Impact of AC Distortion & Noise on Audio Equipment

[amirm]

Depends upon what you mean by measurements. The PS sensitivity of Class A and low feedback amplifiers is amplifier design 101, flip open say Douglas Self on the subject and you will find a significant body of work discussing the issues and designs. It stems from pretty basic circuit theory. Obviously the individual amplifier implementation will vary, and how good the PS is will vary dramatically. This is why you see regulated PS in some class A amplifiers.

I know about sensitivity to voltage, ripple and such but not harmonic and noise content of AC.

 

[Vini darko]

Hi Amir thanks for this test very intresting. Good to see the ps audio regenerator atcually does it's job (I had doubts).

The biggest problems I encounter with mains using linear supplies are. DC offset causing mechanical noise and heat in transformers and spikes on the line causing pops from transducers. Switch mode supplies simply dont care so far as I tell about any horrors on the AC line.

Is it possible to use the fun new test instrument to add DC offset to the AC mains signal?

 

[amirm]

Is it possible to use the fun new test instrument to add DC offset to the AC mains signal?

I don't have any ready instrumentation that generates AC+DC at mains voltages. As I noted in the post above, if there is DC and your equipment is sensitive to it, I see no issue with buying products to solve them. That is not the reason people buy these things.

 

[Mrgoogle]

 

[Francis Vaughan]

There are designs directly feed AC voltage to the heater in the tube right? I think those can obviously show some difference. But again those designs are probably not good ideas to begin with.

That is an interesting one. A common trick it to elevate the heater supply relative to the cathode, which seems to significantly lower the effect. But indeed, heater coupling is a real thing. YOu get amusing arguments in the tube guitar amp forums where the purists will tell you that a regulated DC heater supply is both unnecessary and the work of Satan. A bit of AC on the sound is considered as part of the vintage sound, and some digital amplifier modellers even add it, and even add AC related intermodulation products.

Anyway, for audiophile stuff, it is likely a limitation, but starting from a low base.

All your gear I suspect would provide a useful exemplar of high quality performance that is not effected by noise and for which a noise conditioner is useless.

 

[amirm]

I tested the one from EquiTech and it failed to produce any improvements: https://www.audiosciencereview.com/...s/equitech-1-5rq-balanced-power-review.24948/

 

[Francis Vaughan]

Almost everyone buys these things to add to their systems even though they have not detected any audible problems with their system.

Which things? I know I'm being pedantic, but I didn't think this article was about power filters or conditioners. I though it was about gear that had problems with AC distortion and noise. If the intent is to prove that all power conditioners are a waste of time, perhaps the title should be modified to reflect that. But the entire first post you made had no mention of this goal. I honestly thought it was about the sensitivity of gear to AC distortion and noise, not about the value or efficacy of power conditioners

 

[voodooless]

I never said it did.

I know, it was more meant as a general observation to emphasize the point.

Right now we have learned that two cruddy tube amps are rubbish with both clean and distorted power feeds. That is a data point, but hardly a conclusion that leads us to believe that all devices are immune from mains power supply noise, or in what manner they are sensitive.

Sure, they are just data points. And I'm also sure there are examples to be found of devices that do have issues with bad AC. But this only strengthens what I said:

Stating the fact that there might be examples that exhibit this problem, doesn't justify them, nor the devices that pretend to fix these issues

 

[magicscreen]

But... but I can hear the difference!

You should do a double blind-test.
Yesterday my CD player sounded better than my DAC. The DAC played the same track ripped from the CD.
Today morning I did a blind test.
I can randomly choose a source on my amplifier using the remote controller.
So I listened the first track and it sounded badly. Yes, I was sure this was then the DAC.
But it was the CD!
For me during blind tests everything always sounds bad.
Why is this? Is digital audio basically inferior quality? And does the blind test show that fact?

 

[amirm]

Which things? I know I'm being pedantic, but I didn't think this article was about power filters or conditioners. I though it was about gear that had problems with AC distortion and noise.

It was both. I showed that very clean AC makes no difference and neither does ultra dirty. As such it encompasses the full gamut of AC filters/conditioners to regenerators.

