[sdiy] buffer opamp configuration [was: 1/8th inch questions]

[Grant Richter]

>> Unity gain (non-inverting) buffers can be problematic since opamps are
> less stable at unity gain, especially when driving capacitive loads.  There
> seem to be two common configurations to give stability:
>> (a) Put a capacitor and resistor in series between the opamp inputs, and a
> larger resistor in series with the input signal
>> (b) Put a capacitor and resistor in series between the opamp inputs, and a
> larger resistor in the feedback loop.
>> Note that both these ways increase the AC noise gain, and decrease the
> buffer bandwidth.
> 
> Method (b) is normally used to compensate a pole that comes from the opamp's
> *input* capacitance. It's always recommended if you have large feedback
> resistors.


Which is why you see a 5 pf cap across every feedback resistor in the LM318
data sheet.