Instead of putting the Juno-6 DCB/MIDI converter thing in a box, trying to fix the envelope and chorus noises in the Jupiter-4 clone, or actually trying to make music, I made this helper box for my SH-5, which doesn’t get as much love as it should.

Basically there’s a switch on the front to allow me to flip between playing the synth from the keyboard or the CV/gate inputs, which saves all the faffing about around the back. Also there’s an attenuator for the VCF mod CV input, and as a bonus prize, the switchable portamento nicked off the MC-202.

Here’s a demo! Only I don’t do very much demo-ing of the actual box, oh well.

Bass is System 100, strings bit is JX3P, drums are TR-606 (and I need to start using something else, because I think I’ve worn the 606 out for now). The MC-4 is varying the VCF CV a bit, and I’m switching the portamento on and off using the MPX output on the channel.

Here’s the portamento stripboard:

I’d publish the layout but it’s all wrong, the Kicad symbol for the LM317 that I happened to pick had a couple of the pins swapped – luckily I noticed before I soldered it up. In the end the simplest thing to do was to insulate one leg and just bend them round into place.

It’s run off 12V DC, regulated down to 9V by the mini LM317, so it won’t cover the full 10.67V of the MC-4 but pfft, I can live without that octave. The LM358 won’t quite go down to 0V either, but the SH-5 goes low enough anyway from the octave switches, it shouldn’t be a problem.

Here’s the mess inside: just ram it all in, it’ll be fine:

…although I did insulate the base and the back of the circuit board.

I cut two holes in the front by mistake, so I bunged a power light on there (always forget to do those usually, they’re handy) and just a LED lens to cover up the other one. I wished I’d included a LED driver to show when gate or MPX was on, but there wasn’t a lot of space. I got lucky that the board fitted vertically in the pedal box.

Speaking of which, I love these Hammond pedal enclosures. Even though they’re a bit boring looking. Maybe I should’ve bought one of the bright orange ones instead.

Anyway it’s good to integrate the SH-5 a bit more. Also I could do with some sort of mega-switch-box as well so I could flip between triggering synths from the MC-4 without having to unplug things. One for another day. Probably I should actually try and make some music as well.

Onwards with the questionable Juno-6 modification – what I thought would be some Christmas fun turned into January work, and then February annoyance.

It works now, although cleverly I’d swapped the +V and ground on the 74LS14, so it needed a bit of a bodge with a track cut and some dodgy wiring.

I couldn’t get the 4MHz clock to start with the substitute I’d perhaps naïvely used, a 7402. In the end I wimped out and bought a Toshiba TC40H002 (with a date code of 1988!) and it started up.

Once I’d got the board populated and the clock running , the next thing was to see if I got any output on the connector to the Juno. I used a program from this thread on the Arduino forums as a starter-for-ten – and it seemed like I was getting some activity on the socket, and it was within safe limits, so I felt like it was safe to connect it to the Juno connector, which is direct into the Juno’s CPU.

In the meantime, I’d heard a thing about there being a hole for a connector in the back of the Juno behind the serial number plate – and so there was:

It’s a rectangular hole, looks like it was meant for a DCB-shaped connector – maybe a never-released upgrade? If you look to the left of the warning plate, you can see a couple of holes that are exactly sized for the serial number plate to move to. It all seems planned by Roland, but I’ve never seen any mention of an upgrade in literature of the time.

The DCB connector is an Amphenol DDK (D-shaped) connector, and would likely have been a pain to buy and fit. Also I found out that Kenton’s pre-made one-way DCB connector wire is £44, which put me off the whole thing. I was interested to see if a DIN socket would fit, let’s try it…

…success – so some cutting up metal in the garage led to this, which I’m strangely proud of:

It’s a little bit wonky but it’s probably the best bit of metalwork I’ve ever done. (You should see my previous crimes). The edges could’ve done with a bit more filing, but it’s near enough.

Here’s my forest-of-wires test set-up, with an old spare Arduino Duemilanove as the controller at top left – the intention is that this will live in an external box. I wanted to leave the connector on the outside of the Juno as (electrically) DCB in case I ever come across a non-stupidly-expensive MSQ-700, although chances seems slim now.

The code from the Arduino forum sort-of worked, but I was getting some weird triggering, where the next key actually played the last note pressed. Eventually I realised that the end code (&FF) did need to be sent, and then everything fell into place.

Well, almost. I found that when the DCB board was powered off the Arduino board, everything was fine, but then when run off the 5V connector on the Juno board it wouldn’t respond to MIDI input.

