Supreaux

The Supreaux is a DIY guitar effect circuit that puts the character of the vintage Supro 16T amplifier into a stompbox. It was designed in 2004 by Runoffgroove, the free project site whose designs have seeded a large share of the home-build and boutique pedal world. Instead of using tubes, the Supreaux rebuilds the Supro amp's gain structure with JFET transistors, the approach Runoffgroove used across its amp-emulation projects¹.

The circuit matters to players for two reasons. First, it is a well-documented, freely available design that a builder can put together from a layout on a stripboard or a printed circuit board. Second, it is the documented ancestor of a commercial pedal: the original Supreaux, designed in 2004, is notable for being the source for the JHS Superbolt, one of JHS's most popular pedals, which makes the Supreaux one of the DIY designs that reached mainstream pedalboards².

Where the Supreaux came from

Runoffgroove designed the original Supreaux in 2004 as a JFET adaptation of the Supro 16T amplifier¹. Supro amps of the 1960s have a distinctive overdriven character that players associate with vintage American recordings, and the Supreaux was Runoffgroove's attempt to capture that character in a battery-powered pedal format rather than in a tube amp head.

Runoffgroove's projects circulate widely in the DIY community, and other designers openly build on them³:

• GuitarPCB's Red Special project started from the RunoffGroove MayQueen circuit before Tonmann tweaked it further for tonal changes⁴.
• General Guitar Gadgets' Thunderchief distortion is a runoffgroove.com design, with the site credited directly⁵.

The Supreaux sits in that same tradition: a free schematic and build document that anyone can etch, tag or order a board for.

How it works: J201 JFETs in place of tubes

The core idea of the Supreaux is transistor amp emulation. Tubes amplify in a way that produces particular clipping and compression behavior, and JFETs, junction field-effect transistors, are the semiconductor that DIY designers most often reach for when they want a tube-like response from a 9V circuit. The J201 in particular is a small-signal JFET used across this style of build.

The approach is not unique to the Supreaux, and seeing it elsewhere helps explain what the circuit is doing:

In each case the designer maps a tube stage onto a transistor stage: the JFET's gate, drain and source stand in for the tube's grid, plate and cathode, and the biasing resistors around each JFET are set so the stage amplifies and clips in roughly the way the original tube stage did. That is the technique behind the Supreaux's recreation of the Supro 16T.

The controls and trim pots

The Supreaux Deux is a direct adaptation of the original circuit, but with two modifications². The most significant one for a builder is power: the original circuit needs 18V power to sound right, so a charge pump has been added to get 18V from a standard 9V input². That means the Deux can run on the same 9V supply as the rest of a pedalboard while keeping the headroom the original design was voiced around.

Trim pots of this kind are standard across DIY amp-style circuits, and their job is always the same: set the gain or bias of a stage that the player cannot reach from the outside. Some examples from other projects show the range of what they do:

On a Supreaux, the trim pots are adjusted by ear in the same way:

1. Power the pedal and play through it.
2. Turn each trimmer until the stage is biased where the gain and the clean-to-breakup transition feel right.
3. Revisit the settings once the pedal has warmed up, since every batch of JFETs varies, which is exactly why the trimmers are there.

There is no factory setting, because the transistors themselves differ from piece to piece.

Supreaux Deux: the revamped version

In 2008 Runoffgroove redesigned the Supreaux as the Supreaux Deux, with the aim of being more accurate to the sound of the Supro 16T amp². The original 2004 circuit was a first pass at the amp; the Deux is the refined version, and it is the revision that most later projects trace back to.

A redesign of this kind, where a maker revisits an earlier circuit to sharpen its accuracy, is common in the pedal world. Revv's G4 V2 Canadian Edition adds a V2 circuit revision with additional versatility in lower gain ranges and a more clear, cutting midrange¹², and Oneder Effects' Old Blue Overdrive V2 follows V1 with updated circuitry¹³. The Supreaux Deux is the same pattern applied to a DIY design: the schematic was reworked so the pedal lands closer to what the amp actually does.

For a builder choosing between them today, the Deux is the version to start from, since it is the later, more accurate take on the same amp².

Pedals based on the Supreaux, including the JHS Superbolt

The Supreaux's best-known descendant is the JHS Superbolt. JHS Pedals sells the Superbolt V2 as an amp-style overdrive in its current lineup¹⁴, and the company's Ruby Red signature pedal for Butch Walker uses the SuperBolt overdrive as its left side¹⁵. JHS describes the Superbolt as its own design in the usual way a maker does.

The independent circuit record tells a more specific story. The original Supreaux version is notable for being the source for the JHS Superbolt, one of JHS's most popular pedals²¹. JHS describes the SuperBolt as an all-analog pedal based on the sound of the Supro S6420 Thunderbolt allegedly used on early Zeppelin records, and it includes a high/low mini-switch that replicates the dual inputs on some of those old amps¹⁶.

So the answer to whether the Superbolt is a Supreaux clone is a matter of attribution rather than a simple yes or no: published circuit analysis found the Superbolt to be a Supreaux with light modifications, while JHS markets it as its own amp-style overdrive. Both statements can sit side by side; the Superbolt is a commercial pedal whose circuit has been traced by independent builders to the Runoffgroove design²¹.

The Superbolt family also reaches the DIY world directly:

• PedalPCB's Taqueria overdrive project is offered as a compare-to for the JHS Superbolt, also known as the Tacobolt¹⁷, which gives builders a printed circuit board route to the same circuit.

PCBs and DIY builds

Because Runoffgroove publishes its designs freely, the Supreaux and Supreaux Deux live mostly as DIY builds. The typical route is a printed circuit board from a layout house such as PedalPCB, or a hand-drawn stripboard (vero) layout of the kind DIY blogs publish³².

A basic build needs the usual DIY pedal parts:

• An enclosure, jacks and a footswitch
• Pots for the external controls
• The JFETs themselves, plus the trim pots
• Offboard wiring

Builders working with SMD J201s can use TO92 adapters to fit them to through-hole boards⁹. The trim pots are then set by ear as described above.

For a player coming to the Supreaux from commercial pedals, the appeal is straightforward: it is a documented, low-cost way to build the Supro-style overdrive character yourself, and its lineage runs through a pedal you can buy off the shelf if building is not your thing²¹⁸¹.

Pedals on this page

Oneder Effects Old Blue Overdrive

Oneder Effects · Overdrive

$179 list price

JHS Pedals Ruby Red

JHS Pedals · Boost

Questions