 

[Francis Vaughan]

I too own a ferro-resonant transformer (SOLA) ex-server room gear

Ha! Guess what brand mine is. Local brand, so not a surprise. Sits in the cellar and has not moved from there in a very long time. I keep wondering whether I should just get the scrap copper value of it. Sentiment rather than logic keeps it safe.

 

[pma]

It was both. I showed that very clean AC makes no difference and neither does ultra dirty. As such it encompasses the full gamut of AC filters/conditioners to regenerators.

You would have to test the complete audio chain (not only a single component as you always do) and see the effect of the conditioners that have transformer isolated outlet plug for low-power device like DAC or pre. Thus it interrupts the galvanic signal groundloop in case of all-class I components.

 

[Mrgoogle]

I tested the one from EquiTech and it failed to produce any improvements: https://www.audiosciencereview.com/...s/equitech-1-5rq-balanced-power-review.24948/

that you test it , it is not Tours transformer , Tours has special winding . they use old patented old school to get rid of both common mode noise and differential noise , reason for big transformer is transient power handling and low main frequency !

 

[Francis Vaughan]

It was both. I showed that very clean AC makes no difference and neither does ultra dirty. As such it encompasses the full gamut of AC filters/conditioners to regenerators.

Sure. But if you close it off at just power conditioners, I feel a bit disappointed. I would really like to explore the questions involving poorly designed (and often boutique) gear. It isn't just total junk like the tube amps you tested that matter. I suspect there really are some awful boutique and high end products that are significantly compromised by AC issues. Whether there are filters or conditioners that can provide enough filtering to fix them is another matter.

The woo surrounding things like zero feedback, class A, all manner of stupid overpriced weirdness. There should be rich pickings to discover the range of incompetence out there. There may also be some outlier otherwise good gear that is compromised.

The admonition not to go out and purchase line conditioners is good. But it isn't the end of the story.

Heck, you could add feeding bad AC to devices to your usual arsenal of testing. If it proves valueless stop again, but given some of the woo products that cross your desk along with the competent ones, I suspect that you might find yet more reasons to award headless panthers.

 

[restorer-john]

It was both. I showed that very clean AC makes no difference and neither does ultra dirty. As such it encompasses the full gamut of AC filters/conditioners to regenerators.

With the utmost respect Amir, it appears you are prosecuting a line of reasoning and laying out tests and investigations to lead yourself to a preconceived position. So, no, you are no remotely covering "the full gamut of AC filters/conditioners to regenerators"

I know 1050Hz aberrations on the mains waveform. I can hear them everyday (and night). And
a) they make it through to reproduced audio on many (not all), of my own amplifiers of all different pedigrees, brands and costs. They are all conventional transformer based Class A or A/B designs. And
b) how an inexpensive (relatively) filter can remove the effects of those line related anomalies completely.

So I am 100% confident, as are the thousands of people who buy similar filters, that distortion on the mains (which ripple control is) can be ameliorated by passive and frequency specific filtering. You cannot throw all mains filters in the snake oil basket.

For our state these guys make a specific filter:
https://www.gayrad.com.au/ripple_control_or_off_peak.html

 

[amirm]

You would have to test the complete audio chain (not only a single component as you always do) and see the effect of the conditioners that have transformer isolated outlet plug for low-power device like DAC or pre. Thus it interrupts the galvanic signal groundloop in case of all-class I components.

Not a reason vast majority of people buy these products.

 

[restorer-john]

Not a reason vast majority of people buy these products.

That is true. I have to admit that most people are looking for a tweak, not a solution to a problem.

 

[Lorenzo74]

This is an ASR research project to see what impact AC noise and distortion has on performance of audio equipment. I have been wanting to write this article some three years ago and finally getting a chance to do the testing and release it.

As you will see, the heart of this study is a special instrument: the BK Precision 9801 Lab AC programmable generator:
View attachment 145395

With this machine I can generate a wide range of AC voltages, frequency and as you will see, distorted AC waveform. It is a massive box despite its smallish front. It goes way back and has a noisy fan to keep it cool. Heat is generated because this is basically a high-voltage audio amplifier. The audio source is a computer generated waveform but the rest is not much different than amplifier other than being above to generate hundreds of volts (which causes a lot more heat generated). The 9801 is rated at 300 volt-amps. There are higher power AC generators but they get massive in size and weight.

