Going Modular!

The Ultimate Form of Sound Synthesis

I have been dreaming of a modular synthesizer for quite some time. All those photos of the early synthesizer studios with walls full of potentiometers and billions of patch cables running wildly everywhere have such a lovely mad scientist vibe that you just got to love those machines!

Buying a ready-made modular synth has never been an option for me. Soldering everything together is part of the charm. I even started building one about 10 years ago and bought the components for a DIY oscillator and filter. I managed to build the oscillator on a vero board but it never oscillated and I somewhat lost the interest on the project. The biggest problem is that you have to build quite a list of modules before you have a synthesizer. Yes, you get sound from an oscillator right away but it's quite boring and useless until you add a filter, vca, envelopes and some modulation. Even if I had managed to get the oscillator working it would have required significant amount of work to get the basic synthesizer signal path working.

Second Round

This spring I once again fell in love with electronic music, thanks to artists like Deadmau5 and Gus Gus. After seeing all the cool live Youtube videos with modular synths I just had to restart my old synth project. Instead of debugging the old crappy oscillator build I spent some time studying the current DIY offering and found out that things are completely different from what they were 10 years ago. Nowadays we have the euro-rack standard with dozens of manufacturers providing all kinds of modules, enclosures, power supplies, DIY kits and stuff! Awesome!

After quite some research I found out about the Doepfer DIY Synth. It's a single pcb analog synthesizer with an oscillator, a filter, an lfo, ADSR envelope generator and a VCA. So practically it's the minimum analog synthesizer signal path in one PCB. With temperature compensated oscillator it only costs about 120 euros. Unfortunately it's only sold as a ready-made PCB so it's not as DIY as I would have liked but with that price and all the required features included I decided to give it a go. I can anyway switch back to more DIY mode with the modules I will be adding to the system later after the basic signal path exists.

The starting point. Doepfer DIY PCB, pots etc.

Enclosure Considerations

There's lots of euro-rack enclosure options available in all kinds of formats. As I have always had the image of a huge synth wall in my mind so I skipped all the portable smaller enclosures right away. The standard 19" rack format seemed to be an easily expandable format for an ever growing monster synth I had in mind. I also had a Yamaha TX81Z fm synthesizer from the eighties so I could install it to the same rack. Empty 19" rack panels are dirt cheap so I ordered a 3 unit high panel for the synth. A decision I would regret later.

As the euro-rack standard is now so popular I needed a way to combine it to the 19" rack idea. There's rack enclosures available from Doepfer and several other manufacturers but unfortunately they are really expensive. I would have wanted to build my Doepfer DIY synth into euro-rack format but as it eats half of one rack mounted euro-rack enclosure it would have meant at least 100e extra cost when compared to building it directly to a 5euro 19" rack panel.

Unfortunately I had already started building the synth to the 19" rack panel when I found out that the euro-rack standard is also used on other fields of electronics and not just synthesizers. There are more generic sub-rack assemblies available with lower prices in generic electronics stores. I ended up ordering 2 racks from Reichelt. As I was also going to install a Doepfer PSU3 in to the enclosure I had to make sure it's robust. Mains voltages have to stay safely in the right places.

The minimum setup:

• The rack, 35e
• threaded inserts, 8e
• Screws, 2.5e (The inserts use smaller screws than for example Doepfer euro-rack modules so you need these even if you are planning to only use ready-made modules)

And optionally:

• top and bottom covers, 8e/each, (these are good to have to protect the circuits inside)
• Empty panels in various sizes for the back and front of the enclosure and your DIY modules

So with less than 50e you get a nice industrial grade enclosure for your eurorack modules! Of course you also need a power supply but I already had a Doepfer PSU3 available so this was a perfect solution for me. There's also lots of panel mounted power supplies available that fit nicely into this kind of enclosure and take away the need to tweak any dangerous mains voltage stuff.

When installing the rack please note that back rails and front rails are different. Front rails have a lid to make the front panels stay nicely in place. I only figured this out after having everything installed and it was quite a task to switch them.

The cheaper euro-rack rack.

Wires, Wires, Wires!

As already mentioned I had started to build the synth to a 19" rack panel before discovering the cheaper eurorack enclosure options. If I had known that these generic sub-racks exist I would have built it to a 42HP wide eurorack panel to get a more compact and rigid setup.

Doepfer only provides the PCB and it's up to the builder to design and implement the panel and connections. I got inspired by the already sold out Little Dieter Project that has nice panel layout and good wiring instructions. After that I spent several evenings drilling, soldering and cutting wires:

Holes drilled. Looks horrible. I should invest on proper drilling tools.

Jacks and Pots in place. I later got rid of the brown ones.

First ground connections soldered.

More panel-to-panel connections soldered. Still looking nice and clean!

All wires soldered and PCB in place. Not so nice and clean anymore...

I added some Dymo stickers to the panel. Looks ugly but at least it's now clear what the pots and jacks do.

The result

I Finally got everything done and installed. The DIY synth is powered with Doepfer PSU3 power supply installed into one of the eurorack enclosures. Power is distributed with simple bus boards. I also installed some ready-made eurorack modules that I had bought:

Finally attached it to the 19" rack. Power connector from a DIY bus board. There's room for another one in the panel.

The mighty synthesis tower! Lots of room for future DIY projects!

Well, how does it sound? I haven't done a proper demo yet but here's a short video that shows the first sounds from the oscillator. I need to extract my midi2cv board from an earlier synth project and move it to eurorack format so that I can get some real musical notes out from this beast. In general the sound is really good and I love the way the VCA and VCF can be overdriven to get some awesome acid bass sounds!

In total I'm really pleased with the Doepfer DIY synth and this whole project. Now I finally have a modular analog synth and can continue expanding it infinitely! I already have several ideas what to build next...