Transformer to Diode Frequency Doubler

Using a transformer splitter and diode rectifiers to perform frequency doubling is a basic electronics concept. The use of such a circuit as a guitar effect is credited to Roger Mayer and his Octavia pedal built specifically for Jimi Hendrix.

The Octavia uses a completely passive circuit for it's frequency doubling effect. A two transistor driver circuit provides the gain and initial distortion before the full wave rectification stage.

For those who may be unfamiliar with transformers, the output coil will produce mirror image, 180 degree out-of-phase copies of the input signal voltage at each end of the coil. Note that the center of the secondary (output) coil is tied to the ground node. This is called a "center tap."

The transformer is a bulky, expensive, and somewhat fragile device. Roger Mayer's original units used a particularly fragile type of transformer that broke often and caused him to revise the circuit.

As far as I know, only direct copies of the original Octavia use transformers as the splitting device (see Tycobrahe unit). The early Octavia imitators (see Superfuzz, Blender, and Scrambler) used transistor splitters instead.

Examples:

Roger Mayer Octavia (original "wedge" units, not the rocket enclosures)

Tycobrahe Octavia

Fulltone Octafuzz