DiBiQuadro has released Mars800Free, a free amp sim plugin that emulates the classic Marshall JCM800 guitar amplifier. It’s available for Windows and macOS in VST3, AU, and AAX formats.
If you’re after that gritty and bright British, Mars800Free is an excellent free option. This freeware single-channel amp simulates the EL34 power tubes with a precise 64-bit engine and delivers a convincingly raw and aggressive sound.
I’m not much of a guitar player apart from playing some very basic riffs and solos for fun, but I gave this one a try, and it’s excellent for crunchy rhythm guitar and leads.
The front panel is pretty straightforward with Gain, Bass, Mid, Treble, Presence, and Master controls. That said, the tone is anything but limited.
Plugins like this one, especially being free, remind me how much guitar amp sims have improved over the last ten or so years.
This is a fantastic, responsive amp model that feels like the real deal. It captures the dynamics and nuance you’d expect from playing a real amp.
DiBiQuadro says that some of this is due to their approach to circuit modeling. Their “Non-Plus-Ultra” preamp engine combines double-precision nonlinear computing with high-quality algorithms to better simulate the original amp’s internals than most free (or paid) offerings.
Mars800Free uses DiBiQuadro’s proprietary Non-Linear Convolution (NLC) tech to model the power amp, speaker cabinet, mic, and preamp chain as a single cohesive unit. You get four “Pwr/Cab” configurations included, and the sound is noticeably more dynamic and detailed than basic IR-based cabinet sims.
Be that as it may, I’m no DSP expert, but there’s no denying that this amp sounds great.
There’s also a “Shaper” section that runs pre-preamp and lets you slot in things like EQs, compressors, or overdrive/distortion circuits. On top of that, you get component-level control of effects like Wah, Overdrive, and Distortion, including options for diode type, clip symmetry, and mode.
Every parameter can be automated in your DAW, and if you want to render more CPU-heavy setups offline, DiBiQuadro includes a standalone app called The Renderer.
Honestly, it sounds and feels more like a premium plugin than a freebie. If you’re a fan of classic Marshall tones or need a versatile rock amp sim, you’ll want to grab this one while it’s available. DiBiQuadro has hinted it might not stay free forever.
Mars800Free is compatible with 64-bit Windows and macOS systems (Intel & Apple Silicon) and runs in VST3, AU, and AAX formats. You’ll need to download it via the DiBiQuadro Center app, but no iLok or serial number is required.
Oh, and if you want a nice overdrive to go with this amp, you can still grab Safari Pedals Gorilla Drive for free.
Download: Mars800Free
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Last Updated on August 23, 2025 by Tomislav Zlatic.
