Impedence Calculation (another one...sorry)

[sjaltenb]

http://www.muzique.com/lab/splitter.htm

Trying to figure out how to calculate the input impedence for this splitter. There are three resistors there. I really would like to learn, not just have answer..

I am looking for an input impedence of 1Mohms for this circuit....not sure what those values should be. I read the whole article but got confused...

Thanks for any help, my project is 98% done!

[Labaris]

If you have some experience in electronics try this one:

1- Kill DC supply for an "AC analysis" (instead of being connected to 9V those terminals connect them to ground). Of course not really, just for calculating.
2- Capacitors in AC are "like" just a wire, so replace them with a line in the schem.
3- A few more steps, and the use of a model of the transistor will bring you the answer. The three resistors before the transistor, in parallel, determine Zin (for both circuits, as they have the same "input structure").

[sjaltenb]

thanks for the reply!

I Thought they might all be in parallel, but I was not sure. That explains why the 10m, and 2x 2.2m (they come to ~990ohms)

Thanks!

[Mike Burgundy]

That's very low, low enough to really start loading your signal - 991k, isn't it?