. There are well established standards for conducted and radiated immunity and most FCC and CE products do quite well. See the tests Amir did. However in a network of audio devices you can find chassis leakage and noise currents between the boxes that can get into the audio. Line filters may or may not help, it all depends. The old Japanese thing of flipping the polarity of the power cord does have some validity, due to this leakage issue but was always a real PITA to deal with. And even more so with grounded power cords.

 

[amirm]

Measuring and quantifying power line noise is an undertaking needing a wide band spectrum analyzer and an interface to prevent the junk on the power line from frying your expensive analyzer.

The application here is audio. I am measuring output of such devices up to 90 kHz which is way, way beyond audible limit. What possible reason would there be to measure higher frequencies?

What my analyzer can do which your wideband analyzer can't is bit depth and dynamic range. I can dig down to -170 dB and have done so with zero improvement shown from line frequency filters in the output of audio devices. You will be lucky to have any wideband analyzer go to -96 dB let alone the levels I am testing.

 

[amirm]

However in a network of audio devices you can find chassis leakage and noise currents between the boxes that can get into the audio. Line filters may or may not help, it all depends.

They don't help. Sadly many people go and buy them only to find that it does them no good. You need to use balanced interconnects to avoid ground currents to become part of the audio signal.

 

[amirm]

The old Japanese thing of flipping the polarity of the power cord does have some validity, due to this leakage issue but was always a real PITA to deal with.

I have done that many times with non-polarized two pin AC cables and switching power supply. In rare, very rare cases it makes a tiny difference. In vast majority of cases, it doesn't change a thing as the leakage and hum is due to other sources.

 

[1audio]

It's not the audio output that needs the wideband tools, it's the power line itself. And some power supplies pass the rf. through to the internal electronics which do not necessarily evidence as a simple output.
I tried to point out that products tested for FCC and CE compliance usually won't have issues.

 

[amirm]

It's not the audio output that needs the wideband tools, it's the power line itself. And some power supplies pass the rf. through to the internal electronics which do not necessarily evidence as a simple output.

Your speakers and headphones have no ability to play RF. And neither does your ear. In rare cases, RF can get demodulated but if it does, then you hear that interference. This has nothing to do with the reason people buy these devices. They buy them without any indication of problem.

I have 3 GHz spectrum analyzer. If I thought it would do some good to use it, I would. But it doesn't.

 

[KSTR]

Puh, why does this look like another fruitless discussion to me, between a nobody and a very knowledgeable real industry professional?

On topic, besides the differential RF noise signal test @1audio suggested, another nice test is applying common mode RF cross current through the device, entering at the mains/supply/USB/etc connection and leaving at the audio connector "grounds" or whatever path the RF might take. Basically the same test as done for EMC (see Ott's "Electromagnetic Compatibility Engineering" for details)... were the go/no-go criterion is not very well defined for audio devices, ususally the interference's effect is not actually measured on audio outputs but rather a subjective judgement is made: if the modulation frequency (3kHz, typically) can be actually heard in a typical use case, then fail.

And of course line filters do help if they have true 3-wire common mode impedance or at least a PE choke.

The test is also very useful at mains/audio frequencies as it quickly uncovers ground wiring/routing issues inside the device.

 

[amirm]

On topic, besides the differential RF noise signal test @1audio suggested, another nice test is applying common mode RF cross current through the device, entering at the mains/supply/USB/etc connection and leaving at the audio connector "grounds" or whatever path the RF might take. Basically the same test as done for EMC (see Ott's "Electromagnetic Compatibility Engineering" for details)... were the go/no-go criterion is not very well defined for audio devices, ususally the interference's effect is not actually measured on audio outputs but rather a subjective judgement is made: if the modulation frequency (3kHz, typically) can be actually heard in a typical use case, then fail.

There is nothing "on topic" in your post. I can't believe how much the plot is lost here. For the tenth time, audiophiles buy these products to improve fidelity of their systems thinking it improves direct fidelity of the sound they hear. They are not worrying about ground loops, audible artifacts, etc.

