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CR2032 adapter installed in Marshall JMP-1

I often receive e-mails requesting I look into various aspects of this legendary MIDI valve pre-amp. One request I receive a lot, has led me to develop a CR2032 adapter for the Marshall JMP-1. This replaces the factory soldered battery, with a clip CR2032 holder allowing for the battery to easily be replaced.

CR2032 adapter for the marshall jmp-1
Something to make our lives a little easier; my CR2032 adapter for the Marshall JMP-1.

While readily available several decades ago, CR2032 batteries with solder tags have dropped out of fashion and even if you can find one, there's a good chance that it won't be exactly the same as the one that fits in your gear. As I often say "the nice thing about standards is that there are so many to chose from".

Original battery in Marshall JMP-1
Here's the original battery in Marshall JMP-1. As you can see, it's soldered to the PCB.

My little CR2032 adapter for the Marshall JMP-1 takes care of that, well at least in the JMP-1. 🙂 It's not rocket science but can make life a little easier.

Unfortunately the main PCB has to be removed to fit this adapter and that's not an easy job. It's a process which requires time, patience and of course, the right tools but which is detailed in the installation manual, available after purchase. In fact, the installation manual goes into so much detail, it's ended up being the most comprehensive manual I've written for something so incredibly small!

Marshall JMP-1 main board
This bad boy takes a lot of work to get to and doesn't come out easily but don't worry, my detailed and fully illustrated installation manual will help you all the way.

To prevent tilting during battery swap-out, the underneath of the adapter has a 2mm rubber pad which keeps it very flat and secure.

CR2032 adapter installed in Marshall JMP-1
Fits like a glove and perfectly secure thanks substantial support underneath the adapter PCB.


UPDATE - 9th February 2024

Marshall JMP-1 stuff at Plasma Music

With so many bits 'n' pieces available for the JMP-1 and always thinking of new stuff to make for our favourite MIDI valve pre-map, I decided to make a category just for the Marshall JMP-1 in my on-line store. You can check it out here.

Marshall JMP-1 Service
Marshall JMP-1 Needs Attention
Eclipse Marshall JMP-1 Data Encoder Fix
Marshall JMP-1 Nuts, Knobs and Bezels
PML-TX01 replacement transformer for the Marshall JMP-1
CR2031 battery adapter for Marshall JMP-1
RE-JMP-1 replacement rack-ear reinforcement brackets
Screw Kit for the Marshall JMP-1
Oracle Battery Eliminator for the Marshall JMP-1


MARSHALL JMP-1 FACTORY RESET PROCEDURE

IF YOUR JMP-1'S BATTERY ISN'T DEAD BUT YOU STILL WANT TO SWAP IT OUT, THEN PLEASE DO REMEMBER ONE THING BEFORE REMOVING IT: If you have your own edited presets in your JMP-1, you MUST back them up prior to removing the battery, otherwise they'll be lost.

If you need to reinitialise your JMP-1, here's how:

  1. Switch off JMP-1 via the power button on the far right.
  2. Hold down the OD1 button and the CLEAN 1 button.
  3. While holding down these buttons, switch on the JMP-1.
  4. Wait a few seconds while the display flashes and then release the OD1 and CLEAN 1 buttons.

Marshall JMP-1 Factory Reset

Now then, you're JMP-1 might NOT reset! Yes, that's right. If your machine is locked, performing a factory reset will be useless unless you unlock your JMP-1 first.

To check the memory protect status of your JMP-1, simply try to save a patch. If the display shows 'St L', then your JMP-1 is locked and you will need to unlock it prior to performing a factory reset.

Unlocking is simple. Just follow this procedure:

  1. Try to save a patch.
  2. While 'St L' is displayed, press the <CHANNEL> button.
  3. The unit will unlock.
  4. You can now perform a factory reset as above.

MARSHALL JMP-1 MEMORY BULK DUMP

While you're here, you may find it useful to know how to dump the entire memory of your JMP-1 to a sequencer or sysex package like MIDI-Ox or SEND-SX.

  1. Just connect the MIDI OUT from your JMP-1 to the MIDI IN of your sequencer or computer's MIDI interface.
  2. If using a computer, select that port in your sysex package.
  3. Now just press <Patch> and <Volume> simultaneously on your JMP-1.
  4. THE END!

You may also find this dedicated JMP-1 editor useful: http://jmp-editor.mattzick.com/download.html

Marshall JMP-1 power supply

I regularly receive two questions from those interested in my PML-TX01. Both are about the Marshall JMP-1 input voltage selection:

  1. Is the PML-TX01 replacement transformer for the Marshall JMP-1, 230V or 115V?
  2. Are the voltage selector components diodes, ferrite beads or just fancy wire links?
Marshall JMP-1 voltage selection with PML-TX01
Here are the link locations to select the voltage rating of the primary windings for the transformer in a Marshall JMP-1. The example shown is set to 230V.

