Amplifier Input low pass filter issue ?

Hi all
I want to use 1k and 100pf for input of amp to make it a fast amp.but it needs to increase to 330pf value for not burning the zobel when touching input by finger.Is it possible to use 100pf again but with a more powerful zobel circuit? Will it burn speaker ? Thanks
 

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It may be that your amp is unstable for certain source impedances - presumably its fine open-circuit and with a low-impedance source, but the finger represents a highish reactive impedance.


I suppose it is possible you are injecting RF directly at high level by touching the amp, but that would imply you are close to an active transmitter.
 
I wouldn't expect there to be that much high power RF in a normal environment - the 100pF should be taming it anyway. Instability can be due to the input impedance being "seen" by the feedback point through the input device capacitances - it indicates the amp as a whole is too close to oscillation for comfort. Adding more input capacitance might help for this.


You know that there's no need for a fast amp to have a fast input? The high bandwidth in an amp allows more negative feedback to be available at high audio frequencies, its not so ultrasonic inputs can be amplified.