square wave

MFOS – Weird Sound Generator

Sometimes you don’t want to have to spend hours researching designs and finding parts to build a project… sometimes you just want to buy everything you need at once, solder it up, and have fun without the worry of troubleshooting your design. At those times a kit is perfect and in this case that’s just what I did.

I’ve posted about MFOS before. They manufacture a number of kits from entry level to advanced synthesis kits. I decided to go with the ‘WSG’… or Weird Sound Generator. Ray Wilson has some excellent designs that are really fun to put together. I managed to get this up and running in a weekend without any hassles and it sounds great. It’s basically two squarewave generators with LFOs and a resonance filter. If your just starting out this is perfect… and even though I’ve been doing this for a while it was still a ton of fun. Ray’s taken all the hard work out of the process and made DIY synthesis simple, straight forward, and well documented.

He provides all the documentation you could need including wiring diagrams, pcb templates, schematics, block diagrams, and parts lists so I won’t duplicate that here. I’ll just add some comments on the build and a video of the finished project at the end of the post…

Here we have the parts list laid out…

Most of the components have been soldered to the PCB at this point. All the parts are included in the kit and none were missing.

The finished PCB sans ICs.

I used a aluminum enclosure from an old broken gemeni turntable mixer I bought off of ebay. I’ve had great luck finding things like this for 10 bucks or less sometimes and they’re perfect when you need spare knobs, op amps, or enclosures. I just flipped it upside down and took of the rubber feet. Holes were drilled using a step bit (these are a must have for drilling good holes in aluminum enclosures).

Here is everything wired up.

This is the PCB finally wired up. One complaint about this is that the holes on the PCB for all the wiring are placed all over the PCB which makes for really messy wiring. I found that extra care was required to make sure the wiring didn’t bend too much and come detached from the PCB. It seems like using headers would be a much easier way to go about this the next time around.

When I put this together I first soldered the hookup-wire to the board, then to the components on the panel which makes it really difficult to keep things neat and tidy. Next time I will wire up the panel first, then complete the board, then make my connections to allow for a cleaner layout.

Just a tip for beginners… don’t shrink the heat shrink tubing until you’ve tested your work and are certain it works. It’s a major irritation to have to remove heat shrink tubing after you’ve already… well, shrunk it.

PAIA Theremax Theremin

Because of a lack of new content I’ve resorted to posting old projects. This is one of the first builds I completed somewhere around 1995, a PAIA Theremax Theremin. PAIA has been around since 1959 and has been making DIY kits for musicians for decades. In addition to several analog modular synthesizers, Reverbs, EQs, a vocoder they also have their twist on the Theremin, the Theremax.

From PAIA’s website:

…In addition to the traditional mellow sine-like tone, Theremax’s Timbre control can mix in a harmonic rich square wave to produce a signal that’s ideal for use with external filters and processors. And to control outboard units, there are Pitch and Volume Control Voltage outputs.

But the features that really set Tmax apart as a gestural controller are it’s Velocity Control Voltage (proportional to how fast you increase the Volume) and Gate/Trigger outputs. A convenient foot switch input allows muting the internal tone source without disabling the CVs…

Panel controls:

  • Pitch & Volume Trim – these control provide a vernier null of the reference and variable heterodyneing oscillators in the Pitch and Volume control circuitry.
  • Pitch CV – controls the range of control voltage produced in response to hand proximity to the vertical pitch antenna on the right side of the instrument. Clockwise rotation increases range up to a maximum of 6 Volts. This control does not effect the sensitivity of the internal pitch circuitry.
  • Timbre – controls the brightness of the internal tone generator. At full counter-clockwise rotation the output is pure sine wave. At full clockwise rotation the output is a square wave. Intermediate settings produce a mix of the two.
  • Velocity – controls sensitivity to rate of change of volume level. At min, there will be no velocity response no matter how fast volume is changed. Rotation toward max produces increasing response. At max, the Velocity Control Voltage output will produce a 4 Volt change in response to the quickest possible hand gestures. This CV is a transient with a time constant on the order of a second. Internally, this CV biases the VCA for asymmetrical distortion, with no distortion at the min setting.(asymmetrical, transient distortions are responsible for some of the perceived “punch” in natural instrument) This control also sets Gate/Trigger sensitivity, at max sensitivity the gate will respond to very slow movements of the Volume hand.
  • Volume – adjusts the sensitivity of both the internal VCA and external Volume CV output to hand movement relative to the Volume antenna. Output level is adjusted here, but more importantly this control is capable of driving the VCA into symmetrical distortion. (symmetrical distortions are responsible for much of the “loudness” of instrument when played fortissimo)


