Best sounding op-amp

If op amps influence sound as much as people are saying, then op amps are being used in circuits where they don't belong. The headphone amp cited by Chillysalsa is probably a prime example. Op amps, even "good" ones are a lot cheaper than circuitry implemented with discrete transistors, so I suppose that widespread use is inevitable. Tubes anyone?

The little differential small signal amplifiers, packaged as integrated circuits, and commonly called "Op Amps" are called that because they are not often designed or used as linear amplification devices. The important characteristics of an op amp are very (absurdly) high open loop gain and very high slew rate. Linearity is of no importance. The op amp drives its output so as to match its input and follow changes of the input. The "signal" that drives the op amp is not the signal that you feed into the circuit. The signal that drives the op amp is the difference between the op amp output and what you are feeding in. The high gain makes sure that this difference is driven down to zero, and the high slew rate makes sure that rapid changes of the input can be followed closely. The characteristics of the op amp circuit are overwhelmingly determined by the design of the feedback loop within which the op amp works, and the electrical components of this loop. In most cases substitution of an op amp with superior specs will have no effect on how the circuit performs.

As always, there are some exceptions. Soime op amp ICs are more noisy than others. In some high gain applications, such as a phono preamp, the op amp may play a significant part in overall circuit performance. (The practical solution to this problem is not to use op amps, even $50 items, in high gain phono preamp stages).

So, don't waste money replacing all the op amps, when few, if any, will have any effect. Make a review of the circuit before you "upgrade" op amps.