The reason I wanted to ask this question is because I was designing a project for an electronics course I was taking last semester. The idea was simple. Take input from a microphone and amplify it sufficiently to turn an LED on/off depending on the frequency that was passed. Now, in my research I came across an article that stated OP Amps (unless very expensive) are a source of tremendous electrical noise in their high-gain applications. So, I resolved to a two-stage design with a BJT amplifier (~50 gain) and an OP Amp (~gain 2) for an overall gain of 100 to reduce the alleged noise issues.
So, in short, why do OP Amps have electrical noise issues (if at all), and what is the source? Why are Op Amps more noisy than other types of amplifiers (BJT and MOSFET, for example)?
It seems that any application of amplifiers in general would potentially be a source of 'amplified' noise if there exists such noise in the input signal. Perhaps Op Amps lack sufficient filtering capabilities that are inherent to BJT and MOSFET design? Op Amps are, internally, transistors anyway, so why the noise difference?