Electrical THD does not matter?

A stereo repair tech told me THD under 2% is inaudible through quality components. I know PS Audio lowers it to .1. Is this true or wrong information? Please only answer if you know about this. Thank you

A Stereo Repair tech who has never heard how a clean power source like a Power Plant can affect the audible performance of a high quality system can do. A P10 made an astonishing improvement in the performance of my system. Beware of deaf scientists!

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I said only answer if you know! He has used a variac to introduce noise and measured the output from various components with a scope This is exactly why many passive units work fine as well. The P10 made differences in your system for other reasons. Mainly holding the voltage constant. Your post answered my question, none. I am glad you are happy with it.

Based on what I have read, the conventional wisdom is that THD becomes imperceptible at less than 0.1%. However one man’s imperceptible is another man’s totally unacceptable, and you are talking to a predominantly audiophile community here, who are concerned with the tiniest nuances of sound!


I would probably reverse it a little. The better and more resolving equipment you have, more there is to be heard. THD value is not specific about distortion characteristic or type, therefore that 2% does not tell anything, because some distortion is more audible than the other.

Yes, that is why I asked PSA if they measure high frequency THD. They said they do not. They would be shooting themselves in the foot. A P20 sounds very good but the THD deal is a little misleading. It is not of so much importance really under 2% across the board. What is important is a sinewave with no flat or chopped tops and consistent voltage. That is what it is doing that we hear. Everything in your home adds noise. Your wall could be 15% or more THD. Even on dedicated runs. They are still bonded at the same junction. PSA may chime in but I believe THD wide spectrum under 2% is fine. They might only be measuring 20HZ-20KHZ. In MHZ and GHZ it is much higher obviously. This will affect digital equipment over 2%. However, I doubt the P20 is above 2% in those ranges even though they have not measured it. There are much more important things it is doing. That is what we are hearing from it. .1% THD at low frequency may in fact make a difference but anything that filters noise will do that. I should have phrased that differently. Wide spectrum. I assure you the P20 is not .1% in GHZ range but I bet it is in fact under 2% which is fine. I would like to know what frequency range the screen display is measuring though. To sweep in GHZ is more expensive than the P20 itself anyways. A top Agilent oscilloscope may run 100 Grand or more. Also, the better the equipment is the better power supplies it probably has! So often it is dealing with it on it’s own anyways. This is why amps in the wall may sound better than the P20 in some instances but certainly not digital front ends. If the p12 employed what the P20 has I would simply use it on digital equipment. The P20 is still better though. Just kind of a waste depending on how you look at it. Although they do not make a smaller unit with the better technology. So be it. I got Two P20’s to plug in amps but ended up using a different type of passive power conditioning for them. Me, buying Two of them was kind of a waste in fact to me in retrospect. It is all good though. No, I am not selling off one of them.

You are right, we don’t know these details from PSA. We also don’t know the resolution of power plants, as in, how sensitive they are. As an example, they may only be able to sample and correct up to 1ms (1khz) in mains voltage, any noise above that would just pass through, and these figures may indeed not be included in THD calculation. There is, however, undeniably a benefit of power plants, in my view, PSA engineers done a tremendous job making something that works well with most audio products out there. It is an incredibly difficult task to suit every one as there aren’t 2 systems that sound same…

From screenshots of PPs, where difference is displayed, these look quite choppy suggesting the resolution is low, but this is only screen data. The actual resolution where it matters could be a lot higher.

Of course we measure full range and know exactly what a P20 is doing. You’re correct that the P20
itself does not measure that high on its analyzer because there’s no information relevant to its purpose above about 1kHz. I don’t mean to imply there’s no reason to worry about high frequency noise components on the AC line. It’s just that
stating it on the front panel scope on the P20 misses the point of why the scope and THD analyzer are there in the first place.

We put the scope and THD analyzer on Power Plants to demonstrate how they perform a task power conditioners do not. Fixing the problem of AC power that matters most. As 2chan4ever suggests, the repair of the flat top waveform by replacing the
missing energy is the first job of the Power Plant and the massive lowering of impedance through tight dynamic voltage regulation is the second.

