From the moment rock ’n’ roll exploded onto the scene, one name has been at the heart of its most electrifying moments - Marshall. For generations, Marshall amplifiers have defined the sound of the electric guitar, pushing music to new heights and shaping the very essence of modern rock. From the soaring blues-rock of Eric Clapton and the incendiary performances of Jimi Hendrix to the seismic riffs of Jimmy Page, Eddie Van Halen and Angus Young, Marshall’s unmistakable roar has been the foundation of legendary tone.

At the core of this legacy stands the Marshall Plexi - an amplifier so iconic that it has remained a benchmark for tone since its introduction in the 1960s. Originally built to meet the demand for more power and volume, the Plexi starts with bold, sparkling cleans at lower settings, but as the volume is increased, it gradually transforms - first into a rich, overdriven bite and finally into the thick, harmonically rich distortion that became the voice of rock guitar. Whether it was the blues-infused crunch of the late ‘60s, the hard rock revolution of the ‘70s, the high-octane shredding of the ‘80s, or the grunge and alternative explosion of the ‘90s, the JMP remains the amp by which all others are judged.

Now, Synergy and Marshall have joined forces to bring you the ultimate tribute to this legendary amplifier. Combining Synergy’s cutting-edge patented modular technology with Marshall’s historic circuit design, this new Synergy JMP preamp module delivers the unmistakable growl, touch sensitivity and dynamic response of a cranked JMP- at any volume. Whether on stage, in the studio, or at home, this is your chance to harness the sound that built rock ’n’ roll. The legend continues.

Key Features

• All-Tube - The Synergy Marshall JMP is an all-tube preamp module based on the legendary Marshall JMP “Plexi” amplifier, featuring 2 x 12AX7 preamp tubes for rich harmonic performance.
• Era Switch - The JMP module features two vintage-era switches, allowing you to choose between different classic JMP models. The ’60s mode delivers a rounder, smoother JMP tone, while the ’70s mode provides a tighter, more aggressive response - perfect for capturing the evolving sound of rock across the decades.
• Classic Control - The Marshall JMP preamp module features two identical channels, each with Volume 1, Volume 2 and Master controls as well as an independent EQ and Bright switch. The two channels can be dialled in for variations on the same tone or for jumping between different rhythm and lead settings. Volume 1 and Volume 2 controls function much like jumping the inputs on the original Plexi, allowing for precise control over your gain structure. Additionally, independent channel master volumes let you dial in the full spectrum of Marshall Plexi tones -at any volume.

On-Board Phase Inverter – 0-Watt Poweramp

Think of this as our way of fitting an entire guitar amp into a preamp module. In a traditional amplifier, the preamp section shapes the tone and provides gain, while the poweramp delivers the volume, punch, and dynamic response that make a tube amp feel alive. To authentically recreate this experience, the JMP module incorporates a “0-watt poweramp” design, complete with a phase inverter and a small transformer. This innovative approach faithfully captures the harmonic complexity and dynamic response of a cranked Marshall poweramp, delivering the rich tone and feel of a full-sized amp - all within a compact all-tube module.

Dual-Channel, Tube Preamp

The Marshall JMP module delivers the unmistakable tone and dynamic response of one of Marshall’s most legendary amplifiers. Designed to recreate the raw power and harmonic complexity of the original non-master volume JMP, this module features two identical, independent channels, allowing you to dial in everything from bold, articulate cleans to rich, overdriven crunch and searing distortion.

Independent three-band EQ (Bass, Middle, Treble) offers the interactive tone shaping of the original JMP, while Volume 1 represents the brighter input and Volume 2 is the darker, “Normal” input. These controls work together to craft the perfect Marshall tone, with independent master volumes on each channel to precisely balance your levels.

Bright Switches

The Bright switches - four in total - allow you to adjust the bright cap on each volume control. Simply put, the bright cap on a Marshall JMP influences how much high-end (treble) frequencies pass through the volume control, making the sound brighter and more aggressive. On a traditional JMP, this adjustment would require an amp tech, but the JMP module lets you customise the brightness of your Vol 1 and Vol 2 controls. By blending the two channels, you can mix the brightness of Volume 1 with the warmth of Volume 2 to achieve the perfect balance of attack and thickness.

Cathode Select Function

The Marshall JMP module features a three-position switch on the PCB, which allows you to configure the input tube bass response to match the original circuit of the selected module. These settings affect the feel and tightness. Each amp designer has a specific combination of components that make up their input tube circuit. We have selected the three most popular combinations which you can access with this switch: position 1 (1.5K resistor and 22uf capacitor), position 2 (2.7K resistor and .68uf capacitor) and position 3 (1.8K resistor and 1uf capacitor). Of course, you can experiment and try any position to see which you prefer. The JMP module is preset to position 1 (1.5K resistor and 22uf capacitor).

Specifications

• All-tube preamp module based on the legendary Marshall JMP “Plexi” amplifier
• 2 x 12AX7 preamp tubes ensure rich harmonic performance
• Built-in 0-watt power and phase inverter circuit
• Two Identical channels each with Volume 1, Volume 2, Bass, Middle, Treble
• Volume 1 & Volume 2 are the same “Bright” and “Normal” input volumes as found on a Plexi
• 60’s / 70’s Switch Per Channel
• 60’s early era JMP with fatter bottom end and smoother overall tone
• 70’s later era JMP with tighter bottom end and more aggressive bite
• Master Level per channel allows you to precisely balance your levels between channels
• Easy to install and remove from Synergy preamp docks