The answer to the first question is, just like the original TXMA-00014, my PML-TX01 has two separate primary windings, each rated at 115V. So…

  • EUOPEAN / UK VOLTAGE SELECTION. Wired in series, the primary becomes a single 230V winding. To wire in series, connect ONLY LK2.
  • USA / CANADA / JAPAN VOLTAGE SELECTION. Wired in parallel, the primary becomes a single 115V winding. To wire in parallel, connect LK1 and LK3.

The Marshall JMP-1 input voltage selection is quite easy to change. The JMP-1 can make it look complicated, especially with the use of those eighties style wire links but the original links were JUST WIRE LINKS and nothing else, so you can use wire.

JMP-1 Input Voltage Selection Schematic
This representation might make things a little clearer. Apart from the higher quality material used for the laminates, the PML-TX01 is a direct drop-in replacement for the original Dagnall TXMA-00014.

IMPORTANT

The above is a simple schematic REPRESENTATION of how the links are connected to configure the primaries for either 230V or 115V operation. The physical configuration of the voltage selector links however, is a bit unconventional and suggests that the transformer's primary windings are mirrored with START and FINISH for each winding not being where one might expect! The STARTs, for example could be the the two middle pins and the FINISHes, the two outside pins. Normally, transformer windings would be laid out START - FINISH, START - FINISH. I thought it might therefore be helpful to provide an illustration of the actual (physical) layout of the power input in the Marshall JMP-1 (below).

Marshall JMP-1 Input Voltage Physical Layout
Here's the actual layout of the input voltage side of the Marshall JMP-1. Note that the start and finish of the transformer coils aren't where you might expect.

SIDE NOTE

One might ask why the two individual primary windings are put in parallel for 115V. Why not just use one winding?

Well, a system uses a certain amount of power. Power is the product of voltage and current: P = V x I.

You can probably see now that if you half the voltage, you'll need twice the current to deliver the same amount of power. Placing the two primaries in parallel does just that, it doubles the current going into the system. 🙂

Check out my PML-TX01 low heat and low noise replacement transformer for the Marshall JMP-1 here.

And lastly...

! ! ! DON'T FORGET TO CHECK THE FUSE RATING ! ! !

So as I've just intermated, the power requirement of a machine is the same whatever the supply voltage. Since power = current x voltage, if you're halving the voltage, you'll be doubling the current.

Marshall JMP-1 fuse
Don't forget to select the correct fuse rating for your region.

If running at 230V, the JMP-1 fuse should be 80mA (230V x 0.08A = 18.4W).
If running at 115V, the JMP-1 fuse should be 160mA (115V x 0.16A = 18.4W).

'T' stands for 'time delay' so use a time delay fuse.

 

Every since I launched my replacement knob and bezel sets for the JMP-1, people have asked if I can supply either the original or a Marshall JMP-1 replacement power switch button.

Well the original button isn't available anymore but relating to JMP-1 fans' desperation, I persevered, looking for a suitable alternative.

Replacement power switch button for the Marshall JMP-1
The bottom JMP-1 has the original power switch button. With a slightly lower profile and indented top, my replacement power switch button isn't absolutely identical but it's still a pretty good match.

A few days ago, I think I found one! Three or four millimetres shorter than the original, it does actually fit but when depressed, sits a little closer to the front panel facia than the original. Apart from that, it looks good and works. 🙂

Replacement power switch button for the JMP-1 in the 'OUT' (off) position
My replacement power switch button for the JMP-1 in the 'OUT' (off) position
Replacement power switch button for the JMP-1 in the 'IN' (on) position
My replacement power switch button for the JMP-1 in the 'IN' (on) position

As such, my Marshall JMP-1 replacement power switch button has now been added to both my performance and studio knob and bezel sets. You can check them out here.

Many will know that I have a thing going with the Marshall JMP-1. Despite having a small collection of vintage Marshalls, I keep mon coming back to this little box only too often.

Marshall JMP-1 Full Service

I know the Marshall JMP-1 inside out and do what I can to keep those that are still breathing, going a little longer. 🙂

I've designed a couple of things for this special little box like my Eclipse bounce eliminator which stops the data entry knob from jumping or skipping. Then there's my recently released PML-TX01 replacement transformer which runs a lot cooler than the original, thanks to the use of a higher quality material for the laminates. Unable to convert the outputs to balanced, due to a severe lack of space and appropriate PCB connections, I promote my Transformer Coupled Interface Type 1, as the perfect interface to connect your JMP-1 to your desk or DAW.

I regularly keep an eye out for developments in the world of JMP-1 and sometimes come across little jems like this cool editor: http://jmp-editor.mattzick.com/

And of course if you just need your JMP-1 looked at, don't hesitate to contact me.

A replacement transformer for the Marshall JMP-1, my very quiet PML-TX01
And here it is... my PML-TX01 transformer for the Marshall JMP-1.

This project has taken months but after tracking down Graham Sopp, the guy who designed the original TXMA-00014  JMP-1 transformer, I'm delighted to announce that my PML-TX01 upgraded transformer for the Marshall JMP-1 is now available, featuring laminates made with a higher quality material.

