Marshall JMP-1
Marshall JMP-1

JMP-1, Guitar amplification from Marshall.

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racerevlon 11/17/2012

Marshall JMP-1 : racerevlon's user review

« A great alternative if you don't have $$$ for a JVM!! »

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The JMP-1 is a valve MIDI preamp. Let's break this down into components. Valve: there are two 12AX7/ECC83 valves on-board that help the preamp generate the gain and the classic Marshall sound. MIDI: the preamp is MIDI-controllable in addition to the simple 4-button foot switch and has 100 user preset locations. Preamp: I think this is where most people get confused. This is a preamp ONLY--it still requires a power amp, whether you have a dedicated rack power amp, or you run into the loop return of an amp head, you'll need a way to power this unit. The only exception is if you're using the emulated out to record directly to a console. All of the usual suspects are on-board: Bass, Middle, Treble, Presence controls, a mix for the effects loop, individual buttons to select each channel, and a "Bass Shift" feature that alters the frequency range affected by the tone controls. There are standard mono or stereo output jacks for connecting to a power amp, emulated line out jacks for connecting directly to a recording console, and an effects loop with a -10/+4 button for connecting and controlling the effects loop. All in all, fairly flexible for a 1U valve preamp.


The JMP-1 on its own is only half of the equation. I've heard a JMP-1 sound absolutely atrocious through one type of power amp, then absolutely magical through another type of power amp. You have to keep in mind what's down-stream of the JMP-1 to ensure you get the best sound out of the preamp. Historically, the selection dial on most of the earlier units was "jumpy" and didn't track very well, something I heard Marshall fixed in later releases. The preamp is simple enough to use if you spend five minutes playing around with the controls and learning what every control does. Saving MIDI parameters is simple enough, requiring only a double-press of the "Store" button to save a MIDI preset/patch.


I've owned this unit long enough to know that experimenting with different types of tubes DOES make a difference. The best sound I've got from the JMP-1 is using Mesa Russian-2 tubes, which is what I still use today. That said, it's really easy to make the JMP-1 sound horrible. My suggestion, as with many things, is to dial in the JMP-1 with your ears and not your eyes. The B/M/T/P controls range from -6 to +6 but don't set the controls where you "think" they should be, set the controls where they sound the best to your ears. If you find that you get a great sound with the bass set to -6, so be it. Don't let your brain override your ears by thinking, "well, that can't be right--there's no way it could/should sound good with the bass fully cut." It can and it will. Always keep in mind this is a PREAMP, not a full amp. If you like the idea of Marshall's latest offering, the JVM series but don't have the cash, a JMP-1 and a good power amp are an excellent compromise. You get four channels, each with a gain control that ranges from 1-20. Even on the clean channels, you can get some good bluesy crunch if you crank up the gain and have fairly strong valves on-board. The key is that you have to spend time dialing in the sound you're looking for with the JMP-1, again, with your ears, not your eyes, and always be mindful of what you're using for power and speakers. Taking something like the JMP-1 and plugging it into a cheap solid-state power amp with cheap speakers will sound, well, cheap. However, go the other direction and run the JMP-1 into a nice valve power amp like a Marshall EL34 50/50 or 100/100, VHT 2/90/2, or even a Mesa 20/20, and you'll get MUCH better results. I run my JMP-1 into a Marshall EL84 20/20 and can get so many great sounds out of it that I actually sold my JVM410H. Just like a pedal/stomp-box, the JMP-1 is ONE piece of a larger puzzle.


The JMP-1 is incredibly flexible and puts a ton of different tones right at your fingertips. You can go from Jazzy clean to death metal with almost no effort. Now that they're out of production and prices are way down, I think the JMP-1 is an excellent value for the price, especially considering that the emulated line out, while sounding "slightly" what I would describe as "transistor-y" is still absolutely viable if you're recording on a budget. I've also owned an ADA MP-1 and would say that they're two different beasts. The JMP-1 interface is much easier to master, but the MP-1 has the on-board light chorus effect that really punctuates the 80's rock sound. Being a rack unit, it's somewhat of a pain to experiment with different tubes but once you find the sound you like you're good to go. Many modern players/bands (Iron Maiden, Def Leppard, Billy Gibbons, etc.) still use the JMP-1 as a staple of their live tone due to its MIDI-switching capability and its virtual warehouse of almost the entire Marshall tonal history. If something were to happen to mine I would replace it without hesitation.