[sdiy] Three new student draft circuits: Alex, Josh, Brian & Erin

[René Schmitz]

Hi Aaron and all,

> Brian & Erin are two of my Savannah-based students; they're working on 
> using FETs in a distortion pedal to try to get a natural amp breaking up 
> sound. They are also working on other novel ways of torturing op amps in 
> twisted ways.

Interesting arrangement of FETs.

> Alex wants to try using FETs to add VC resonance to the Rene MS-20 (that 
> seems popular among the students - it was my canonical Sallen-Key 
> example, and the way the schematic is drawn it's easy to follow). He's 
> already soldered up on perfboard the main part of the filter, instead of 
> breadboarding it (I figured that would make Harry happy!)

The + input of the clipping opamp should be properly biassed, add a 100k 
or so to GND there. Also I wouldn't drive the gate of the FETs directly 
from the opamp outputs. Chances are you're going to destroy the gates if 
the voltage at the input becomes negative. I'd suggest adding some 
resistor in between the opamp output and the FETs gate.

Cheers,
  René

-- 
uzs159 at uni-bonn.de
http://www.uni-bonn.de/~uzs159