Impact of AC Distortion & Noise on Audio Equipment

[Raindog123]

Yeah, I've used regenerators on really sensitive lab equipment before. It's pretty rare, but now and then it makes sense for really critical measurements

We’ve tried using lab power-regenerators too — in attempt to improve noise measurements of super-sensitive SQUIDs (superconducting quantum interference devices)… Tried and abandoned, as we did not see any real improvement. (Running our experiments late at night — when the RF background is quieter — did help somewhat though! )

 

[H-713]

That caliber of test gear requires a strong metal workbench. Tack on another $2000.00+ for the workbench/table. Actually how large is this thing...lol. Might need a pallet.

Probably rackmount, if I had to guess, and probably 4U or bigger.

 

[Rja4000]

Everything should carry over just the same to 240 volt/50 Hz.

I'm personnaly sure it does.
But who do you aim this review to ?
You want to demonstrate to "believers", don't you ?

 

[GXAlan]

@amirm
1) what about turntables which have AC motors? LP's have poor measurements relative to digital, but would there be a measurable degradation?

2) what about amplifiers? I know you said most line conditioners don't handle it, but look

PowerPlant 12 – PS Audio
1250W

https://www.accuphase.com/technical_information/ps-1230_230v-type_technical_information.pdf
80AMPS!

 

[Rja4000]

With a conventional linear power supply yes the power supply output voltage will be reduced. With a PWM/switched mode power supply the drive IC will compensate and drive a bit harder to make up for the reduction in AC mains voltage or even a reduced DC supply if there is a external DC supply.

Of course, we don't know any of those AC "filters" that would do anything about low frequency changes...

 

[Doodski]

Probably rackmount, if I had to guess, and probably 4U or bigger.

It appears to be a 3U with lotsa fans. 17.3” x 5.2” x 21.1” (439 x 131.4 x 535.7 mm)
I just love test gear. I had a full time mechatronics job but I hung around a test gear shop till I was given a part time job. Then I progressed to buy gear from them.

 

[H-713]

@amirm
1) what about turntables which have AC motors? LP's have poor measurements relative to digital, but would there be a measurable degradation?

I would think that the mass of the moving parts in a turntable would provide sufficient filtering that it wouldn't matter in this regard.

The one thing that occurs to me is that the noise from really messy AC power coming in could be an issue for electronics located near that AC motor. I almost never deal with turntables, so this would be a good question for somebody else.

 

[wwenze]

Oooooh yeeeeea, that's one dirty AC.

BTW did we miss a chance to see how much those power conditioners can clean that up, or does it not matter anymore.

One day if I get the chance I plan to measure the AC before and after the power transformer (without the rectifier connected) just to see the frequency response - It's probably pretty low bandwidth. Then measure the frequency response with the rectifier and capacitors connected. That would give us the transfer function of the power supply, or should we call that isolation / rejection. So that would be enough proof that our power supply can attenuate any noise we throw at it.

This set up would be part of another investigation tho - To see how those pesky voltage spikes from inductive loads somehow make themselves audible.

 

[H-713]

It appears to be a 3U with lotsa fans. 17.3” x 5.2” x 21.1” (439 x 131.4 x 535.7 mm)
I just love test gear. I had a full time mechatronics job but I hung around a test gear shop till I was given a part time job. Then I progressed to buy gear from them.

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Alright, so it's a little big... but I just had to move a Sorensen 40V 300A power supply out of a rack, and so suddenly all of these little 3U 100 pound boxes seem cute and small to me.

Really, 3U is a nice manageable size. The 5U and 6U rackmount jobs are a lot less fun to deal with.

 

[Frank Dernie]

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.

Splendid, exactly as one would expect, or at least hope, from a properly engineered mains driven product.

 

[Frank Dernie]

You failed to improperly implement a null test to show an erroneous difference.

Still, this ought to about do it for AC conditioning as a fidelity enhancer.

Ought to yes, but it won't will it, for the "true believer" based on previous experience...?

