Easiest way to detect sound


Joined Dec 20, 2007
Did you mean to state that in the inverting opamp circuit in question, the (-) input of inverting opamp in your above statement was ZERO volts rather than ZERO ohms?
If the inverting opamp is operating in a linear fashion (not clipping) then its (-) input voltage will be the same voltage as its (+) input (within a few micro-volts). So if the inverting opamp has a dual-polarity supply and its (+) input is connected to ground then the resistance to ground of its (-) input is zero ohms and it will be zero volts.

In the presense of negative feedback, the output impedance of the opamp is very nearly ZERO ohms.
Yes, the open-loop output impedance is 50 ohms for some opamps. If the opamp has a DC and low frequency gain of 1 million and is linear, not clipping then its output impedance at those frequencies when its gain is 10 is 50/1 million= 0.0005 ohms.