Kalali, that’s an excellent question, and I’ve wondered the same thing myself. While I’ve seen a number of reports over the years of solid state amplifiers self-destructing as a result of having to drive cables having ultra-high capacitance, I don’t think I’ve ever seen a report of an amp being damaged from having to drive an electrostatic speaker.
But while I’m not sure how to explain that, if I were to hazard a guess I’m thinking it may be related to the presence of the step-up transformer that I believe is used at the input of nearly all ESLs. Perhaps the bandwidth limitations and/or other characteristics of the transformer cause the amp to see a load impedance that is much less capacitive at ultrasonic and RF frequencies than it is at audible frequencies, and in comparison with the impedance of a highly capacitive cable at ultrasonic and RF frequencies.
And my suspicion is that the destructive oscillations which have been reported to result from the use of high capacitance cables typically occur at ultrasonic or RF frequencies, not at audible frequencies.
Also, I believe that the few ESL designs which don’t have a step-up transformer at their input, such as some older Acoustat models, have a built-in amplifier to step up the input voltage. In those cases presumably the built-in amp provides a relatively non-capacitive input impedance.
Best regards,
-- Al
