Catching up one evening with my friend, Guy Wilkinson and on the back of my 'Replacement Aftertouch Sensor for the Roland JX-8P' project, it was a no-brainer to have a go at developing a similar, FSR-based, easy to install replacement aftertouch sensor for the Roland JX-10.
Guy has a pristine JX-10 but the aftertouch was shot. I'm very aware that he's attempted several repairs but it just keeps on packing up. He told me that it kind of works but is either off or on and cannot produce a varying signal that's proportional to well, pressure. I was keen to see if I could help and like my JX-8P aftertouch project, possibly develop a replacement aftertouch sensor for the Roland JX-10, that anyone with a little technical competence could install.
So what the hell does 'FSR' stand for? What is a FSR?
Invented in 1985, force sensitive resistors didn't make it into mainstream music technology applications for a long time. The technology was just too expensive and even more so in custom shapes and sizes. FSRs would often require end-user assembly which increased production times and failure rates.
When I was at Simmons Electronics, we developed the Silicon Mallet and later, the SDX, both of which used FSR technology to trigger sounds, MIDI, etc. The SDX soon became famous for its zone intelligent (ZI) pads, for example. At a cost of about 13,000 GBP in 1987 for the basic model, go figure!
Today, FSRs are used extensively for aftertouch and electronic drum pads so I've been meaning to try them out to fix aftertouch issues on vintage instruments for a long time. After motivating success on the JX-8P, I turned my attention to developing a replacement aftertouch sensor for the Roland JX-10.
Unlike the JX-8P, the JX-10 used a much simpler, twin carbon-track bottom contact membrane and a similar but single carbon track top membrane. The whole thing is much thinner than the JX-8P aftertouch sensor assembly but despite the use of carbon as opposed to copper (like in the JX-8P), the tracks were still quite exposed and vulnerable to the ingress of contaminants as well as wear.
Having installed my replacement FSR-based aftertouch sensor into several JX-8Ps now, I knew that the implementation of the technology worked just fine on these vintage instruments. Often described as two JX-8Ps in one, it's no surprise that there are many similarities between the JX-8P and the JX-10. In fact, it's quite intriguing just how Roland can be seen to apply its experience, learning from previous instruments, implementing the latest technologies and yet keeping all the good stuff that worked well. I guess in the natural world, that's called evolution!
So, with very similar technologies and construction, there wasn't too much new to suss out. The real challenge with the JX-10 however, was physical. The height of the sensor assembly might have been an initial issue, for example. At between 2mm and 3mm, it was about half the height of that in the JX-8P.
The second issue was limited width. The JX-10 used the familiar rubber bubble key contacts secured to a PCB which sits on top of the JX-10 keyboard chassis. The distance between the front of this PCB and the front of the keyboard chassis was only 21mm so I had no choice other than to use a narrower rubber strip over the FSRs, than I did on the AT-JX-8P aftertouch sensor project.
So, first things first. When developing the project for the JX-8P, I removed and stripped the entire keyboard chassis so that I could completely clean all traces of almost forty-year old glue! I figured I'd have to do something similar with the JX-10 and if so, that would require removing the two voice-boards, to get at the rear screws that secure the keyboard chassis. Oh BUM!!!! 🙁
Reluctant to take apart Guy's lovely JX-10 just to remove and clean off the remains of the bottom tracks of the original aftertouch strip, I thought I'd have a go with keeping the keyboard assembly in situ.
Knowing that the key tension springs for white keys are of a different length to those on the black keys, I removed the springs for the white keys first and grouped them together, before doing the same with the black keys.
With a little trick, removing the keys can be done without removing the transparent plastic key retainer that sits underneath and at the back of the keyboard. All you have to do is gently poke down with a small screwdriver at the key locator at the back of each key, thereby pushing the key retainer down. The keys can then be gently pulled forward and off the keyboard chassis.
The JX-10's membrane type sensor terminates in a convenient plug-in 2-way connection situated to the left of the keyboard. Hey, no desoldering. 🙂 ... yet!
