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Roland Alpha Juno 2 Replacement Aftertouch Sensor

Being able to convey feel to the sound after the keys are played, can transform a performance into something quite unique and almost magical. Indeed, Roland was definitely on to something when aftertouch began appearing on it’s synthesisers in the mid-eighties. Today, many classic synthesisers have aftertouch strips that either don’t work or are a shadow of what they used to be. Almost forty years later, my Roland Alpha Juno 2 replacement aftertouch sensor which uses modern FSR technology, has considerably more dynamic range and is infinitely more reliable than the second-generation transducers that Roland originally used in the AJ-2 and transcends the instrument into another dimension.

Doner test bed for replacement aftertouch sensor for the Roland Alpha Juno 2

A couple of months ago, I received two Roland JX-8Ps with amongst other issues, failed aftertouch sensors. It was a great opportunity for me to try out something I've been meaning to do for a few years now. In no time, I'd developed a force sensitive resistor (FSR) based aftertouch system for the JX-8P. My friend Guy Wilkinson then lent me his JX-10 and 'AT-JX-10' appeared a couple of weeks later. After launching these products, something unexpected happened; I got contacted by a few AJ2 owners asking if I had considered developing a Roland Alpha Juno 2 replacement aftertouch sensor. Well, I hadn't but hey, here it is! 🙂

Roland launched the Alpha Juno 2 a year or so before I joined the company in '86 / '87 but like most music tech' at the time, instruments like the MKS-80, Juno-106, JX-8P and JX-10 were the ones that seemed to pop my eyes. As such, I never paid much attention to the Alpha Junos until many years after I'd left the company.

Roland Alpha Juno 2

Today, the Alpha Juno 2 is a much respected synthesiser which has also proved to be very reliable... apart from the aftertouch. It was kind of a no-brainer therefore, to sort this out, especially following on from the success I'd recently had with the JX-8P and JX-10 replacement aftertouch sensor projects. There was only one problem; I didn't have a Roland Alpha Juno 2. 🙁

The development costs of designing peripherals for vintage equipment can be considerable and I was reluctant in this case, to whack on a good sum for a second-hand AJ-2. Having said that, I very almost did. But then...

Jumping to the rescue, my friend Guy Wilkinson suggested he contact a friend of his, who's an Alpha Juno 2 owner and indeed Jonathan was only too happy for me to use one of his his synths as a test bed. Yes, Jonathan has two Alpha Juno 2s!

So now I had a Roland Alpha Juno 2 but...

You need to be careful when taking apart an Alpha Juno 2 because the front of the main-board isn't simply screwed to any part of the chassis. Instead, Roland decided to have it supported in slots underneath the keyboard chassis. Removing the keyboard chassis without knowing this and hence, taking precautions, could easily snap the main-board! 🙁

Slots in the keyboard chassis supports of the Roland Alpha Juno 2
Here's the underside of the AJ-2's keyboard chassis. Highlighted are slots that the front of the main-board slide into.

The original aftertouch strip looks kinda FSRish but it's not. Similar to the sensor found in other synthesisers at the time, it's simply a couple of plastic strips with carbon tracks sandwiched together.

Original aftertouch sensor in Roland Alpha Juno 2
The original aftertouch sensor looks pretty hi-tec for the mid-eighties.

The Alpha Juno 2 is a slim instrument and wherever you look, space is limited. Even the front of the keyboard chassis is narrow. My replacement aftertouch sensor for the Roland AJ2 is 20mm wide and I just got lucky that it fitted.

My Roland Alpha Juno 2 replacement aftertouch sensor only just fitted
Not much space for a replacement aftertouch sensor on the Roland AJ-2.

Being basically refined versions of the type of carbon-track sensors that Roland originally used but delivering a lot more dynamic range as well as other benefits, FSRs are perfect for this kind of application. In fact, modern aftertouch sensors and even some drum pads use FSRs. The principle is the same but the resistive polymer material is of a modern composition and the manufacturing process makes FSRs considerably more robust and reliable than previous pressure sensors.

How FSRs work
Cross-section of a force sensitive resistor (FSR) illustrating how they work.

Having done this twice already and very recently and being very familiar with this synthesiser, developing a replacement aftertouch sensor for the Roland Alpha Juno 2 mainly involved measuring up and fine-tuning my FSR Aftertouch Interface (FAI) PCB.

FSR aftertouch interface PCB for Roland Alpha Juno 2 replacement aftertouch sensor
My FSR Aftertouch Interface (FAI) PCB has a cool little secret on-board; switchable aftertouch sensitivity ranges!

What I mean by 'fine-tuning' is that FAI provides the facility to switch aftertouch sensitivity ranges (what a cool little feature). By simply moving a jumper on FAI, you can select between 'Norm' or 'Hi' sensitivity. Hence, I need to play around with some resistor values until things feel right in both modes.

