Traynor TS-50B, help with understanding circuit

[spacelabstudio]

I had a friend's Traynor TS-50B bass head in to repair this weekend.  It was a simple PCB patch.  Cool sounding amp, though.  I thought I'd peek the schematic and see if I could learn something.  I'm looking at the schematic in Doug's archive:

http://www.el34world.com/charts/Schematics/files/traynor/traynor_bass_ts50B.pdf

I haven't looked at the power section yet.  I can more or less grok the preamp up to a point.  The input section mostly makes sense to me.  I'm guessing the 2N5245 FET is just being used as switch to connect or disconnect those three components to ground and change the feedback loop of the opamp.  The tone stack is really cool with the T filter for mids.  Then an emitter follower as a buffer.  Then... my brain explodes.

Can anyone explain what's going on with those 6 BJTs?  I can see there's some paralleling going on, and three different filters that get applied to three different inputs.  But it doesn't make a whole lotta sense to me.  If that kind of circuit has a name, telling me what it is is probably sufficient.  I can Google from there. 

Thanks!
Chris

[PRR]

> Can anyone explain what's going on with those 6 BJTs?

Yes, but life is short.

It's a soft diode-clipper with gain. Several frequency-zones.

[spacelabstudio]

> Can anyone explain what's going on with those 6 BJTs?

Yes, but life is short.

It's a soft diode-clipper with gain. Several frequency-zones.

Aha!  That helps.  Thanks!