DIY Arduino String Synth

DIY Arduino String Synth With Analogue Filter

***Updates at bottom of page - Easy to read Schematics etc****

Just like the Arduino Drum Machine, this is another build based on the amazing work of Jan Ostman, who is generous enough to share the code over on his website;

***Old website***

https://janostman.wordpress.com/how-to-build-your-very-own-string-synth/

***New Website***

http://synthworks.eu/arduino-string-synthesizer/

The suggested $3 dollar donation is quite simply amazing value for money, so if you use this, don't forget to tip!

On top of Jan's work, I've added a 12db filter with resonance (based on this design) to add a bit more sound sculpting to the synth.  Filters are a massive part of synthesis to me (mainly because I can't play but can quite happily turn knob) and an analogue filter really adds to the warmth 'wobble' of the synth.

The filter has a separate on/off switch and bypass switch.  Looking back it would've been better to build that into one switch, and also to move the output further to the right.  Ahhh the power of hindsight.

I wanted the synth to look very Minimoog-ish or Prophet 5-ish, which I think I achieved, but building the case was by far and away the hardest part of the build (due to my own inexperience/stupidity).

Total build time was spread over 3 months and probably took about 20 hours (most of that time was spent staring at nothing trying to think what to do next).  If I were to make it again I think I could get it down to about ten hours, if luck was on my side.

Here's a quick video of it in action;

Parts

The total cost of parts came to about €60, with most of that going on the MIDITECH midi keyboard. I used a cheap Chinese Arduino Nano clone to keep the cost down (around €2), then a few pots and resistors etc again from China. Also high quality plywood from Modulor for €2.90 (I think it was 6.5cmx250x500). The perspex was also from Modulor. Obviously if you don't already own wood stain and glue etc your cost will be significantly higher. For the panels I used my banggood laser engraver, which I think adds massively to the look of the synth.  If you don't have one of these you could use a label printer.

Electronics

Jan's website documents the build process pretty well, so go check there for schematics etc.  I did manage to draw up the wiring diagram which may save somebody a bit of time when hooking up the keys (find it somewhere below).

I started by taking apart the MIDITECH and unplugging the ribbon cables;

You won't need this part any longer so remove it to save some space;

I soldered the Arduino Nano to some perfboard to make it easier to handle (and to screw down to the chassis later on).

Then using some ribbon cables I began to figure out how to connect the keyboards out's with the Arduino's In's.

Eventually I figured out what went where and soldered it all down and covered the connectors with heat-shrink. You'll probably save a bit of time if you use this;

That's the majority of the synth finished!  From the nano's output I added a bypass switch and then the 12db filter.  I forgot to take any pictures of that though until it was already attached - sorry!  But it all fitted onto another small perf-board;

The Case

I started by cutting some cheap board and securing the key-bed onto it.  This gave me an idea of the final size of the synth to which I based my design around.  I kept the bottom plastic of the MIDITECH (always capitals!) keyboard because it would secure down easier (using it's screw holes) and also because it would probably be a pain to try and re-construct it any other way.  I also added some 'feet' at this point.

Feet...

With bottom panel size known,  I sketched out the rest of the case...

The side panels;

All the parts have been cut here (the other bit of perspex with the dials on was temporary just to make sure it was still working);

Notice the pencil with my name written on it.  That's mine it is.

Then using my old friend Ponal Wood glue I started sticking everything together (including fingers, clothes and everything else);

Then it was time to design the front panel and the laser engrave it onto perspex.  The smell was awful (and toxic)...  I stayed in the room long enough to feel faint.  I did sleep well that night though.

Running a test on card;

Burn!

After it was engraved I filled it in with white acrylic paint;

 With the panels and case completed it was time to stain the wood.  I used a mahogany brown stain, using two or three coats.  The trick here is not to use to0 much and to keep it moving when it's been applied, otherwise you'll get an uneven finish.

