I built this mic preamp circuit for use with an electret mic.
The mic I have is this PUI AOM4544 electret mic
I have plugged this mic preamp circuit to my soundcard line in. But I think the gain is so low that I cannot hear anything. I built this to use as a measurement mic. I tried measuring the output from the mic alone without the mic preamp (supplied 3 V power to mic) using a voltmeter; I measured 0.001 V AC when I blow at the mic. Is this mic preamp circuit a wrong one to use?
That's a crappy circuit. Don't believe everything you find lying around on the internet.
For reference, here is your circuit:
The 10 kΩ pullup to power from 3 to 9 V should be good enough for most electret microphones. C1 then feeds just the AC part of the microphone voltage to the amplifier stage. That's all fine.
The problem is the poorly designed biasing for this common emitter amplifier. The transistor will be on with only a little more than the B-E drop on the collector. This leaves little room for the output to swing low.
A quick bandaid for this circuit is to add another 100 kΩ resistor from the base of Q1 to ground. That with R2 will then form a voltage divider so that the collector DC voltage should be in the 1 to 1.5 V range. That leaves some room for it to swing both ways.
Another problem with this circuit is the unpredictable gain. The gain applied to the microphone signal has a high dependency on the gain of the transistor. In good transistor circuits, everything works well with the transistor gain from some minimum specified value to infinity.
Another problem may be the rather high output impedance of this amplifier, which is about 10 kΩ. That together with the sound card input impedance forms a voltage divider. If the sound card input impedance is 600 Ω, for example, then the signal will be attenuated by over 15x when connected to the sound card.
Check that your line-in is correctly connected and that it is enabled in the sound card properties. Also check the mixer settings. Be sure you haven't plugged into the microphone input accidentally.
Use a program like Soundcard Oscilloscope to see what is really going into your soundcard. This will show you the input, and you will really notice when you speak or blow into the microphone. It also has a selector so that you can see really weak signals.
A Voltmeter usually isn't much good at detecting audio - the AC function often assumes that you will be measuring AC at 60Hz or 50Hz (depending on your local power line frequency) and doesn't really behave well when confronted with audio signals.
Once you do all of that and still don't get any signal, check the tips that @Olin Lathrop gave you in his answer.
BTW: I agree with Olin about that being a crappy circuit. You might do better to go with a better design (like this one) especially since you mention wanting to use this for meaurements.
The circuit is not so bad. You have to measure DC voltage between collector and ground. It should measure about half of power supply voltage. If not - You can change the R2 for bigger value or lower.
The gain is predictable, it is equal of R2 divided by electret microphone output impedance (electret microphone output impedance should be around 10k in this circuit) so if the bias is good - voltage gain is:
\${{100k}\over{10k}} = 10\$
