Modeling the Input Impedance of an Amplifier

[dimensionless]

I'm trying to model a circuit. Part of this circuit is a guitar amplifier. I don't know what kind of circuitry is inside the guitar amp, it manufactures often list the input impedance in the product specifications.

When they say input impedance, do they mean the impedance between the signal input and the ground? Can I simply treat the input impedance as a resistor?

 

[berkeman]

When they say input impedance, do they mean the impedance between the signal input and the ground? Can I simply treat the input impedance as a resistor?

Yes. The input circuit for an input like that will generally look like a resistor for small signals.

 

[dimensionless]

Would it be correct to say that for AC signals there is negligible capacitance and negligible inductance?

 

[berkeman]

For the audio amp you mention and for audio signals, then yes, the input impedance should not present much series inductance or parallel capacitance. Otherwise, it would distort the audio signals. Well, I guess that can be a desired thing sometimes with an electric guitar...

 

[dimensionless]

Generaly there shouldn't be signal distortion, but if there is a 1dB roll off around 4KHz I'd like to know about it.

 

[berkeman]

Generaly there shouldn't be signal distortion, but if there is a 1dB roll off around 4KHz I'd like to know about it.

Well, you'll only be able to determine that by testing, or by getting the actual schematic for your simulation. You can't use "black box" specs for a detailed simulation.