LED mods for Arp 1601 clone

Still time for a quick one before it’s ‘BYE BYE 2016’! :)

While building my TTSH I also got myself a DIY kit of a Arp 1601 sequencer clone. The build itself was so straightforward that I didn’t see the point in blogging the details. However I made some LED mods to it and thought maybe this would be of interest to owners of this device. So if you ended up here looking to change the color of LEDs on your Arp 1601 clone, look no further! If you’re in a hurry, check the summary section at the end of this post.

While you can also find my posts related to the mod at Muffwiggler (Muff) forum, I thought my blog here is a more compact way to present the information. For one, since forum threads at Muff are created by product / project, there’s a number of discussions going on at the same time (esp. if a DIY build). So a thread can become convoluted. Second, threads which span years (or multiple production runs of a kit) can become l-o-n-g, adding to the ‘needle in a haystack’ effect. Third, if you’re not logged in the board system won’t show post attachments or the like. So it can be quite the dig looking for information you need.

But don’t get me wrong, I love the Muffwiggler board and a lot of highly skilled people dwell there. It’s just that often the format isn’t good for finding information that you need instantly.

Well maybe my ramblings aren’t either, but let’s not follow that tangent! :D

My finished 1601 build

My finished 1601 build

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ProtoTypo PT1 – WOTI

Yay it’s a firstie, my soft landing to the world of Eurorack: A DIY version of Xaoc DevicesPOTI expander for Batumi (a quad LFO module). “What is ProtoTypo?” you might wonder? Then check my previous post.

The Build

Simple one yeah: three toggle switches mounted on a 3HP euro panel and connected to a 6-pin ribbon cable. Haven’t done anything this straightforward in ages, but still it’s a good crash course into eurorack mechanical specs and the like. As for Poti, there’s a good set of pictures of it at the Schneidersladen webshop, from which it’s easy to interpret wire connections.

Heatshrink stress relief for the cable solder joint

Heatshrink stress relief for the cable solder joint

Here’s a good generic build tip: As switches are connected to Batumi using flat cable (see photo below), it’s very much recommended to add some heat shrink tubing to cover solder joints. This is because flat cable is thin and flexible, and soldering any of its wires creates a sharp stiff-to-flexible transition point. If the cable is moved or flexed repeatedly then the wires will easily break off at this spot. So adding heat shrink over the joint will distribute the weight of cable to a wider area and thus lessen the risk of broken wires.

Cabling overview

Cabling overview

...and how it connects to Batumi.

…and how it connects to Batumi.

I have quite a neat leftover piece of this 4cm thick oak kitchen tabletop (from Ikea), so I figured I might just as well use some for building Euro panels. After all 4cm = 8HP (in Euro spec 1HP = 5.08mm / 1/5″) so it’s a perfect match size-wise. Once the oak is cut to 4HP slices 2mm thick, it’s very easy to trim down to required width. Simply running a sharp carpet knife along a ruler repeatedly will eventually create a straight groove deep enough to slice the thin wood panel in half. Minimal sanding required, yay \o/

So with panel cut & drilled, I treated it with white wood stain and then designed and printed a panel decal to a leftover Lazertran sheet (from my x0xb0x build btw!).

Now I have no clue if ‘Poti’ means anything, but I’m a big fan of abbreviations so I chose to call this build ‘WOTI’. That’s short for Wooden Output Toggle Interface. You know, oak panel and all! ;)

The finished module, fancy innit?!

The finished module, fancy innit?!

So there it is, ProtoTypo PT1. Of course I added it to Modulargrid.net too :). You can download the panel decal here for your own build. Poti manual is available from Xaoc Devices’ website.

The design of this module could be squeezed to 2HP too, provided that the switches were of sub-miniature type and/or oriented vertically. However I wanted a design to match Poti, so it was 3HP for me.

That’s that. Next up a ProtoTypo build with even some electronics in it!


Time for a bla-bla-bla post, some personal history to start with..