 Once this had dried it was time to add the varnish.  Like with the stain, I find it's best to use only a tiny amount and spread it out as much as possible to get the best finish (you can always add another layer later).  With this synth I found one layer to be enough;

Once this has dried you can now put it all together.  For extra security I also used some hot glue to do this (and it's not fallen apart yet)

I added screws to secure the perspex panel but can't find a picture of that. But I'm sure you can imagine what it looks like.

Conclusion

Overall I'm pretty happy with how it turned out, with only a few gaps in the wood caused by my rubbish cutting/maths skills.  Should I make it again I'd move the output over to the far-right as I've noticed it's possible to knock the cable when going mad on the filter (you should only touch a synthesisers knobs as if they are really hot, otherwise you're not a real synthesist).

I've been learning C for a while, but it's a massive mountain to climb.  From here though I've bought the following book;

When I eventually get around to reading it, it should give me a better idea of what's going on in the code, then I'd like to attempt a version 2 using maybe an Arduino Due and add some more controls.

Thanks!

****UPDATE****
SIMPLIFIED SCHEMATICS

Below is a simplified schematic for the string synth...  Sorry it's not the best quality I'll try and take a better picture later, but hopefully this should be of help those of you new to schematics that want to try and build this synth.

The connections where it says 'goes to keyboard', you can see elsewhere in this blog for another detailed diagram of where and how these can be wired up to the keys.   As for the potentiometers, I *think* I've drawn them the correct way (if you make this and the pots are working the opposite as you'd expect, swap around the ground and 5v connections on each pot).  If the drawing is incorrect, let me know and I'll re-do it. Even if this version is wrong, nothing will break & it'll still work OK (just the pots will work in reverse).

You can see where the pots 5volt and ground connections need to go in the diagram, I didn't join them in the picture because the wires would start overlapping and become confusing.  It's pretty obvious what to do though.

Also drawn is the audio out headphone socket, with the positive voltage/audio signal coming from the output D11, which then goes through the resister/capacitor (which acts as a filter to reduce some of the noise from the Arduino).  The other side of the audio goes to the ground signal.  If you don't know how to wire up a audio jack, maybe google 'audio jack pin-out' or 'audio socket wiring diagram'.

If you plan on adding the analogue filter, you'd leave off the audio jack and have the previously mention positive wire go into the input of the filter.  You'll have to learn to read the schematic for that I'm afraid, as I couldn't really simplify it without it becoming more complicated than a normal schematic.  Give me a shout if you get stuck though.

Good luck!

P.S

I'll draw a simplified schematic for the Arduino drum machine soon.

****UPDATE PART 2******

Below is a wiring diagram to add a bypass switch to the filter;

...And if you were struggling to figure out how to wire up the Pots for the filter, I've drawn out a simple picture showing how (I've had to do this whilst away traveling, so it's partly drawn from memory but I'm pretty certain it's correct)...

Obviously the drawing only shows how the pots are wired and not the full schematic.  Go look at the proper schematic for the rest of the plans, but this will give you a good idea of how to wire up the pots.

Powering the filter from a 9v Battery will give it it a bit more 'oomph', so if you'd like to do that, the below illustration will give you an idea.  Further, should you want an LED indicator showing if the filter is switched on or not, see the chequered box;

I only had SPDT switches available when I built the synth, so that's why there's separate switches for both the on/off & bypass, but you could easily just use one 2PDT to save space.  You could even add an audio in jack at the start of the filter to process other audio.

Good luck!

***UPDATE Arduino Drum Machine****

Simplified Schematic

Ok, so this 'simplified' schematic might not actually make things any simpler!  But some people have asked for it, so maybe it'll help clear somethings up a little bit - especially how to wire up the audio output and pots/switches.  This was drawn from memory so I hope it's correct - give me a shout if not and I'll update (the pots might work in reverse, but they'll still work).  I'd also urge you to look at the schematic on Jan Ostman's website for more help;

https://janostman.wordpress.com/the-o2-source-code/


Thanks!

Korg Mini-Pops DIY Drum Machine

Korg Mini-Pops DIY Drum Machine 

This is a really cool build;  It a recreation of the Korg Mini-Pops drum machine, an instrument which has been on a ton of records the most famous of which might be Jean Michelle Jarre’s ‘Oxegen’ album, hence this clone being called the ’O2’.  

