MATRIXSYNTH: Replica Buchla 100 series modular synth: LA67 Mort’s Barge

Sunday, July 30, 2023

Replica Buchla 100 series modular synth: LA67 Mort’s Barge

video upload by Tom Churchill

"This video is about Mort’s Barge - a replica mini-system of five Buchla 100 series modules that were used by electronic music pioneer Morton Subotnick in the mid-1960s. I recently built the 4U DIY modules from LA67, and in this video I walk through the features and create a few patches that show what they’re capable of.

My build notes are here:

Find out more about the Mort’s Barge DIY set on the LA67 website:"

You can find additional posts featuring Mort's Barge here.

Notes and pics via Tom Churchill's post on Mod Wiggler:

"I thought I’d share a couple of things I learned along the way which maybe aren’t immediately obvious from the BOMs alone, in case anyone else is planning to tackle the build and is looking for some tips.

Some of this stuff has no doubt been covered earlier in the thread, so apologies for any repetition. Also, a lot will probably be obvious to experienced builders, but I’m definitely not in that category yet, so for anyone else (like me) who’s only built Eurorack kits previously, maybe isn’t super-familiar with circuit theory and component sourcing, it might be useful.

After I ordered the panels and PCBs from LA67 I contacted Julian at The Beast to ask about his 6U Buchla boats. As luck would have it he still had a couple of the special boats he supplied to LA67 for the pre-built Mort’s Barge systems, with matt black coating and pre-drilled holes for power inlet, power switch and grounding banana socket, so I snagged one.
I added some rubber feet to allow a bit of clearance for the screws I used to mount the PSU PCB (see below) and to avoid the underside getting scratched.
For mounting the modules, I bought a pack of 20 M3 speed fasteners (aka captive nuts, aka Tinnermans) from eBay, and secured the modules using M3 6mm screws with plastic washers.
The PSU PCB doesn’t require any caps and you just need to solder one bridge as marked. (This is now clear on the Mort’s Barge PSU BOM, but it wasn’t at first.)
I mounted the PSU PCB on 8mm M2.5 standoffs via the pre-drilled holes in the bottom of the boat.
I added a DC inlet and wired a 20mm round rocker switch in series.
I added a single banana socket connected to 0V to provide a ground for any other cases I might want to use with it (and for connecting to Eurorack - see below).
For the AC-DC converter I just used a standard 12V 2A wall wart I had lying around, with a 2.1mm centre positive barrel connector.
I used the 2-pin Molex connectors as per the BOM to distribute power to the individual modules (with the power cables hard-wired to the individual module PCBs)
Component sourcing:
I combined the individual BOMs for the five modules into one master BOM, ticked off what I already had in stock (mostly resistors), then ordered any other required resistors, trimmers, pots, 2N3904/6 transistors and various bits of hardware from Tayda; caps, specialist transistors, diodes, switches, knobs, lamps etc from Mouser.
I’m in the UK and banana sockets worked out slightly cheaper from Thonk, so I ordered those there. I also bought the necessary matched transistor pairs from Thonk to save time (I don’t have the tools or experience to match them myself!)
This might be sacrilege to Buchla purists but I went for Switchcraft 3.5mm sockets instead of Tini-Jax - I already have lots of 3.5mm patch cables and it makes for easier integration.
The 910p film caps on the BOM are huge - 10mm lead spacing - and expensive. I ordered them before I realised this, and with a bit of leg straightening/bending they do fit fine in the 158 and 180 boards, but I replaced them with these much smaller and cheaper 1n mylar film caps for the 140 - ... apacitor-5 - and they work just fine.
The BOM has since been corrected, but slightly annoyingly at the time I was ordering, the part code for the Dialight lamps in the 123 was out of date, so the ones that arrived in my original order were the wrong size. I had to do a separate order for the correct parts, 609-1122-130F. These aren’t cheap, so double check that you’re getting 9mm ones!
On the 158 BOM, there’s a suggestion to use 1n5 instead of 47n for C11 to reduce saw wave distortion. I put sockets in for that and tried both - the 1n5 definitely gives a much cleaner saw so I’ve stuck with that. I also left out C8 as suggested to improve sine shape - I didn’t try it with it included but the sine is definitely a good shape without so I’ll stick without it.
General tips:
I built them in the left to right order they’re shown on the LA67 photos - 158, 110, 180, 140, 123. It was pretty easy to test this way.
Calibration-wise there’s not much to do - the trimmers on the 158 adjust the sine shape and upper and lower frequency limits; use the 110 trimmers to minimise clicking with a raw trigger in; the 140 trimmers set the upper and lower period (I haven’t really touched these)
For the wiring, I soldered pins to the PCB and used a bunch of F-F Dupont jumper wires, cut in half, so if I ever need to take the board off I can simply pull these off and don’t need to desolder anything. For the multiple outputs I mostly just used old resistor legs to bridge them.
Integrating with Eurorack clock is easy - both the 180 and the 123 respond to triggers as low as 5V (e.g. from Pam’s). I don’t use a format jumbler, just a 3.5mm to two bananas cable, with the ground banana connected to the spare ground I fitted near the power switch. I don’t think I’ll ever bother trying to send CV from Eurorack but this way I can at least clock it to the rest of my system if I want to, and maybe even play around with some more complex rhythm patterns.
Anyway, hope that’s handy for someone - I’ll share a bunch of patches on YouTube soon!"

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