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Give your Roland SH-101 a little TLC

Recently, one of my regular customers put his Roland MPG-80 up for sale, having acquired a Retrtoaktiv MPG-8X. I’ve always, always wanted a MPG-80 to (obviously) go with my MKS-80 but I’ve never seen one in the kind of condition I’d like. Dan’s MPG-80 however, was pristine so I made him an offer which he conditionally accepted, the condition being that I provide him with a Roland SH-101 service.

Dan told me that he’d picked it up at a knock-down price but although cosmetically things seemed okay, some sliders weren’t working properly, some keys were intermittent as well as similar problems with power. Hmm… Okay, let’s have a look.

Well, when I took this thing apart, I was shocked to see the dust and grime within. On top of that, it had sustained fluid damage and from what I could tell, twice!

This SH-101 was completely full of crap! It was clear that this poor ol’ gal had been kept in a smoker’s environment. The pads that cover the switches, just crumbled. That’s right. Tobacco smoke doesn’t just discolour, it reacts with certain materials, making them stiff and brittle.

Roland SH-101 serviced at Plasma Music
The dust covers underneath the Portamento and transpose switch levers, just crumbled. Difficult to see in this picture but I managed to replace them with some of my black magic thingy!!!

It was no surprise then, to suss out why some keys were intermittent and why some sliders had quite poor performance. Dan, this is a little more than a standard Roland SH-101 service, mate!

I stripped the whole machine so as to wash the knobs, buttons, slider caps, keys and even the plastic top-case. With the afore mentioned exposure to smoke, I was very concerned that the keyboard contact strips would break as I removed them but I got lucky.

Roland SH-101 keyboard bed after decades of neglect
Roland SH-101 keyboard bed after decades of neglect and being kept in a smoker's environment.
Keyboard contact strip after decades of neglect
Same with the keyboard contact strip. Looks absolutely awful.
Roland SH-101 keyboard bed and contact strips after cleaning
Before and... after. I got lucky with this one. After such a long time (and especially after long-term exposure to tobacco smoke), it's quite common for the contact strips to tear when removing them from the keyboard bed.

There were a few dry joints which were to be expected and some of the sliders couldn’t be cleaned and therefore required replacement.

While I was at, I also cleaned the sockets hoping that they would be okay. Dan supplied me with a power switch which I fitted but I also changed the DC input jack as the original seemed lose and let’s face it, after thirty-something years, why not?

After a gruelling seven hours, Dan’s SH-101 was back together again, so time to fire up. The machine switched on first time. Playing around the the DC input, power now was stable. Although I had sound, the HOLD function was stuck on. This is a relatively common problem and is often caused by the HOLD jack socket being stuck open. I’d already checked the sockets and quickly traced the source of the issue to a dry-joint that I had missed.

After an extensive testing of all functions, it was time to flip the machine over and recalibrate. As it turned out, things were quite good and I ended up not doing too much at all.

It’s unfortunate that the plastic pillars used to secure the metal bottom-case to the top-case, are so fragile. During my thirty years of fixing SH-101s, I haven’t yet found a way to cost-effectively and reliably repair these. Fortunately, so long the majority  of them are intact, it’s not too much of a problem.

A sadly familiar sight to many Roland SH-101 owners - a broken screw post
A sadly familiar sight to many Roland SH-101 owners - a broken screw post.

One of the pillars that secures the metal bottom case to the keyboard chassis was missing and the other had an incorrect self-tapping screw rammed into it at some point in its life, which has completely ruined it. The original pillars are very hard to come by and with a couple of the internal plastic pillars broken, it was important to ensure that the bottom-case is properly secured. I therefore fitted brand new M3 PCB spacers to the keyboard chassis, in place of the original pillars. Of course, I also had to dig out a couple of nice, shiny black M3 machine screws. It all ended up very secure and looking very tidy.

Replacement M3 pillar on Roland SH-101 keyboard chassis
Here's one of the two replacement M3 support pillars that I fitted on to the keyboard chassis. Two non-self-tapping screws, pass through the metal bottom-case and into these pillars.

Kept near a heat source at some time, the battery compartment cover had warped slightly. The deformation was subtle but resulted in the cover sitting ever so slightly proud of the top of the top-case. Not too big a deal, in fact it’s hardly noticeable. I was tempted to gently heat the cover to see if I could make it straight again but these things are so fragile, I decided against it.

Roland SH-101 serviced at Plasma Music
Dan's Roland SH-101 almost looking like new again and definitely feeling and sounding a lot better than when it came in.

There’s a lot of talk on-line about the infamous Roland SH-101 discolouring. The SH-101 was released in three colours; red, blue and grey. ALL versions discolour and no one really knows why. Exposure to ultraviolet (sun) light seems to be the most common opinion but my own SH-101 has been kept in an artificially lit, smoke-free environment for most of its life and is now more pink than red! I can understand why people blame UV, however. Removing the battery compartment cover reveals  the ‘original’ colour of your SH-101 suggesting that everywhere else which is of course exposed, will be discoloured by ambient UV. Oh well, just one of those weird mysteries of life, eh!

Nice shiny looking and smooth feeling keys
WOW! Nice shiny looking and smooth feeling keys.

Another slightly annoying issue with the SH-101 is that it's very GROOVY!!!!! Yes, that's right. Those nicely aesthetic lines cut into the top-case add to the SH-101's cool look but they also gather all sorts of dust and crap over the years. Even if kept in a nice, clean environment, the grooves in the SH-101's top case do get dirty and getting it out can make a Roland SH-101 service a little longer than anticipated. 🙁

The brittle plastic, the weird decolourisation and the dirt gathering grooves in the top case don't of course detract from the SH-101's attributes. That classic analogue, mono-synth sound and the pure ease with which it can be manipulated, are what the SH-101 is really all about and perhaps decades after its launch, the niggles now simply add to its cute character.

