This Week on the Breadboard: BJFe Baby Blue OD

Chuck D. Bones

Circuit Wizard
This out-of-production pedal from BJFe uses 3 JFETs and a pair of Silicon diodes to create distortion, compression and dynamics similar to a tube preamp. Contrary to what some have alleged, this is nothing like the Mad Professor Sky Blue OD.

The the only schematic I could find online is marked for FSB use only, so here is my LTSpice schematic.

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The FSB schematic did not assign a part number to the JFETs. BJFe used a variety of JFETs in his designs, including the MPF4393, so I tried those. They biased pretty well using the stock resistor values. Rgain1 & Rgain2 are the top and bottom halves of an A500K GAIN control. The GAIN pot has a 10K resistor between pin 1 and ground. Rtone is an A50K TONE control. D3 & D4 were spec'ed as 2A1200, which I believe are high voltage rectifiers. 1N4007 is probably a good sub.

This is a very bright pedal and it generates a huge amount of 2nd harmonic, giving notes a very sharp metallic buzz with some octave-up overtones as the note decays. I don't know how else to describe it. Not one of my favorite ODs. I tried a few things to tame it, with little success. If you use different JFETs, be prepared to fiddle the source resistors. I think we want the drains on all three JFETs to be around 6V.
 
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