 

[Jas0_0]

Before discovering ASR, I would often look for advice on other subjectivist forums. It seems that all the items of kit that have been shown by Amir not to make any difference are the same items of kit that would kick off massive ranty threads about whether they made a difference or not. Stuff that does make a difference - e.g. speakers - never seemed to spark much debate. I don’t go on those forums any more, but if I did, I’d now know that if people are arguing fiercely about whether or not something makes a difference, it doesn’t.

People are strange.

Thanks Amir!

 

[wwenze]

A bit of thought experiment:

A full amplitude fully square wave with infinitely fast slew rate would be a good source of distortion

But that is actually the ideal waveform for our AC-DC power supplies. Not counting the amount of complaints the transformer would have when seeing this kind of waveform. But hey, UPS produces this kind of waveform, so we know it works.

Which means any waveform that is in-between pure sine and a pure square would make zero difference.

 

[Chrise36]

Is there a chance you can measure any of the different types of ups for powering small devices like dacs and headphone amps?

 

[Francis Vaughan]

You have seen any measurements to indicate such?

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.

You mention amplifier. Most people won't run their amplifiers through such boxes. They don't have the power capability usually so they are reserved for source devices, and preamps.

Well I would hardly expect any audiophile to own a BK Precision 9801. (Why would they deliberatly add distortion to the input power anyway.) But it does appear it can deliver up to 300VA, so running a medium sized power amplifier should not be beyond it capabilities. If you are measuring the "Impact of AC Distortion & Noise on Audio Equipment" I would have thought power amplifiers are part of your remit. As we have seen, there are plenty of high power devices that claim to filter AC. I own a ferroressonant filter that is rated to 2kVA and is able to deliver squeaky clean power. Used it in a server room to protect sensitive equipment. Never thought about using it on my audio system, but it isn't as if these devices are not about.

The reality of the impact is the purpose of the study is it not? Not the capability of after market filter devices to fix the problem. So we want to understand the impact. See if there is a problem that needs fixed. If a device is already so busted it cannot be fixed, it isn't going to be a useful device for discussing the impact of AC distortion and noise. You need to test a range of devices, not just the low ball junk.

 

[uwotm8]

Of course the explanation is clear: all of these devices first convert mains power to DC and then use it

Excuse me but 3 out of 3 use PWM power supply units; why not to check some with "analogue" linear PSUs?

 

[GWolfman]

Here is what it looks like with PS Audio P300:

@amirm Why is the output only ~1/2 what it should be (compared to the other two devices)? It's still 120VAC, right?

 

[JohnYang1997]

Excuse me but 3 out of 3 use PWM power supply units; why not to check some with "analogue" linear PSUs?

It's basically the same. The best mains noise filter is the rectifier with the large capacitors. The biggest noise as DC supply is what? It's the 50/60hz mains frequency residuals.

 

[DualTriode]

Hello,

I have breadboarded many tube amplifiers. Most often to test tubes to determine the sweet spot for volts and bias current vs noise and distortion. I have done the same for JFET amplifiers.

Some circuits are much more sensitive to mains hum buzz and power line harmonics than other amplifier topologies that have a higher Power Supply Rejection Ratio.

I tend to think that the amplifier should be designed with a power supply that is capable of filtering out all that power line supply noise.

Some tube amplifiers are better than others. Some tube amplifier designs scrimp on DC filtering.

Power conditioners may offer some help for an amplifier with a not so good power supply.

If you think about it, the amplifier power supply may be its’ own worst enemy in terms of rectifier switching spikes and poor L C R type filtering or even DC regulators.

Switching power supplies are often problematic for systems with a large proportion of computer, lighting power supplies and variable speed controlled fans and pump motors. Power Factor will vary with load. All the noise and distortion will show up on the neutral conductor and even on the safety ground. Many engineers and facility owner will require isolated power for sensitive critical equipment.

There are salesmen that will attempt to sell you a solution that you do not really need.

Startup testing and commissioning is always worthwhile to verify that the system performs as specified.

Thanks DT

Yesterday, on I80 West near Davis Ca, I saw a truck mounted test load bank that filled a flatbed semi trailer.

 

[Ata]

But... but I can hear the difference! sorry could not resist