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Double Doepfer!

Getting Rid of the Empty Panel Half

As already mentioned in my earlier post, I started my modular synth with a Doepfer DIY Synth kit. It happened to take exactly one half of the 3 unit rack panel. It was clear that sooner or later I would need to add something there because the half empty panel looked somewhat silly.

"Must fill panel! Must fill panel!"
You might have noticed that Doepfer gives a rather nice discount promise in the DIY synth webpage: If you build one and send some photos to be added to the page you will get 50% discount for another diy synth board! (Or possibly an extension board in the future). After I had documented my modular synth beginnings into this blog I sent a link and some photos to Doepfer. Pretty soon I got a reply from Dieter Doepfer himself! You can spot my synth in the page now.

At this point it was pretty clear that I would build another DIY synth to fill the panel. I had already been missing another oscillator and ADSR and this would give me an extra unit of everything with a super friendly price! It would also allow two completely independent synth voices to play different things because one DIY synth contains a full mono synth signal chain. One voice for bass and one for lead for example.

My other option was to use empty panel half for mixers, amplifiers, multiples and other simple utilities but as the 3U panel already full of potentiometers and wiring is quite awkward to work with I wanted to get done with it at once and then continue my DIY adventures in smaller Eurorack format. So another DIY synth it is!

Making the Same Mistakes Again...

The build process was somewhat boring as there was nothing new this time. I had the finalized unit right next to the new one so I could just copy everything from there. While doing this I managed to spot several mistakes I made with the first unit. For example the distance between pots in VCF is half a centimeter wider than elsewhere. Probably a measurement mistake. I managed to notice that and the second unit has a bit more even panel layout.

Trying to draw a more even layout this time...

...and still everything gets messed up because of my bad drilling skills and/or tools!

My fingers ache when looking at this picture. Attaching all the pots and jacks is painful! Trying to compensate the pain with some Laphroaig.

This side looks good already! I ran out of green knobs so had to use brown ones. I have ordered more so it will change color soon.

And then the soldering part. With the first unit I left too little space below some of the pots and unfortunately copied the exact same problems to this one too. Luckily there's space on the side so I could get away with it by twisting the pots slightly. The Little Dieter wiring instructions also show several ground connections to the leds and I managed to mess it up and grounded both terminals of the LED again just like with the first unit. I wonder how many units I would need to build the learn...

First wires in place

All wiring done!

Discovering new issues

After all set up I switched the power on and tuned the new oscillator. Everything seemed to work well until I tried to route both oscillators to the same filter. Really weird things happened to the signal and after some debugging I noticed a mistake in the Little Dieter wiring instructions. The VCF audio input and fm input in JP7 connector are messed up just like somebody points out in the comment I didn't notice. So instead of summing the two oscillator signals it was modulating one with the other one! No wonder it sounded weird. I wish I had noticed this earlier. It was quite tricky to fix it without burning all the other wires already in place. Twice!

Double Doepfer, Twice as Fun!

After fixing the final bug my synth started to look quite good! Here's a quick test video for my synth rig: https://www.instagram.com/p/BTyTbqKlxRv/

In the meantime I also added a sliding shelf for all the desktop gear so that I can quickly start fooling around with the synths without all the boring unpack/wire/initialization work.

It's already starting to look like a modular synthesizer!

I should probably stop building more modules and start making some music for a change... 
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