Hi All,

I have noticed the following thing, if I put a 25k resistance between the output and ground, the gain is very close to R4 / R3.  The lower the resistance, the lower the gain...  What is the purpose of this resistance?  Is it to set the output impedance?

Thanks,
Stephane.

That resistor is actually taking some of your signal and shunting it down to ground. Like a small pot that's turned all the way up.

Hi smoguzbenjamin,

thanks for your answer.  Are there any 'sane' values for this resistance?!?!  Currently, I don't have a resistor in my buckeroo design, but I will probably include one because it effects the predictability of the gain.

Thanks,
Stephane.

This resistor makes a voltage divider together with the internal resistance of the circuit. As Smoguz said if this resistor is to low, the internal resistance takes to much of the output voltage.

The output reistance is set by the 25k resistor you use paralel to the internal resistance of the circuit. Roughly you can say Rinternal = R4

Use at least a resistor 10 times bigger as R4, but 100k will be ok there.

Hi Joep,

Thanks once again!  I will definately try the modification.  When simulating the circuit, you are right, pretty much anything above 20k gives about the same result!!!

Thanks!
Stephane.