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Antonio J. wrote:

I suspect the APS does more or less the same that my friend proposed. It probably has a class D amp which makes some kind of PWM with a so so smoothing circuit, hence the tooth saw trace of the voltage line, some PS which probably is a switching one feeding a battery charger, and an oscillator tuned to produce a 60Hz wave with the amount of signal required for the 120V output. Its problems may come from a not so good D-amp that distorts the signal when load increases. Why? I don't know, I'm no technician, I ignore how a switching or battery power supply interacts with a digital amp when the load increases. Maybe a traditional PS were a better approach.

Actually, would be the Class AB or Class D implementation is VERY loaded question. I have some ideas on the subject but I need a properly operating Class D implementation (APS) to make any further comments. Looking what APS does now against a poorly resistive load it obviously something is screwy with my current unit. Richard from APS claims that his tests units under the same conditions behave (at least measured) very different. He told that he will be sending me data but he never did so far.  I do not know if they want to replace my unit or perhaps to find a way to fix it… Let see what happens. I know that if they replace my unit them I will implore them to test it before they send it out.

Antonio J. wrote:

This would be a very affordable DIY option, but regarded from the mains net isolation perspective, maybe the AC generator and electric engine makes more sense.

Yes, it should not be complicated D-amp DIY option but it is not the direction that I would like to go. I usually go for the self-implementation if the alternative off-the-shelf options are not good. All that would be necessary is to find a D-amp that can swing 120V… Still, the result that I get from the PurePower unit I presume is not the result that they intended to demonstrate: the APS guy told me that I am the only one person among their customers who differentiated the quality of sound with loading of the unit…  Well, I presume that I am probably also the only person among their customers whose APS unit can not hold a normal sinusoid shape without a load or into a resistive load :-) …

Anyhow, let see what a new day will bring…

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