AC line repair and dynamic regulation are the two key elements we all need in delivering power to our equipment. Only a Power Plant can do this under even the most strenuous of conditions requiring upwards of 70 amp peak delivery. Power conditioners
of any kind do not do this and only make these two critical conditions worse.

We added the THD analyzer and scope to counter the silly false marketing claims Richard Gray’s power company were making at the time (when they were in business). They were supposedly using a “flywheel effect” to add missing energy back into the
line and “fixing” the power. The device they used was a large parallel inductor that had a tiny amount of stored energy that was captured on the sine wave’s upswing and released on its way back to the zero crossing point. Not only was this meaningless in the
best sense of the word but we felt it was dishonest.

Claims were made that the RG device lowered distortion, fixed AC problems, etc. And RGPC weren’t the only ones (and still aren’t). We felt this was something we needed to expose, so we designed a scope and THD analyzer on the front of our Power
Plants (which actually did fix the problems). When the AC sine wave out of the wall is flat topped or distorted in shape we can say it has higher THD. Dealers and customers who had been fed this pole of crap could plug the Power Plant into the wall and measure
what was happening. Then, it’s a simple matter to plug the Power Plant into the RGPC and compare how much the sine wave was “improved” by their flywheel effect.


That’s why we added it and why we still encourage people to have a look.


Try a direct comparison on a highly resolving system and you will find a variac or passive components will degrade the sound not enhance it. The P-10 not only improves the sound by it’s low source impedance and regulation but also by lowering the THD by multiples of 10. I trust my ears more the i do some guru with test equipment!

Thank you MR. McGowan.
Sixpack1, that was the whole idea behind the testing. for the variac to make it worse and then measure what could correct it. He is correct that only the PP can do this. there is no other product out that does AFAIK.

You’re welcome and while I appreciate the kindness, I feel uncomfortable being referred to by Mr. McGowan. :neutral_face: I prefer Paul if that’s alright

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How about “Sweet Polly Purebred”? Underdog references really show my age. Sorry I couldn’t resist.

I see I am also the only one that calls Ted, Mr. Smith. I suppose Ted is okay. too. I am past middle age. I just feel it is respectful to people I do not personally know. You folks are really down to earth. I appreciate that. I did not mean to make you feel uncomfortable! how many companies is the CEO speaking with his customers! In fact you folks are awesome!

BTW, A while ago a company in Illinois bought out Richard Gray. Pretty poor investment if you ask me! You can also plug a Transparent product in the PP and the THD is much higher. I think I was correct though that THD measures higher at higher frequencies? I figure as long as it is a true complete sinewave and voltage is steady it is taken care of. Regardless of scope on there? I think that is pretty much what you said?

are we talking EVEN HARMONIC or ODD HARMONIC Distortion?..BIG difference

I am embarrassed to say I do not even know the difference! I do not know a lot of electric/electronic stuff. I do know what sounds good to me. However, that may not sound good to many others either.

I just pulled a Torus out of a “little” very high end system. By little, I mean it does not draw more than 3 amps. I just replaced it with a P12. OMG the difference! PSA is killing it over here! It went from dull and lifeless to full of zazz. I know, not audiophile terms to boot. You get the idea. It does not hum like my taxed P20’s either. Very happy I got it. I was afraid it would hum. With almost no load I guess not.

Although when I plugged it in, it said “BP volt out of range, shutting down”. Went through this several times. Scratched my bald head. Turns out there was a short in a high end power cable. Other “conditioners” did not even recognize it. Could of got hurt or fire! PS Audio not only saves your sound, it saves your life! Luckily that power cord has a lifetime warranty.

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When I posted I had failed to realise that the OP was referring to the THD of the electrical supply, and my response was about amplifier distortion. I agree with you that the acceptability of some forms of distortion varies. Low even harmonics, particularly second order, are considered by some an enhancement, hence the popularity of SET amps. High order, especially odd, harmonics are not generally liked. THD alone will not tell how well an amp sounds to you.

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one of the main reasons i prefer horn speakers is because the projecting sound waves are more predominantly Even harmonics… Even harmonics can have globs of distortion and not pay much attention to it…but, even a very small sampling of Odd h.d. is fatiguing…

i also tweaked all the resonance of the horn itself down to 2hz…wow, what a difference. (removes the ringing/coloring/smearing because of the resonating horn structure)