And so my modular journey begins

January 7th, 2011


So here’s the deal. A couple of years ago a friend of mine introduced me to the world of modular synthesizers at a school where he was enrolled, where they had a pretty big, original ’70s Serge with cherry-picked set of modules (I’m assuming) as well as an original Buchla 200 series system from that era. I like the sound of the Buchla oscillators, but in all other aspects, I’ve fallen in love with the Serge. You see, I’m an engineer type of person and I appreciate the atomic structure of the Serge paradigm. As for any Serge-lover of rank, my favorite module is the DUSG. You’ll have to look long and hard for a more versatile module. If I could build a rack consisting of several pieces of only one type of module, that would definitely be it.

So, I quickly learned the basics of knob twiddling and banana sex, () but both me and my friend had the problem that we didn’t have our own modular systems. Using a fully equipped system at an institution is great, except that you need to actually go there etc. The next logical step is obviously to get our own synths. He is a lucky bastard who happens to have a rich mom, with the effect that he has bought 1-2 modules a month for two years straight. He now has 9U or so worth of Euro.

I on the other hand am piss-poor and a terminal procrastinator but have access to a component store and even a PCB manufacturing facility at university. The outcome is obvious. I decided to build a DIY modular. I have a number of mostly finished boards without panels, which is what I’m working on now. However, none of the boards are Serge clones, which would be nice. With a the exception of a couple of modules available from CGS, it’s pretty difficult to find Serge schematics. Which I can understand since they’re still in production.
Right now, I wish I had the schematic for a Wilson Analog Delay, for example. (I just realized I have a TDA1024 delay circuit. If you have the schematic, feel free to contact me. No questions asked, and I’ll promise not to spread it or use it for profit.) My homemade modular will use banana all the way (of course).

Build log of my first finished module

So, I finally finished a first module the other day. (I have PCBs for more, but I need to make panels and I also don’t have enough LM13700s and I’m also missing a couple of other chips.) I’m doing all of this work on my university’s electronics student club, so part of the challenge I’ve partaken, is trying to use their component stock as far as I can. This is sometimes difficult, as most of their components are surplus donations from companies.

This is the first module I finish in the sense that it has a workable front panel. The module is an Oakley VC-LFO.

First things first, I added a Doepfer style pin header in place of the MOTM/Oakley header.

Add some superglue for stability…

… and some hot glue for more stability.

Tada! This is an odd pin header with an extra notch, that I don’t know the use for. Doesn’t really matter.

(If you’re observant you’ll notice that this isn’t actually the VC-LFO board pictured below, but another board. But I did the same process to all the Oakley boards I have.)

Here’s a shelf that will house 12 U worth of modules some day. Note the marks where I’ll drill holes for the screws so I can secure the rack ears.

Ok, onto yesternight’s build. First some space planning.

Drilling the holes. I made a mistake here. I laid out the design on the wrong side of the board so I need to have the side with the more scratches and the markings facing the front. (Unless I flip it in either direction.) Oh well…

This is the side that is now the front:

This is the side that is now the back:

The board, with a home-made angled bracket. I reused this kind of aluminum sheet because it already has holes in it at regular distances. Also note the other ugly things. The upper right IC socket should have held a matched transistor pair in a DIP package but I didn’t have one. Tried to match the transistors the best I cold, still. The empty IC socket isn’t completely empty. Look closely and you’ll realize there’s a small piece of wire there. This was because my DG403 hack (see below) didn’t quite work out.

This is my DG403 hack. The schematic specifies DG403, which is a dual DPST-type analog switch. All I could find in the lab was DG404, which is supposedly a weird half DG403 equivalent, which I could only find a Japanese datasheet for. Oh well, close enough, so I thought I’d stack two of them on top of each other and wire up my own makeshift DG403. However, it didn’t work out too well; it just didn’t work. This was after many hours of being awake, so I didn’t bother troubleshooting the thing. Instead, I just hardwired the default-on setting with a piece of wire, which works but disables the sync function for now.

Here’s the board attached to the panel. Getting closer (to falling asleep) now…

Fully equipped. Note that everything is modular, so you can release the board and all frontpanel components without cutting any wires or destroying anything else. Note that I drilled a hole too much. Not sure what to do with it yet. Perhaps AC-coupled FM…

And finally, the thing in all its glory. The panel is 3 U high (fits a Euro rack) and some unspecified width (less than 19″ wide.) I’m obviously planning to add one or more additional modules to the same panel.

In the future, I’m planning to do the following:
Finally make panels for the module boards I have. This includes:

Oakley triple VCA
Oakley slew generator
Oakley noise generator
(Managed to buy three Oakley board for cheap)

2*filter, home-made by someone (LP/BP/HP -12 dB/Oct)
A homemade ADSR envelope that someone had thrown away at the lab! Thank you, Someone!
A 16-step 4067-based sequencer (still needs a digital part for control. I’ll probably whip something together on my Arduino.)
Homemade polarizing mixer.
Probably something more that I’m forgetting.

Gotta build me a DUSG, too! (Very important! Could save someone’s life one day!)

I also have a couple of guitar pedals that I’m hoping to modularize.

Furthermore, I found a bunch of surface mount CA3080 in the lab. I’m planning to make a LM13700->CA3080 adapter with place for two CA3080s and optional diodes and drive transistors.

Sounds like a plan, uh? Just gotta make sure I don’t go back to procrastinating…

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