Op-Amp example with audio in going to Amp out


#1

I am working on designing an op-amp audio amplifier with digital audio level control and using the project http://fritzing.org/projects/op-amp-audio-amplifier as my template. The template shows that the audio jack for audio in the left channel is connected to the output of that Op-amp, whose positive input comes from the high end of the Pot (using DS1809), and the right channel in goes to + of the other Op-Amp and it’s output going into the low end of the pot, and the wiper going to the speaker.

Why is the left plugged into an Op-Amp output and why connect anything to the high end of the pot?

I attached an organized version of the above link with the digital pot but before I add the bandpass filter.

Audio Amplifier Align.fzz (27.7 KB)


#2

I think the basic answer is that the project you started from likely doesn’t work as shown. The original project doesn’t have schematic routed (and I am too lazy to try and route it), but looking at breadboard the op amp negative inputs are both grounded and the positive inputs connect to signals. Without feed back resistors this will act as a comparator not an amplifier. As long as the signal in is higher than ground the output will be the positive supply voltage if the input is less than ground, the output will be ground. You likely need to find a working op amp amplifier circuit (I’d suggest building it to make sure it works) and then make your changes with the digital pot. There are lots of op amp tutorials on the net.

Peter