You don't need to be a rocket scientist to notice that the original transformer in the JMP-1 is not particularly stressed. Just take a peek at the regulators and you'll notice an obvious lack of heatsinks suggesting that the current draw from the supply lines is far from excessive. Measuring the input voltages to the regulators indicates that the voltage drop across them is not too much and of course we all know that the valves take very little current.

Marshall JMP-1 Regulators
The regulators in the JMP-1 don't have any additional heatsinking because they don't run hot.

So why then, does the JMP-1 transformer get so hot?

Well, it's due to the fact that the transformer's laminates oscillate. That's right. They oscillate so much that apart from the hum, a considerable amount of heat is also produced.

WARNING - THERMAL MELTDOWN IMMINENT

I've heard of people putting rubber or foam between the top of the transformer and the inside of the JMP-1's lid, to reduce the the hum. DO NOT DO THIS!!! I've just mentioned that the oscillating laminates produce a huge amount of excess heat. Whilst the hum is annoying, with the top of the transformer in contact with the lid, any heat produced at least has a dissipation path. If you put anything on top of the transformer, it'll act like a blanket and you're just going to burn it out quicker. 🙁

Pictured below is an original TXMA-00014 that I removed from a faulty JMP-1. Displaying random behaviour and poor sound quality, when I opened her up, the results of thermal stress were quite obvious.

Burnt out Marshall TXMA-00014 transformer

I spent a lot of time looking at the mystery of the Marshall JMP-1 humming transformer, refusing to acknowledge any issue with the laminates as I just didn't want to believe it. Once the penny dropped though, it all made sense.

My PM-TX01 is of course pin-for-pin compatible with the original Marshall TXMA-00014
Made in the same factory as the original, my PM-TX01 is of course pin-for-pin compatible with the Marshall TXMA-00014

It took a while but my first batch of PML-TX01 transformers is now here. With considerably less hum and heat than the original Marshall TXMA-00014, I thoroughly recommend that you consider this upgrade.

PML-TX01 transformer for the Marshall JMP-1 installed
Looking quite at home, my PML-TX01 fits easily into the JMP-1.

MARSHALL JMP-1 VOLTAGE SELECTION

I regularly receive two questions from those interested in my PML-TX01:

  1. Is the PML-TX01 replacement transformer for the Marshall JMP-1, 240V or 120V?
  2. Are the voltage selector components diodes, ferrite beads or just fancy wire links?
Marshall JMP-1 voltage selection with PML-TX01
Here are the link locations to select the voltage rating of the primary windings for the transformer in a Marshall JMP-1. The example shown is set to 230V.

The answer to the first question is, just like the original TXMA-00014, my PML-TX01 has two separate primary windings, each rated at 115V. So…

  • EUOPEAN / UK VOLTAGE SELECTION. Wired in series, the primary becomes a single 230V winding. To wire in series, connect ONLY LK2.
  • USA / CANADA / JAPAN VOLTAGE SELECTION. Wired in parallel, the primary becomes a single 115V winding. To wire in parallel, connect LK1 and LK3.

The original links were JUST WIRE LINKS, so you can use wire.

JMP-1 Input Voltage Selection Schematic
This representation might make things a little clearer. Apart from the higher quality material used for the laminates, the PML-TX01 is a direct drop-in replacement for the original Dagnall TXMA-00014.

IMPORTANT

The above is a simple schematic REPRESENTATION of how the links are connected to configure the primaries for either 230V or 115V operation. The physical configuration of the voltage selector links however, is a bit unconventional and suggests that the transformer's primary windings are mirrored with START and FINISH for each winding not being where one might expect! The STARTs, for example could be the the two middle pins and the FINISHes, the two outside pins. Normally, transformer windings would be laid out START - FINISH, START - FINISH. I thought it might therefore be helpful to provide an illustration of the actual (physical) layout of the power input in the Marshall JMP-1 (below).

Marshall JMP-1 Input Voltage Physical Layout
Here's the actual layout of the input voltage side of the Marshall JMP-1. Note that the start and finish of the transformer coils aren't where you might expect.

SIDE NOTE

One might ask why the two individual primary windings are put in parallel for 115V. Why not just use one winding?

Well, a system uses a certain amount of power. Power is the product of voltage and current: P = V x I.

You can probably see now that if you half the voltage, you'll need twice the current to deliver the same amount of power. Placing the two primaries in parallel does just that, it doubles the current going into the system. 🙂

And lastly...

! ! ! DON'T FORGET TO CHECK THE FUSE RATING ! ! !

So as I've just intermated, the power requirement of a machine is the same whatever the supply voltage. Since power = current x voltage, if you're halving the voltage, you'll be doubling the current.

Marshall JMP-1 fuse
Don't forget to select the correct fuse rating for your region.

If running at 230V, the JMP-1 fuse should be 80mA (230V x 0.08A = 18.4W).
If running at 115V, the JMP-1 fuse should be 160mA (115V x 0.16A = 18.4W).