I also have a PS Audio P300 AC regenerator. It is even larger and heavier than the 9801 because it doesn't use a fan. It is much more limited though as you can only change the frequency. I will show its performance but to keep this project manageable, I am only going to show its spectrum.

General Test Protocol
I am going to show you the performance of three different audio products. Each will be powered by generic AC coming out of the wall, then by 9801 AC generator with and without distortion. Each one of these three modes has massively different AC spectrum of noise and distortion. If there is something to AC power making a difference in audio equipment, we will see it.

There are a lot of large dashboard shots here so you may want to review this article on a computer or a tablet. Maybe hard to read them using a phone.

PS Audio P300 and BK Precision 9801 AC Quality Measurements
Let's start as usual with analyzing the spectrum of noise and distortion of AC on my workbench. The source is a 20 amp feed going to a very stout power strip in my equipment rack that powers my workstation, Audio Precision Analyzer, and audio equipment being tested. A shared supply like this helps a bit to keep ground currents lower. Here is what AC looks like from my last review a couple of nights back:

View attachment 145396

We see our mains peak at 60 Hz which is delivering the bulk of the power. With it though we see harmonics of it and noise going all the way up to 90 kHz bandwidth of the measurements. Total distortion+noise is 1.9% and that is enough to visibly distort the waveform where the tops of it no longer look like a nice sine wave. Here is what it looks like with PS Audio P300:

View attachment 145397

Much nicer now. The sine wave looks like a sine wave now. SINAD as a measure of noise+distorion jumps massively from 34 dB to 61 dB. Second harmonic is down to -65 dB which is what mostly determines that figure.

Now let's examine the spectrum of BK Precision 9801:

View attachment 145398

Our sine wave is pure as before. SINAD is improved to 65 dB due to second harmonic dropping a few dBs. There is however mid-frequency noise that is higher than PS Audio P300. Overall, this shows that the P300 is doing its job to produce very clean power.

By the way, I am using a high voltage differential probe to sample the AC power. It divides the voltage by 100. That probe itself has some distortion. I measured that it and it is at or below 0.01%. So it is not making hardly any contribution to the numbers and waveforms you see above. I did not capture its output by it only has a tiny second harmonic spike and nothing else. So our instrumentation is much better than what we are measuring as it should be.

As I noted in the introduction, the BK Precision 9801 has a special feature to create distorted waveforms. What it can do is simulate what comes out of a light dimmer which chops off parts of the AC waveform. This causes the duty cycle to lower and with, produce lower power to the light bulb. I can adjust the amount of "dimming" by degree. Here is what the AC wavform looks like when I set that to 35 degrees (just a random number I picked):

View attachment 145399

Let's agree this is the mother of all dirty AC feeds! Due to step response in the AC waveform, we create infinite harmonics which you can see as a spray in our FFT graph. SINAD has dropped to just 15 dB and THD+N has shot up to 18%. Surely if our audio equipment cares about quality of the AC power, it should produce far lower performance using this type of AC feed. Let's see if this is the case.

Audio Equipment AC Impact Measurements
Let's stay with state of the art audio device because anyone searching for AC mains tweaks is surely also investing in the best audio gear they can. And at any rate, I never see any company advertising that their AC filters/regens are for poor performing audio equipment. Let's start with generic AC coming out of the wall:

View attachment 145400

Superlative performance as we have seen. Distortion is down to -128 dB in the form of third harmonic. Now let' switch to running it on our 9801 lab AV regenerator:

View attachment 145401

No difference at all. We expected this from prior testing of AC cleaners and such. But now let's subject it to the "torture" test of dimmer simulation in 9801 with its 18% THD+N:

View attachment 145402

Not a difference. Zilch. Nada. Clearly the A90 is filtering the AC mains well enough that even a highly distorted AC waveform doesn't bother it.

So people say that maybe a "low quality" audio device cares. Hard to know what this device would be. I looked around and found this old California Audio Labs Sigma tube DAC I had bought in an auction as a donation to our local audiophile society. Let's first run it with generic AC again:

View attachment 145403

Looks like we found our low performing device! It is actually not bad for a tube device but certainly miles different than what we like to see around here.

