I'm connecting an electric guitar to amplifier circuit and the output of the circuit to ADC. I've checked the output of amplifier with the osciloscope. The signal seemed fine, but after connecting it to ADC (maybe because of capactive load?) it become asymetric. The output signal doesn't go below ~500 mV when the output is connected to 'something' (I've tried also to connect it to hifi stereo system, with the same result) so it gets badly distorted. I need it to be in range 0 - 3 V. How to get rid of this effect?
- Op amp: LM324
- ADC: MCP3202
- R1, R2 give DC offset by 1,5V. R1+R2 = 1M
- gain close to 1
EDIT I've tested the circuit with square wave to illustrate the problem.
On the first plot below is the unloaded version of the circuit (op-amp output isn't connected to anything), Vmin is 80mV which is almost what I want. On the second one we can see the loaded version, output connected to hifi, however conneting it to ADC results in the same effect, Vmin doesn't go below 500mV: