Montarbo Sinfhoton

The Montarbo Sinfhoton is a fuzz pedal made by the Italian company Montarbo in 1968. Writing on the DIY layout site Guitar FX Layouts, Zach described it as "very Big Muff like in tone, but seems to have a bit more clarity in the notes"¹. It belongs to the wider family of fuzz pedals, and its circuit has drawn enough interest among builders that stripboard layouts for all of its versions have been published¹.

What it does

The Sinfhoton is a two-stage style fuzz with an unusual control set for a fuzz pedal: there is no Fuzz control at all, just Bass, Treble, and Volume¹. That means the amount of fuzz on tap is shaped largely by how hard the circuit is driven, most often from the guitar's own volume knob.

On the two knob version, Zach found that with an orange LED in place of D3, the pedal responds to the guitar volume in a way players of overdrive pedals will recognize¹:

Versions and the DIY scene

Over time there have been three different versions of the Sinfhoton, and layouts for the early, later and two knob versions were published on Guitar FX Layouts in February 2016¹. An earlier vero layout, tagged Fuzz, had already appeared on the same site in March 2013².

The original BC149 transistors are hard to come by, though they do turn up on eBay. Zach suggested the usual higher-gain substitutes: 2N5088, 2N5089, MPSA18, BC109, and BC108¹.

For the two knob version, the final builder mods were 2N5089 transistors, a 10k linear tone pot, a 50k log volume pot, a 220uF filter cap, 2D503b diodes for D1, D2 and D4, and an orange LED for D3, facing north¹.

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