Anyway, at long last, this Roland SH-101 now looks, feels and sounds fantastic. Nice and shiny, smooth and responsive controls and a solid keyboard, it's almost like new! It's always really exciting for me, when customers come over to collect their gear and I know Dan's busting to check out his refurbished Roland SH-101. 🙂

Launched in 1983, the humble but amazingly well-known and popular Roland SH-101 is pre-MIDI not that many seem to care! Being equipped with CV however, means that the SH-101 can be controlled by another source and as many of my customers will know, my favourite MIDI gadget / upgrade manufacturer, Kenton Electronics, offers a couple of options to to get your SH-101 controllable via MIDI. The SH-101 MIDI CV kit for example, is installed into your SH-101 and although requiring holes to be cut into the case for MIDI sockets, it does mean that you won't have another box floating around.

Kenton Pro Solo Mk 3
One of several gadgets made by Kenton Electronics that'll get your Roland SH-101 connected to your MIDI studio, the Pro Solo Mk 3 stand-alone MIDI / CV converter, is fast and accurate.

Kenton also makes a range of stand-alone CV / MIDI converters like the USB Solo, Pro Solo Mk 3 and Pro 2000 Mk 2. These gadgets are very fast and accurate and  don't require any modifications to your synth's case. I've already mentioned that I've always been a big fan of Kenton's products, so if you do want to get your SH-101 connected, then I strongly suggest you check out their MIDI / CV converters, here.

As well as owning a SH-101 myself, I've worked on hundreds of them over the years and know it inside-out, so if you've got one that's in need of a service or if it just needs a little TLC, please don't hesitate to get in touch. 🙂

Read more about the Roland SH-101 here:

Vintage Synth Explorer - Roland SH-101

Roland Icon Series - SH-101



Hiwatt amp found in pyramid
A truly remarkable find - Rokatiti tomb, chamber 3C showing Hiwatt DR-103 amp, tucked in round the back.

A couple of months ago, one of my regular customers called me in a blinding panic telling me all about these Hiwatt amps that had been found in a pyramid excavation and how he’d acquired them. For a civilisation that didn’t invent the nail, this was truly a remarkable find.

Hiwatt amp found in ancient tomb
And this is chamber 21F. Check out the Hiwatt DR-103 at the back.

Adrian explained that the tomb in which the amps were found, was that of the previously unknown Pharaoh Rokatiti. Having been targeted by tomb raiders at some point, archaeologists believe that the amps remained untouched for the simple reason that no one knew what they were.

The amps in question were DR-103s and Adrian couldn’t think of anyone better qualified and experienced to have a look at them, before they were switched on.

We arranged a COVID friendly drop-off and a couple of weeks later, after making some space in my schedule, I was able to check out these beautiful amps.

Hiwatt DR-103 found in ancient tomb is full of sand and rubble
Ancient Egyptian sand and rubble inside this Hiwatt DR-103.

As expected, both of them were full of sand, like SERIOUSLY FULL OF SAND. One had been modified and had holes drilled in the front panel and in the serial number plate on the rear panel. Most unfortunate but there didn’t seem to be too much wrong with either of them, at least not on initial inspection.

Hiwatt amp found in ancient tomb needs cleaning before anything else
These amps needed serious cleaning before I can do anything else.

Having been dormant for almost three thousand years, the first thing I did after cleaning them up, was to check the ON / OFF and STANDBY switches. The switches on one of the amps looked particularly bad and although I wanted to keep things as original as possible, I also wanted these amps to actually work... and safely.

Hiwatt DR-103 switches need replacing. One has been replaced before.
Quite unsafe, these switches on the second DR-103 really didn't look too healthy. In fact, at some point, one of them had already been changed.

As I proceeded, some hardware just crumbed and I had to replace a lot of screws, all of which were understandably but annoyingly imperial and not metric.

New switches on Hiwatt DR-103
Satisfying the two objectives of keeping things as original as possible and making these amps sing again, was a challenge but for the sake of safety, I decided to fit new switches on the second amp.

The fuses in both amps were intact suggesting that things were okay last time they were used. My main concern was the output transformers.

A couple of resistors had to be replaced as they either broke or crumbled, too. That led me to check other components, just for integrity. I also ripped out the bad mods on the ‘second’ amp.

Hiwatt Attention to Detail
Check out that wiring! No wonder these Hiwatts were often referred to as "posh Marshalls".

Famously, the wiring of Hiwatts is an engineer’s dream and these amps typify the attention to detail with which Hiwatt did things. Everything looks so precise. Everything looks just so tidy. Compared to a Marshall, a Fender or even a Mesa Boogie, these things are just beautiful inside. This kind of precision arrangement surely contributed towards the well-known, superior signal-to-noise ratio associated with those old Hiwatt amps.

Remains of several shark-fin guitars were also found with the amps and in other chambers, prompting expedition artist Tony Burlinson to knock up an impression showing Pharaoh Rokatiti doing his thing in the desert.

Archaeologists didn't find any evidence of a band and speculate that Rokatiti was a solo act. Perhaps he was ahead of his time.  Perhaps like the nail, ancient Egyptians didn't conceive the idea of a rock band. Perhaps we'll never know...