'T' stands for 'time delay' so use a time delay fuse.


A WORD OF CAUTION

The transformer is soldered to the now very old, double-sided main board in the JMP-1. Please take care when removing the original transformer. It's a relatively heavy device and the through-hole plating isn't exactly the best quality. The last thing you want to do is strip it!

IMPORTANT

My PML-TX01 upgraded transformer for the Marshall JMP-1 is a high specification drop-in replacement for the original TXMA-00014 only. It is NOT suitable for other pre-amps such as the Marshall 9001.

If you have any questions about my PML-TX01, please don't hesitate to contact me or you can just

This item regularly goes out of stock, I'm afraid but... I encourage customers to back-order. Unfortunately, the crappy e-commerce plug-in I use, only tells the links (like the one above) that the item is out of stock. What 's the bloody point of that?!?!?! So if you want this, then please just visit the PML-TX01 page on my e-store here.


UPDATE - 22nd July 2023

I often get asked about the memory back-up battery in the Marshall JMP-1 and with soldered batteries not really being in fashion anymore, replacements are difficult to get hold of. I therefore decided to knock up a small PCB that mounts into the original battery location but which has a CR2032 clip. This allows for easy battery changing with a standard (you guessed it) CR2032. Measuring the voltage on the battery is a little easier, too. 🙂

CR2032 adapter installed in Marshall JMP-1


UPDATE - 9th February 2024

Marshall JMP-1 stuff at Plasma Music

With so many bits 'n' pieces available for the JMP-1 and always thinking of new stuff to make for our favourite MIDI valve pre-map, I decided to make a category just for the Marshall JMP-1 in my on-line store. You can check it out here.

Marshall JMP-1 Service
Marshall JMP-1 Needs Attention
Eclipse Marshall JMP-1 Data Encoder Fix
Marshall JMP-1 Nuts, Knobs and Bezels
PML-TX01 replacement transformer for the Marshall JMP-1
CR2031 battery adapter for Marshall JMP-1
RE-JMP-1 replacement rack-ear reinforcement brackets
Screw Kit for the Marshall JMP-1
Oracle Battery Eliminator for the Marshall JMP-1

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 ¼-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! 🙂

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 ¼-inch but the threading at the front isn't quite the same as many other similar style ¼-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 🙁 , 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!!!!!! 😀 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.


UPDATE - 9th February 2024

Marshall JMP-1 stuff at Plasma Music

With so many bits 'n' pieces available for the JMP-1 and always thinking of new stuff to make for our favourite MIDI valve pre-map, I decided to make a category just for the Marshall JMP-1 in my on-line store. You can check it out here.

Marshall JMP-1 Service
Marshall JMP-1 Needs Attention
Eclipse Marshall JMP-1 Data Encoder Fix
Marshall JMP-1 Nuts, Knobs and Bezels
PML-TX01 replacement transformer for the Marshall JMP-1
CR2031 battery adapter for Marshall JMP-1
RE-JMP-1 replacement rack-ear reinforcement brackets
Oracle Battery Eliminator for the Marshall JMP-1

Marshall JMP-1 data entry is via a data encoder

I regularly receive Marshall JMP-1s for service and customers often complain about the skipping or jumping of the data entry control. Cleaning (yeah, right) or even replacing the data encoder, doesn’t always resolve the problem. Hence, I designed the Eclipse Marshall JMP-1 skipping data encoder fix.

Eclipse Bounce Eliminator for the Marshall JMP-1

Unlike a potentiometer which comprises a wiper that's in constant contact with a resistive track, a data encoder is basically a series of switch contacts with the wiper moving from one contact to the other, as the encoder is turned.

Difference between potentiometer and encoder
This is a very simplified representation of the inside of a potentiometer (left) with a continuous resistive track and a data encoder (right) with a series of contacts.

As you may have guessed, this means that there’s a gap between each switch contact (correct) and as the wiper moves, there’s a region of zero contact between the wiper and any switch contact. When the wiper leaves or comes on to a switch contact, the electrical signal can be quite transient and messy, similar to an electrical mains spike that sometimes occurs when switching lights on and off but obviously not as big. This is called contact bounce and if the data from the encoder is going directly into a processor, then it should come as no surprise that the processor just wouldn’t know what to make of it. All it wants to see is noughts and ones at nice regular intervals (a pulse). Modern data encoders are optical and so there's no physical contact between a wiper and a track and hence, no bouncing.

To overcome the problem of bounce on mechanical data encoders, a bounce eliminator (or bounce filter, as it's sometimes referred to) is required to remove the spike, thereby making the signal look more like the regular pulse it's supposed to. What the processor wants to see is kind of ‘underneath’ the spike.

For some crazy reason, Marshall, didn’t incorporate a hardware debounce circuit in the design of the JMP-1. Debouncing can be done in software but generally, designers aren’t keen on this approach. I have no idea if the firmware of the JMP-1 includes debouncing suffice to say that if it does, then it doesn’t work! A hardware solution is always preferred.

