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Megalith Dual Drive

Based On
ZVEX® Box of Rock
Effect Type
Amp-like overdrive
Build Difficulty
Project Summary
A two-channel drive composed of cascaded MOSFET boost stages. The drive channel and boost channel can be combined or selected independently.
Megalith Dual Drive printed circuit board

Printed Circuit Board

What's included?
PCB only. Build instructions and parts list can be viewed or downloaded from this page.


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Complete Kit

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Project overview

The Megalith Dual Drive is a hybrid of the ZVEX Box of Rock and Distortron, two pedals made of cascaded SHO boost stages.

The Box of Rock came first in 2006. In addition to the three cascaded stages, it also includes a fourth SHO stage at the end for switchable volume boost. The Distortron followed in 2009 as part of the lower-cost “Vextron” series, which also included the Mastotron. The Distortron omits the boost, but adds two toggle switches for gain (low or high) and “subs” or bass (3 different settings).

By combining the Distortron’s switches with the Box of Rock’s extra boost stage, we can have the best of both worlds. The Megalith is a touch-sensitive low- to medium-gain pedal that overdrives naturally and responds very well to the guitar’s volume knob.

The Box of Rock was designed as a 2-channel effect, with the SHO as the “always on” clean foundation to which the drive channel can be added (demonstrated in ZVEX’s original demo video). The boost comes after the drive when both are engaged. This is a perfectly reasonable way of using it, but it won’t work with every rig.

Because of this, the Megalith adds an internal slide switch allowing the order to be changed so that the boost comes before the drive. In this mode, the boost stacks with the drive and adds to the gain rather than just boosting the volume as in the default ordering.

Note that since the gain stages are identical to individual SHO circuits, the two gain controls (the main circuit gain and the boost level) exhibit the characteristic “crackle” of the SHO when they are adjusted, since they are directly biasing the MOSFETs. This is normal.