Boss OD-3 BD-2 Question - Help (R.G.?)

[Rayman]

Can anyone explain how the circuit involving the q11 (pnp), q13 (jfet), and q14 (jfet) transistors on the Boss od-3 schematic works?  This same type of circuit is used in the Boss BD-2, but I can't find anything in this forum or on the web that explains this configuration.

[R.G.]

Do you have a link to the schematic you can post, so we're talking about the same thing?

[Rayman]

yes, here it is.

http://www.freeinfosociety.com/electronics/schemview.php?id=2299

[R.G.]

OK. It's a discrete opamp.

Q13 and Q14 form a simple differential amplifier, biased by R50. Q11 is a voltage gain stage, converting the signal from R37 into an output voltage. The output pin is the junction of R52 and Q11, the + input is the gate of Q13, and the - input is the gate of Q14.

R36 and R49 are a bias voltage divider. D10/D11 are a feedback clipping diode network, and Drive, R38, R51, and C33 perform much the same function as the clipping opamp stage in the tube screamer.

[Rayman]

thank you so much.  I see it now.  If I new what a discrete opamp was, I probably could have seen it.  that explains it perfect.  I need to do some searching to better understand discrete opamps.  thanks again R.G.

Rayman