The variable gain, inverting, AC coupled
single supply amplifier
I had bread-boarded about 5 to 6 amplifier circuits when I felt that a simple plug in module would simplify circuit building and idea testing. I do not have a dual polarity power supply (YET... see dual polarity power supply project) so I am often whipping together a single supply amplifier. There is a decent amount of time taken up every time I have to build one of these circuits, so I decided to make one circuit permanent. Gains are selectable by an input resistor and a feedback resistor by a jumper block. I also included a 50K pot to allow for variable gains. Since it is a single supply amplifier, I had to create a ground that was 1/2 way between VCC and GND. This required the use of input and output capacitors if I wanted to amplify a signal near ground. By sheer accident, there is also a direct input pin to the circuit.
Brainstorm: by adding a connection points across the feedback path, one could easily turn this circuit into a low pass filter.
The schematic of the circuit is as follows:
the op-amp is a general purpose 741, but I would replace it with a much higher-end op-amp. There are some serious limitations and shortcomings with the 741 in this circuit. For instance, gains over 10 cause the output to clip at one rail much sooner than the other rail. I feel this has something to do with input offset current and input offset voltage. I will leave the circuit as is for right now because despite its flaws, it will simplify some of my circuit building.
