The Concrete Sound Lab Slab JFET Preamp and Boost is the brand's first ever pedal, designed by Josh and released in July 2025. Guitar Pedal X describes it as a Boost, Overdrive, Distortion and Fuzz multi-gain pedal, meaning one circuit that walks through several flavors of gain rather than committing to a single overdrive, distortion or fuzz character. At its core is a JFET tube-emulating circuit, which Guitar Pedal X calls "possibly somewhat Fetzer adjacent"1.
The controls: six knobs and two footswitches
The Slab's panel carries six knobs and two footswitches, laid out as follows1:
| Control | What it is |
|---|---|
| Pre-Gain Low | Shaping before the gain stage |
| Pre-Gain High | Shaping before the gain stage |
| Gain | Sets the amount of gain |
| Boost | Sets the boost amount |
| Tone | Post-gain low-pass filter |
| Level | Sets output level |
| Boost Footswitch | Engages the boost stage |
| Main Bypass Footswitch | Bypasses the pedal |
The two pre-gain knobs work ahead of the gain stage, so they shape what the JFET circuit is fed. The Tone knob sits on the other side: Guitar Pedal X identifies it as a post-gain low-pass filter, meaning it trims highs from the signal after the gain has been applied rather than altering the input1. The Boost knob and Boost Footswitch work as a pair, letting the boost stage be dialed in and then switched in and out independently of the main preamp1.
What reviewers said
Guitar Pedal X's Stefan Karlsson reviewed the Slab at its July 2025 release and called it "an incredibly strong start to a brand", judging it a pretty perfect execution overall, while noting that touch-sensitivity and dynamics are qualities a player assesses in use rather than from a written account1. On the look of the pedal, he wrote: "The swirly Purple marbled paint job is fantastic, obviously I live those silver-top Boss-style knobs too - which are cre"1.
As a first release from a new maker, the Slab's long-term availability is not something any published source has yet addressed. The $200 price is as reported on 17 July 2025.
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Questions
What does the Concrete Sound Lab Slab do?
The Slab is a JFET preamp and boost pedal that Guitar Pedal X describes as a Boost, Overdrive, Distortion and Fuzz multi-gain pedal. It uses a JFET tube-emulating circuit, and its controls cover pre-gain shaping, gain, boost, tone and level, with a separate boost footswitch alongside the main bypass switch.
Does the Slab have a separate boost footswitch?
Yes. The Slab carries two footswitches: a Boost Footswitch and a Main Bypass Footswitch. That lets you bring the boost stage in and out independently of the main preamp circuit, alongside a dedicated Boost knob.
What does the Tone knob do on the Slab?
On the Slab, the Tone knob works as a post-gain low-pass filter, according to Guitar Pedal X's review. It sits after the gain stage, so it shapes the top end of the already-distorted signal rather than changing what goes into it.
How much does the Concrete Sound Lab Slab cost?
Guitar Pedal X reported on 17 July 2025 that the Slab is priced at $200 from the Concrete Sound Lab Webstore.
Is the Slab based on a Fetzer circuit?
Not exactly. Guitar Pedal X describes the Slab as a JFET tube-emulating circuit that is possibly somewhat Fetzer adjacent, meaning it draws on the same family of JFET gain-staging ideas without being a straight Fetzer build.
Is the Slab the first pedal from Concrete Sound Lab?
Yes. Guitar Pedal X reported in July 2025 that the Slab JFET Preamp and Boost, designed by Josh, is the first ever Concrete Sound Lab pedal and the brand's first release.
Sources (1)
- Guitar Pedal X, Guitar Pedal X, 2025-07-17