Impact of AC Distortion & Noise on Audio Equipment

[b4nt]

@pma Anyway, this is now nicer so, and much more close to @audio2design expectations. Using 90°, the mains input current of that DUT PSU was definitively different. Did the DUT fail? No.

And anyone shall know that the real life problems will arise connecting together several boxes, which each individually succeeded in lab tests. A known issue of EMI compability. In our setups, first problem could be caused by a PC, as a source, and a USB port; I wouldn't fix that with a mains conditionner; many fix that using Toslink.

Man, I was hoping to get more work done but seems this is the fastest path to stop the theorizing. So I set everything back up and set the dimmer emulation to 90 degrees. Here is the AC waveform coming out BK Precision 9801 now:

View attachment 147077

Distortion has now risen massively from 18% to 54%. Noting about the AC waveform looks like a sine wave. Further, RMS voltage has sunk down to 84.6 volt.

Here is our Topping A90 again *with mains AC power first*:

View attachment 147078

This is what it looks like when fed with the dimmer emulation at 90 degrees:

View attachment 147079

Nothing has changed whatsoever. Not even a hint.

As it should be. As I explained already.

 

[rdenney]

I did deliberatly use that wording. Arg as an expert, and demonstrate why I do need a Niagara 1200.

Others will buy such conditionners considering it really improves their audio. Many will wonder, I'm also, and are waiting to know how such a conditionner could improve an audio system.

Before you can ask whether there is an improvement, you must ascertain that there is a deficiency.

There are specific cases where power-line transients, hum, and noise cause problems, and when those problems appear, there are strategies for correcting them. Those symptoms and strategies warrant discussion.

But I completely agree with Amir that power line conditioner sold to make general improvements in audio in the absence of those specific problems is a waste of money. One has to provide an explanation that makes sense to engineers as to how noisy power can cause any general diminishment of audio quality plus test data to show the effects on general audio-quality measurements outside the realm of those specific and obvious problems. Chasing some subtle improvement in (fill-in-the-blank-attribute of sound that is long on adjectives and short on evidence) by buying a power-line conditioner will have, at best, a placebo effect.

And I also agree that most of those other problems can be solved using low-cost strategies, because it's usually a bad connection, a bad ground, or a ground loop. Sometimes, it's a poor power supply in the equipment, but that can't be fixed except by replacement. Correcting a poor power supply with an external conditioner is like correcting the lack of effective coatings on a lens by putting a clear filter on the front.

Rick "who runs heavy copper strips as a grounding bus in his amateur radio shack--that stuff is often working at signal levels in the noise floor for weak-signal work" Denney

 

[rdenney]

You are one of not too many who knows what he speaks about. Mains IMD is usual especially in power amplifiers with poor PSR (power supply rejection ratio). As this amp below runs in bridged mode, basic 50Hz and multiples are well suppressed. But not the IMD products.

View attachment 147090

P.S.: it is not any "jitter" as we sometimes read here as a wrong explanation.

The problem isn't power leaking into audio--that's just bad design. The problem is power deficiencies (that may be filtered out upstream using a conditioner) causing the leak. In the case you illustrate, the power causing the problem you note can be a pristine sine wave with power-line distortion of 0.001%, and you'll still see those intermod distortion products. No power conditioner can fix it--only a better power supply can.

But even with the example you showed, will you hear those intermod products that are at -90 dB FS? If so, your ears are better than mine. Now, the harmonic distortion of that amp, which seems to peak around -40ish dB for the third harmonic, is clearly audible and also really dreadful. The power-line intermod isn't causing that harmonic distortion, though you can see power-line intermod around the audio distortion products. I wonder if a person hearing those obvious audio distortions, and reading something about the power-line intermod of that amp, would think that this poor amp could be improved with a conditioner. One would hope not, because it won't work even to resolve the intermod, let alone resolve the amp's poor audio distortion performance.

I agree that testing a product with a bad amp and a good power supply isn't as interesting in the original article as would be testing a good amp with a poor power supply, but that is a separate discussion, already in the record.

