Microphone amplifying small project

[gsz]

Hey guys,

I've been having trouble trying to do an extremely simple amplification setup for a microphone hooked up to a breadboard.

I'm using a 741 op amp with basically the simplest non-inverting setup possible:

With 1 kohm for R1 and I've tried a few values for R2. But the output of the amplifier stage is just nothing when I hook the input up to the mic. The mic outputs pretty low voltages, but whether I use a lower (27 kohm) or higher (100 kohm) value for R2, nothing shows up at all.

If I use a function generator as the input, if R2 is too high I see a lot of railing or distortion in the output. The 27 kohm produced about 25X (very rough measurement) amplification so that's close to what it should be. Higher R2s don't seem to produce more than 20x amplification and that's with all the distortion.

So: theoretically, the amplification factor is 1 + R2/R1. Did I make bad choices in selecting R1 and R2? Why does the distortion occur with the function waveform generator input, and why doesn't anything output when I try connecting to the microphone?

Much thanks...it just seems theoretically, it's fine (if simple), but there must be things I am completely not considering.

 

[audioguru]

The 741 opamp is 42 years old, has too much noise and a poor high audio frequency response. Use a TL071 low noise wideband audio opamp instead.
Your opamp is not powered and its (+) input is not biased properly.

 

[gsz]

Oh - well, V+ and V- weren't a part of that picture but it's being powered by +5 and -5 V.

What do you mean by + input isn't biased correctly? Should the + and - inputs be switched? Much thanks I'll check out the other amplifier.

 

[audioguru]

Since your supply is plus and minus 5V then the opamp must be designed for such a low voltage (a 741 opamp is not designed to work with less than plus and minus 15V) and the (+) input must be biased at 0VDC.
If you switch the inputs then it will not work.