Eight years later! And still not quite finished.

OK, so buying an actual 102 took the wind out of my sails a bit, and then there were all the diversions into silly projects like “let’s make a System 700” and “let’s do a Jupiter-4 clone in a rack” which both dragged on forever and are somewhat dead at the moment, but it feels like this is… almost… nearly… there.

The wires poking out of the side hint at the genuine nightmare behind the panel. No, we’re not going to look round the back. At this point Roland were wiring straight to potentiometers, and I’ve done mostly the same. Here’s a view inside the original.

I did make small boards for each set of slide pots so that I could keep the screw fixing to the panel as unobtrusive as possible.

I just about managed to scrape together slide potentiometers of the right (or near enough) values to make this. And the stalks are different lengths and materials. And they don’t even feel that nice – the big one below felt the best but I couldn’t use it in the end, I think the slide cap I was using didn’t fit.

I actually considered going into the 30mm slide potentiometer business – or at least buying whatever minimum amount the manufacturers would sell of each value (seemingly 1000) and flogging the surplus. Thankfully they never got back to me, it would’ve been too far down the rabbit hole.

Anyway, enough complaining about wiring – these are the things I added

• external CV input for the VCA
• white/pink noise (straight from the model 101)
• multiples! 
• one-octave down SH-101-style sub-oscillator normalled to the external input socket
• optional gate boost (the envelope is finicky about the voltage it needs to trigger)
• switch for boosting the otherwise fairly quiet envelope output
• plus/minus one octave switch
• fast/medium/slow LFO ranges
• LFO reset (already there on the model 101 version of the board)
• switch on the S&H clock to the envelope
• envelope fast/normal speed
• extra cv/gate inputs on the far left

There’s probably more I could’ve bunged on it, but I was trying to keep to the look of the 102 as far as I could. Here’s the whole thing propped up a fruit bowl on our kitchen worktop.

I wimped out on the design slightly because I had my doubts that the printing process would be able to reproduce the (grey? green?) original colour scheme. Given that this panel cost £150 back in Nov 2019 from Schaeffer, it was strictly going to be a one-shot thing. I’d hate to think how much it’d cost now.

Now I look at it again, the absence of the block colour gives it a moody sort-of Sys100/SH-09 crossover look.

The only thing that doesn’t work yet is the phones output because I’m missing the Sansui ST-31 transformer, which seems to be hard to get hold of these days, although I’ve seen photos of boxes full of them on the internet, just to taunt me.

Here’s the usual out-of-tune bonky MC-4-driven demo that doesn’t really demo anything, mostly just showing the pulse-width mod/suboscillator and envelope fast/normal switch.

I’ve got a power supply board made up, a clone of the one in the 104, which I actually intended to make but never got round to because of the strange Sanyo TV channel selector switches which it uses. (Also it turns out that the 100M 182 is more fun)

I was going to run the whole thing off a Yamaha PA-20 and keep the transformer outside the box, just to keep it as compact as possible.

And it needs a box making up, and then it’ll be ta-daaa. Hopefully this side of 2030.

Bonus photos ‘cos I was asked: here’s the panel as it arrived, just opened up the package from Schaeffer:

Slightly grim photo of my panel (taken in near darkness, for some reason) balanced on top of my 101, just to show a comparison against the original 102. My version is a bit too wide, I think I must’ve take the full inside width of the original as the graphics edge-to-edge measurement.

I need to try and shift things about to fit things in, maybe on the left of the 102 like in Jack Dangers’ studio; still need that 103 though… (and I’m working on the 100M).

I tried to keep all the slightly idiosyncratic typographical decisions like, for example WAVE(tiny space)FORM and picking out the abbreviations in PULSE WIDTH MOD and VOLTAGE CONTROLLED OSCILLATOR.

Last one; you get the idea.

Here’s my second go at the potentiometer board for my version of the SEM (previous post here).

