Guitar Pre-Amp stage/filtering and STM32F4
Here's what I did, in a very similar situation. Not a tuner, but a digital effects pedal. Firstly I'd personally suggest using a 9v battery for the analog gain stage, because the output of the guitar can actually be quite high, and it saves you a couple of diode clamps on the input. In a real product of course, you'd add them in anyway, and I've pictured them because you said you didn't know about "clamping" and it's pretty important if you want your electronics to survive unexpected scenarios. In any case the TL082 won't like only a 5v supply.

The following circuit will provide some gain (set by R1 &amp; R2), with a single-supply op-amp, and an output biased to half of the microcontrollers' supply.







simulate this circuit &ndash; Schematic created using CircuitLab

I haven't included any anti-aliasing for your input because for a guitar tuner application you can probably do that in software with little trouble. Also there's 11x gain in the op amp, which might be more than you need. Hard to say - and again having an overdriven signal for the tuner also might not matter. The two diodes are essential, you run a real risk of destroying the ADC in the micro without them, because if you drive your guitar hard you could easily see a couple of volts out of it, which the op amp will turn into tens of volts (well, 9 volts because of the battery, but still..), which won't end well.

The op amp is configured for an AC gain of 1+(R2/R1), but a DC gain of 1, because of the capacitor C1. Making C1 smaller will make the amplifier act like a highpass filter too, which might be useful.

In my case I actually had a FET input stage and three anti-alising stages before this amplifier, but like I said I think that would be overkill. The FET input is just for tone really, and in a tuner that doesn't matter.