Eurorack modular synthesizers. You’d think that these things would be the obvious and instant end stop for a DIY synth builder like myself. But I’m my case, not even remotely so. Sure, I’ve been on the map about modulars ever since I started studying sound synthesis in early 90s, and the Euro(rack) format since around 2002. But I just sort of dismissed the whole thing thinking along the lines of ‘looks fun but not my cup‘, and went on to build this and that instead. I’ve even had a number of friends suggest that I should really look into the Euro, but all of that fell to deaf ears!

I don’t know exactly why, but the modular stuff previously never kind of resonated with me. For one, I guess it might have much to do with the fact that what I’ve had the chance to play around with the most, has been dominantly the software kind.. Say, programs like NI’s Reaktor. While software is far more versatile than hardware, for me it lacks much of the spontaneity that patching hardware can offer. Connecting software modules using a mouse just feels more a cumbersome chore than fun, and despite you’re DIYing as much, it lacks all the physical crafting.

Second, I also never stopped to connect all the obvious of what I like. Tinkering with bits and bobs, like a second nature to me. Making compact or miniature builds, yes please! Building or bending audio hardware at my will, hell yeah!

It’s funny really, how much one can be in the middle of it all and not realize the obvious..


Photo of my (at the time) work-in-progress Arp 2600 clone build

Now if you’ve been following this blog you know that some months ago I completed my TTSH build, a semi-modular analog synthesizer. The more I got into patching sounds with it, I was quickly met with how limited a system it actually is to work with. So I then moved on to build a Arp 1601 sequencer clone (pending a blog post btw!).. After which I found myself putting together a Eurorack skiff to host some utility modules, all to expand the system.. And while building the skiff I got into modifying some of the things.. So here we finally wind up to subject of this post..:


I figured that since I’m going to build and mod some Euro modules, I might as well brand that stuff for the fun of it. And perhaps to have something to group/label the modules at places like Modulargrid.net. So after giving it a good thought I chose to go with ProtoTypo; not to copy-cat the other Prototypos around the net, but because I feel it sums up in a fun way what the essence of my Euro builds will be. Like these one-off prototypes that may contain errors created in the heat of all the joy of DIY. Perhaps like what the electronics equivalent of a ‘typo’ is to written text.

What’s to come

So yeah, under Prototypo I’ll be messing around with commercial (DIY) Euro modules, building new or modding existing gear to Eurorack format (eg. my incomplete Monotron Delay Expander springs to mind!). As I get builds done, I’m going to add them to the official ProtoTypo page here on this blog with build details included, just in case there’s someone out there who wants to make one too.. Or perhaps peer-review the circuits, suggest improvements or whatever :)

Builder caution is advised as usual: As I often say, it’s after all just stuff you found online. If there’s a post for a module then I’ve managed to make a working one, but even so I don’t recommend plain blindly following my scribblings. Things to come, stay tuned!


TTSH, Gate Booster mod

If you’re all new into how analog synthesizers can be controlled, you may first want to take a look at this Wiki article on CV/Gate for some jargon busting. Other than that, let’s dive right in.

Among the first electronics mod I wanted to add to my TTSH was the Gate Booster. To fully open the ADSR envelope generator of TTSH a +10VDC gate needs to be applied, thus in it’s stock config the envelope can’t be fired properly by using eg. any external gear that outputs a +5V gate. Add to the common CV/Gate specs, the TTSH envelope generator also needs a trigger signal (very short pulse) to work properly. This can be used to restart the envelope without disabling gate signal.

So what the Gate Booster does is, it converts low voltage level gate signals to higher voltage and generates the trigger signal from the gate input. The particular circuit board I bought for myself is this modified version (sold by Oshpark) with a socket for a Midimplant MIDI-to-CV/Gate converter board. Having MIDI (keyboard) input just made so much more sense than eg. building a CV keyboard like the Arp 3620.

Gate Booster board all populated.

Gate Booster board all populated..

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TTSH, speaker baffle mod

This was a quick “let’s see what happens” kind of mod for my TTSH.

In their stock config, the TTSH loudspeakers are supposed to be fastened to the circuit board, which is then fastened to the front plate. Handy approach eg. for having the electronics as a entirely separate, single ‘module’ for servicing etc. But problem with this is that it leaves a ~12mm gap between the driver and the front panel. Read More…