The encoder is connected directly to the processor in the Marshall JMP-1
RE0 and RE1 off the data encoder, go straight to pins 12 and 13 of the processor with no bounce eliminator circuitry.

One hardware approach is to use passive filters, a combination of resistors and capacitors but due to the unpredictable nature of bounce, this approach can also be unreliable and so Eclipse uses the preferred third option which is to delay the reading of the signals coming off the encoder, thereby missing the bounce. This is achieved using what are called Schmitt triggers.

This is how Eclipse affects the signal from the JMP-1's data encoder.
This is how Eclipse affects the signal from the JMP-1's data encoder.

Fundamentally, Eclipse Marshall JMP-1 skipping data encoder fix, is an active bounce eliminator which can be easily fitted between the JMP-1's data encoder and the main PCB and hence, the inputs to the 8031 processor. The data encoder in the JMP-1 is attached to the motherboard via a 3-way Molex connector. Unplugging this connector and plugging it into Eclipse and then plugging Eclipse into the socket where the encoder was originally connected, only leaves one wire to be soldered to a filtered +5V supply point and you're done! You don't have to remove the main board and as mentioned, there's only one solder point to make. Unless you intend to change the rotary data encoder at the same time, you don't even have to remove the front panel. Simple, eh?!? 🙂

Eclipse bounce eliminator fits between the data encoder and the PCB connection in Marshall JMP-1
3-pin Molex connection between data encoder and main PCB. This is where Eclipse conveniently connects to.

I always seem to have a couple of JMP-1s in for service but just before Christmas 2020, I had one that was of particular interest. The customer mentioned that amongst other things, the data entry control on his JMP-1 was skipping, making it difficult to manually select patches and change parameters.  I told him that finding a suitable replacement isn't easy and  it sometimes doesn't fix the problem anyway, as the problem isn't actually the encoder but the lack of filtering between the encoder and the processor. Stuart volunteered his JMP-1 to be the guinea pig for Eclipse.

Eclipse bounce eliminator for the Marshall JMP-1 installed

I wanted Eclipse to be easily installable by anyone with a little technical competence but I also wanted it to be as small as possible. In fact Eclipse was originally designed using surface mount devices (SMD) but the build-time was ridiculously long making it just too expensive. With a little ingenuity however, I was able to get full-size components on to the original board size!

So with Eclipse measuring only 37mm x 24mm and weighing just a few grams, I could use self-adhesive nylon PCB spacers, allowing for end-user easy mounting close to where the data encoder connects to the main PCB.

Eclipse bounce eliminator up and running in a Marshall JMP-1

The prototype Eclipse was soak tested in Stuart's JMP-1 all over Christmas 2020 as I put it through its paces, suffice to say, that it all worked like a charm! I'm really happy with this little upgrade. "Simple but brilliant, Mr. Bond".

Eclipse actually worked better than I intended, as it doesn't just solve the data knob skipping problem. It makes the whole thing feel smooth, responsive and accurate, how it should have been in 1992!

Although not as open as a potentiometer, the data encoder isn't hermetically sealed meaning that contaminants can get inside the encoder casing. The ingress of dust and dirt and more importantly, years of wear, won't do you any favours when it comes to skipping and like all electronic components, these data encoders have a limited shelf-life.

THE BAD NEWS

The data encoder that Marshall used in the JMP-1 was discontinued by Bourns, the manufacturer, in 2012 due to the lack of RoHS compliancy and is really difficult to find, now. Bourns did release a RoHS compliant version and I'm not sure why even this is hard to track down.

THE GOOD NEWS

Sometime ago, I did manage to find a bunch of original data encoders as used in the JMP-1 and while I try to source an equivalent part, I'm making Eclipse available with the option to buy a  replacement encoder. I strongly suggest that you snap one up while I still have some.

I have pre-wired the data encoders with a 3-way Molex connector so that you don't have to fuff around taking the wires off the original encoder and attaching them to the new one. My wired connections are a little longer than the original, thereby giving you a bit more leeway when it comes to the placement of Eclipse.

Eclipse bounce eliminator for the Marshall JMP-1 is available with optional replacement data encoder
Eclipse bounce eliminator for the Marshall JMP-1 is available with optional replacement data encoder.

MASSIVE TIP

If your data encoder isn't too bad, if it's just started skipping or jumping, please still consider buying Eclipse WITH a replacement data encoder! Just fit the Eclipse board and keep the data encoder that you bought with Eclipse, in the supplied ESD bag, somewhere safe.

As I've already said, these things have a limited shelf-life so it will wear. Even if your JMP-1 is in a super clean environment, the contacts will degrade. Eclipse will help reduce the effects of wear of your encoder but a point will be reached when it's just going to have to be replaced. These data encoders are getting increasingly more difficult to procure but hey, now you've got a spare! 🙂

Each Eclipse is hand built by me and fully tested on... you guessed it, a Marshall JMP-1, before it gets sent out.

