Malacandra Overdrive PCB

Malacandra - Xotic AC/RC Booster Guitar Pedal PCB



Version 2 update now available. if you have version 1 (prior to 6/26/2020), documentation can be downloaded here.

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Project overview

The Malacandra Boost / Overdrive is a recreation of the Xotic AC Booster and RC Booster, two nearly identical pedals that feature a two-band EQ for independent control of bass & treble frequencies. The result is a flexible tone machine that lets you go from a clean volume boost to a thick overdrive.

Looking at the schematic for the AC & RC Booster circuits, it’s very similar to a Tube Screamer, starting with an input buffer and an op-amp feedback diode clipping stage. The two major topological difference are that the AC/RC circuit uses an inverting op-amp stage for clipping (the TS is non-inverting), and the Tube Screamer tone control has been replaced by a Baxandall stage with bass and treble.

The BB Preamp (also available from Aion FX, called the Perelandra) is a similar circuit. The main difference is that it retains the Tube Screamer’s tone control section in between the clipping section and the Baxandall tone stack, hard-wired at the 9:00 position.

Version 2 of the Malacandra has been updated slightly based on direct traces of the current-production AC Booster and RC Booster as well as the Bass RC Booster. With the Malacandra PCB, you can build any of the three circuits by changing a few parts. Instructions are provided for each variant in the documentation.

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Circuit history

The AC and RC Booster were released in September and November of 2002, respectively. “AC” is a reference to the Vox AC30 amplifier, and “RC” stands for “Rig Conductor”.[1] The BB Preamp, released a few years later in 2005, is a reference to the Marshall Bluesbreaker amp.

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Notes & references

  1. A TGP user in 2015 says he emailed Xotic to clear this up and they confirmed the “Rig Conductor” name. However, I found several more references going back as early as 2005. So I think we can safely dispels the rumor that “RC” stands for “Really Clean” and “AC” stands for “Almost Clean”.