Single NPN Emitter-Follower in amplifier's input stage
If the output from Q1 is biased close to ground then a PNP will drive effectively close to ground better than an NPN would.  As drawn, the PNP has an effective impedance of 150k(R2) divided by the Hfe of Q1 which is likely to be 100 or so.  If we turn the input circuit upside down and use R3 as a pull-down then the output impedance is 33k.  Keeping the output of Q1 biased to a low voltage improves supply rejection and minimises the voltage on C2, which could reduce cost and possibly microphonic effects.  So a PNP is preferable but an NPN could be used.