John, I’ve noticed that apparent anomaly in the specs of the Pass .5 amps in the past, and I’m pretty certain it is a mistake in the specs, and what was intended was 20K single-ended/30K balanced.
Al, thanks for your input. I might have to contact Pass directly to get the true numbers.
I just assumed that the 30K SE/ 20K BAL was correct because of Threshold history.
Many old Threshold amps had a SE input impedance of 50Kohm while the Balanced inputs were rated at 600 ohms input impedance.
https://www.stereophile.com/content/threshold-stasis-sa12e-power-amplifier-specifications
Also, Coda amps, which were designed by 3 ex-Threshold engineers, always had very low balanced input impedances as well.
The spec sheet on the Model 15/15.5 shows an SE input impedance of 50K with a Balanced input impedance of 1K ohms.
http://coda.cc/product/index.php
So I just assumed it was something in this family design that always had the balanced input impedance lower than the unbalanced input impedance.
It does look like Nelson has addressed this flaw with the .8 series.
Cheers,
John
PS: I see in Stereophile's measurements of the XA60.5 amps they measured a 17K input impedance in both SE and BAL. Who knows which figure is right?
https://www.stereophile.com/content/pass-labs-xa605-monoblock-power-amplifier-measurements