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Feb. 1st, 2019 09:43 am![[personal profile]](https://www.dreamwidth.org/img/silk/identity/user.png){kind=small}
stormdogI've spent hours on this circuit and cannot figure it out.
It ought to be really simple, right? Nine volt positive rail is the source voltage for an LM386 audio amplifier chip. An AC signal is introduced at TP2. That signal goes through a 100Ω resistor, then is coupled through a small cap to a 50kΩ pot that serves as a voltage divider to ground. The attenuated signal goes through another cap (Why 2? I don't quite understand. Posi said it's for tuning the circuit.) to the non-inverting input of the amplifier. The amplifier's inverting input is tied to ground.
The lowest my frequency generator seems to go is about 2 volts peak-to-peak, so that's what I'm introducing at TP2. Probing the input line after the caps with my scope shows that they are stripping out the DC offset from the generator so it's just a sine(ish) wave centered on 0 volts. But my VOM says that the LM386 puts out 15 volts AC no matter how I set the pot. The speaker makes a low hum when I first turn the circuit on, and if I raise the volume (the pot voltage divider) even just a little bit, it gets really loud.
The pot should be able to attenuate the input signal from 2 volts PtoP down to basically 0. Stupid thing. More troubleshooting to do. Maybe I connected something wrong.
It ought to be really simple, right? Nine volt positive rail is the source voltage for an LM386 audio amplifier chip. An AC signal is introduced at TP2. That signal goes through a 100Ω resistor, then is coupled through a small cap to a 50kΩ pot that serves as a voltage divider to ground. The attenuated signal goes through another cap (Why 2? I don't quite understand. Posi said it's for tuning the circuit.) to the non-inverting input of the amplifier. The amplifier's inverting input is tied to ground.
The lowest my frequency generator seems to go is about 2 volts peak-to-peak, so that's what I'm introducing at TP2. Probing the input line after the caps with my scope shows that they are stripping out the DC offset from the generator so it's just a sine(ish) wave centered on 0 volts. But my VOM says that the LM386 puts out 15 volts AC no matter how I set the pot. The speaker makes a low hum when I first turn the circuit on, and if I raise the volume (the pot voltage divider) even just a little bit, it gets really loud.
The pot should be able to attenuate the input signal from 2 volts PtoP down to basically 0. Stupid thing. More troubleshooting to do. Maybe I connected something wrong.