Just read one review of them and you hear the message loud and clear. Here is the latest one from top of Google search: https://www.stereophile.com/content/shunyata-research-everest-8000-power-conditioner-page-2

You think your EMC test has any relevance to this kind of belief?

How about this bit he says after the above:

Still think you should be examining the AC lines instead of what comes out of audio device to counter this nonsense?

Here is one from another outfit on Audioquest noise filter: https://www.theabsolutesound.com/ar...ara-7000-low-z-power-noise-dissipation-system

Expanding soundstage? Where would I read that in Henry's book?

The only way to prove or disprove such claims is to see if the waveforms coming out of an audio device have changed with modification of mains.

If you are not familiar with this market and how it uses the product under test, then stay out of the thread.

 

[Peter E]

I have not read through all 27 pages in detail so perhaps I missed someone linking to this recent review. This must be some kind of record...

https://audiobacon.net/2021/08/06/the-worlds-best-audiophile-linear-power-supplies/

 

[b4nt]

I have not read through all 27 pages in detail so perhaps I missed someone linking to this recent review. This must be some kind of record...

https://audiobacon.net/2021/08/06/the-worlds-best-audiophile-linear-power-supplies/

That link doesn't seem to point to a review, but to an ad, to pay for a review... before paying for any "audiophile" grade low noise power supply.

I see the author used a USB cable costing from $599... and an "audiophile" LAN switch costing $999. What is now wrong also with common ethernet and UDP/TCP/IP stacks?

 

[audio2design]

I have not read through all 27 pages in detail so perhaps I missed someone linking to this recent review. This must be some kind of record...

https://audiobacon.net/2021/08/06/the-worlds-best-audiophile-linear-power-supplies/

Audiobacon is a joke IMHO. I can't take anything seriously there.

 

[audio2design]

It's not the audio output that needs the wideband tools, it's the power line itself. And some power supplies pass the rf. through to the internal electronics which do not necessarily evidence as a simple output.
I tried to point out that products tested for FCC and CE compliance usually won't have issues.

1) Power supplies can pass relatively high frequencies which can and do affect internal electronics and depending on the RF modulation, can generate analog perturbances primarily through AM demodulation which can occur if the RF has AM modulation or is pulsed.

2) The effects above will absolutely have effects on the output if anything audible is happening and yes, this would be defined as a simple output.

3) FCC compliance is no guarantee of the above happening at all. Depending on the product type, if the full CE testing is done, it will be more indicative as CE standards for specific product types have considerably more susceptibility requirements that FCC does not.

 

[audio2design]

There is nothing "on topic" in your post. I can't believe how much the plot is lost here. For the tenth time, audiophiles buy these products to improve fidelity of their systems thinking it improves direct fidelity of the sound they hear. They are not worrying about ground loops, audible artifacts, etc.

One should never underestimate the excuses the audiophiles come up with (nor manufacturers) to justify the products they buy or the products they sell. Go to any audiophile subjective site and there is tons of discussions about ground loops, line noise, dedicated AC lines, power conditioners, power filters, etc. to remove things perceived to be in the output of their audio system not just for direct fidelity improvements.

 

[audio2design]

I think I should build a different probe, following that model:

I buy a pack of 5 of these for about $10 and they are made with proper stiff material. Used copper wire in a pinch, but can be a recipe for a nasty short when it buckles.

 

[NiagaraPete]

Thanks for this awesome test. You saved me from dragging a device home from my audio dealer.

 

[audio2design]

@amirm, since you’re online, any thoughts on the Cardiac Electrophysiology data and how that might translate into moving coil phono measurements?

The big difference is that in electrophysiology, they are looking at visual waveforms that are amplified. May have no bearing to what is audible if that waveform was converted into audio.

But the voltages they talk about are in the range of MC amplification…

Moving coil cartridges are very low impedance sources. They are not remotely comparable. In medical devices, you are often measuring very small voltages sources by very high impedances. It is a far more difficult situation compared to audio. Because of those very low voltages and very high impedances, triboelectric effects become real, not perceived as claimed in audio.

 

[audio2design]

here comes how main voltage looks in London city UK , outlet in home , all of these harmonics IS in your audio system .

Now put a capacitor and resistor across it, just like in any piece of equipment.