The brilliant Jan Ostman built this using only an Arduino nano and a few barebone parts.  Jan is giving away the full details on his website and is only asking for a $3 donation in return.  Bargain!

https://janostman.wordpress.com/the-o2-source-code/

***Update***

If the linked website is no longer working, use the Internet Archive to visit a cached version of the site (copy and paste the address and choose a date from around when this pages was posted: around Dec 2016).

***MIDI update***

From the forums of Look Mum No Computer, somebody has posted the code but with the MIDI update;

https://www.mediafire.com/file/5hwyuvykzn8kszg/O2minipops2midiout.ino/file

(Read the forum for more info and schematic).

***More Advanced Model Update***

If you'd like to build a more advanced version, head over to the NoiseyMaker website for more info and a nice detailed guide.  This version builds on the original & adds some advanced features like a display and even pitch control of the samples.  Also the drum patterns have been updated to be a bit more 4/4 time 'electronic-style', rather than than some of the 3/4 time waltz in the original code (you could always copy & paste these over to the old code if you wished).

....

I started by building my first version using a cheap Maplin plastic enclosure, but I thought it was worth spending a little more time on it so I got the table saw out. 

Because the table saw has a maximum cutting width of 7cm, I based the case around this limitation.

The switches mute the individual drum hits. The pots select the pattern and its tempo.

V3.

***UPDATE Arduino Drum Machine****

Simplified Schematic

Ok, so this 'simplified' schematic might not actually make things any simpler!  But some people have asked for it, so maybe it'll help clear somethings up a little bit - especially how to wire up the audio output and pots/switches.  This was drawn from memory so I hope it's correct - give me a shout if not and I'll update (the pots might work in reverse, but they'll still work).  I'd also urge you to look at the schematic on Jan Ostman's website for more help;

https://janostman.wordpress.com/the-o2-source-code/

Thanks!

DIY Jesus & Mary Chain Fuzz Pedal

DIY Jesus & The Mary Chain Fuzz Pedal

This was my attempt at the Jesus and Mary Chain Shin Ei Fuzz Wah.  The Mary Chain pedal was famously faulty which I wanted to incorporate the same nastiness into my version.  Also the original pedal was a wah-pedal, but I don't have the means to build that.  So I thought about it; a wah-pedal is essentially just a filter, so why don't I just add a filter onto the original schematic, so that you can drive it into self oscillation creating the feedback that it was known for?

After building a few different schematics I'd found on the web, I went with this one as it sounded the best to my ears;

http://www.generalguitargadgets.com/pdf/ggg_secf_sc_bst.pdf

However, note that this isn't the actual fuzz pedal schematic, but just the fuzz part of it.  That's ok, because this is where I add the following filter tat's capable of self-oscillation;

http://electro-music.com/forum/topic-51780-0.html&postdays=0&postorder=asc&highlight=

I've put this filter into loads of different build before because it's simple but sounds pretty good (or nasty if that's what you want).

I then added numerous bypasses, and the ability to run the filter and fuzz separately.

For some reason after building this I put it away in the drawer and forgot about it, which is a shame because it sounded pretty much like the mary-chain in a pedal.  I should probably get a batch of PCB's made if I build any more because it was a lot of work making it on perf-board.  

One day I'll do that and post some audio-examples.

Korg Volca DIY Stand Guide

Korg Volca DIY Stand

I’d seen lots of nice looking, but very expensive cases for the Korg Volca series, so to save some money I thought I’d try to build my own, with the very real possibilty of losing a few fingers :-)  

It actually all turned out pretty ok with no digits lost, however the problem I did have was with the case of the volca stand; this was either my poor woodworking skills or perhaps not having the correct equipment.

Where the case has a fold in it I managed to nick the other side, so it isn't quite as neat as it should, but it’ll do for now.  It's maybe a job for a dremel to do properly.  

I found that I had to use a thicker piece of wood for where the Volca sits, as otherwise because of the size of the screws, the wood will split (you could of course use smaller screws here but I didn’t have any).

