[sdiy] Log amplifier circuits

[Harry Bissell]

Hello all. Playing with LTspice I used a ln (natural logarithm) math function and it worked
well for me. I tried to make a log amp using a diode or transdiode configuration, but the dynamic
range is much more limited than the math function was.

I tried to play around with the input resistor value (more of less current into the log amp) but that
didn't have much effect.  It seems like the values are limited to voltage ranges right around the
forward drop of the diode(s) or transistors.  

anyone have any ideas or circuit references for me to look at ?

tia

H^) harry