I’m fairly happy with it, apart from the fact that my additions have pushed it over the original size a bit, meaning I won’t be able put two together in a 19″ box like the ObieRack.

Extra/different stuff:

• second LFO (hence the wonky LM13700)
• plus/minus one volt octave switches for the VCOs (hence a few references and a quad opamp)
• LED indicators for the LFOs (couple of op-amps)
• LED indicator for the second envelope (which is a bit pointless)
• switches for oscillator shapes and modulation sources (due to the general lack of centre-tapped pots)
• external connections routed one side of the board

There’s loads wrong with my paper and cardboard test front panel (it’s too small, for one), but this is some kind of idea of how it might look. The circles around the pots were just to work out maximum sizes for the pots and spacing while I was arranging it.

The attack pot for the first envelope is something like 1mm too far to the right on the board, aargh. Forget doing the board again though.

Initially I was just going to make two, then I ended up making four of them, because why not.

I mean, Mr Splitradix has five of the things, and Vince has bloody ten of them, so just keeping to four seemed fairly (almost) restrained.

This now means I’ve got to build some sort of panning mixer for the four voices. And also a MIDI interface and maybe some sort of flexible cv/gate assigner thing so I can round-robin play and hold the four voices from one or two channels of the MC-4.

And now I think about it a bit more, it’d be a good idea to have some common VCO pitch and cutoff tuning controls as well. And a common LFO. Let’s cover the world in LFOs.

(I hadn’t really thought this whole “let’s make a load of SEMS” thing through, really.)

I’m definitely not doing common envelope controls though. The envelopes on the boards aren’t voltage controllable as they are; it’s said that the FVS used early versions of the CEM3310 for this, and that just sounds like a massive faff. Even more of a faff.

One thing that I absolutely love about the SEM from a construction point-of-view is that the front panel just plugs into the voice board – here’s a photo of one of them balanced in-between some plants on a windowsill:

OK, so it looks strangely wonky in the photo but everything connects up so easily, and it’s just so compact.

I guess this’ll be no surprise to anyone building Eurorack modules, but after having wired up a System 100 model 102 clone all point-to-point, the relative lack of wiring is glorious.

Fuck wiring! It’s no fun!

There was good discussion on the Analogue Heaven mailing list recently (yeah! mailing lists! from the old days!) about the FVS versus the OB-X, and there was some thought that the OB-X sounded somehow nicer because of the OTA used in the audio summer (and the pre-distortion technique they used to counter-intuitively reduce the distortion on the super dynamic signal), so it’s tempting to try and implement that in the output section.

I’d been working on a track and moved a bunch of stuff around, including my battered Poly61M. After recording I turned everything off for the night. And mistakenly left the Korg on.

I woke up at about 3am thinking “what’s that godawful smell?”

Yeah, that looks wrong doesn’t it?

Mmmm, 30-plus years of dust. In the middle we have a bulging Rifa 33nF paper capacitor. It doesn’t smell very nice.

The synth still works, but worryingly the power switch doesn’t actually turn it off any more, so the capacitor has failed short.

I found the recommended replacement according to the Rifa datasheet – here’s the bottom of the old burned-up one on the left and the new one on the right.

…and now it works fine again: boring fix, sorry everyone.

Here are some random photos of the inside. I had to take the keyboard out to get the power supply board out, gahhh

Here’s the main voice board, socketed SSM2056 and all

And this is probably the main processor board – there’s another board wonkily attached for MIDI on the left which I cleverly didn’t get a photo of.

Yes, the 80s:

The electrolytic capacitors in the power supply could probably do with replacing – as could the tactile switches on the front panel – but that’s a job for another day.

Oh and the keyboard barely works as well, which is standard with these. I’ve been in it before to try and fix it but they always die again, it’s one of those inherently shit designs. Good thing it’s the M version and I can control it externally.

I managed to threaten a few keys into action by banging seven bells out of it – here’s me absent-mindedly stepping through some presets and CLICK-CLICK-CLICKING the half-dead buttons.