I have a rather strange problem. I have a breadboard circuit on a double sided PCB with plenty of ground plane and a good well decoupled power supply. I am amplifying a small medium frequency signal (mV, hundreds of kHz) and bandpass filtering the region of interest.
Initially, I thought to use the AD829 - very low noise, plenty of bandwidth. The problem appears to be the it is too good! I was getting lots of noise especially at high frequencies leaking through. So, changed the AD829s with the cheap TL051 (10x worse noise spec, 30x lower bandwidth). Problem solved - noise gone!
Now obviously the problem has disappeared because the TL051 cannot handle much in the way of high frequency, which is fine. What worries me is two things. First, how legitimate is it to use low spec components to "hide" a problem like this. And second, do manufacturers ever "upgrade" the spec of their amplifiers? One day, will I put in a TL051 that has been improved and discover the product now longer works?
This is the bandpass section which really looks bad with AD829s