  • Mute – a foot switch, or S-trigger to this jack mutes the internal pitch producing circuitry. CVs are not effected.
  • Pitch CV – Control Voltage proportional to hand proximity to the Pitch antenna as ranged by Pitch CV control.
  • Volume CV – Control Voltage proportional to hand proximity to the Volume antenna as ranged by Volume CV control.
  • Velo. CV – Control Voltage proportional to how fast a hand is moved in proximity to the Volume antenna as ranged by Pitch CV control.
  • Gate/Trigger – This TRS jack provides a 5 V. gate signal at the “tip” when Velocity exceeds a threshold. The “ring” connection is an S-Trigger compatible closure to ground. The LED lights to indicate a triggered condition. (note that the gate responds to change in volume, i.e. how quickly the volume control hand is moved, not the static location of the hand)
  • Audio Out – Output level is adjustable with the volume control but is nominally -10 dB.

I didn’t have the cash for the nice wooden desktop enclosure so I built my own out of spare wood and used metal shish kabob skewers for the antennae (not pictured). The Theremin still works well to this day although I’ve always had a little bit of a problem with the volume control. The 9v DC power supply is hard wired into the unit which was a poor decision on my part. An easy fix if I ever get to it. I’ve used the gate output to trigger an old Alesis D4 with good effect. The voltage control outputs are perfect for controlling various parameters of an analog modular synth.

If you’re comfortable around a soldering iron this is a great kit, an easy build, and for just the electronic kit it’s only $115. Money well spent considering what you’re getting.

Jakob Lysgaard and the Dub Siren


Jacob Lysgaard recently contacted me while he was working on building the Dub Siren I posted here and on Flickr. His documentation and description of the required parts, where he bought them, his findings, troubles, and experience while building it is far more informative than my images and flagrant plug for Bastard Jazz.

I’m happy to see someone has not only successfully built the dub siren but is finding use for it in their performance. All the best to Jacob.  You can find the post on his blog here:  DYI Dub Siren – the complete rubdown.

Alpo Can Ring Modulator

This is a ‘ring modulator’ similar to the one used in an ARP Odyssey… this version operates by the input of two square waves into a 4011 quad NAND gate. I didn’t have a 4011 available so in this version I use a 4001 quad 2-input NOR with two inputs wired to ground (low) instead of wiring the 4011 with two inputs wired to Vcc. If I did my logic correctly the 4001 works the same when wired this way. I included the logic tables on the schematic.

Ring Modulator Schematic

The two square wave tones passing into the gates are compliments of a simple op-amp square wave generator circuit. Information on how to wire one of these up is widely available on the web. Here’s one good resource. The original schematic and idea was found on simple-answer.com here. A brief reference to the ARP Odyssey and this ring modulator is mentioned on Wiki here.

Alpo Can Ring Modulator board top

Obviously this is in an Alpo Can. The circuit board can be viewed on Flickr (see link below) but it was pretty small so it had no trouble squeezing in there. The knobs were found on eBay for dirt cheap. The hardest part about modifying this can was getting the sharp edges off the holes drilled into the can. To get the top off without cracking open the dog food… and to be able to take the top on and off the can you’ll need one of these: Kuhn Rikon Safety Lid Lifter

More photos and comments can be found on Flickr here:

4001 Ring Modulator in an Alpo Can

Sound Samples:

Dry, without Effects

Wet, with effects

Tone Generator

This is a square wave tone generator based around three 555 timers wired up as oscillators. I took some inspiration from the dub siren and figured if two were good then three would be better. This was mostly true. