Catalinbread site: The distortion engine of the D+ is a simple op-amp with a large 1M pot setting the voltage gain. At minimum, the Distortion knob delivers just 3.5dB of gain, but at maximum there’s 46.5dB of gain, a full 11.5dB more than the next benchmark in purposeful distortion, the Boss DS-1. Yes, that is loud. But right before reaching the output jack, the signal is clipped by a pair of anti-parallel germanium diodes that clip the waveform heavily, leading to distortion. If you were to take a pair of wire cutters and remove these diodes from the D+ board, you would dramatically increase the volume at the expense of saturation. 

This acts sort of like an amp, in a roundabout way. The forward voltage of the diodes ensures that the signal is clipped once it passes a certain threshold. And until the player crosses that threshold, the diodes won’t turn on and the signal remains unaltered by them. Turning the distortion control up amplifies the signal to intentionally clip and compress, which sounds an awful lot like tube amp distortion if you squint your proverbial eyes. 

Despite its no-frills facade, the D+ is quite an important piece of gear history and has served as a crude blueprint for what distortion effects would become in the future.

It's a vintage pedal, but it is still in gorgeous condition. An excellent starting point for the MXR collectors out there!

Optically 8/10. Its fully functional and has no modifications!

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