[SOLVED] Microphone Op Amp Schematic not working

[notawizard]

Hello edaboard forum,

I'm very new to electronics, so please keep that in mind. What i am trying to do is to measure input from my microphone (this one:

) using an Op Amp.

I am using this schematic:

But it does not work, i only get 3.5V on the output and it does not change when i talk into the microphone at all. Hopefully you can find the mistake i am making so i can understand it better.

Thanks in advance!

-notawizard

 

[betwixt]

You have problems but you are on the right track:

1. If the microphone is a dynamic one, you need to add a coupling capacitor in series with the 1K resistor. Dynamic microphones conduct current and will pull the voltage across them toward ground. As the amplifier is inverting, this might account for the outout voltage going higher.

2. If the microphone is an electret one (most are these days) you need to provide it with a load resistor. Try connecting a capacitor (100nF will do) in series with the 1K resistor and also adding a 10K resistor from the microphone output to the 5V line.

Brian.

 

[LvW]

Notawizard - as far as I can see you provide positive feedback through the two 10k resistors. (instead of biasing for single supply operation).
Please, check again.

 

[Audioguru]

I looked in Google for details about the KONIG CMP-MIC3 microphone and it is sold for a low price in millions of languages but has no details. Nobody knows if it uses 3 wires like on its plug or if it is dynamic, electret or any other type of mic. It is not on Konig's website anymore.

A dynamic mic might be balanced with the signals at the tip and ring and the sleeve of the plug is the ground and the shield of the cable.

A 2-wires electret mic has its tip and ring connections shorted together and they are the signal output that need a resistor to a positive voltage as a drain load for the Jfet inside. The output must have a series coupling capacitor to feed the preamp that should be non-inverting for a high input impedance and have a gain of 100 to 200 times.

A 3-wires electret mic has the ring as the positive voltage to the drain of the Jfet. The tip is the output and is the source of the Jfet and needs a resistor to ground.
The output also needs a series coupling capacitor and a non-inverting preamp with high gain.

The sleeve is the ground and the shield of the cable.

 

[betwixt]

I completely missed the op-amp inputs being swapped over. :|
Must be having a bad day - I'll get my psychiatrist to increase my medication. :lol:

Brian.

 

[notawizard]

Adding capacitor and resistor solved the problem and i can now read values from the microphone in my arduino. thanks for the help guys!