High impedance EH LPB

[chi_boy]

Hi All,

I'm working on a project where I need a high impedance preamp circuit, similar to the Tillman preamp. 
http://www.till.com/articles/GuitarPreamp/

But I would like to have more available output, more like an EH LPB.  Perfectly clean is NOT the overall objective, so some dirt at the high end would be good, but not required.

My question is, if I use the GGG layout: http://www.generalguitargadgets.com/pdf/ggg_cb1_sc.pdf  if I change R6 from 1.5M to either 4.7M or 10M, will I increase the input impedance?  If it is that simple, what are the other implications that I don't know enough about to ask specifically?  Would such a change significantly alter the output?

The application is for a piezo pickup.

Thank for the help,
George

[Solidhex]

Yo

  That's the pulldown resistor for pop prevention. Its the 43k you have to worry about. Why not try the AMZ  mosfet booster? 10meg input impedance and plenty of output...

--Brad

[chi_boy]

cool.  I'll check out the amz booster.  is the output similar to the LPB?

I knew that was an added pull down resistor.  When I looked at the Tillman the resistors that set the impedance looked like pull downs too.  that' what prompted the question.

-G

[petemoore]

I'll check out the amz booster.  is the output similar to the LPB?
  Output what? Yes, they both boost.
  Amplitude?, the Mosfet wins.
  Cleanli-ness?, wins again.
  Sounds like an LPB?, mosfet doesn't really do that.

[chi_boy]

Why not try the AMZ  mosfet booster? 10meg input impedance and plenty of output...

--Brad

Brad,

Took a better look at the AMZ and it looks like it will do quite nicely for my project.  Since the LPB is such a simple circuit, I'm going to experiment with that resistor and see what it does.  I may try on the other side of the input cap.  Time to get out the bread board.

Thanks again for the tip,

George