Rock Faro Rokatiti
Undoubtedly the loudest 100W amps ever, Pharaoh Rokatiti could be heard jamming with his Hiwatt, for miles.

Anyway, once the chasses had been cleaned and I had checked the amps were safe, I moved on to the cabinets and spent several days getting the boxes to look like they might have, a couple of thousand years ago.

Hiwatt DR-103 renovation - new screws and screw-cups
New screws and screw-cups where appropriate, made a big difference.
Hiwatt DR-103 renovation - new feet
Having disintegrated to a few millimetres in height, the original feet were at the point of crumbing into dust and so I fitted new ones.

While I was doing that, I ordered valves and capacitors from my good friend, Derek Rocco at Watford Valves. Derek has been supplying me with valves and caps for decades and I've had the privilege of seeing his digital test / calibration equipment in action. My customers expect the best, so I simply won't source these vital components from anywhere else.

Hiwatt DR-103 with Marshall branded EL34s
I decided to use Shugaung manufactured EL34Bs in these Hiwatt DR-103s. Derek passes on the great deal he gets from Marshalls, on to his customers. Hey, check out that heatshield at the back and err... no sand!

Co-designed by Marshall and the Shugaung factory in China, the EL34B is an evolution of the famous ‘Winged C’ EL34 which, by 2007, Svetlana was having problems supplying.

Today the Shugaung EL34B is used by all the big valve amp manufacturers including Hiwatt. Here's what Derek Rocco says: "What I have found with the EL34B, is that in clean mode the valve remains cleaner at higher volume but when driven, it breaks up easily with plenty of rich harmonics."

Replacing the valves was straight-forward enough but the large power supply capacitors were going to be a bit more challenging. It would have been easy enough to rip out the old caps and drop in the new ones but I wanted to retain that lovely Hiwatt wiring.

Hiwatt DR-103 - original and new replacement capaciotrs
The difference in terminal orientation and pitch between the original capacitor on the left and the new capacitor on the right, isn't normally an issue. On this occasion however, I was keen to retain the famous, tidy Hiwatt wiring which made the power capacitor transplant really quite challenging.

Although roughly the same size, the terminals on the new capacitors were orientated differently and they had a different pitch, to the originals. The difference was enough to make things a bit tricky, even after I'd carefully disconnected the old caps. It took a while and a lot of patience and careful thought to the arrangement. In fact I treated the replacement of each of the five capacitors, as a separate operation... and of course after having done one amp, I had to do it all over again.

Second amp after clean up
Here's the second amp with new power capacitors. Notice the holes in the rear of the chassis which were part of the mods and which I didn't hesitate to remove. I later cleaned these up and then plugged  them.

As mentioned, amp 2 had three mods; one provided a feed off the speaker outputs which was poorly buffered. Another provided a feed off the master volume and the third, which had been partially disconnected, looked like a line input, bypassing the first couple of valve stages. Perhaps Rokatiti wanted to connect his amps somehow. Hmm... If that was the case, I would have expected to see similar mods on the other amp. Anyway, wanting to put these amps as close to factory as possible, I ripped all of them out .

Plugged mod hole in front panel of Hiwatt amp found in pyramid
It was unfortunate that the second amp had holes drilled in the chassis. I did my best to cover these up as tastefully as possible.

I'd run out of plastic 11mm hole plugs so I had a couple of frustrating days' wait until my reorder arrived in the post.

One of the holes in the rear panel, had been drilled straight through the serial number plate and although the serial number itself was still quite legible, it just seems such a shame. I did try to contact Hiwatt asking if I could get a replacement serial number plate but disappointingly, I'm still waiting for a response. 🙁

Hiwatt DR-103 with plugged mod holes
You can get away with a couple of holes on the rear panel but straight through the serial number plate? SERIOUSLY?!?!?!

After a couple of days, the job was done and I plugged in the first amp into my custom-built dummy load which has a feed that allows convenient connection to my oscilloscope.

Power on... No big bang, just that gentle hum that we associate with valves amps. Wait a minute for the valves to warm up and then.. Standby, off...

Pre-amp valves in Hiwatt DR103
Harma ECC83 pre-amp valves from my friend, Derek Rocco at Watford Valves.

I set my signal generator to chuck out 1kHz at -20dBm and slowly wound up the input gain on the Normal channel. Then I inched up the master volume. Yes, that's right. The DR-103 was a master volume amp and was a little ahead of it's competitors.

The oscilloscope displayed a perfect sinewave. Well that's a good start. I tested the amp at several frequencies allowing me to check the functionality of the tone controls. Wow! Very smooth, no drop-outs or sudden bursts.

Testing Hiwatt amps found in pyramid
It was always felt that the only way to get an overdriven sound out of a Hiwatt, was with an overdrive or distortion pedal. Indeed the headroom on the inputs and the power amp is considerable.

Okay, now I need to plug this into a cab and check it out with a guitar. I chose not to use a power soak and was prepared to crank this. Following the flood at my studio last August, I'm still working from home, so this all happened in my kitchen!

Boy, is this thing loud! I was so taken back that I forgot all about the fact that the amp actually worked. I played for about half-an-hour, loving every second and everything remained solid. The second amp was next and performed exactly the same as the first. Amazing. After a couple of thousand years, these things still frigin' rock!!!! 🙂

Hiwatt DR0193 renovation 1

"Hiwatt Amps Found In Pyramid" Well, not quite but it is April fools' day, LOL. 😀 Although a challenge, restoring these Custom Hiwatt 100s has been a real pleasure. Showing their age but after a full refurb, they're actually in remarkably good condition and despite a couple of new fittings, are pretty original, too. More importantly, they just sound amazing!

