Input voltage waveform - opinion needed

I have “new to me” P10 purchased from a dealer, demo stock.
Unit is in excellent shape and looks amazing. I connected it today , still did not loaded with any components, will do that this weekend.

Background info, i have had issues with both my PPP’s.
They click into protection occasioanlly and display high THD input values in the 6-8%.
The THD fluctuation happens randomly and ONLY for a few seconds. As if a disturbance in the AC line is inserted for a few seconds. This sends the PPP into protection. I have 2 PPP, same behaviour at same time.

Today i got a glimpse at this behaviour when it happened (i have the PPP and P10 connected ).
I got to record 3 seconds (first 3 seconds of the video) of the high THD with my phone, when the P10 was displaying the waveform on the scope.

Here it is, what do you think this is ? Why ?

Also, during these 3s i get a “buzz” in the speakers. This is what caught my attention first.
Do you think i should report a problem to my Distributor company ?

No ideas on what can be causing this ? Do you think it can be a malfunction home appliance?

What’s even more troubling is the clipped peaks when the power is supposedly “stable!” That waveform should be a smooth sine wave, not the clipped peak you’re showing us. You can report that to your power provider as a substandard power input to the house. Fix that first, then worry about the 3s transient later as they may be related (e.g., you may be on an overloaded transformer that can’t put out enough power for everyone on the circuit so when one user turns on a heavy load you get that ugly 3s transient)

Best of luck!


Your PS audio does not show a clipped peaks sine wave on the input ?
I looked at different times during the day, even when the input THD is only 1.8% the peaks are clipped.

Nope. It’s weird, it looks like there’s a Zener or equivalent component that’s preventing the waveform from reaching peak voltage. That may be how the power company prevents over-voltage by physically limiting the peaks. I’d call the power company, they got some ‘splaining’ to do!

Squashed peaks of the sine wave from the power company is what most customers will see. You are very fortunate if you are not seeing any distortion.

That is one of the main things a Power Plant corrects.

I doubt the power company would ever purposely “prevent over-voltage by physically limiting the peaks” even if they could.

I am lucky ? What are those first 3 seconds then ???

Distributor company is coming to install an 8 day period analyser.
Then they will read it and respond.

In my mind, with all respect to PSA, the power units are not test equipment, they don’t score well against oscilloscope or even simple multimeter. These displays are to entertain. How THD is measured is also not known. Take these readings with a bit of salt.

That’s as bit overstated. The scope’s real and based on a A/D converter looking right at the line or the Power Plant’s output as is the THD analyzer. If you’re unfamiliar with how a THD analyzer works I can help. A THD analyzer is essentially a metering system with a notch filter. That filter removes the fundamental frequency under scrutiny and what’s left is then measured and expressed as a percentage. So, for example, if we’re measuring a 1kHz sine wave we remove that frequency and measure the residual—what’s left over. In the case of the Power Plant we know exactly what the incoming power frequency is because we have a very precise PLL that synchs our internal low distortion oscillator to the incoming AC frequency. This then gives us the exact frequency to form our notch filter and the resulting THD is actually quite accurate and handled in real time.

Paul, many thanks for explaning, I have huge respect for engineering these devices. They do what they claim, no doubt. I was coming from perspective knowing that before mains power hit the unit, it is going through passive filtering, including passive protection via varistor in parallel. It is an altered unaccounted signal already.

Still, how come the P10 cannot filter this out ?
The output wave still is a little distorted within the few seconds window, and i still get a buzz in my speakers when this happen…

EDIT : during the 3-10 second window i get this very distorted AC input, the THD raises from 2% to 5% input and from 0.1% to 1% output.