I did some head-scratching, and didn’t get very far until I had a look at the DCB out on the MSQ-700:

…and it turns out they’ve used a bunch of 4.5nF capacitors to ground on each output line, so I replicated this on the lines from the Arduino to my DCB connector on my breadboard, and then everything was alright.

Initially I had it going with MIDI from my MPC1000, but really I want to use it from the MC-4, so I altered the code to run off CV/gate.

Here’s a demo of it playing a fairly random tune. The first couple of bars are just one voice of the Juno, and then when the bassline comes in (on the 100M clone) there are additional wonky harmony notes played from CV2, triggered when MPX goes high.

Anyway, you get the idea.

I need to put the Arduino and supporting circuit in a box, with a switch for MIDI or CV/gate operation, and possibly a switch for mono operation to let it go as fast as possible, and also perhaps for passing CV2 through to the filter CV input.

I could do with cleaning up the code so I can bung it on here, it seems fairly reliable, but I’d like to check. I realised when playing the Juno through the MC-4 from the System 100 keyboard (which was a bit weird), that if you play legato it doesn’t pick up the change in pitch, so that needs tweaking as well.

In terms of timing, from looking at audio output only (alright, not very scientific) I’ve managed to get it down to triggering between a half and one millisecond later than a note from the 100M clone, which seems acceptable enough.

I was thinking of how that might compare to the OP-8, but I can’t find any specs or service manual for it. There’s some suggestion it uses the same Intel 8048 microprocessor as the CSQ-100 and 600, which runs at a terrifying 365kHz, give or take 10kHz. Not sure it’ll be too sharp, in that case.

Actually, thinking about it I’ve got a couple of CSQ-100s, although only one (sort of) works, and the other is dead, and bit me severely once when I tried to poke about inside with the power on.

It’ll be nice to be able to make a bit more use of the Juno – over the years I’ve mostly used it for drones, triggered it off the arpeggiator clock input, or – horror of horrors, actually had to physically play it. Shudder.

Continuing with the late-70s Japanese synth recreations that I’ll probably never finish – that thing I was working on back in January has grown into this:

Four voices, “compuphonic”. You know. My version has a sawn-off version of the originals’ motherboard in the vague hope that I might be able to fit it in a 4U (or maybe 3U?) box. Maybe in some alternate universe this actually happened and was released with a Roland model number, maybe MKS-4?

So many problems, some of which have been fixed. The chorus sounds a bit too swooshy. The envelopes leak clock noise into the output. The LFO leaks into the audio path, although that one is at least a known problem with the original.

The oscillators required some resistor-twiddling to get the pulse-width wave square. I fret I might have altered the level of the VCO into the filter slightly, I could do with checking further.

I mean, it can sound quite good. With all four voices in unison and chorus on it’s proper shouty raaaargh full-on “I am a synthesiser”.

We’ll get to the chorus later on but here’s a bit of pulse-width single voice then unison:

Also the LFO randomly goes quite fast on that, quite nice for making a horrible racket.

Pile of (not quite finished) boards!

Initially I made voice boards with single row connectors but they were really wobbly. And the voice board was the wrong way round.

I changed the spacing on the card connectors so they’re on a 0.1″ grid, with the initial thought that I would build the motherboard on stripboard, but eventually decided I was done with such masochism for this one.

Predictably then the module controller board and the voice board don’t quite line up in the same way as the original does. I’d re-do the motherboard and the module controller but… it’s a lot of work. Otherwise the voice board and the module controller should be the same as the original, the track layout should be fairly close.

As IR3109s aren’t falling from the sky (give 2020 a chance, though) I went with the rev D voice board, meaning that I had to make loads of BA662 clones. Praise be to openmusiclabs.

Here’s one of the billions of 662 clones/clowns, missing the two transistors and resistors for the buffer ‘cos they weren’t needed in this case:

Maybe if I get round to doing a Promars I’ll try building it with LM13700s in adaptors, using homemade 662s is an exercise in masochism.

The chorus works and sounds ace but for the none-too subtle swooshing from the LFOs. I bought two sets of MN3007 from eBay – inevitably the cheapest pair made my power supply panic, I guess they were MN3207 or something, re-marked.

Here’s a bit of that – listen out for the (stereo) chorus kicking in second time round the bass loop. Later on (at about 39 seconds) when the filter closes you should be able to hear the zapping on the chorus, and some clock noise from the envelopes.

Poking at the output of the BBD with an oscilloscope suggested that the two outputs are at slightly different levels, so maybe I have to balance them out to cancel the swooshiness. Originally the JP-4 didn’t have anything here for trimming the individual outputs from the BBD, but the System-100M delay/chorus module does.

