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I have a lot of requests for parts and information for the Marshall JMP-1. To keep things simple and straight-forward, I've therefore decided to make dedicated Marshall JMP-1 category in my on-line store.

Marshall JMP-1 stuff at Plasma Music

I don't offer original Marshall spares as they're obsolete and therefore impossible to procure. My new Marshall JMP-1 category in my on-line store however, does comprise some goodies which are either very close to the original items or 'smarter', if you know what I mean. My performance knob and bezel set which bears a close resemblance to the originals, is for example, offered alongside a 'studio' knob and bezel set which looks very cool.

Marshall JMP-1 Knobs Nuts and Bezels
From the bottom (why didn't I stack them the other way around) we have original knobs, my performance knobs and then, my studio knobs.

I've developed things like Eclipse which fixes the annoying skipping of the data encoder as these things are getting rather old now. What am I saying? Marshall didn't do this properly in the first place! πŸ™

Eclipse Bounce Eliminator for the Marshall JMP-1
Eclipse bounce eliminator for the Marshall JMP-1.

And then there's myΒ PML-TX01 replacement transformer for the Marshall JMP-1. Comprising laminates that are made from a different (more expensive) material than was used in the original, my transformer runs cooler and will theoretically live a lot longer. I even managed to get this made in the same factory that made the original Dagnall TXMA-00014.

A replacement transformer for the Marshall JMP-1, my very quiet PML-TX01
My PML-TX01 replacement transformer for the Marshall JMP-1 fits like a glove and runs cooler and quieter than the original.

Recently, I finished designed my RE-JMP-1 replacement rack-ears for the Marshall JMP-1 and my first batch have just been delivered. I'm really happy with these.

RE-JMP-1 Rack-Ears for the Marshall JMP-1
Supplied with six black crosshead screws, my new RE-JMP-1 replacement rack-ears for the Marshall JMP-1 look amazing and fit perfectly.

I've also got together a screw kit for the Marshall JMP-1 which I hope, will help out a few JMP-1 die-hards.

A complete set of screws for the Marshall JMP-1
A collection of black, crosshead external screws for the Marshall JMP-1.

There's also a top-secret JMP-1 project under development which I'm busting to share with but... well, just check in regularly!


I often get asked to modify equipment with a view to changing the sound and indeed the Marshall JMP-1 is no exception, with requests to do so, being received on a semi-regular basis. My response is always the same...

"If you don't like the sound, buy something you do like the sound of."

Yes, I know what you're thinking...

"How can you say that Alex, when you make so much stuff?"

Well, take a closer look, guys. All the peripherals I design and manufacture, have two objectives in mind:

  • To improve reliability
  • To increase longevity

It's that simple and nothing I offer, changes the sound of the equipment we all love.

Yes, there are exceptions. My modular switched-mode power supplies like Aurora, Supernova and Galaxy for example,Β  inadvertently remove transformer generated hum and power supply induced noise. Nebula was designed to give the Roland MKS-70, balanced outputs but it also (and inadvertently)Β  improves fidelity. Hey but they're all good things, right? πŸ™‚


UPDATE - 10th April 2024

So when I posted this article, I mentioned a 'top secret' project. Well here it is, everyone!

Oracle JMP-1 battery eliminator for the Marshall JMP-1

Oracle JMP-1 is my latest upgrade for our favourite MIDI valve pre-amp. It eliminates the requirement for a battery to back up the memory. You can read all about here.

Three Marshall JMP-1 different looking front panels
At the bottom is a JMP-1 with factory knobs, bezels and nuts. The JMP-1 in the middle, is fitted with my PERFORMACE set of knobs, bezels and nuts. The top JMP-1 is fitted with my STUDIO set.

At the moment I have three of my favourite MIDI valve pre-amps in for service and two of the customers have asked if I offer replacements for Marshall JMP-1 knobs, nuts and bezels.

Well too be honest, it wasn't easy. You see the knobs although cosmetically the same, have different shaft fittings. The volume pot knob for example fits a 6mm spline shaft and the data encoder knob fits a ΒΌ-inch D-shaft. Trying to find a knob that has the same diameter as the original, preferably a similar height and colour-wise would look good on the front panel of a JMP-1 is a tall order. Of course if that knob isn't available in versions that fit the two types of shaft, it's useless.

Anyway, I persevered and came up to a couple of options. Having said that, one of them needs to be modified so as to fit the data encoder shaft.

The PERFORMACE knob set looks very similar to the original and also has a similar rubber feel. It has a white position indicator instead of the grey line on the original. I personally think it's just easier to see.

Performance replacement knobs for the Marshall JMP-1
Performance replacement knobs for the Marshall JMP-1

The STUDIO knob set is a little more posh and resembles knobs found on equipment like high-end mixing desks. It too has a white position indicator. Not as wide as that on the Performance knobs, the white position indicator on the Studio knobs, is a little more subtle.

Made of hard plastic, it's got quite a different, clean feel when compared to the original. Unlike the Performance knobs, it's not a simple push-fit but requires securing via a recessed allen screw. Very posh, indeed! πŸ™‚

Studio replacement knobs for the Marshall JMP-1
These are my STUDIO replacement knobs. I personally think they look stunning and so I've got them on my own JMP-1, LOL.

In 1992, Marshall used a slightly non-standard input socket and headphone output socket on the front panel of the JMP-1. When I say 'non-standard', of course they're both ΒΌ-inch but the threading at the front isn't quite the same as many other similar style ΒΌ-inch jack sockets and so 'normal' nuts don't fit properly. How annoying!

Again, I have managed to precure a bunch of these things. Available in two options, the first is a single high-quality moulding, in which the bezel is integral with the nut. Two of these are included in my Performance set.

Replacement single-piece Performance nut and bezel for the Marshall JMP-1
Replacement single-piece PERFORMANCE nut and bezel for the Marshall JMP-1.

The second option has a separate bezel and nut. While the nut has a matt finish, the bezel is very slightly glossy. The combination looks pretty cool, in my humble opinion. These nuts and bezels are included in my Studio set.

Separate nut and bezel replacement parts for the Marshall JMP-1
My Studio package includes a pair of nuts and bezels as separate components. The slight difference in finish between the nuts and the bezels is an eye-catcher.

So if your JMP-1 is looking a bit sad πŸ™ , please do check out my on-line store for my Performance and Studio replacement Marshall JMP-1 knobs, nuts and bezels.


Update - 22nd January 2021

Wow! I've only just put up this post and I've already received e-mails from visitors asking why the top JMP-1 in the picture at the top of this post, is a different shade of gold, to the other two.

Not a trick of the light, it is indeed much darker, perhaps a golden gold as opposed to a white gold. This unit is much older than the other two and I'm guessing that Marshall changed the company that did the plating on the facias, some time after the first few production runs. Pure speculation but what else can I say? Looks good, though!


UPDATE - 17th October 2021

YES, YES, YES!!!!!! πŸ˜€ After many requests, I'm delighted to announce that I have finally found what I believe to be a suitable replacement for the Marshall JMP-1 power switch button. This item is now included in both the Performance and Studio kits.

Replacement power switch button for the JMP-1 in the 'OUT' (off) position
Replacement power switch button for the Marshall JMP-1 is now included in both of my replacement knob and bezel kits.

On the back of the button is a square receptacle that mates with the front of the ON / OFF switch. To fit, all you have to do is line up the orientation of the button so that the receptacle is square to the JMP-1's front panel and then gently push, clicking the button on to the switch.