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Hello everybody

I have a difficulty. On the attahced .jpg file one can see 2 symbols of an opamp. But one opamp has 2+ instead of 1+ and 1-. Does this means that the oparational amplifier is used as not as an non inverting amplifier.?? Also how can I make it without any gain??

Also when I have to build this circuit, those amplifiers have to have no gain. so for the normal non inverting opamps, I do not do the feedback resistors??
??? ??? ???
Thanks for your help and patience

post-9454-1427914326232_thumb.jpg

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1) The microphones have a very low level so each one needs a preamplifier. The preamplifiers have very low output impedances so the value of the 10M resistors is way too high. Replace the 10M resistors with 10k.
2) Very few good opamps work with a supply voltage of only + and -2.5V. Use + and -10V.
3) The old 741 opamp is noisy and has a bandwidth to only 9kHz at full output. Use an audio opamp like the TL071 that is low noise and has a bandwidth to 100kHz.

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Opamps don't work properly without negative feedback.
Look at the datasheet for the opamp. Without a negative feedback resistor, the voltage gain is 1,000,000 at DC and at low frequencies, then the output would be saturated against a supply rail due to the opamp amplifying its own input offset voltage.

With line level input levels then the voltage gain must be reduced to about 1 with negative feedback.

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