Rick "hmmmmmmm" Denney

 

[b4nt]

But I completely agree with Amir that power line conditioner sold to make general improvements in audio in the absence of those specific problems is a waste of money. One has to provide an explanation that makes sense to engineers as to how noisy power can cause any general diminishment of audio quality plus test data to show the effects on general audio-quality measurements outside the realm of those specific and obvious problems. Chasing some subtle improvement in (fill-in-the-blank-attribute of sound that is long on adjectives and short on evidence) by buying a power-line conditioner will have, at best, a placebo effect.

@Peter E had noticed that link, as a "kind of record": https://audiobacon.net/2021/08/06/the-worlds-best-audiophile-linear-power-supplies/

@pma @audio2design There are several spheres, one will not appreciate at all the latest test Amir has run, feeding a DAC with 220V "dimmed", now at up to 90°. And yes, engineers will complain because this isn't that much representative of what happens in our setups. But that last test with 90° can be representative of a poor AC with noises at its peaks.

Another sphere will still wonder how such a conditionner could improve the sound stage... or which benefits some get from.

And I also agree that most of those other problems can be solved using low-cost strategies, because it's usually a bad connection, a bad ground, or a ground loop.

I agree with that, in most cases, the problem will need a diagnostic, and could be addressed using a basic/cheap solution.

 

[Pdxwayne]

Again, I am asking this question:

Is testing a single device at a time with just 1khz tone adequate?

 

[b4nt]

Again, I am asking this question:

Is testing a single device at a time with just 1khz tone adequate?

You have to start with something. Your DUT being so connected to mains (or to 5V source), to an audio source and to a recorder/ADC. It is an environment for the DUT also.

Problem is that the environment of the same DUT in a setup will be different. If something is wrong in this setup, the DUT or the setup will fail. How do you want to ensure a DUT will work correctly in any sort of setup? Your explanations will be welcome

 

[Pdxwayne]

You have to start with something. Your DUT being so connected to mains (or to 5V source), to an audio source and to a recorder/ADC. It is an environment for the DUT also.

Problem is that the environment of the same DUT in a setup will be different. If something is wrong in this setup, the DUT or the setup will fail. How do you want to ensure a DUT will work correctly in any sort of setup? Your explanations will be welcome

We don't listen to DAC alone (we can't anyway. ) playing 1khz tone.

At least, for single item test, do the whole suite of tests, like Amir typically does when evaluating a new DAC, not just 1khz. I would like to know about multitones results, etc.

Once we are satisfied a single item is good, move on to next item in the typical audio chain, one by one.

Then, measure the whole chain, like normal people listen to music. For example, with TV, AVR, amps, preamp, players, subs, etc, all working in the same circuit.
: P

 

[b4nt]

We don't listen to DAC alone (we can't anyway. ) playing 1khz tone.

At least, for single item test, do the whole suite of tests, like Amir typically does when evaluating a new DAC, not just 1khz. I would like to know about multitones results, etc.

Once we are satisfied a single item is good, move on to next item in the typical audio chain, one by one.

Then, measure the whole chain, like normal people listen to music. For example, with TV, AVR, amps, preamp, players, subs, etc, all working in the same circuit.
: P

Ah Ok... That 90° test has mainly stressed the PSU of the DAC. If that first 1k test had shown no diff, it means the PSU did his job. Other tests shall succeed exact the same.

What is a typical audio chain? All of us have up to very different sources and amps. PC, Pi, Pi3, Pi4, laptop, Mac, ChromeCast, streamers of any brands...

Testing some full chains, listening, then conclude a conditionner or any low noise PSU impacts/improves the sound stage or the hights? That is the ground of non technicals, promoting or using up to very expensive power cords, and so.

 

[audio2design]

Again, I am asking this question:

Is testing a single device at a time with just 1khz tone adequate?

No obviously.

 

[b4nt]

No obviously.