Alex with two Hiwatt DR-103s that have been refurbished after having been discovered in pyramid
Hiwatt amps found in pyramid looking like new and sounding BIG! Hey, Alex, is that one of Pharaoh Rokatiti's Shark-Fins???.

If you're lucky enough to have found a couple of Hiwatt amps in a pyramid, or perhaps at the back of your attic, please do contact me. I'd love to know about them!

These Hiwatt DR-103 amplifiers are a unique link to a bygone age. I’m not talking about a time when thermionic valves ruled, or Pete Townsend of The Who or Dave Gilmour of Pink Floyd, were household names. I’m talking about a time when the likes of Jim Marshall and David Reeves (founder of Hiwatt Amplification), actually cared about their products, the craftsmen who made them and their customers.

I was and always have been a Marshall man but the truth is Marshall, Hiwatt, Fender, it didn’t matter. As a budding rock star, owning one of these amps made you feel like you’d just joined an elite club and that stardom was now somehow, guaranteed. That big black box wasn't just an amp. It was a thing of magic. In fact, back in 1980, when I got my very first Marshall, it sat on my parents’ dining room table for a couple of days, with me err... just staring at it.

I fondly recall the front cover of the Electric Warrior album by T. Rex which pictured a silhouette type image of Mark Bolan playing his famous Les Paul, in front of one of those old stacks. Oh wow! That image was just so inspiring and now I was the owner of a real Marshall amp and there was suddenly a connection between me and Mark Bolan. I felt like someone special and I just knew that all I needed to do now was to record that hit song.

Electric Warrior by T Rex
Simple but iconic, the album artwork on Electric Warrior by T. Rex. When I saw this awe-inspiring image, I just knew what I wanted to do for the rest of my life.

Well, none of that ever happened but I was definitely sold the dream!

Indeed, the dream-maker package disappeared a long time ago. Digital processing, modelling and IR technology means that you can now dial up a patch to sound ‘like’ whatever or even whoever.

Rock was the sound of anarchy and loud, overdriven, low-slung electric guitar, was the symbol of a non-conformist youth. I remember bunking off school to play guitar. Today kids go to school to learn to play rock. Seriously?!?!!?

"Well now-a-days, it's all about the music." I hear people say. Hmm... I remember a time when it was (all) about a whole "lotta" love, I mean more...





MCK-70 Memory Checker for the Roland MKS-70 and JX-10.

Introducing a fantastic utility, MCK-70 is a memory checker for the Roland MKS-70 and JX-10, developed by non-other than Guy Wilkinson.

A few weeks ago, I received a Roland MKS-70 from a customer in Canada. He’d just had it upgraded with Guy Wilkinson’s fabulous VFD module and Fred Vecoven’s PWM mod but then weird things started to happen. This machine was then sent a couple of thousand miles across the Atlantic to see what I could do with it.

The first thing was to fix the power supply. It was totally shot. Signs of heat damage and all regulated outputs showing zero volts except the -15V line which was reading -21.5V, wasn’t a good start. Oh dear. Anyway, I got that going temporarily as the customer agreed to have Guy Wilkinson’s P0004 switched-mode power supply installed.

The next issue was that some voices weren’t playing. After going over the voice-boards and confirming that they were both okay, I decided to look at the assigner (CPU) board.

To keep things simple, I disconnected the Vecoven PWM mod and I also installed the original Roland firmware. This meant that I had to have the voice-boards connected which is a bit of a pain.

After a lot of testing, chatting with Fred Vecoven and Guy Wilkinson, it seemed clear that the machine had a memory issue.

Guy told me that he’d developed a little bit of software to test the RAM in the Super-JX and we agreed that this would be a perfect opportunity to actually check it out.

Guy e-mailed me the bin file, I promptly burnt a ROM, installed it into the MKS-70’s Assigner-board and switched on. Oh wow! This is so cool!

MCK-70 in action

Running in the processor's on-board memory and thereby leaving all other memory free, MCK-70 systematically checks not only the main RAM but also the gate-array RAM, writing all zeros as it sweeps. After a few seconds, you end up with an ultra-clean slate, a Super-JX that's cleaner than factory!

I then loaded some factory stuff into the MKS-70. Wow! All looking good so far. Programming a very simple tone and patch confirmed that everything was working and that the issues that were present before, were all gone. Guy, you’re a genius! THANK YOU, my friend. 🙂

MCK-70 Boot
MCK-70 will work on the Roland JX-10 as well as the MKS-70.

It was obvious that MCK-70 would be really useful to others and so Guy and I decided to make MCK-70 Memory Checker for the Roland MKS-70 and JX-10, available to purchase in my on-line store.

A great tool for anyone who may have similar MKS-70 or indeed JX-10 memory corruption problems, MCK-70 will save you a lot of hassle and money. Removing the TC5564 RAM chip requires removal of the assigner-board and unlike the voice-boards, the assigner-board has a couple of delicate membrane cables connecting it to the display board and the cartridge board. You really want to avoid disturbing these, if you can.

On top of that, the TC5564PL-15 isn’t at all easy to get hold of and hey, why on earth would you want to change the RAM chip in your Super-JX if you could know that all that’s happened, is that the memory’s got a little… well, bent?


  • When purchasing, you can select your preferred format; a downloadable .bin file or a physical ROM. If you buy the former, you'll need a ROM burner to put the program on to a 27C256 ROM. If you buy the physical ROM version, that'll be sent out to you.
  • This will totally delete the memory in your machine. Don't mess with it unless you actually have an issue or your machine's memory is backed up.
  • Although I've used a real case study involving a customer's MKS-70, MCK-70 will work in the Roland JX-10!

