How do you go about calculating Zout for a phono stage?

[andyr]

EDIT: actually, I should have said "calculating or measuring the Zout".

Can anybody tell me how I go about finding out what the output impedance of my JFET-based phono stage is? It has a BC547 as the output buffer, if that is relevant.

Thanks,

Andy

 

[Mark Kelly]

Measuring is easy: put a largish known resistor in series between the output of the stage and the output of a signal generator. Short the input of the stage, turn the signal generator up enough to get say 1 mA across your known resistor and measure the voltage to ground at the output (of the stage, not the generator). The output Z is the residual voltage at the stage output divided by the resistor current.

Calculating is easy if you post the schematic.

 

[andyr]

Thanks, Mark, I'll email you the schematic this evening.

Regards,

Andy