I use op-amps in electric guitar effects pedals in conjunction

[luna5]

I use op-amps in electric guitar effects pedals in conjunction with transistors to create overdrive, distortion and other musical effects. My knowledge is limited technically but I learning through practical experience. I have come across an unusual circuit that I Canaletto sense of: the parts that are confusing are 2 diodes in series and 2 transistors in series the weird par to me is that one of the transistors is a NPN and the other is a PNP. I am trying to follow the input which seems to go through the opamp, then the diodes and then the transistors. Of course there are resistors and capacitors in the circuit it I think I understand their functions.

[Mr.Grumpy]

Overdrives and distortion circuits typically use a pair of clipping diodes, either in the op-amps negative feedback loop, so-called "soft clipping", or between the output of the op-amp and ground for what's called "hard clipping." It's also possible to wire two MOSFET transistors as clipping diodes. A few distortion pedals have both soft clipping and hard clipping. There are a few pedals that use one clipping diode, or use two diodes but of different types to deliver asymmetrical clipping. There's a few rare distortions that don't use any clipping diodes at all, but count on the op-amps limited headroom to clip the signal. 

The Ibanez Tube Screamer is a "soft clipping" overdrive; the ProCo RAT and Boss DS-1 are "hard clippers." The FullTone FullDrive MOSFET version uses MOSFET transistors wired as diodes in the feedback loop in what is essentially a close copy of the TubeScreamer circuit. 

You may want to check out freestompboxes.org, it's an effects builders' forum with a lot of information and schematics.