Eclipse Test Bed
Looks a bit nuts but this is my Eclipse test bed, attached to my spare Marshall JMP-1.

If you're getting really frustrated because your data entry knob is skipping and if you have a little technical competence, then  the Eclipse Marshall JMP-1 skipping data encoder fix, should be of interest to you. Please don’t hesitate to contact me to learn more or alternatively, you can just...

There's not too much out there resource-wise about the JMP-1 but these links might be of interest:


UPDATE - 7th May 2021

It's coming up to three months (where has the time gone) since I launched Eclipse and I just want to say a big THANK YOU to all those who have bought it and specifically for all the very kind-worded e-mails that I've received.

Designing a product to resolve an issue on a vintage piece of equipment is a challenge. For a start, the market you are aiming for, is constantly shrinking as there are of course, no more JMP-1s being made. So, you're not doing it for the money, right? In fact the reasons you do it are because you love what you do and have empathy for owners of the equipment.

Once designed and tested, an installation manual needs to be written and again, THANK YOU so much for all the compliments I've received regarding that bit of hard work. I'm so glad that everyone has found the installation manual comprehensive and easy to follow, making Eclipse a breeze to install. 🙂

Here's a heads-up, everyone; I have two more products coming out for the Marshall JMP-1, some time over the next few weeks, so stay tuned!!!! HINT: If you have a dead Marshall JMP-1 with a blown transformer, DO NOT THROW IT AWAY. 😀


UPDATE - 23rd June 2021

TCI Type 1 2-channel unbalanced to balanced converter

So here's the first product which will help you squeeze the best out of your Marshall JMP-1; it's my Transformer Coupled Interface (TCI for short) Type 1.

TCI Type 1 is a passive 2-channel line-level unbalanced to balanced converter which will allow you to properly interface your JMP-1 with your recording set-up.

Just plug in whatever outputs you use from your JMP-1 (direct or speaker emulated) using short jack-to-jacks and then plug the XLRs into your mixing desk or DAW recording interface. Oh and don't forget to set the output level switches on the back of the JMP-1 to +4dBm!

You can read all about my TCI Type 1, here or you can check it out in my on-line store, here.


UPDATE - 21st September 2021

At last!!!! 😀 My PML TX-01 replacement and upgraded transformer for the Marshall JMP-1 is finally here!

PML-TX01 replacement transformer for the Marshall JMP-1
And here it is... my PML TX-01 transformer for the Marshall JMP-1

UPDATE - 22nd July 2023

I often get asked about the memory back-up battery in the Marshall JMP-1 and with soldered batteries not really being in fashion anymore, replacements are difficult to get hold of. I therefore decided to knock up a small PCB that mounts into the original battery location but which has a CR2032 clip. This allows for easy battery changing with a standard (you guessed it) CR2032. Measuring the voltage on the battery is a little easier, too. 🙂

CR2032 adapter installed in Marshall JMP-1


UPDATE - 9th February 2024

Marshall JMP-1 stuff at Plasma Music

With so many bits 'n' pieces available for the JMP-1 and always thinking of new stuff to make for our favourite MIDI valve pre-map, I decided to make a category just for the Marshall JMP-1 in my on-line store. You can check it out here.

Marshall JMP-1 Service
Marshall JMP-1 Needs Attention
Eclipse Marshall JMP-1 Data Encoder Fix
Marshall JMP-1 Nuts, Knobs and Bezels
PML-TX01 replacement transformer for the Marshall JMP-1
CR2031 battery adapter for Marshall JMP-1
RE-JMP-1 replacement rack-ear reinforcement brackets
Screw Kit for the Marshall JMP-1
Oracle Battery Eliminator for the Marshall JMP-1


Plasma Music Limited - I'm deeply concerned about the environment and the exploitation of labour and so  I always use local manufacturers in preference to the Far East, with the following in mind:

  1. I can be confident that workers are treated fairly and earn a proper wage.
  2. I can be confident of the standard of quality of each item that is delivered to me.
  3. Communication is important and using local manufacturers, all correspondence is quick and understandable.
  4. I believe in supporting the local economy.
  5. I can be confident that the disposal of manufacturing waste is managed properly and in accordance with national and EU law.

Plasma Music uses local manufacturersUsing local manufacturers isn’t the cheapest option but the above points are important to me. I hope that they’re important to you too.

Marshall JMP-1 Full Service

I’ve seen a few Marshall JMP-1s in my time and as some will know, I really do like this simple and straight-forward MIDI valve pre-amp. As such, I love working on them and enjoy testing the results even more! Having a Marshall JMP-1 in that needs a little attention is never tiring.

Anyway, last week a customer who had just bought one of these off eBay, took the initiative and sent it to me for a full service.

Although dated 1992 making it an original production example, you just wouldn’t guess it from the condition of the unit, it’s pristine. What a find!