Let's switch to BK Precision 9801 and see if performance improves:

View attachment 145404

Nothing of note. The tiny bit of variation is due to vagaries of this tube product.

I was just about to switch the 9801 to dimmer mode and the DAC went crazy with its noise floor jumping way up and then down. I played with a bit but could not get it to be stable. So I had to abandon it at this point.

I looked around and found a Loxjie P20 tube headphone amplifier I had bought last year but never tested. Here is how it does with generic AC:

View attachment 145406

We definitely have a distortion factory here. Let's feed this one clean power to see if it makes a difference:
View attachment 145407

Nothing. Everything from distortion to mains hum and general noise remains the same. But maybe the torture test of dimmer simulation does it:

View attachment 145408

Nope! Tiny variations are native to the device. There is no trace of this device caring one bit about quality of the AC mains input.

Conclusions
Up until now we have tested a number of devices that reduce AC noise/distortion only to find them do nothing for the output of audio products. In this little research project, we went the other way, producing very dirty AC feed. Yet three devices from very different origins show zero, and I mean zero, dependency on AC quality. You could argue that we got unlucky with three devices not being sensitive but hard to make a case that they simply did not care.

Of course the explanation is clear: all of these devices first convert mains power to DC and then use it. DC by definition means no variation so filtering is used to remove noise and distortion. Sure, some remains but the rest of the circuit also has immunity to power supply vagaries. By the time we look at at the output of the audio product, we are so, so far away removed from AC that its "fidelity" makes no difference.

With both engineering knowledge and objective measurements backing each other, the conclusion that you don't need to worry about quality of your AC mains is exceptionally strong. This is in the context of fidelity of course where vast majority of these audio tweaks are sold.

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As always, questions, comments, recommendations, etc. are welcome.

Any donations are much appreciated using: https://www.audiosciencereview.com/forum/index.php?threads/how-to-support-audio-science-review.8150/

Another landmark to wipeout audiopholeries and smoke sellers.
I’m wondering how respectable Hifi magazines still review “subjectively” such products.
What about companies that praise the quality of their AC cleaners?
Should we avoid them while selecting any AMP-DAC?
Is Advertising AC cleaners a lack of engineering knowledge proof?

My Best to all
L

 

[wwenze]

I have this Torus Power , it is day and night , it filter both common mode noise and differential noise , watch following, it is based on old patent from Valve tube radio time . Amir measure differential mode noise , what about common mode noise ?!

Ok, there's a question with regards to that statement

Common-mode noise as referenced to what?

If we assume the context of making the FCC happy, then yes, the definition of common-mode noise is clear.

But in the context of common-mode noise showing up on our speakers, things are more complicated. Technically speaking, your 2-pin floating equipment are all at common-mode voltage of half-AC, but you don't hear any noise. Because the whole equipment is floated together, the common-mode voltage is the same between them, even if it is actually 50VAC w.r.t. safety earth. So, no noise.

A proper EMI filter would be at least a pi filter, meaning a shunt component on both sides of the series component. In other words, low impedance to ground, high impedance to mains wiring. This brings the common mode of this equipment closer to earth and makes the FCC happy. (The sharp-eyed would notice I did not consider primary side vs secondary side, but let's just put that aside for now.) But what happens when you connect this equipment to another equipment without such a filter? Will it be better or worse? To know, then we start considering the common-mode voltage before vs after the connection, and hence the ground currents. Not simple and never universal.

 

[amirm]

I know 1050Hz aberrations on the mains waveform. I can hear them everyday (and night).

Once more: 99% of the people buying these products cannot identify any audible problems like this. If someone did, sure, buy whatever and if it solves your problem, good for you.

Hang around any high-end forum and you clearly see why people buy them. They get them, plug them in, and all of a sudden veil is removed. Backgrounds are darker, microdynamics improved, etc., etc. Stuff like this review of Niagara 1200 from AudioQuest:

http://v2.stereotimes.com/post/audioquest--niagara-1200-power-conditioner/

This is what you are hearing, is it?

Or this: https://www.audiophilia.com/reviews/2020/2/14/audioquest-niagara-1200-power-conditioner

Are you having "layering" problems with your stereo that such devices solve? Let's pray not....