rotary 100M rampage

Here’s my second attempt at the slightly-boring-but-I-like-it-anyway 100M. The last (mostly stripboard!) one I made is somewhat delicate but works really well, and is permanently attached to the MC-4, but I wanted to do some of the other modules outside of the D-set.

And I wanted to do a closer clone of the style of the 100M, just not with bastard slide pots. And also to do all that wiggly track bullshit again, as if it makes any difference. Here’s a couple of 182s (one missing the step number switch) and a 110, the panel is just paper and card while I test for now:

System 100M 182 sequencer and 110 voice clones

Just poking out of the right of the middle 182 is my rough attempt at replacing the 2SA798 dual transistor with a BCM857, which works better here. Hopefully I’ll just about get away with the height. I should’ve really just put a footprint in for the surface mount transistor, I can’t see there’s much point in trying to get hold of the original.

Replacing the 2SA798 dual transistor with a surface-mount BCM857 on my 182 sequencer clone

The 182s are really basic (wot no reset, etc) but have actually proved to be loads of fun, which I wasn’t really expecting. I was never that bothered by the 104 sequencer, and the SQ-1 I’ve got somewhere hasn’t seen much use either. Maybe it’s the portamento, it makes everything a bit techno.

On the 110 I had a boring problem with the green LED not coming on in the VCA section, with the red LED just barely flickering, which turned out to be a duff transistor at Q18.

Should be polystyrene caps in the filter here, I know, the other 110 I’m building up will have those, just wanted to compare them. For some reason I’ve a feeling the film caps will sound a bit nicer.

110 voice board detail

Maybe too much authenticity here; the original has the diodes and resistors limiting the filter resonance tacked on the back of the pot board. The service manual refers to cutting tracks to include these, which rather suggests there wasn’t any technical reason on the original beyond “whups, left those out”. Cover your eyes, this is a crime.

board hack to include resonance limiting diodes on the 110 VCF

I’d intended to include footprints for these on the board, I just…also forgot.

For the 140 envelope, finding the right sort of 2P3T switch for the trigger source selector was proving to be a pain in the arse so I ended up using my usual DPDT 3 position ON-ON-ON and having that switch a 4066. It will eventually get some push button manual gate switches, I didn’t have any at the time.

Also I added a couple of opamps and some LEDs to give a visual indication as to the state of the envelope, ‘cos it seemed wrong that Roland didn’t have those on the original.

The extra components made routing the control panel so that all the connectors are over on one side a bit more tricky.

140 dual envelope/LFO clone

The envelope and LFO seem to work without any fuss apart from the second envelope being pinned high until I replaced the buffer opamp on the output, must’ve been a dead one.

Brilliantly I got the orientation of the Alpha rotary switch completely wrong on all of these boards, so a D-type knob will point off at a funny angle. There’s probably something horrific that I can do with a hacksaw to bodge it, I don’t really want to do another run just for that.

Another shot of the 140 dual envelope/LFO clone

There’s a couple of my versions of the OpenMusicLabs 662 clone/clown on the LFO, one for voltage control over the LFO rate and another for the LFO delay.

I had a load of dead ones after that Jupiter-4 attempt I made, so I’ve worked out a brutal way of reviving them, which essentially consists of connecting the dead 662 to power, then seeing which transistor starts to smoke, and then replacing that one and testing again, until it no longer makes the power supply panic and it works in my VCA test board.

140 dual envelope and 130 dual VCA clones from the front

All the main boards are as close as I can get them to the originals without driving myself round the bend, with the only major changes being the power/internal routings connector and more regular spacing of the connections at the front of the main board PCBs. Wonky tracks!

I tried to keep to the original track layout for the boards; this shows the wonky tracks on the 130 VCA and 140 envelope/LFO

The control boards are completely different because of the rotary pots and my desperate need to avoid manually wiring everything up as I did on the System 100.

Currently the control panels are just attached to the main board through the friction in the connectors and good intentions, so I added some holes to allow for some for some sort of mini-bracket to fix the two boards together. But then again, it might actually be easier just to use a zip-tie. Which feels wrong, but would mean I can avoid doing any potentially self-maiming metalwork.

Here’s the 172 phase shifter/audio delay/gate delay, and the 132 mixer/voltage processor:

172 phase shifter/audio delay/gate delay and 132 CV/audio mixer and voltage processor from the front

MN3004s are hard to find as NOS and no longer made, so I’ve gone with an MN3007 instead with the intention of changing the timing capacitor to overclock it to get closer to the original specs, but I quite like it as it is. I struggled to measure it at the shorter end but the delay time pot looks to give a range of about 1.7ms to 66ms, with clock noise creeping in at longer delay times. The original 172 delay is specified as between 0.3ms and 7ms.

Because the old Toshiba 4013s work differently to modern versions, I again used Fitzgreyve’s tactic of using a 4049 to get a modern 4013 to oscillate and clock the 3007 correctly (nuff respect, hat tip).

The 132 is super basic but I still managed to mess something up on the control panel; I swapped the first and third pins, which are the input and output pins for the first mixer. Another thing to bodge.

I spent a bit of time trying to work out why the red LED wasn’t lighting with input, but as should’ve been obvious, this is just to show an overload condition, which is the standard in the rest of the system.

Here’s a few of them lined up for a test in half-darkness, mostly trying to show off using three 182 sequencers at once, and struggling a bit with the tuning (but that’s techno, right?)

The 182 on the far right is connected to the 140 and the 110 and occasionally going through the audio delay on the 172, while the other two 182s are playing my original stripboard 100M and the barely-working remains of my dodgy clone System 700. I’m also putting the 606 through the phase shifter here and there, took me ages to match those transistors.

I’ve still got some more to do, such as the control boards for the more recent modules (165/173/174), as well as both boards for the 131 output mixer, and the control board for the 121 VCF with its annoying 4 position switch for the high-pass filter.

Seeing as though Roland never did a multimode filter for the 100M, and Alfa have got their IR3109 in production, I’m tempted to do a dual version of the Jupiter 6 VCF in this format.

And they all need actual metal panels as well, the annoying bit. I quite like them in white, but it’d be good to get them done in something like the original grey.


102 almost

System 100 102 clone in my kitchen

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.

original System 100 102 wiring inside front panel

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.

30mm slide potentiometer mounting circuit boards

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.

my wonderful collection of different 30mm slide potentiometers

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.

front view of System 100 model 102 clone

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:

System 100 102 clone panel 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.

Comparing my panel with an original 102

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.

102 testing


SEM pot board

SEM pot board

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.

SEM with test front panel

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.

potential four voice SEM

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.

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