Cheetah MS6 and Custom Power Supply 1

Just before Christmas 2020, I got sent a SoundLab SST-19 guitar pre-amp and a Cheetah MS6 synth module. Both needed power supplies. The SST-19 was immaculate and the customer was confident that it was working (when it had a power supply, of course). You can read all about that here soon. The MS6 however, was a different story all together. The customer told me that one day it just went bang. In fact, it tripped the electricity supply to his house! After a brief conversation via e-mails, he sent me his machine requesting a complete Cheetah MS6 power supply build.

Cheetah MS6 Front Panel
This customer's blown Cheetah MS6 has definitely seen better days!

Again, I was told that the machine was working prior to the bang but of course I had no idea if the unit had been damaged by the fault. It was a gamble and there weren't too many resources available on this thing, either. Here’s a list of useful stuff that I did find:

Readable schematics were also thin on the ground and when I did find a copy that was readable, that’s all it was, a schematic with very little useful reference.


To speed things up in the long run, I spent a couple of hours cleaning up and organising the best schematics I could find. My small contribution to the the Cheetah MS6 community and hoping this will be useful to someone, organised and readable schematics can be downloaded here. 🙂

So, where were we? Oh yes... The unit turned up and I took off the lid. Ah! So, someone’s been in here before. Three of the four regulators had been replaced. They’d been attached to a thin aluminium strip which had then been glued to the inside of the case and I'm sorry but the soldering was atrocious! After taking the board out, it was obvious that this box had sustained fluid damage at some point in its life. Hmm… looked like I had my work cut out. Oh and the original firmware had been swapped out for the Maad KM 3.0 custom version. Sceptical at first, after some research, I have to confess that I've only heard good things about this. 🙂

Anyone who’s familiar with the Cheetah MS6 will be aware that the power supply is well, bloody awful. It’s not uncommon for example, for the case to go positive. Yes, you read correctly. The transformers (yes, there two) apart from being underrated are quite unreliable and the original heatsinking is totally inadequate.

My initial approach to the project was to build an external box which would house two uprated transformers and then provide a suitable connection from the box to the MS6. The latter part would require a hole or two to be drilled into the rear case of the MS6.

There are four regulators supplying +/-5V and +/-12V. The backend was such that I could remove the original transformers and drop connections to the main PCB where the secondaries of those transformers come on to the board. Since the supplies were complimentary, each utilised a centre-tap. I found a suitable enclosure all-be-it, a little larger than I initially had in mind and began plans for the metalwork company.

Cheetah MS6 Original Transformers
The blown transformers that I removed from this MS6. I'm afraid that these will go BANG sooner or later.

While that was going on, I cleaned up the PCB, getting rid of as much sign of the fluid damage as I could.

Next was the post transformer part of the power supply which as I’ve already mentioned, was a real mess. The PCB seemed quite fragile around the rectifier diodes, capacitors, etc so I had to be careful. While I was in design mode, I knocked up a drawing for a proper heatsink.

Well, I took the stripped-out case, the enclosure for the external power supply and my drawings to Lenton Engineering in Watford and a couple of weeks later, I got the call informing me that everything was ready to collect.

The transformers, switches and connectors all fitted into my external enclosure, perfectly so if nothing else, I would end up with a groovy dual-voltage AC power supply. 🙂

Cheetah MS6 Custom Power Supply Enclosure 1
Here's the external power supply enclosure showing the connector and cable that interfaces with the MS6.

The heatsink also fitted perfectly. This was a particular relief as the distance between the mounting holes on the heatsinks of the regulators didn’t seem particularly uniform and I kind of had to compromise (not my usual style).

Cheetah MS6 Custom Heatsink
This custom heatsink that I made for this sick Cheetah MS6 is considerably more substantial than what was in there originally. In use, it only gets slightly warm.

I’d already made the cable that would connect the external box to the MS6 so all that was left to do was to drop in the actual connector and then wire it to the main PCB.

Cheetah MS6 Custom Power Supply Connection
Here's the connection on the back of the MS6 that comes from the power supply. I really just wanted to have a single cable

So, all was done pretty quickly and it was test time. As usual, I cleared a big space, just in case it all went bang... again. Well, it didn’t. In fact, nothing happened at all for a few seconds. While the unit was still on, I quickly measured voltages and all looked good; +/-5V and +/-12V. Then characters appeared in the display but not as expected. All that was shown was ‘FE’ which was flashing and every now-and-then, some random stuff. I had read on-line that this could be an initial boot routine. Indeed, there was no voltage on the memory back-up battery. The other issue was that the buttons on the front-panel were totally unresponsive.

After sometime, I noticed that one of the multiplexers was seriously hot, so I switched off. I replaced the CD74AC138E and tried again. Wow! It all fired up! It still seemed to go through some kind of initialisation sequence after displaying 'FE' again but this time, only for a couple of seconds.

I hooked up a MIDI keyboard and attached the output to my mixer. Hey, I’ve got sound, too. More than that, all the voices were working. This was all quite relief.

While I had the opportunity, I decided to implement my Live Forever battery mod.

Cheetah MS6 Original Memory Back-Up Battery
The original battery in the Cheetah MS6 is a Ni MH type. This should be changed.

This required a slight modification to the battery back-up circuitry as the original battery was a rechargeable Ni-MH. I was dropping in a lithium battery which I really didn’t want the MS6 to charge when it was in use!