But I beleive this is the way devices are tested for CE/EMC compliance. Individually tested and stresssed in a known environment.

 

[Pdxwayne]

Ah Ok... That 90° test has mainly stressed the PSU of the DAC. If that first 1k test had shown no diff, it means the PSU did his job. Other tests shall succeed exact the same.

What is a typical audio chain? All of us have up to very different sources and amps. PC, Pi, Pi3, Pi4, laptop, Mac, ChromeCast, streamers of any brands...

Testing some full chains, listening, then conclude a conditionner or any low noise PSU impacts/improves the sound stage or the hights? That is the ground of non technicals, promoting or using up to very expensive power cords, and so.

Still want to see more measurements to convince me. 1khz alone for me is not enough. I am not asking for a lot, just Amir's typical suite of tests.
: P

Also, the whole chain is not a DAC. I am sure Amir can setup something that kind of representative of a typical chain.

 

[audio2design]

The problem isn't power leaking into audio--that's just bad design. The problem is power deficiencies (that may be filtered out upstream using a conditioner) causing the leak. In the case you illustrate, the power causing the problem you note can be a pristine sine wave with power-line distortion of 0.001%, and you'll still see those intermod distortion products. No power conditioner can fix it--only a better power supply can.

But even with the example you showed, will you hear those intermod products that are at -90 dB FS? If so, your ears are better than mine. Now, the harmonic distortion of that amp, which seems to peak around -40ish dB for the third harmonic, is clearly audible and also really dreadful. The power-line intermod isn't causing that harmonic distortion, though you can see power-line intermod around the audio distortion products. I wonder if a person hearing those obvious audio distortions, and reading something about the power-line intermod of that amp, would think that this poor amp could be improved with a conditioner. One would hope not, because it won't work even to resolve the intermod, let alone resolve the amp's poor audio distortion performance.

I agree that testing a product with a bad amp and a good power supply isn't as interesting in the original article as would be testing a good amp with a poor power supply, but that is a separate discussion, already in the record.

Rick "hmmmmmmm" Denney

Bad design, or cost limitations of an architecture chosen for euphonic purposes chosen to satisfy a target market?

In the case PMA posted, the test signal is 1KHz. It would be more appropriate to sweep usually at 1KHz, PSRR is pretty good. Where you can get anomalies is with an IM test.

Single stage switching supplies without PFC normally have pretty good loop bandwidth so it is not surprising they would reject frequencies into the several KHz range. It is like having a linear regulator after a capacitor bank in a linear supply (which amplifiers normally do not).

Then again, this is just low frequency power harmonics, not mid-high frequency noise injection (which also have to occur on neutral-ground for full testing). Nor is it a full system test with a range of connected equipment which is often where noise manifests. Probably want to throw things in there like a turntable and a phono stage (lower level signals) whether you like vinyl or not. Many audiophiles do.

Is the external noise filter the best way to solve the issue if you have one? No, not if you know what you are doing. How many audiophiles know what they are doing? In the total market, that would be a small number. But you can't claim it does not solve an issue until such time as you actually manifest the issue and test it.

 

[b4nt]

Still want to see more measurements to convince me. 1khz alone for me is not enough. I am not asking for a lot, just Amir's typical suite of tests.
: P

You will stress again Amir

@pma @audio2design Years ago, I tested xDSL modems. We didn't go outside to test modems in every and all fields and environments conditions. We followed a standardized test suite, in labs. https://www.lanpark.eu/tests-adsl-tr-067

Edit... Dec 11, 2002, DSL tops 30 million lines worldwide https://www.networkworld.com/article/2338824/dsl-tops-30-million-lines-worldwide.html

Edit... TR067 of December 2004 seems to be here: https://www.broadband-forum.org/download/TR-067.pdf

 

[b4nt]

Then again, this is just low frequency power harmonics, not mid-high frequency noise injection (which also have to occur on neutral-ground for full testing). Nor is it a full system test with a range of connected equipment which is often where noise manifests. Probably want to throw things in there like a turntable and a phono stage (lower level signals) whether you like vinyl or not. Many audiophiles do.