The anatomy of the original JX-10 aftertouch sensor is very simple and actually has a modern feel about it. With no metal parts, it only has three components (one of which is the top-felt) making it very low-profile and sleek.
Well, I was pleasantly surprised; removing the old Roland aftertouch sensor was amazingly straight-forward and I hardly had anything to do when it came to cleaning the keyboard chassis.
Although the physics is different, the anatomy of the new sensor is quite similar to the original. Of course, being several decades since the release of the Roland JX-10, things have moved on and modern FSRs are much more reliable and with an actuation count of over 10,000,000, they're going to last a while.
To make life simple, my replacement aftertouch sensor for the Roland JX-10 includes a small FSR Aftertouch Interface PCB, otherwise known as FAI. Using Molex connectors, getting the signals off the FSRs is straight-forward. Originally wanting to develop a solderless kit, things didn't quite work out like that, though. Here's why...
My AT-JX-10 replacement aftertouch sensor for the Roland JX-10 will work fine if just connected to the volume-board (via FAI). The aftertouch control on the JX-10's front-panel however, will have a very short travel due to the higher output produced by the FSRs and the high gain of the aftertouch op-amp in the JX-10. Some will find the whole system too sensitive.
The gain of the the op-amp stage that buffers and amplifies the signal from the the aftertouch sensor, is a tad over 300. To calm things down, a resistor on the volume-board should really be changed if implementing this upgrade so while I was experimenting with the aftertouch gain stage, just like my AT-JX-8P project, I decided to incorporate switchable aftertouch sensitivity ranges into FAI.
By simply moving a jumper on FAI, you can change the gain of the aftertouch op-amp stage. Even the high sensitivity setting however, is only about 50% of the original gain and it's ample!
Listening to the results as I experimented was one thing but I had to be sure that the MIDI response was good too. Hence, with the JX-10's aftertouch control on the front panel set to about 75% and an average finger pressure, I recorded the MIDI from a couple hits; one set with FAI in Norm mode and another with FAI in Hi mode.
As can be seen, the response of the FSR-based aftertouch sensor is nice 'n' smooth when FAI is set to Norm mode. Things happen quicker when FAI set to Hi mode. Full scale MIDI value 127 aftertouch can be reached in both modes. You just get there quicker and with less pressure, when FAI is in Hi mode. Note the nice linear response in both modes! 🙂
And don't forget; the aftertouch slider control on the JX-10's front panel works in both modes, as it did before.
Guy lending me his JX-10 wasn't just about fixing the aftertouch in his instrument. It gave me the opportunity to measure up and design a rig so that my replacement aftertouch sensor for the Roland JX-10 could be 'manufactured' with precision and consistency.
While working on Guy's JX-10, visiting customers were asking questions about the open synth in my lab. Suddenly I had another JX-10 come in for one of my new replacement aftertouch sensors! Okaaaay...
I've now been able to test my AT-JX-10 on a couple of instruments and it works great! 🙂
The AT-JX-10 is obviously very long and I'm currently sorting out the best packaging. While I'm doing that, you can pre-order here:
UPDATE: 21st May 2023
This afternoon who should pop over but my friend Guy Wilkinson to pick up his JX-10, now with fully working aftertouch. After playing with his JX-10 for a while, Guy said that he's now smiled nine times this week! 🙂
From Guy's website:
"I just picked up my JX-10 that I loaned to Alex of Plasma Music to develop an exciting new product. He has developed a new aftertouch sensor strip that simply reinvents the expressiveness of the keyboard. Simply put, I am so happy with this upgrade!!!
So we had a celebratory launch moment with my JX-10 in his fabulous workshop."
UPDATE - 29th May 2023
Now in development:
- AT-AJ-2 - Aftertouch sensor for the Roland Alpha Juno 2.
- AT-D-50 - Aftertouch sensor for the Roland D-50.
Please let me know if you're interested in these FSR-based replacement aftertouch sensors.