Below you can clearly see the difference between the the two modes. In Norm mode, aftertouch responds smoothly but requires more finger pressure to reach full scale deflection (MIDI value 127). In Hi mode however, aftertouch gets to full scale deflection a little quicker and of course, requires less finger pressure to achieve this.

FAI AT-AJ-2 MIDI Responses
With hits of around MIDI velocity 95 and subsequent average finger pressure, you can see the difference between FAI's Norm and Hi modes.

In the AJ-2, aftertouch can be assigned to DCO, VCF or VCA and you have scope for further adjustment of the affect of aftertouch on the respective parameter.

Like all of my replacement aftertouch sensors, the AT-AJ-2 employs two FSRs and it's not practical to simply connect them to the original aftertouch wires and so FAI also makes life easy by passively combining the signals off the FSRs.

Although quite small, again with limited space inside the chassis, the positioning of FAI had to be carefully considered. FAI couldn't go behind the pitch-bend assembly like my AT-JX-8P and AT-JX-10 installations.

FAI installed in Alpha Juno 2
FAI mounted close to the main-board and not behind the pitch-bend assembly as with other FSR-based aftertouch systems I've done.

Different to previous FSR-based aftertouch projects, designing and installing my AT-AJ-2 presented some unique and interesting challenges. It wasn't quite the 'walk-in-the-park' I thought it would be, that's for sure. The Alpha Juno 2 was for example, particularly fussy about the height of its aftertouch strip. Having already designed a couple of FSR-based replacement aftertouch sensors, the height of the whole sensor assembly is of course, one aspect I pay a lot of attention to. If the sensor is too high, when a note is pressed, contact with the second carbon nipple in the contact bubble might not happen and you'll get no sound. If the sensor assembly is too low, you'll potentially wear out the key contacts quicker. Seriously, a fraction of a millimetre can make a significant difference.

Wanting this system to be available to all AJ-2 owners however, meant that not only did I have to overcome these challenges but I had to do so in a way that any technically competent person could easily follow. Operating on vintage synthesisers requires patience and an appreciation of how the manufacturer did things back in the day. You can't just take things for granted!

"So what does my Roland Alpha Juno 2 replacement aftertouch sensor sound like?"

Well, that's actually the wrong question! With a dynamic range that's quite literally in a different league to the second-generation transducer that Roland used in the Alpha Juno 2, my AT-AJ-2 feels just magic! The new system delivers a conversion of human touch to sonic expression that is perhaps what Roland had in mind in the mid-eighties but was unable to realise at the time.

If you want to know more about the fabulous Roland Alpha Junos, then you might find this interesting reading.


UPDATE - 10th July 2023

Yesterday my friend Guy Wilkinson came to see me to collect Johnathan's Alpha Juno 2 and to catch up about a whole bunch of other stuff. Not knowing too many people who speak my language, it's great having Guy over. When we meet up, it kind of gets a bit geeky 😀 but it's so much fun!

Anyway, Guy messaged me later in the evening with a link to his home page. Here's what he had to say:

"Repeat 9th July 2023: Alex did it again for the Alpha Juno 2, such a sublime upgrade because the synth is such a lovely sounding and traditional polysynth (less is more)……a great Aftertouch performance really makes it shine expressively. I have spent a lot of time with it, enjoying the synth in a new way. Shame I have to hand it back 😁

If you are interested in one of these fabulous kits with an extremely long life modern sensor, then check out Alex’s site pages:  JX-10 ,  JX-8P & Alpha Juno 2.

Bring the expression back into your Vintage synthesizer."

Thank you for your kind words, Guy.

A special  T H A N K  Y O U  to Jonathan W for lending me his Roland Alpha Juno 2.


PACKAGING

The AT-AJ-2 is sent out complete and in one straight piece. Although it weighs very little, the external double-sided carboard box is just under 1.2m long. Using normal courier methods worked out to be horrendously expensive and so I engaged the services of a shipping agent.

Packaging the AT-AJ-2 starts with sandwiching it in between two pieces of hardboard. The wires are then neatly folded and secured to the hardboard with masking tape.

FSR Aftertouch sensor sandwiched between hardboard strips
It's important that the sensor is kept straight so I sandwich it in between two pieces of hardboard.

To keep any moisture off the sensor during transport, the package is then put into a long polythene bag.

FSR Aftertouch sensor packed in polythene
A polythene bag is then used to reduce the potential ingress of moisture and damp during its travels. FAI and any other bits are put into an electrostatic bag and then into a small bubble-wrap bag.

The protected sensor is then packed into a double-sided cardboard box and wrapped in black pallet-wrap which gives the package a little security and added protection against damp and moisture.

FSR aftertouch sensor packed for shipping
Final external packaging is pretty robust!

 


UPDATE - 28th July 2023

My AT-D-50 FSR-based replacement aftertouch sensor for the D-50 is a go! You can read all about here.

Roland D-50