Marshall JMP-1 Full Service

Stuart said that he’d like the valves checked as well as the back-up battery. He also commented that the data encoder was skipping. This latter issue is quite common. Marshall didn’t incorporate a hardware bounce eliminator into the JMP-1 and the outputs of the encoder, go straight into the processor. I therefore, took this opportunity to design something that would sort this problem out once and for all. In fact, Stuart's JMP-1 became the first unit to have my 'Eclipse' bounce eliminator for the Marshall JMP-1 data encoder installed and you can read all about that here.

The valves were original and electronically, they will probably last another thirty years. Without modification, we know that the valves don’t really contribute too much to the tone of the JMP-1 but on this occasion, I decided to change them anyway, just so that everything’s nice and clean and so I dropped in a pair of cryogenically treated premium valves sourced from my good friend Derek at Watford Valves.

The two ECC83 in the Marshall JMP-1.

The most disturbing observation when I took the lid off, was the back-up battery. It was obviously swollen and although still backing up the memory, was in desperate need of changing. This point is of particular importance. I leaking battery could render your JMP-1 useless! Please do check out my post of Battery Acid Damage.

Soldered CR2032 in Marshall JMP-1
Just about to pop, the CR2032 as fitted in the Marshall factory twenty-eight years ago.

I explained my Live Forever memory back-up battery mod’ to Stuart and he loved the idea so we went ahead with that.

I cleaned the volume pot on the front as well as the sockets which although looked okay, hadn’t been touched for almost thirty years.

Rear sockets on the Marshall JMP-1
The back of the JMP-1 is simple but comprehensive.

Since the unit had just been bought, there were no user patches of significance so I initialised the memory. If you need to initialise your unit, follow my guide here.

I put the lid back on, plugged it in and WOW! This machine looks, feels and sounds like it was made last week. FANTASTIC!!!!

Marshall JMP-1 looking, feeling and sounding like new
Marshall JMP-1 looking, feeling and sounding like new.

People love their Marshall JMP-1s and I often get asked to supply more than a service. As an example, I recently had a JMP-1 in, that had a data encoder knob which looked like it had spent half-an-hour in boiling water! The rest of the unit was pristine.

Of course, being discontinued for well over twenty years, Marshall don’t really hold a lot of spares for the JMP-1 and sourcing alternatives isn’t easy.

There are two knobs on the front panel and although they look the same, the fittings are quite different. The knob for the volume pot has a 6mm spline shaft and the knob for the data encoder has a ¼” D-shaft. Finding a knob with the correct base diameter, height, ergonomics and colour is hard enough. To find a knob that satisfies all of that and is available in two versions, one with a 6mm spline shaft fitting and another with a ¼” D-shaft fitting is well, kinda impossible. So, while my hunt continues, I am forced to improvise. Having said that, customers seem well chuffed with the results.

Marshall JMP-1 replacement knobs, nuts, bezels
Replacement nuts and bezels for front panel sockets, knob to fit 6mm shaft of volume pot and the same but modified knob to fit the 1/4" D-shaft of the data encoder.

The other items which often get lost or damaged, are the black nuts on the front input and headphone jacks. Well you’ll be pleased to know that I have managed to track down this rare beast including the black bezel for these particular jacks.

Check out my post on replacement Marshall JMP-1 Knobs Nuts and Bezels to learn more or just visit my store to buy.

As mentioned, I don’t tire of working on these machines, so if you’ve got a Marshall JMP-1 that you feel could benefit from some attention, just contact me.


UPDATE - 23rd June 2021

TCI Type 1 2-channel unbalanced to balanced converter 

The JMP-1's outputs can be set to run at +4dBm line-level but they're unbalanced, which was quite a common thing at the time. To help you squeeze the best out of your favourite MIDI valve pre-amp, I've developed my Transformer Coupled Interface (TCI for short) Type 1.

TCI Type 1 is a passive 2-channel line-level unbalanced to balanced converter which will allow you to properly interface your JMP-1 with your recording set-up. Just plug in whatever outputs you use from your JMP-1 (direct or speaker emulated) using short jack-to-jacks and then plug the XLRs into your mixing desk or DAW recording interface. Oh and don't forget to set the output level switches on the back of the JMP-1 to +4dBm!

You can read all about my TCI Type 1, here or you can check it out in my on-line store, here.


UPDATE - 21st September 2021

At last!!!! 😀 My PML-TX01 replacement and upgraded transformer for the Marshall JMP-1 is finally here!

PML-TX01 replacement transformer for the Marshall JMP-1
And here it is... my PML TX-01 transformer for the Marshall JMP-1

The laminates of the PML-TX01 are made from a higher specification material, thereby reducing hum and hence, heat generation, too.

Exactly the same size and pin-for-pin compatible with the original TXMA-00014, my PML-TX01 is a true drop-in replacement.