Cheetah MS6 Live Forever Battery Mod
Tucked away in the corner, is my Live Forever memory back-up battery mod. Some modification to the original back-up battery circuit is required .

Once that was done, I tried again. You know what? This thing doesn’t sound too bad. Of course there's better but you have to bear in mind the price bracket that this was in when it first came out.

The power supply in these machines is notoriously bad. In fact, I’ll go so far as to say “it’s not a matter of if but when”. On top of that and as has been proved by the customer of this unit, they don't need to fail 'quietly'. This is a real shame as the synth is actually really quite good with six analogue voices and even multitimbrality. It’s also a shame that the MS6 has an old-style Ni-MH battery. If not charged regularly, there’s a significant chance of this leaking… all over your main PCB!

So, if you have a Cheetah MS6 that you love dearly, please don’t hesitate to contact me regarding

  • an external power supply,
  • my Live Forever memory back-up battery mod

In my humble opinion, I think it's worth it but please do something before it blows up!

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!

Live Forever battery mod at Plasma Music
Large capacity CR123A battery mounted off-board in a Roland MKS-70.

My Live Forever back-up battery mod does more than just extend memory back-up battery life. It's not rocket science. It's not even particularly clever but an incredibly simple upgrade to many synthesisers, sound modules and effects processors, this upgrade offers the following advantages:

  • Reduced risk of battery leakage.
  • Reduced risk of damage to sensitive electronics as a result of battery leakage.
  • Easier replacement of memory back-up battery.
  • Easier measurement of memory back-up battery voltage.
  • Higher capacity battery means that it'll probably outlive you!

So just about all digital equipment has some sort of mechanism to provide memory retention. Your equipment has patches, right? So those patches are 'remembered' by your gear after power is removed, with the use of a memory back-up battery.

Newer equipment doesn't always have a memory back-up battery. Instead, memory is held within what is known as non-volatile RAM.

Anyway, older stuff does have a memory back-up battery and if left unchecked, the consequences can be devastating. I recently did a post on a gorgeous Sequential Circuits Prophet 5 Rev 2 that hadn't been touched for over thirty years. During that time, the back-up battery had degraded and had in fact leaked all over the CPU board. It's going to take me months to sort out the mess and that's going to be expensive!

Battery Acid Damage in Prophet 5 2 (2020.12.16)
After thirty years, this battery in a Sequential Circuits Prophet 5 is more than just flat!

My Live Forever battery mod doesn't just involved replacing the original battery with a larger type. If possible, I try to mount the holder for the new battery, usually a lithium CR123, directly on to the chassis and off any PCB. In the event that the battery does leak, then it won't damage any circuitry.

Of course mounting the new battery on to the chassis isn't always possible. The Marshall JMP-1 is a good example. There are two versions of the  JMP-1. One has a case with a little room to allow for a CR123 battery holder to be mounted to the metal. The other and more popular version doesn't. In situations where the battery can't be mounted off-PCB, I simply have to find the best place to put it.


Most vintage equipment that uses a memory back-up battery does so with something like a CR2030, CR2032 or similar type 'coin' battery that's soldered to a PCB and located close to the RAM (memory chip). This isn't always the case, though. The Roland MKS-80 for example, used a CR-1/3N battery as pictured below.

Back-up battery in Roland MKS-80

My Live Forever battery mod involves replacing the original battery with a much higher capacity CR123 type cell which is also small enough to fit into many situations.

Super Nova has on-board back-up battery for Juno-106 memory back-up
My Super Nova replacement switched-mode power supply for the Roland Juno-106 comes with my Live-Forever memory back-up battery mod on-board.

The default battery chemistry is lithium or rather lithium manganese dioxide (LiMnO2). They're cheap, readily available and very reliable.

Lithium CR123s however, aren't the only option that can be used for replacing the original memory back-up battery. While sticking with the CR123 form-factor, I'm a big fan of Lithium thionyl chloride batteries (LiSOCl2), for example. Designed specifically for very low-current, very long-life applications, they're ideal for the job. They are however, more expensive and more difficult to procure.

On the left is a standard Duracell manganese dioxide (LiMnO2) CR123 battery. On the right is the super performance Saft Lithium thionyl chloride batteries (LiSOCl2) CR123 battery.

Finally, a long time ago, I experimented with clip-on retainers that fit over the CR123 battery holder, thereby offering more physical security to the actual battery.

Well, apart from having installed my Live Forever battery mod into countless machines over the years, all of my own gear is fitted with my mod. In over thirty years, I have NEVER experienced a battery being dislodged from the battery holder and feel that any impact that would be strong enough to do that, would most likely seriously damage the machine that it's fitted to!

The main reason I don't supply the retention clip however, is that they have a very (VERY) tight fit. I'm concerned that if the battery ever does need to be removed, damage to the unit may occur while simply trying to remove the clip! 🙁

Anyway, my Live Forever memory back-up battery mod is available for just about any synthesiser, sound module or effects processor so don't hesitate to contact me if you have any questions. Don't forget, it does more than just extend the memory back-up battery life in your favourite vintage gear. It'll give you peace of mind too!

In the meantime, if you'd like to learn more about lithium manganese dioxide and Lithium thionyl chloride batteries, please check out these links:

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-1Unlike 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 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".

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 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.


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


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 your data encoder 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 to prolong the life 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, you've got a spare! 🙂

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:

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.


Super Nova switched-mode power supply for the Roland Juno-106
Super Nova, the world's first switched-mode power supply for the Roland Juno-106.

