I have often seen circuits for guitar pedals that use an emitter-follower configuration as the input and output buffer (see example below). If an op-amp can provide a greater input impedance / lower output impedance, why are they not used instead?

Is it simply the case that a single transistor circuit is cheaper to mass produce? Some people (audiophiles) say that transistors sound better, claiming that op-amps have a more "clinical" less warm sound. I am quite skeptical about this since there is no obvious difference in the frequency response at audible levels.

[!["Tube Screamer" input stage](https://i.stack.imgur.com/XzUbC.png)](https://i.stack.imgur.com/XzUbC.png)

If I'm not trying to mass produce a pedal and I'm looking to build something of quality, is there any reason not to use an op-amp as a buffer? In your experience, do op-amps have any intrinsically negative effect on the sound?