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Most electret mic preamp circuits are similar. Maybe a more expensive opamp can be used for less hiss.do you know any other good preamp for Electret MICs(half duplex)?
A digital teleconference system does not have the 4-wire-to 2-wire converter used for a telephone line so the only feedback will be long distance feedback. A half-duplex circuit is separate from a mic preamp. Motorola (Freescale) make some half duplex speakerphone ICs that work better than most cheap speakerphones. I made a pretty good voice-switching speakerphone with a Motorola IC about 29 years ago.I am using ready-made DM368 processor based board, which have audio input & output port. I want to use audio in (MIC) for conference.
My preamp circuit has a gain of 215 times when the 470k trimpot is turned to maximum. That is plenty of gain. If you want more gain then increase the 470k to 2.2M and/or reduce the 2.2k to 470 ohms. With more gain then you will have more background noise and more electronic noise. Two preamps each with a gain of 215 times makes a total gain of 46,225 times which is stupid.I was asking, if I use same two preamp ckt(based on TL071) i.e. output of one preamp connect input to another preamp. I think noise more boost up as compare to signal.
The preamp cannot drive an impedance less than 10000 ohms. But a speaker is only 8 ohms so it must be driven by a power amplifier. The preamp drives the power amplifier.When I am using this preamp ckt with PC (giving external 9V) for audio recording, Its able to record high quality audio. Why different behavior with speaker?