BIPOLAR BEAR – Dual Overdrive

The Bipolar Bear is a dual overdrive with on one side (South Pole) an overdrive derived from an OD820 with Mosfets in the clipping section and a mids control inspired by a modification Mark Hammer posted about the Shin-Ei FY-2. The South Pole side runs on +9V/-9V using a charge pump and its drive knob can go from full overdrive to clean boost (using a dual pot).

On the other side (North Pole), a distortion derived from all kinds of Mu-Amp circuits, mainly BSIABII but with bits from the OKKO Diablo, Dirty little secret and probably others. It also has a mids control (that I snatched from GrindCustoms’ Ultrastoner because I thought it worked particularly well) alongside the usual BMP tone control.

I’m glad I added the mids control on both circuits as this is what I usually miss on most overdrives and distortions, makes it much more versatile and adaptable.

Originally I wanted to really like a Klon I had built but it somehow was not for me, so I came up with this instead. What I really liked about the Klon was the drive knob that could go all the way to clean boost but I did not like the Klon’s dirty sound and just could not compute the whole network mess of filters. Makes me nervous when I have no clue what is going on inside a pedal :-\ I spent hours and hours trying to figure out a way of doing that clean/dirty blend with a single pot, convinced I was smarter than Ibanez and Bill Finnegan combined … but I was not … There was always some drawback and in the end I went with a dual.

I’m really happy with the results and the flexibility the two circuits offer, individually or cascaded (South Pole into North Pole).

My PCB had a couple of issues though …
First the pinout for the JFets does not match any existing JFet known to me … so I had to twist 2 legs of the J201’s I was using. Not sure what I was thinking …
The other thing is an issue with oscillation when both circuits are engaged and I’m connecting my guitar directly to the pedal. The oscillation vanishes as soon as there is a buffer between the guitar and pedal. Must be a path of both circuits being too close that makes it oscillate when the impedance at the input is too big, don’t know for sure… As there will always be a buffer before it anyway I’m keeping it like this for now but I might get back to this at some point and redo the layout (because I will sleep better if I do… :) )

Here is a short demo of me noodling around:

Update: I did a new PCB layout and by keeping it as a buffered bypass (like the Klon for example) and rerouting some traces I was able to get rid of that oscillation 🙂

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