See what I had added at around #404

This wasn't the tests Amir was willing to do. Now he did more, with the 90° test.

 

[b4nt]

You created a heavily distorted VOLTAGE waveform that would make almost no difference to the far more important current waveform. Essentially you created a waveform that did not do anything in a real world system.

I am understanding just fine thank you. I am not the one defending the indefensible. The test with the simulated dimmer waveform did not accomplish anything. Your claim of high distorted waveform is misleading as the current waveform, the one that matters, would be barely impacted.

People make fun of people who post subjective listening results but here you are expecting respect for and defending a highly flawed test as opposed to understanding the flaw and accepting the mistake.

Of course I know nothing about the impact and measurement of AC line noise in electronic systems. The $15-20K in AC sources in my personal lab is just for show.

View attachment 147069

That 90° test now being representative of what you could run in your own lab, using your Chroma 61501.

Does your own box feature more? Edit... may be with an AWG.

 

[rdenney]

Bad design, or cost limitations of an architecture chosen for euphonic purposes chosen to satisfy a target market?

Doesn't matter--nobody's going to hear it, and if they did, then there is no solution but to buy something better.

Being bad on purpose doesn't mean it isn't bad. I don't think even the euphonic-distortion crowd would be happy with the >1% THD that I see on that plot, but in any case, the manufacturers of those products probably claim far better. Power-line intermod that's 50 dB below that doesn't seem the worst sin there.

An otherwise transparent amp with that same crappy power supply and resulting intermod would report a distortion peak of -90 dB, which actually isn't bad. But it would report that in all of Amir's test cases of clean(ish) power, distorted power, and dirty power. The intermod is baked in, for better or worse, not the product of crappy supplied power.

Rick "not interested in noise above about 24 KHz" Denney

 

[DeepSpace57]

@amirm, thank you again for an informative review.

I have actually long waited for an objective review of Loxjie P20 by you. I know it was on your shelf for a couple of years. Many people having this little amp lean towards buying a power supply with high current, and they claim its sound somehow improves. I even watched someone using a 15V adapter ( the given one is 12V/1.67A) says an absolute improvement. I believe this guy from the ASR community sticks to this forum rather than the other subjective forums.

I am just curious about when you will perform a test for this popular Loxjie P20.

 

[amirm]

Again, I am asking this question:

Is testing a single device at a time with just 1khz tone adequate?

I tested three devices, not one. In previous reviews of such products I have tested others. Not a hint of improvement is shown.

The test is also not dependent on 1 Khz. A full spectrum of device output is shown allowing you to see any noise or AC components to be seen. Nothing like that was seen or even hinted at.

I just wasted time running one more test that people insisted would show a difference but didn't. I can't keep chasing ghosts here.

 

[b4nt]

I even watched someone using a 15V adapter ( the given one is 12V/1.67A) says an absolute improvement.

Does he still have +115V with a 15V adapter? The box features two valves, their filaments probably being powered in serie. At 15V, this could be up to 7V5 per filament, too much...

That is probably a different aspect. Depending of the adapter one uses, he may get out more or less better or different sound. This being reasonable tweaks using cheap solutions, to get out the best. As long as the bundle dosn't cost much more.

Power section inside that unit seems basic. But the Loxjie P20 may feature 0.02% to 0.006% ?

 

[Pdxwayne]

I tested three devices, not one. In previous reviews of such products I have tested others. Not a hint of improvement is shown.

The test is also not dependent on 1 Khz. A full spectrum of device output is shown allowing you to see any noise or AC components to be seen. Nothing like that was seen or even hinted at.

I just wasted time running one more test that people insisted would show a difference but didn't. I can't keep chasing ghosts here.

Amir, my point was you tested "one device at a time", not that you only tested one device.

All my living room equipments, including the amps and subs, are connected to my power conditioners. I would love it if you can do a "whole chain" comparison vs "one at a time" comparison.