Hello,
I have been looking around and cannot find the answer to my problem no matter what I do. I am still learning about Op-Amps and I have the task of taking an audio input from an MP3 player, typically at .2v peak to peak and I want to increase its gain as much as I can before it clips say 10x - the plan is to have the signal go into a VCF I have which is working fine but for testing purposes I have the output of the opamp only connected to my oscilloscope and nothing else.
First for a test I tried a 741 and a 071 but then moved to a LM358. Below is my circuit it is a simple non-inverting amplifier. The top op-amp is my half supply reference and the bottom 2 is my 2 attempts. First I tried bottom left (a unity gain buffer) - It works fine and outputs the signal exactly the same as the input on my oscilloscope but the one on the right doesn't! it just flattens - I was trying to make 10x gain.
when I remove the 1K resistor to Vref in the feedback so the feedback is only a 10K resistor it outputs the signal with a lot of noise!! why is this? is it oscillation? or thermal noise?
I also want to ask about input impedance as I plan to use a similar circuit on the output of the VCF is it right to assume because of the very high input impedance of the amp that it will be roughly speaking the 1M ?
I have been looking around and cannot find the answer to my problem no matter what I do. I am still learning about Op-Amps and I have the task of taking an audio input from an MP3 player, typically at .2v peak to peak and I want to increase its gain as much as I can before it clips say 10x - the plan is to have the signal go into a VCF I have which is working fine but for testing purposes I have the output of the opamp only connected to my oscilloscope and nothing else.
First for a test I tried a 741 and a 071 but then moved to a LM358. Below is my circuit it is a simple non-inverting amplifier. The top op-amp is my half supply reference and the bottom 2 is my 2 attempts. First I tried bottom left (a unity gain buffer) - It works fine and outputs the signal exactly the same as the input on my oscilloscope but the one on the right doesn't! it just flattens - I was trying to make 10x gain.
when I remove the 1K resistor to Vref in the feedback so the feedback is only a 10K resistor it outputs the signal with a lot of noise!! why is this? is it oscillation? or thermal noise?
I also want to ask about input impedance as I plan to use a similar circuit on the output of the VCF is it right to assume because of the very high input impedance of the amp that it will be roughly speaking the 1M ?