Fulltone PlimSoul

The Fulltone PlimSoul is an overdrive pedal from Fulltone that answers a question most gain pedals force on you: do you want soft-clipped overdrive or hard-clipped distortion? Instead of making you choose, it puts both clipping types in one box with independent controls, so you can run either one alone or blend them together¹². Fulltone describes the circuit as an independent dual-stage clipping design meant to replicate the sound and feel of a tube amp, including its subtleties and complexities¹.

The original PlimSoul shipped with what Fulltone called a patent-pending circuit, and the pedal is still covered by a patent held by Fulltone Musical Products today²³. The current version is the PlimSoul mkII, released in June 2021 and listed in the Fulltone USA store⁴⁵.

What it does: two clipping types in one pedal

Most overdrive and distortion pedals clip the signal one way. Soft clipping, the approach behind pedals like the Ibanez Tube Screamer, rounds off the waveform gradually for a compressed, bluesy voice. Hard clipping, the approach behind old-school distortion pedals, chops the waveform more abruptly for a firmer, crunchier edge. The PlimSoul's pitch, as the technical blog Guitar FX Layouts put it when the pedal appeared, was simple: "What if there was a pedal that offered both? There is now... the Patent Pending Fulltone PlimSoul."²

The two stages work like this:

• Stage 1 accesses the soft-clipping section, for what the blog described as "Softer Bluesey, Compressed capabilities"².
• Stage 2 is a second gain stage you roll in with its own dial, adding "that firmer, crunchier, British output tube style Distortion"².
• The two can be blended in any proportion, or you can run only soft clipped or only hard clipped².

Premier Guitar characterized the second stage as "adding a hard-clip-style gain stage for sounds akin to an old-school distortion pedal or the singing sting of a Marshall" output tube section⁸. Guitar FX Layouts also noted the circuit "successfully emulates the 'sag' and other behaviors" associated with a tube amp's output section and tube rectifier².

Inside the circuit

Guitar FX Layouts traced the original PlimSoul as "basically a Rat and Tubescreamer hybrid," with two high-pass filters at the inverting input of the first opamp arranged exactly like a Rat². The original used LEDs as clipping diodes, and the blog explained why that matters: forward voltage determines the clipping style, and "you get more distortion and compression out of red LEDs with a lower forward voltage" than out of green or blue².

Two other design details from that analysis:

• The pot controlling the hard clipping follows a scheme Jack Orman published years earlier as the AMZ saturation control, and the dual-pot gain control was previously used by Maxon and Klon².
• The original had a 500k input impedance and a super-low 10k output impedance².

The PlimSoul mkII

The mkII, released in June 2021 as one of that month's new gain pedals⁴, keeps the dual-stage concept but revises it. In Sweetwater's demo video, Don Carr walked through the changes:

The impedance bump is the one players will feel most. Carr explained that the input impedance "has been increased from 500k to 700k for better interaction with your guitar's volume control so it responds more like an amp"¹. In practice, that means rolling back the guitar's volume cleans up the signal the way it would into a tube amp's front end rather than going dull and dark.

Carr demoed the mkII playing a Gibson Les Paul through a Mesa Boogie TC 50 on the clean channel in the mid-forward setting¹.

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What reviewers and builders said

Published commentary on the PlimSoul has been positive on both sides of the counter. In Sweetwater's 2021 demo, Carr called the mkII's changes from the original "well considered" and praised its depth, flexibility and simple layout¹. Pedal of the Day, reviewing Fulltone's range more broadly in 2020, wrote that the company's "sound quality and craftsmanship have always been right up their at the top"⁹.

The DIY community's verdict is on record too. Guitar FX Layouts published a stripboard layout of the original in 2012, and a builder reported the next day: "I've built this tonight with the 'stereo' dual pot and it works like a charm right off!"² Another commenter in 2015 said a unit "sounds amazing and has oodles of headroom"².

One detail from the blog's correspondence with Fulltone's Mike Fuller is worth noting for anyone comparing Fulltone pedals: Fuller said he gooped the OCD's PCB for about five years to slow cloners down, "but I didn't bother gooping the PlimSoul"².

DIY clones and the patent

The PlimSoul is one of the few modern pedals with a verified, freely published DIY layout². But anyone building a clone from a commercial PCB should know the legal position: PedalPCB states that "Due to a patent held by Fulltone Musical Products, the SoulDrive is not a 1:1 electrical clone of the Fulltone PlimSoul"³. The patent dates back to the original's launch, when Fulltone marketed it as patent pending².

Where Fulltone stands now

Fulltone closed the California factory that had been building its pedals for over 30 years and relocated to the Nashville area, ending large-scale production in California¹⁰¹¹. The company said it would sell off its final California-built pedals and that new products were on the way¹⁰. The PlimSoul mkII remains listed in the Fulltone USA store⁷, alongside pedals like the Full-Drive 3 and the OCD'Lux.

Videos

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Questions