To build the stand I used;

6.5mm Birch Plywood (250mm x 500mm) €2.60 from Modulor Berlin excl. delivery

9mm Birch Plywood (250mm x 500mm) €3.30 from Modulor Berlin excl. delivery

Black 3,9x30mm screws (€5-ish for 800 from Toom)

You'll also need;

saw/table saw

sander

ruler

pen/pencil

sheet of paper

drill

tape

I started by drawing out the angles of the stands, there were a couple of different angles I could have used, but I finally settled on 30 & 60 degrees.  One thing to note here is that you can turn the stand upside down and use the reverse angle, which gives a sharper incline.

…Then I drew around the sides of the actual instruments, with them being at the correct angles and figured out the correct dimensions from here (remember to give yourself some lee-way here, hence the 11.5cm volcas shown below are each given 11.7mm).  This give you a nicer edge without risk of the Volca overhanging.

Now draw this out on paper...  using the edge of the paper as an exact 90 degree angle (as I'm sure this'll be straighter than anything I could ever cut.

With the paper cut out (use only one piece of paper and simply reverse it for the other-side, you'll save time and get the exact duplicate), now mark out the outline on the wood.

Lovely! Now mark the other one out. 

TIP: Make sure you use the 90 degree angle of the wood, unless you have some quality cutting equipment (again, the people cutting this have better equipment than me, so I'm relying on them to cut straight.  Not the best method really, but what can you do)

With both sides marked, it's now time to cut them out.  To make this slightly easier while using a tablesaw, I'll cut the board into more manageable pieces (you might not need to do this if you're using a saw).

Cutting the wood into more manageable sized pieces...

Then cut out the main bits

At the intersection of the two Volcas, it's almost impossible to cut accurately...

...But with a little patience you can achieve an acceptable result

Cutting the 9mm wood: Use this picture to help cut the board. The length should be the same with as the Volca and the width can be shorter than a volca, as long

as it can sit on the wood without tipping over.

I used: 19.4cm x 9.8cm

The edges will be rough after cutting so we'll sand them down

I used a sander but sand paper will also work.

To smarten up the badly cut intersection, I used these files that you can get in Maplin.

Once all this was complete the boards came out looking pretty good:

Here's a little gif of the preceding steps;















Now we need to think where to sit the board that will hold up the Volcas.  To do this I marked out a line underneath the Volcas while positioned correctly on the board.














Remember the board needs to be 9mm otherwise it'll split , unless maybe you're using smaller screws than me then you might get away with it.  












Roughly draw out the 9mm board outline using a ruler - making sure it won't overhang or anything.

You only need to mark out one board for this.

Use a ruler to find two centre spots for the
two screw slots (look at the picture if that doesn't make sense!).  Remember the distances for later.









Now secure the two sides together using tape.  Make sure they're tight and don't move.











 Also mask where the drill holes will be.  This'll help prevent the wood from splintering.
















With them secured, drill through both pieces at once.


















Photo of all four drill holes successfully drilled.

 



Hopefully you've remembered the distances of the holes, because you need to now mark the same on the two pieces of 9mm wood



















Now carefully drill the exact centres of the wood.  This will create a guiding line for the screw.















Now put the screw in the sides, but don't go through all the way yet;
















With the screws just barely poking through the sides line up the 9mm wood
















Then slowly turn the screws

Tip:  only give a few turns on each side of the screw before changing to the other screw so they go through evenly and at the same time.




 





 Go slowly so you stay precise and don't split the board


















It should be looking almost finished by now, we just need to do the same with the other side.








Now just add the volcas!  You may have to loosen one side to get the volcas in, if this is the case then at least they'll be snug and won't fall out (be careful you don't over tighten it and squash the machines!).  

If you've left too much room you have two options; you can either sand down the side of one end of the 9mm board until the fit, or secure them in place with some double sided velco.

I personally think these stands looks pretty snazzy as is, but you could easily varnish them now if you so wish.

I hope this guide helps somebody!