Building my own wheels for the Launchpad Pro – once again, with style.
Two weeks ago, I started a little sunday afternoon project, sucessfully building my first own MIDI controller – a pitch bend/mod wheel/midi merge device to serve as a companion to my new Launchpad Pro. Using an Arduino, a prototyping board by SparkFun, and community-made code, I succeeded with surprisingly little effort – the most time-consuming part was finding and fixing the errors I had clumsily soldered into my pathetic excuse for a MIDI interface. But it worked!
This is actually a side project to that. I looked at my self-made controller and noticed that it is usable but not very playable – I wanted real wheels for the Launchpad, not sliders. So I decided to redo a V2.0 of the controller, based on the Teensy.
easy to do (requiring only basic soldering skills, if any)
easy to get (by using components that you can buy on Amazon if you have to),
easy to develop (using standard solutions from the Arduino community),
easy to schedule (because the project is divided up into little steps, each of which is a small afternoon sub-project with instant gratification),
easy to participate (by contributing own ideas and code for parts of the project).
I will describe the basic layout of the MIDI upgrade kit project here. Each step, i.e. each sub-project, will then be treated in a new post, depending how fast I (or the community) get them done.
You may know these two gentlemen. If not, grab your VHS player, rent out the BBC’s „Hitchhiker’s Guide“ series, watch. Hurry!
If you have tried to send a message, or use the shop, you may have noticed that it did not work in the last two days – or, you didn’t notice, and are still waiting for an answer. A conflict between the Contact Form 7 plugin, which I have rediscovered, and the WP Cerber security plugin made some readjustments necessary. It should all be fine again now.
On the plus side, I had the opportunity to overhaul my shop pages, so if you are interested in an update for the Akai AX-80 or Kawai SX-240, it is easier to find and order. Concerning the Matrix-6, there is news: A very old bug in the firmware has finally been found and eliminated; it made it impossible to set negative DETUNE (parameter 12) values. Oddly enough, nobody except Gregor from Stereoping ever seems to have noticed, so there is no harm in continuing to use the firmware V2.14.
There is a new version V2.15 though – Bob fixed the bug – so if you feel that you need negative detune values, you may order that. Or you may take the opportunity to buy one of the V2.14 firmware PROMs extra cheap – while stocks last.
This knob is a good place to start: The „glide“ potentiometer is in charge of portamento, and it is one of the first things that might make Jenny fail (see Neil Johnson’s site). A faulty glide pot means that the synth will only ever play the same note regardless of which key you press. So I did replace that pot, which is pretty straightforward – you’ll find some pictures in this gallery. (It is a 2.2M linear type BTW.)
The Glide pot is in the upper left corner of this picture. As you can see it is sitting on a small PCB together with the Noise switch and pot. Remove the knobs and the nuts from the axes of all three, and you can take out the board to replace the potentiometer.
The pot needs to have a 10mm shaft and a 5mm diameter axis. Cut off the axis at about 10mm – which makes the distance from the end of the shaft to the top of the pot 20mm.
Pot soldered and screwed to the PCB. Ready to re-insert and re-attach the board into Jenny’s panel.
Overview of potentiometer values
This is an overview of the potentiometer values, some of them are linear, some logarithmic, a few antilog. The most obvious candidates for replacement, apart from the glide pot, would be Frequency (100k) and Resonance (100k) for the filter, and Tune (10k).
Jenny – my old 70s monosynth – is a beauty, and I love her knobby face. Her smile, though, has yellowed over the decades. So to make Jenny even more attractive, I decided to try and bleach the keys with hydrogen peroxide.
TL;DR: Effect has been minimal, so it’s probably not worth it. But it was fun. If you try it, make the Retrobright bleaching gel, don’t use a hydrogen peroxide bath. And have a good UV source.
Jenny’s keyboard compared to a key from a mid-80s Roland JX8P synth
Well, to change the firmware, you have to open the Matrix and exchange the firmware EPROM for a new one, and doing that, I’ve noticed that this machine was still equipped with its original battery. By lucky chance, I am the proud owner of two Matrixes, and the battery in this one has been doing fine – what kind of super battery did they use in these days, has been in service ever since 1989, and still producing fine 3.0 Volts of power – but I decided to exchange it anyway for a new CR-2032.
As you might know, the battery in the Matrix-1000 is soldered in with most machines, as it was customary with most synths from these days. I guess they never thought that they were building for the anoraks of the future. No problem, I came across battery holders with the same 20.5mm raster used in the Matrix – so no need for drilling, just a simple solder-and-replace job. While soldering, I bridged the backup battery voltage with an external power supply, and I even thought of desoldering the GND terminal first – the rationale behind this being that soldering pens are earthed, so by soldering the positive terminal first you might short out the battery. (Actually bollocks, but I did it anyway.) So I saved my precious memory settings while soldering in the battery holder.
Only to slide in the new battery the wrong way round.
You might not have realised – well, I never do – but the pad connector of a CR2032 is actually the GND terminal, and the housing is Vcc. And is labeled with a clearly visible „+“ sign. Well, I put the battery in the wrong way round anyway, thereby effectively losing all my patch and memory settings.
The battery in its new holder, now in the correct position: the plus terminal facing upwards
This is, of course, no big deal. I keep moving sound banks between my two Matrixes anyway, so I have pretty recent Sysex backups. Unfortunately, the unbuffered RAM chip lost just enough memory to put the machine into an undefined state – it would no longer boot beyond the init routine displaying the firmware version.
