/diy/ - Do It Yourself

>>2553850
>should be the same, as both have six gorillion ohms input impedance.
More from a perspective of noise. I hear inverting topologies are often better for noise, but cascading two amplifiers together might be worse.

>>2553866
There are two R2s, so you'd have to vary them both matched to one another, which is difficult. There's only one Rgain. Personally I'd set the R2s for the lowest required gain if Rgain is removed, get it all properly matched, then use Rgain as the variable resistor. Though check that for stability, I hear it's often better to use a voltage divider than an amplifier with underunity gain.

>>2553874
>piezoelectric
It's a custom condenser with three plates, I just used the crystal+ground symbol because there was no three-plated capacitor symbol. Though maybe using picrel would be better. But yeah same-difference.
>low-pass
I'd consider it a gain stage foremost, the capacitor was just to lend stability (more important before, when the circuit's gain was set to 100), with a rolloff after ~20kHz. Again, same-diff. Normally I'd go for 100pF or so, but the smallest MKT caps at my local seller are 1nF, and I want to avoid ceramics for this project. Considering that 1nF is forcing R7 to be 10k and so limiting my gain, I think I'll just ditch the inverting bit and go for a single non-inverting amp.

>>2553886
I think I've seen it used to null the input offset current? It's probably incorrect, rather I think it matters when there's high resistances in the feedback path that would cause a series resistor to be placed in series with the non-inverting-input. The opposite of my case.