Following on from last summer’s Aurora project (read more about that here), I thought I’d have another look inside one of my favourite keyboard synths and see if I could do something similar. Well, it took me about a week to design the basics of what was very quickly to become the Super Nova switched-mode power supply for the Roland Juno-106.

Being a guitarist, my selection of keyboard synthesisers is quite modest but I consistently find it amusing that many musicians walking into my studio, inevitably make a bee-line for my humble Juno-106.

My Roland Juno-106
My favourite keyboard synthesiser; the Roland Juno-106.

I have always loved this machine! It’s just so easy to ‘draw’ a sound using the top-panel controls and it always delivers. Lush, phase coherent and warm with no mistaking that classic Roland chorus, the Juno-106 has played a big part in my own musical history.

Intended as a budget synthesiser, the Juno-106 was released in 1984, the same year as the MKS-80 and the JX-8P. It’s lack of velocity sensitivity and simple voice architecture didn’t seem to inhibit this monster-sounding machine’s popularity. Indeed, the Juno-106 is probably one of the best-selling synthesisers of all time.

My Roland Juno-106

Today many named artists still use this fab synth and variations like the Juno-106S and HS-60 (or Synth Plus 60) both with built-in speakers, still sit in many a lounge or music room. After more than three decades however, time is taking its toll. Many will be familiar with the failing 80017A VCA / VCO devices, for example. Fortunately, Analogue Renaissance offers a replacement, the AR80017A. My Juno-106 is doing alright at the moment so I haven’t had the opportunity to try these yet. Having said that, I’ve only heard good things about the AR chips and I salute Jeroen Allaert of Cask Strength Electronics for such excellent work. On top of that, they look really, really cool!

AR80017A by  Analogue Renaissance
In my humble opinion, one of the most significant developments for the Juno-106, the Analogue Renaissance AR80017A replacement VCA / VCO modules.

KiwiTechnics has always been a name you can trust when it comes to synth repairs and upgrades and after a couple of years in development, the guys recently launched a seriously powerful hardware / firmware combination for the Juno-106. Known as the Kiwi-106, this is a significant upgrade offering a huge array of fantastic and modern features that well, change everything! In fact one of the reasons Super Nova is red is to match the Kiwi-106 so I strongly suggest that you check out to find out more!

All these people doing this great stuff for the Roland Juno-106 and I couldn’t find anyone making a replacement power supply. Perhaps it's because we all know that Roland power supplies are really quite robust and have stood the test of time.

Roland Juno-106 power supply
In my humble opinion, Roland has always made really good power supplies.

An interesting feature and unlike many synthesisers of that era, the transformer in the Juno-106 is multi-tapped meaning that by moving a wire from one post to another (and changing the fuse), you can use the synth on virtually any domestic voltage supply across the world. 

Juno-106 power transformer
Multi-tapped power transformer of the Roland Juno-106 makes international usage a little easier.

The thing is, power supplies do fail. If the transformer packs up for example or starts humming, then that’s it. That’s why I designed Super Nova. Not just a replacement power supply, Super Nova is a modern, switched-mode power supply for the Roland Juno-106, meaning that for a start, it generates considerably less heat than the original linear power supply. There’s NO mains hum either and since Super Nova's filters are based on my good friend, Guy Wilkinson's design, Super Nova is also super quiet. And of course, being a switched-mode design, you can still plug your Juno-106 into any electricity supply around the world but this time... without having to open it up and change the transformer tap!

Super Nova installed and powered up
Super Nova installed, powered up and showing status LEDs.

Individually coloured LEDs for each supply including the 5V reference voltage, means that you can very quickly check line status with a glance. If you really want to know what's going on, conveniently located test points make measurements a breeze.

Super Nova status LEDs and test points
Super Nova also has conveniently placed test points.

The 5V reference voltage is set when each Super Nova is made, using regularly calibrated test equipment. A multi-turn pre-set however, allows for fine adjustment which may be necessary after several years, due to component value drift.

Super Nova allows for fine adjustment of 5V reference
Although set up when built, Super Nova allows for fine adjustment of the 5V reference. Also pictured is Q2 which is a power-on-reset device to ensure that the processor in the Juno-106's doesn't start running code before everything is powered up.

One of my most popular upgrades to many machines I receive from customers, is my Live Forever battery mod’ and so like Aurora, Super Nova includes a provision to replace the memory back-up battery in the Juno-106 and take it off the CPU board. This has several advantages:

  • A much larger back-up battery can be installed meaning that you probably won’t have to change it in your lifetime!
  • In the unlikely event that the battery leaks, your precious CPU board is safe and won’t be damaged by battery fluids.
  • Battery voltage can be easily checked without fuffing around with the CPU board.
  • Just in case you do have to change the battery, it’s so much easier and doesn't require any soldering.
Super Nova has on-board back-up battery for Juno-106 memory back-up
Super Nova has on-board back-up battery for Juno-106 memory back-up.

The battery connects directly to the original battery points on the CPU board so all components associated with the back-up battery continue to function as as normal.

Like several synthesisers of its day, the Roland Juno-106 is built on a plywood base. Heavy items like the keyboard assembly and power transformer, are attached to the base using machine-type screws that secure into corresponding steel lugs which are sunk into the plywood. The much lighter PCBs however, simply use wood screws to secure them (via spacers) to the wooden base. When you consider that the plywood base in less than 10mm thick, that sounds a little risky. On the other hand, there's no history of 'stuff' coming lose!

