@almarg
The actual reason that Pass amps reach the 1% clipping threshold JA uses so far beyond their rating is because Nelson likes to build big power supplies that deliver a gratuity of voltage. He discussed this strategy in his 2016 BA lecture (selected topics on FET push-pull output stages) where he explains the F5 topology and the parts he used in the XA25, which is basically an F5 with a buffer stage to drive the IXSYS outputs. They have a high gate capacitance which is probably why it has the trouble you describe in the treble region with low impedance loads.
The actual reason that Pass amps reach the 1% clipping threshold JA uses so far beyond their rating is because Nelson likes to build big power supplies that deliver a gratuity of voltage. He discussed this strategy in his 2016 BA lecture (selected topics on FET push-pull output stages) where he explains the F5 topology and the parts he used in the XA25, which is basically an F5 with a buffer stage to drive the IXSYS outputs. They have a high gate capacitance which is probably why it has the trouble you describe in the treble region with low impedance loads.
