|Rick Erickson||Re: opamp imp ques.|
If I understand the original post correctly the cap is a DC blocking cap which will roll off LOW frequencies. It is most definately needed in a single ended supply type circuit since the output will have a dc offset of 1/2 the supply voltage. If you want to control the output volume of this circuit I would advise putting the pot in the feedback loop. If that isn't a workable solution a 10K pot would work well on the output of most any op-amp. The output impedance of this circuit is the combination of the series resistance of the pot to wiper + the series resistor (100 ohms) + the internal impedance of the op-amp,(usually not significant)+ the capacitive reactance of the capacitor combined with the parallel resistance of the pot wiper to ground. For most general calculations you can ignore the capacitor & IC output impedance.
"The power supply type has no relation to the need for that cap. It's just there to roll off highs in your output."