Why do some modders bypass the opamps in cdps and others switch them out? What are the sonic benefits of bypassing the opamps of a cdp entirely? What is the purpose of an opamp anyway?
Opamps (operational amplifiers) are a kind of differential amplifier, which means they react to the differences between two inputs, and produce an output accordingly. They have all sorts of applications, and messing with audio signals is a common one. They are convenient in that from a design perspective, they often do exactly what you need.
But they rarely do it really well. It's hard to make them utterly linear and they tend to have some inherent noise. (Everything does, but sometimes you can get better noise results with discrete components or better opamps.)
Sometimes they are not used to amplify, and are set up to provide no additional gain, but some kind of filtering or feedback instead, or strictly to isolate a signal from the rest of the circuit. Chopping out a "unity gain" opamp to eliminate feedback, buffering or filtering can be a useful trick, if you know exactly what you're doing. It's not something you do on a lark - you need to know exactly what you are giving up, and you'd do it in conjunction with other changes, most of the time.
