I assume from your question that the active crossover does not provide a means of independently adjusting the amplitudes of its high frequency and low frequency outputs.
I'm a little confused, though, by the reference to the 100 ohm output impedance of the preamp. Is the active crossover function provided within the preamp, or is the active crossover a separate component that is connected between the preamp and the power amps? In the latter case, of course, the output impedance of the crossover (not the preamp) would be what is relevant with respect to the input impedance of the power amp.
Re question 1: 200K is undoubtedly already so high in relation to the output impedance of what is driving that input that removing it will have essentially no effect on gain.
Re questions 2 and 3: Can you describe the circuit more fully? Am I correct in understanding that the 20K resistor and the 500 nF capacitor are in series with each other and with one of the inputs of the op amp (as opposed to one end of the resistor being connected to ground)? If so, would that be the inverting (-) or non-inverting (+) input of the op amp? And what other resistors are connected to each of the inputs of the op amp, and what is the value of the resistor in its feedback loop?
Finally, although there are some exceptions, very few line-level output stages in consumer audio equipment can drive 100 ohms (or anything close to being that low) with good results. Although depending on the answers to my questions about the circuit configuration, changing the 20K resistor to 100 ohms may result in an input impedance that is very different than 100 ohms.
Regards,
-- Al
I'm a little confused, though, by the reference to the 100 ohm output impedance of the preamp. Is the active crossover function provided within the preamp, or is the active crossover a separate component that is connected between the preamp and the power amps? In the latter case, of course, the output impedance of the crossover (not the preamp) would be what is relevant with respect to the input impedance of the power amp.
Re question 1: 200K is undoubtedly already so high in relation to the output impedance of what is driving that input that removing it will have essentially no effect on gain.
Re questions 2 and 3: Can you describe the circuit more fully? Am I correct in understanding that the 20K resistor and the 500 nF capacitor are in series with each other and with one of the inputs of the op amp (as opposed to one end of the resistor being connected to ground)? If so, would that be the inverting (-) or non-inverting (+) input of the op amp? And what other resistors are connected to each of the inputs of the op amp, and what is the value of the resistor in its feedback loop?
Finally, although there are some exceptions, very few line-level output stages in consumer audio equipment can drive 100 ohms (or anything close to being that low) with good results. Although depending on the answers to my questions about the circuit configuration, changing the 20K resistor to 100 ohms may result in an input impedance that is very different than 100 ohms.
Regards,
-- Al