So much dust, it’s been here for a while:

The original used a pair of MN3005s but I adapted the layout for 3007s using the tactics published by fitzgreyve.

The brain of this mess is a dusty Teensy 3.6, which is massive overkill for such a simple synth, but the inbuilt microSD card is handy for saving and loading patches. And the plentiful I/O will be handy when I come to making a front panel for it (In about five years, at this rate).

The DAC is a DAC8562, which has two 16-bit channels. It’s comically tiny, especially next to the through-hole parts on the weird circuit board I had made.

The output from the DAC for the compuphonic settings and the MIDI-to-CV is 5V, giving five octaves of pitch, which matches the four octave keyboard (plus one octave down via the transpose switch) range on the original, but I’m not sure if it’s a bit limiting when it comes to the keyspan.

It does a few different voice modes as per the original which may or may not work reliably: different flavours of unison, round robin, voice per note held down, and some bonus single voice modes to help me tune the individual voices.

This demo uses the unison mode for the bass drone and the round-robin for the wobbly lead that comes in at about 21 seconds, so the notes (with a long release) smear over each other.

Early on I hadn’t realised how much current this thing was drawing – the wires I was using were too thin and causing the pitch to wander about, so tuning was a regular thing. Beefing up the cables has mostly sorted the drifting pitch, but I still think about incorporating some sort of autotune.

One downside with autotune is that I’d lose a bit of pitch range, so I’d definitely need to amplify the voltage from the DAC. Maybe that’s against the spirit of the wobbly original though.

Portamento is done in software as part of MIDI to CV – the original used a 662 for each voice but I’d had enough of making them by this point.

All the compuphonic settings from the original are MIDI-controllable. How will I get the MC-4 to talk to it? I guess I could do with some sort of assignable CV/gate input thing on the Teensy.

Another sort of demo – I was enjoying playing in Ableton for a change and actually being able to play chords. Loads of reverb on the pad, maybe a bit of chorus on the unison bass bit and a single voice for the squeaky acid bit at the end.

There’s something pleasing about the stepped voltages from the DAC, although it was a struggle to get them right.

It didn’t help that my 90s-era Philips oscilloscope died quite early on into this project, and it turns out now that the same model is a hundred quid or so more expensive on eBay. This picture is from my replacement scope, which is a Tektronix 2445 that I’m not so keen on.

I found I had be quite careful in the sequencing and timing of the DAC and S&H multiplexer to get reliable behaviour, and even then I’m not 100% sure I’ve sorted it. The DAC8562 is posh compared to my usual MCP4922, but it still needs at least 10 microseconds to settle down to a consistent voltage. Boo physics.

I’ve got a screen! It’s in colour! Although I’m not sure that’s a good idea, because I’m having to shift more bits out through the SPI interface than I would otherwise with a monochrome display. Here’s my cheesy splash screen.

There’s nothing much actually happening on the screen yet, but here’s a video to show off the patch loading and how the parameter changes are represented on the screen. When it comes to patch 5 I’m changing multiple parameters through MIDI, so predictably enough the screen goes a bit apeshit. (And the camera is a bit out of focus on the last part, soz about that)

The envelope noise is really obvious on patch one. The voice mode display currently doesn’t get updated when the patch changes so that’s all lies. At least the voice allocation numbering is correct.

The random noise burst when it turns on is alarming, but I quite like it. It reminds me of Robotron starting up, or a robot angrily being woken from its slumber. It does need sorting out though, it’s on the list.

I spent way too long on implementing the arpeggiator and got tied up in how it should respond to MIDI clock, so that’s in a half-broken state.

On the arp front I saw a rumour (…in YouTube comments) that the original didn’t do a real random, but that it was actually based on a bunch of numbers stored in ROM. So if you hold the right keys down, eventually you get the “Rio” arp line, god help you.

Presumably that would be in the key assigner board mask ROM, which unfortunately hasn’t been dumped out as far as I can tell. Not that I’m sure I’d be able to do anything with it if I had it.

Next move is to experiment with temporarily taking the voice outputs through a different route to see if we can make the induced clock noise from the envelopes disappear. I suspect it’ll mean cutting tracks on the motherboard – there’s already a suggested fix for the LFO bleed on the originals mentioned elsewhere that I’ll look at as well.

I’d already tried to balance out the chorus swooshiness with a pot and promptly fried one of the BA662s on the output, so that’s next after the envelope noise. Still a long way to go.