As most of you who read my blog will know I've been a huge fan of this circuit since I started playing guitar. It was the first distortion pedal I built for myself and I have made it in different forms ever since either as the "engine" for the Tripletone or as the distortion version of my TMKF pedal that I make for charity.
I recently faltered in my love of these after cloning the DOD 250, which is heavily based on this circuit also. However, after this little project I now love this circuit again as much as I ever have. It's such a GREAT little distortion.
While both pedals are obviously very closely related, they each have nuances that make them both very usable separately or combined on the same pedal board.
I won't go into too much history here but this little mustard coloured stomp box launched a thousand bands including one of my personal favorites, and the reason I originally got switched onto it. More on that soon.
It's a simple little circuit that takes a guitar signal and turns it into first a nice soft clipping signal and as the distortion pot is increased, the bottom end gets "scooped" out and the signal is turned into a pleasing harmonically rich square wave with heaps of very usable volume that can push a nice amp into distorted heaven.
The signal is clipped using diodes, although the simple single Op Amp does distort on its own. This simple yet very effective, completely outdated "old school" LM741 chip is part of the charm and tone of this great distortion circuit.
I have built myself versions using other single Op Amps like TL081's which have a better frequency response and cleaner headroom and while I still like the tone of these, this little 741 sure has something nice despite its background noise high current draw.
These little boxes were introduced in the seventies and originally had germanium diodes in the clipping stage. This version has become known as the "script logo" version as the font used on these early MXR boxes were ......... Script.
Later in the seventies the company changed their logo to the now famous "block logo" that is still used today. These are generally known as "eighties" versions before Dunlop bought the rights to manufacture all MXR stomp boxes.
This Tym version gives you the choice of both of these classic early versions of the original MXR distortion. The small toggle switch between the knobs selects either germanium or silicon diode clipping. The germanium setting has slightly less volume and is "warmer" and a little "muddier" whereas the silicon setting is tight and sharp, verging on brittle when used with some amps and pick ups.
Part two is about a very special version of this great little circuit.