My PM-TX01 is of course pin-for-pin compatible with the original Marshall TXMA-00014
My PM-TX01 is of course pin-for-pin compatible with the original Marshall TXMA-00014

You can buy my PML-TX01 here:

This item regularly goes out of stock, I'm afraid but... I encourage customers to back-order. Unfortunately, the crappy e-commerce plug-in I use, only tells the links (like the one above) that the item is out of stock. What 's the bloody point of that?!?!?! So if you want this, then please just visit the PML-TX01 page on my e-store here. Grr....


UPDATE - 22nd July 2023

I often get asked about the memory back-up battery in the Marshall JMP-1 and with soldered batteries not really being in fashion anymore, replacements are difficult to get hold of. I therefore decided to knock up a small PCB that mounts into the original battery location but which has a CR2032 clip. This allows for easy battery changing with a standard (you guessed it) CR2032. Measuring the voltage on the battery is a little easier, too. 🙂

CR2032 adapter installed in Marshall JMP-1


UPDATE - 26th February 2024

Now available in my on-line store,  a screw kit for the Marshall JMP-1

Screw kit for the Marshall JMP-1


UPDATE - 10th April 2024

My latest upgrade for our favourite MIDI valve pre-amp; Oracle JMP-1 battery eliminator for the Marshall JMP-1. You can read all about it here.

Oracle Battery Eliminator for the Marshall JMP-1

So in case your Marshall JMP-1's memory gets screwed up, if you just want to start from a clean slate or you've just changed the memory back-up battery, here's the Marshall JMP-1 factory reset procedure.

WARNING: Implementing this procedure will permanently delete all user-made changes to any patches.

Marshall JMP-1 Factory Reset

  1. Switch off JMP-1 via the power button on the far right.
  2. Hold down the <OD 1> button and the <Clean 1> button.
  3. While holding down these buttons, switch on the JMP-1.
  4. Wait a few seconds while the display flashes and then release the OD 1 and Clean 1 buttons.

Now then, you're JMP-1 might NOT reset! Yes, that's right. If your machine is locked, performing a factory reset will be useless until you unprotect your JMP-1's memory.

To check the memory protect status of your JMP-1, simply try to save a patch. If the display shows 'St L', then your JMP-1 is locked and you will need to unlock it prior to performing a factory reset.

Unlocking is simple. Just follow this procedure:

  1. Try to save a patch.
  2. While 'St L' is displayed, press the <CHANNEL> button.
  3. The unit will unlock.
  4. You can now perform a factory reset as above.

MARSHALL JMP-1 MEMORY BULK DUMP

While you're here, you may find it useful to know how to dump the entire memory of your JMP-1 to a sequencer or sysex package like MIDI-Ox or SEND-SX.

  1. Just connect the MIDI OUT from your JMP-1 to the MIDI IN of your sequencer or computer's MIDI interface.
  2. If using a computer, select that port in your sysex package.
  3. Now just press <Patch> and <Volume> simultaneously on your JMP-1.
  4. THE END!

You may also find this dedicated JMP-1 editor useful: http://jmp-editor.mattzick.com/download.html


I  hope this Marshall JMP-1 factory reset procedure helps a few people but if you get seriously stuck, just message me. 🙂

If you want to read more about what I do with JMP-1s, like general service and repair, finding a permanent solution for the skipping data entry knob thing, sorting out the humming transformer issue and offering nice, classy replacement knobs, then please check out some of my other posts:

Marshall JMP-1 Service
Marshall JMP-1 Needs Attention
Eclipse Marshall JMP-1 Data Encoder Fix
Marshall JMP-1 Nuts, Knobs and Bezels
PML-TX01 replacement transformer for the Marshall JMP-1
CR2031 battery adapter for Marshall JMP-1
RE-JMP-1 replacement rack-ear reinforcement brackets
Dedicated Marshall JMP-1 category launched in on-line store

Marshall JMP-1 Knobs Nuts and Bezels

Apart from service and repair, I sell a few bits 'n' pieces for the Marshall JMP-1 which you may find of interest. Check out my on-line store to find out more.


UPDATE - 21st September 2021

At last!!!! 😀 My PML-TX01 replacement (and upgraded) transformer for the Marshall JMP-1 is finally here! Running much cooler and producing considerably less hum than the original TXMA-00014 my PML-TX01 is an upgrade worth considering.

And here it is... my PML TX-01 transformer for the Marshall JMP-1
And here it is... my PML TX-01 transformer for the Marshall JMP-1


UPDATE - 20th July 2023

I've just brought out an adapter which fits into the location of the JMP-1's battery and allows a standard CR2032 battery to be installed. 🙂 You can read all about here.

CR2032 adapter installed in Marshall JMP-1


UPDATE - 8th February 2024

At last! rack-ear reinforcement brackets for the JMP-1 are on the way!!! 😀 People have been asking me for these for a long time so what the hell... let's get them made.


UPDATE - 9th February 2024

Well, I guess I have to admit that I can't help developing stuff for the Marshall JMP-1. So to make life easier for everyone, I've now got a Marshall JMP-1 category in my on-line store!

Marshall JMP-1 stuff at Plasma Music