I wanted Super Nova to be super secure so although the PCB could have actually been smaller, I chose to extend it, thereby taking advantage of the otherwise redundant M4 lugs that were previously used to hold down the transformer. Mounted on an aluminium plate, both PCB and plate are very securely anchored to the base of the Juno-106. The plate is further held in place with four wood screws.

Super Nova is anchored to redundant transformer mounting lugs
Much more secure than just screwing to the plywood base, Super Nova is anchored to the redundant transformer mounting lugs.

Super Nova fits perfectly into the Juno-106 and is relatively easy to install by anyone with some technical competence.

Super Nova wiring
Super Nova is even easy to wire-up.

It's very efficient, can be plugged into just about any power outlet in the world and has on-board Live-Forever battery mod.

Super Nova fits perfectly into the Juno-106
A perfect fit and there's no messing about!

UPDATE - 6th January 2021

Super Nova has now been fully tested and I'm lovin' it! I've completed detailed and fully illustrated, step-by-step installation instructions so, if you have a Roland Juno-106 with a bad power supply and are considering a replacement or if you have any questions, please just contact me.

Or you could just...

My favourite synth, the Roland Juno-106.

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. 

Super Nova was designed by me and every Super Nova is hand-built and tested by me, here in Hemel Hempstead, Hertfordshire. The aluminium mounting plate is made by Lenton Engineering which is based just up the road in Watford and the printed circuit boards are manufactured by Minnitron Limited in Ramsgate, Kent.

Plasma Music uses local manufacturers

At the heart of Super Nova are four high-performance Vigortronix AC / DC converters which are made in Witney, Oxfordshire.

Super Nova uses Vigortronix AC DC converters made in the UK
Super Nova uses Vigortronix AC DC converters made in the UK.

Using local manufacturers isn’t always 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.

This week I've had two machines come in; a Marshall JMP-1 and a Sequential Circuits Prophet 5 (yes, you read correctly). One was just in time and prior to battery leakage. Unfortunately the other arrived too late and had suffered considerable battery acid damage.

Last week I received a call from someone who had just bought a Marshall JMP-1 and, after stumbling across my article on Marshall JMP-1 Service while doing a little research on-line, decided to send me his new purchase for a once-over.

I got a shock, when I opened it as the battery was right on the point of popping. This was incredibly lucky. With a date of manufacture of 1992, the battery was the original, as fitted in Marshall factory, twenty-eight years ago!

Soldered CR2032 in Marshall JMP-1
Just about to pop, this CR2032 was fitted on to the main PCB of this JMP-1 at the Marshall factory in 1992.

After quickly removing the battery, I tried to take some macro pictures to show  swelling. If you look closely, you might be able to see what I'm talking about. The top of the battery should be flat.

Swollen CR2032 from Marshall JMP-1 (2020.12.15)
Look carefully and you'll notice the slight 'hump' on the top of the battery indicating that although this battery is still holding memory, it's also about to start leaking.

I analogise battery check-up with home security; most of us consider investing in CCTV or an alarm system after an incident! Stuart took the initiative and sent me his JMP-1 shortly after he bought it.

Unfortunately the owner of the Sequential Circuits Prophet 5 wasn't so lucky. Apparently this machine had been stored in a case since it was used with Roxy Music over thirty years ago.

A Sequential Circuits Prophet 5 last used over thirty years ago.
Last used over thirty years ago with Roxy Music, this Sequential Circuits Prophet 5 looks amazing.

It's incredibly sad to see horrendous battery acid damage on the inside of such a beautiful example of this legendary machine.

Battery Acid Damage in Prophet 5 2 (2020.12.16)
Inside the Prophet 5, what a mess!

Many components and quite a bit of PCB tracking are damaged but I'm going to try my best to fix this. Having said that, I've already informed the customer that things aren't looking good.

Battery Acid Damage in Prophet 5 (2020.12.15)
Components in the battery acid affected area have just rotted away. Some components just fell out of the machine as soon as I took off the bottom case.

So, I urge anyone who's buying vintage gear to get the memory back-up battery checked. I also strongly advise all, to regularly check the memory back-up battery in your equipment. Battery acid damage is a terrible thing and can cost a fortune to put right, if at all even possible.

My Live Forever battery mod which is available for most synthesisers, keyboards, effects processors, etc, doesn't just replace the factory fitted battery with something more substantial but if possible, I also move the battery off the main PCB.

Live Forever battery mod at Plasma Music
Large capacity CR123A battery mounted off-board.

Aurora (for the Roland MKS-80) and Super Nova (for the Roland Juno-106), are a couple of switched-mode power supplies that I make and that are either available ready assembled or can be installed by me. I recently released Aurora Board Bx, an option that includes a remote memory back-battery and Super Nova was designed with fully integrated remote memory back-battery facility.

Aurora Bx and Super Nova with on-board Live Forever
Both Aurora and Super Nova have an on-board Live Forever memory back-up battery facility.

I'm currently designing power supplies for several other machines and I'm including the same remote memory back-up battery facility on all of them.


Back-up batteries aren't just wired to memory chips. There's always associated circuitry which depending on the age of the machine, the manufacturer and so on, can do several jobs such as switch between battery and PSU power when the unit is switched on and off, provide current limiting and reverse polarity protection.

Memory back-up battery in the Marshall JMP-1 showing associated components.
As an example, here's a part of the Marshall JMP-1 schematic showing the memory back-up battery and associated circuitry.

Since my Live Forever battery mod connects directly to the original back-up battery connection points, any components or circuitry associated with the memory back-up function remain untouched and fully active. As far as your machine's concerned, nothing's changed!