Switch off the the M-1000, disconnect it from mains, open it.
Disconnect the battery. Leave it disconnected.
Switch the M-1000 on, draining its buffer capacitors. Leave it for a couple of seconds – the completely powerless RAM should be all FF’s now.
Connect the M-1000 to mains, and switch it on. It should start now.
Do a calibration run, just to be sure. (Navigate to Ext. Funct., select 7, Enter, select 2, Enter.)
Reconnect the battery.
Done. Now you may switch off the Matrix, or supply it with fresh patch data.
In case you may have wondered, there is a very simple and effective way to disconnect/reconnect the battery in a running machine: push a strip of paper between the battery and the battery holder’s terminal. Remove it to reconnect.
It enabled NPRN control of the Matrix‘ parameters by removing a small bug
It sped up the VCF parameter control by skipping seemingly unnecessary calculations
It told the synth to discard all parameter edits except the most recent one, thereby keeping the synth responsive.
This is a huge improvement and makes the Matrix feel and behave almost like a modern instrument. But it gets even better.
Matrix-6 project, Matrix-1000 upgrade
Bob Grieb has been analyzing the Matrix-6/1000 code for months. I guess you can say that these days, not even Marcus Ryle does understand the code as well as Bob does. Here is his explanation why the Matrix-6/1000 machines are not real-time responsive to parameter changes in the first place – it is the downside for the immense amont of real-time modulations the Matrix is capable of – 22 fixed modulation paths, 10 matrix modulation slots, 3 envelopes, 2 LFOs and 2 ramps. To implement that in software the programmers used a special technique; a pre-calculated memory area for each voice called the voice update stack. Quote:
This stack contains pointers to code, ptrs to variables, and some pre-computed values. Only pointers to the code needed to handle the enabled features are placed on the stack… This is a very fast and efficient way to update the voice cv’s.
A downside of this approach is that when parameters change, the stacks need to be updated for all six voices. Some parameter changes just affect one number on the stack, so that number can simply be changed very quickly. But some parameters can change the size of the stack. This is a problem, as the update values for that parameter may be in the middle of the stack.
This means moving around chunks of memory to make room for the updated parameters, and it has to be done for all six voices, which takes the ancient 8-bit, 2-MHz CPU a couple of milliseconds. When you turn an external VCF controller, all these parameter changes add up, and the machine freezes for a long, terrible moment, until it catches up. (Read Bob’s full description of the issue here.)
GliGli’s main trick is to tell the machine to discard anything but the last Sysex command. He also noticed that sometimes the stack is rebuilt although this is not technically necessary. And this is the road that Bob has been following. He rewrote parts of the firmware to handle a set of about a third of the parameters much, much faster – including VCF frequency and resonance, DCO PW and LFO control, and VCA level. Changing these parameters with an external controller will be smoother than with older firmware, others – increasing the effect of a modulator in the mod matrix – will still cause the machine to glitch.
Update, 2016: Now that you’ve made it this far, you’ll be glad to learn that Bob made his revised code available for Matrix-1000s and Matrix 6/Rs. You can get a firmware EPROM from him or, if you are in Europe, from me – just follow the links above.
This was originally a project for the Matrix-6, but Bob ported it over to the Matrix-1000. In the process, he also redrew the schematics, so that after all these years, there is finally a legible circuit diagram for the M-1000 on the net. Incidentally, it prompted another guy to scan his printed schematic and send it to Bob, so that there are now not only one usable version but two. (Download link to ZIP archive here.)
Pretty straightforward, this one: Replace the JEN SX-1000’s fixed power cable with an IEC socket. (Like weird German words? You’ll love this: In German, this thing is called a „Kaltgerätestecker“, more precisely, a „Kaltgeräte-Steckverbinderbuchse“, which translates to „Cold unit connector socket“. Don’t ask me.)
No problems here apart from cutting a hole for the socket; I used steel drills to mark the corners of the cutout and then cut the steel with my Dremel tool. Lots of metal dust but fast, and it did the job precisely.
A word on Jenny’s power supply: It’s extremely oldschool – a transformer and a diode bridge generating +/-18VDC, two 7812 regulators generating +12V and -12V, and another 7805 regulator generating the +5V supply rail from the 12V. If you would like your JEN to be a bit more eco-friendly I’d advise replacing those regulators by the 2931CT low-dropout type, but apart from that, there’s hardly any reason to look at the power supply – it’s rather solid and possibly not your primary concern if the synth does not work.
The engineer has decided to abandon the project – he thinks that the performance problems of the Matrixes are a result of fundamental design decisions and would need too much effort to get around properly. But his code definitely improves the chances of doing something useful for the code. Someone with skill and spare time might even backport the M1000’s NRPN and matrix modulation Sysex commands into the M6 code.
BTW: My attempts at starting a documented source code file for the Matrix-1000 can be found here, with a hardware and software primer here. If I can find the time, I’ll try to backport a few of Bob’s insights into the M-1000 code.
With the amount of work waiting for me with Jen, I’m glad I don’t own a M-6…
As they say, the worst thing that can happen is that you succeed. The quick and easy success made me hungry for more – I started a MIDIfication project for my JEN SX-1000 monophonic synth, based on a Teensy, another microcontroller board that can be used within the Arduino development eco-system but is much better suited to MIDI/USB applications.
