I am testing a simple circuit in which an electret mic is hooked up to two transistor preamps, then to an 8ohm speaker. I am using a 9v battery, and the circuit looks like this. This circuit is meant to be simple enough to teach to kids at school.
I have followed it exactly, and it works… somewhat. As soon as I plug in power, a low noise comes from the speaker. When I try to speak into the mic, the sound changes, but you can't actually hear works. Just change in volumes/sound change. I really want a "megaphone" like circuit, without the excess noise and clear amplification.
please note I prefer this transistor amp over a lm386 chip for this particular project as it is for use in a school
What issues could be causing the excess noise?
Edit
Made purpose clearer.
Best Answer
As others have mentioned, that is not a very good circuit. Alas, we can't expect that just because we found it on the internet it will be a decent design. I wold use a circuit more like this one.
Source: http://www.circuitstoday.com/transistor-intercom-circuit
This is billed as an "intercom circuit". But it is a good example of a circuit with sufficient stages of gain to take an electret microphone signal and boost it up to speaker level. The switch (S2) will create a tone to signal the other end of the intercom. You can omit S2 and C3 if you aren't using it for an intercom.