Hi, I need to build a preamplifier for a mic to connect it to a PC soundcard. The mic I am using is a proffesional mic which uses an electret mic capsule inside. I dont need to provide phantom power also coz it operates on a 1.5V battery. Now, the plan is to build a preamp with a female jack into which I can connect the mic's output jack. I tried an instrumentation amplifier circuit which has three 741s in it.The circuit worked fine for a gain of 10. Although I could see a gain of 10 only when I put the mic real close to the speaker.As I moved it farther the mic output(amp input) and also the gain dropped.When I increased gain further, that is to 11 it worked fine too. Then I increased it further to 20. Now the output of the amplifier was zero! Then I tried to give a gain of 2 thru an additional stage(a noninverting ampliflier using 741). So that would be 2*10=20 gain...But again the output was zero. Can anybody tell me where I am going wrong???
The mic without any amplification showed an output range of 5-20 mV. The link to the schematic of the insturmentation amplifier circuit is given below: