What kind of transistor configuration is this?

[igor12]

It's not an emitter follower and it's not a common emitter.  It has that feedback resistor that seems to act like a gain setting resistor.  I have seen similar type of circuit in the phase 90 and I think older big muffs.

http://www.aronnelson.com/gallery/main.php/v/Schematics-etc/trans.JPG.html

[CynicalMan]

It's a common emitter configuration with collector feedback bias.

[igor12]

So where's the emiiter resistor ? And base to gnd resistor? Can you bias this like an ordinary common emmitter? It seems to function like an opamp.  Why not use it instead of an opamp? I guess high Zout ?

[MohiZ]

You don't need a base to gnd resistor or emitter resistor if you can get the right voltages some other way. The two 150k resistors act as a voltage divider to set the base bias, in the same way that resistors from the voltage supply to base and base to ground would do. The advantage of this type of biasing is this: should the transistor have more gain than specified, the collector current would go up and, thus, the collector voltage would go down. This, in turn, would affect the base voltage lowering it, because its bias is taken straight from the collector. This would reduce the base current and that in turn would lower the collector current, negating the effect of the higher gain transistor. The same would work with a lower gain transistor as well.

[CynicalMan]

So where's the emiiter resistor?

Since the emitter is grounded, it's effectively 0 ohms.