I've spent two days playing with op amps. Everything is grand with DC: comparators, followers, neg fb gain etc.
It's when I put a small AC signal in that I run into problems.
I have an input from my sound card, it's line level, +- about ~250mV around the ground on the RCA lead (normal 0V, it's 0V potential to the 0V rail on my breadboard)
The opamp has 0V-12V rails.
I have a 6V virtual ground from either a (variable) voltage divider or an opamp buffer producing 6V.
TLDR;
How do you correctly lift the input "ground" to the rail split virtual ground so you get VMax - Virtual Ground - VMin. In my case 6V +- 250mV and 6V +- 2000mV on the output?
Skipping many hours of reading, you tubing, tinkering and genuine concern for my sound card RCA outputs. I did manage to get an amplified signal. But it had issues.
Basically I had to decouple the input via a series cap, apply a pull up voltage onto that signal to raise it up above the lower rail and I got a signal.
It felt very wrong applying (at first 2.5V) to the "output" of the RCA though even with the series cap "decoupling" it. I tried the opamp buffer (rail splitter) to get 6V which tested out fine, but when I applied that to the input signal I got a pop and the channel went mute ( I mean the sound card cut it's output off and the headphones went off). I don't think it liked it, but it thankfully recovered when I removed the voltage.
Back to using a voltage divider for the "virtual" ground at 2.5V. I was able to get a maximum gain of about x4 before the op amp either clipped or just stopped working and the output collapsed. So that was something like 800mV p-p. If I wound the gain higher I clipped on the top rail, if I wound the reference voltage up the output collapsed.
I gather the issue is the op amp is amplifying the virtual ground as well, so if I give it +2.5V and add my +-200mV AC signal @ x4 gain I getting 800mV peak to peak on a 2.5x4=10V DC offset. 9.2V to 10.8V. I confirmed this with the multi-meter. If I took the ref voltage up the amp clipped until it collapsed against the top rail. If I took the ref voltage down it collapsed against the lower rail.
So do I apply the virtual ground voltage to both inverting and non-inverting or ... more likely am I just in a muddle.
I think I'm just missing one piece of the puzzle or have miss interpreted something fundamental along the way regarding virtual ground on the op amp, versus the input signal ground.
(Also... assuming I get this working, how would I then be able to bias the output 6V -+1000mV back down to normal 0V ground to send on to something like a speaker? Thinking out load, if I pass it through a series cap pulled to 0V ground on the speaker side, will that work?)