I have the following circuit which amplifies a 50 KHz signal and works ok. I would like to increase the gain of the second stage (by making R3 smaller), but when I do the output of the second stage is pulled upto 5V.
There appears to be a small DC voltage being amplified. I though the 680pF capacitor would filter this out, so only the AC component was amplified, the 680pF doesn't seem to help.
Is there a better was I can remove any DC offset at the input to the second stage?
UPDATE: First op-amp output distortion
I have attached two scope images which are both of the output of the first amplifier while experimenting with R3/R4 values. The distorted signal is when the gain of the second amplifier is set to 75 (R3 = 6.8K, R4 = 510K), the clean signal is with a gain of 5 (R3 = 100K, R4 = 510K).
How would the operation of the second op-amp at different gains effect the input signal?
Thanks for the responses all. I have found that adding a 10uF ceramic capacitor in parallel with R6 has improved the circuit massively in my case. This has stabilised the DC offset that is used by both op-amps.