Mike amplifier design

[dr.power]

Sorry Guru, It is hard for me to understand the reason....

Ok plz can you tel me the best way to adjust the mike volume?
Thanks

 

[dr.power]

Sorry I got another important question.
I just noticed that finding a non polarity 10uF cap for blocking the DC in the pic of the post #11 is hard, Can I just incrase the Ri and Rf of each stage by factor of say 10 (use Ri=10k and Rf=250k) so that reduce the 10uF coupling caps to say 1uF? is there any problem ANYWHERE in the circuit by doing so? What if using Ri=100 and Rf=2500k?

 

[audioguru]

can you tel me the best way to adjust the mike volume?

Simply add a volume control to the input like this:

 

[audioguru]

I just noticed that finding a non polarity 10uF cap for blocking the DC in the pic of the post #11 is hard, Can I just incrase the Ri and Rf of each stage by factor of say 10 (use Ri=10k and Rf=250k) so that reduce the 10uF coupling caps to say 1uF? is there any problem ANYWHERE in the circuit by doing so? What if using Ri=100k and Rf=2500k?

If you increase the resistor values then stray capacitance will cut high frequencies, especially on a breadboard that has stray capacitance between all the rows of contacts and between all the wires. High resistor values cause thermal noise (hiss).

In North America, Digikey and many more sell non-polarized electrolytic capacitors or you can make our own by connecting two polarized ones (with the value doubled) back-to-back.

 

[Nigel Goodwin]

Sorry I got another important question.
I just noticed that finding a non polarity 10uF cap for blocking the DC in the pic of the post #11 is hard, Can I just incrase the Ri and Rf of each stage by factor of say 10 (use Ri=10k and Rf=250k) so that reduce the 10uF coupling caps to say 1uF?

You can either arrange your circuit so polarised capacitors are fine, or (as you suggested) arrange your circuit to use smaller capacitors (1K input impedance seems a really poor choice anyway).