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

Started by Rayman, September 30, 2007, 08:20:36 PM

Previous topic - Next topic

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?
R.G.

In response to the questions in the forum - PCB Layout for Musical Effects is available from The Book Patch. Search "PCB Layout" and it ought to appear.


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.
R.G.

In response to the questions in the forum - PCB Layout for Musical Effects is available from The Book Patch. Search "PCB Layout" and it ought to appear.

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