So I just got a new to me P15, I run Audio Research Reference Tube gear…I put the thing in today fired everything up and ran it in its default mode, sine wave, high regulation…I heard an immediate difference, blacker backgrounds and better imaging for sure but it sounded a bit polite or maybe a tad bit slow, dynamic but just a bit un-involving…so I switched it to low distortion mode and BAM it really popped…and I mean I have spun 10 records tonight and everything I am hearing is GOOD really GOOD…switched back to high regulation and…not as good…so what gives…I’ve read here…tubes=high regulation but I am running tubes and liking the low distortion mode by a large margin…what do others hear with the 2 different modes?? The one thing I can think of with my system is that the Audio Research gear has pretty massive power supplies all the way around…so maybe the low distortion mode works because of that???
What do you see as incoming and out going THD and voltage in each mode?
Roughly the same…voltage in LD is 117.5v/120.6v ion HR mode its 117/120.6v
THD in LD is…in 2.5% and .1% out. in HR mode it’s 2.8% and .1%
Whats interesting is before I switch on all the gear the power coming in is close to 120V.
After you switch everything on it sags to 116-118V.
Hmmm. This does not provide me with any hints.
I think its probably a preference thing…I hear more “effect” from the high regulation mode and I think a lot of people would prefer what I hear…Darker backgrounds and more specific imaging…I really liked my system before the power plant but was looking for something to keep it sounding good all day…I have to do some listening during the day when it tends to sound less dynamic and a bit dull…during the peak electricity hours…also when the HVAC system is on in the house…
What is your multi-wave setting?
In my system “High Regulation” sounds best regardless of any other settings. So I have used it continuously.
sine wave
The fact that you can hear a difference means that it’s working properly.
So just choose what works best for your system.
In my case, incoming power fluctuates quite a bit so I’ve been using High Reg for years.
I agree with the OP. I think there is too much emphasis on attaining exactly 120 volts out, when 115 (for example) is well within the standard. I would rather have a cleaner sine wave, with less harmonics, than a slightly higher peak amplitude if I understand the tradeoff correctly.
Having said that it may be possible to have the best of both worlds with low loads. Things get dicey at higher loads and something has to give.
High regulation locks in the voltage to be as consistent as possible. This could be 120 V or 117 or whatever your preference is.
I have not played with Sine vs MW lately, but I have preferred both Sine and MW6 in the past. I tried Low R. a couple times but had to change back to high after one day.
p15 is serving a 65 OLED and a set of Formation Bar/Bass since Monday, and I will play with these settings and hope they would not make any difference on Netflix 
I must say I have never seen better pictures from my OLED big screen before, and it took a day for P15 to work on its magic too (even thought it’s 3 year old🤔). I like Sine wave here also, but it could be due to lower THD I’m experiencing now.
I actually use MW because it seems to reduce transformer hum in some components a bit more. So when I said I like a clean sine wave, I meant waveform in the general sense. I don’t flip back and forth listening to the different modes but, whatever the waveform setting, lowest distortion makes the most sense to me.
Good point Elk, however I’m not too picky about the actual value as long as it’s not drastically different than the input voltage. The voltages indicated on the display are probably RMS values anyway, so their meaning changes as the shape of the waveform changes and gets cleaned up.