Here's another quote from an interview with Mr. Pass regarding active vs passive preamps:
AR: What's your position on passive versus active preamps?
NP: You'd think that a minimalist switch and variable resistor in a box would be as good or better than active stages, but often it is not.
Some of the issues are well understood; for instance if the resistance value of the potentiometer is low, the source can have bass issues due to the output coupling capacitance and higher distortion due to greater load current. At the other extreme, if the resistance is too high it can create distortion and high frequency issues by presenting a high source impedance to the power amp.
Then there are things that don't show up in the usual measurements and we simply observe that the active circuit sounds better than the passive.
I file these under "How About That".
http://audiophilereview.com/amps/nelson-pass-interview.html
AR: What's your position on passive versus active preamps?
NP: You'd think that a minimalist switch and variable resistor in a box would be as good or better than active stages, but often it is not.
Some of the issues are well understood; for instance if the resistance value of the potentiometer is low, the source can have bass issues due to the output coupling capacitance and higher distortion due to greater load current. At the other extreme, if the resistance is too high it can create distortion and high frequency issues by presenting a high source impedance to the power amp.
Then there are things that don't show up in the usual measurements and we simply observe that the active circuit sounds better than the passive.
I file these under "How About That".
http://audiophilereview.com/amps/nelson-pass-interview.html

