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.

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.

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.

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!

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:

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.

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1 comment

  1. 17th January 2022omsonic says:

    I will be so cool to see them with nice panels and in a proper case 😮

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