Given a system that has 4-5VDC on the microphone line, I've made a preamp from three components that amplifies a signal from about 10mV to over 2v. Surely there is distortion, but it's a motorcycle intercom and intelligible speech with a reasonable amount of fidelity is fine.
My question is this: Even one or two other components would be ok if they improved it.
The basic circuit is a common emitter BC548 or similar, a feedback resistor (1M) from collector the base, and the mic feeds base and common, and the output is collector-emitter. The mic lines have DC voltage to power the preamp, and the transistor simply puts an analogous AC signal on top of the DC power.
I had some base-common and collector-base 1pF caps on there to stabilize it, but the ckt performs the same with or without as far as I can tell.
Suggestions? I'll post a 5Spice diagram if anyone is interested.
Ed
My question is this: Even one or two other components would be ok if they improved it.
The basic circuit is a common emitter BC548 or similar, a feedback resistor (1M) from collector the base, and the mic feeds base and common, and the output is collector-emitter. The mic lines have DC voltage to power the preamp, and the transistor simply puts an analogous AC signal on top of the DC power.
I had some base-common and collector-base 1pF caps on there to stabilize it, but the ckt performs the same with or without as far as I can tell.
Suggestions? I'll post a 5Spice diagram if anyone is interested.
Ed