So the question is which way should a unipolar decoupling capacitor(normal aluminium electrolytic) be mounted for electret microphone with bias supply voltage?
positive on the opamp side:
https://www.electronics-lab.com/project/low-noise-mini-electret-microphone-preamplifier/
http://www.minidisc.org/mic_preamp/Simple Stereo Electret Mic Preamp.htm
Positive on the mic side:
https://www.eleccircuit.com/pre-mic-audio-amplifier-with-ic-lm386/
https://lowvoltage.wordpress.com/2011/05/15/lm386-mic-amp/
https://www.epanorama.net/circuits/microphone_powering.html
It amazes me that there are schematics on the internet with the decoupling capacitor mounted either way. What is the justification of those schematics? My quess is there there is no justification and a bipolar capacitor should always be used. Why? well lets consider two scenarios:
1. The microphone is disconnected or its power consumption is very low. The voltage on the microphone side of the cap is equal to supply voltage and the voltage on opamp side is half the supply voltage- So positive terminal should be on Mic side right?
2. The microphone consumes a lot of bias supply current, this means the voltage drop on bias supply resistor (i.e R1 here) is high and the voltage on the Mic positive terminal is fairly low (could be 1/4 of supply voltage). The voltage on opamp side is again about half the supply voltage so the positive terminal should be on the opamp side right?
So either case can be true and if you have detachable microphone, each of these cases can occur during normal use and thus damage the capacitor.
Any thoughts?
positive on the opamp side:
https://www.electronics-lab.com/project/low-noise-mini-electret-microphone-preamplifier/
http://www.minidisc.org/mic_preamp/Simple Stereo Electret Mic Preamp.htm
Positive on the mic side:
https://www.eleccircuit.com/pre-mic-audio-amplifier-with-ic-lm386/
https://lowvoltage.wordpress.com/2011/05/15/lm386-mic-amp/
https://www.epanorama.net/circuits/microphone_powering.html
It amazes me that there are schematics on the internet with the decoupling capacitor mounted either way. What is the justification of those schematics? My quess is there there is no justification and a bipolar capacitor should always be used. Why? well lets consider two scenarios:
1. The microphone is disconnected or its power consumption is very low. The voltage on the microphone side of the cap is equal to supply voltage and the voltage on opamp side is half the supply voltage- So positive terminal should be on Mic side right?
2. The microphone consumes a lot of bias supply current, this means the voltage drop on bias supply resistor (i.e R1 here) is high and the voltage on the Mic positive terminal is fairly low (could be 1/4 of supply voltage). The voltage on opamp side is again about half the supply voltage so the positive terminal should be on the opamp side right?
So either case can be true and if you have detachable microphone, each of these cases can occur during normal use and thus damage the capacitor.
Any thoughts?
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