Last weekend and the weekend before, I have been trying very hard to get a good small 8 ohm speaker amp with a preamp for a dynamic mic to work with no luck. It seems like every design I try has problems like this weird oscillation I got changing pitch if I touched different wires.
I even half-broke my left output from my iPod with one design It now will not play music quiet (scratchy sound), but oddly works above 80% audio level to the output jack. I will have to try to build an external POT volume control I guess :( .
So I have a dynamic mic , or a telephone pickup coil. How can I amplify this with the least distortion, and highest efficiency to drive an 8 ohm small speaker with a volume adequate enough to hear in a semi-quiet room (maybe a small fan running) up to 8 feet away from the human ear.
I also have one more question:
How can you learn from experience if you can't identify the problem and just hope the circuit works the next time you attemt to build it.