Custom Mosfet-based Overdrive (Verified)

[Tom F]

I had some spare time, so I put this layout together and built the circuit last night. Consider it verified. Basically, I noticed how the Zvex SHO has only a gain control, which can't attenuate, while the EQD Black Eye only has a trimmer to set the gain, and can only attenuate with an external volume control after that is set. Since I like the way this circuit crunches up and overdrives, I thought why not take the circuit, put the gain and volume controls both on the outside, add a tone control, and turn it into a drive pedal?


So that's exactly what I did. I also added a three-way toggle to select a couple of asymmetrical diode configurations. There's enough room on the layout that anyone who builds it can probably play around with their favourite diode choices. Also note that while I list a 5k linear pot for the gain control, as that's all I had at the time, a reverse log taper would work much better.

These aren't exactly groundbreaking changes, but fans of the SHO and similar circuits should enjoy the increased versatility. When the diode switch is off, and the tone and volume controls are maxed, it works pretty much like a normal SHO. However, if you want to add some edge to your sound, you can add in the diodes. If you want to tame the highs, you can use the tone control. If you want the driven sound at a lower level, turn up the gain and turn down the volume. All pretty simple additions to the circuit, but all very useful at the same time.

Because this circuit is so simple, I'm probably going to continue making changes and building up from it in an effort to create my own unique overdrive pedal. I may try doing some crazy stuff like some of Jack Ormon's saturation controls or experimenting with different tone stacks. Kepp an eye out for future posts.