To this end from their website:
View attachment 38198
I suspect a lot more people buying this amp for its purported "sound" then any kind of need to get into electronics hobby.
Hopefully my measurements here bring an ounce of realism to counter the above mystical claims.
Yep, that is me (Mitchba) with the quote. I wish they had included that I use them on 113 dB @ 2.83v/meter horns (ooops I mean waveguides ;-) When I bought the kits in 2012 (13 can't remember), there was not too much to choose from and my main criteria was low noise into a highly efficient compression driver/waveguide combo. As Amir measured, they are very low noise. Putting my ear right up to the waveguide I can only hear the slightest hiss.
I am quite sure, even at really loud levels, I have never exceeded 1 watt or maybe even 1/2 watt (1/4 watt? didn't do the math). At reference level (83 dB SPL) at the LP some 9ft away, to my ears, they do sound good. I have some acoustic distortion measurements around here somewhere and I think if I remember, the distortion was below 0.5% with both the amp and compression driver across the CD's bandpass. I don't hear any distortion and I have tried a variety of amps with these horns, and subjectively, these sound best to my ears.
I knew well before hand what "Papas" designs are all about and so do most people in his "camp". He uses various distortion profiles to colour the sound. It is as simple as that. If you don't like, don't buy it. The first watt F5 is perhaps the only exception and noted for it's "dry and analytical" sound, which if you look at the distortion profile, means it is a (much) lower distortion amp ;-)
@amirm if you still have the amp, it would be interesting to pop the lid and adjust the bias pot to see where the null is for the lowest distortion. After the hour warm up, it would take about 10 minutes to find the null for the lowest level distortion...
Perhaps another way to look at this is to realise that our ears are not that sensitive to distortion and is frequency dependant (i.e. even in the double digits distortion at low frequencies from loudspeakers, most cannot tell). I would love to see some blind tests where folks can determine what level of distortion can really be heard. Until then, enjoy the music.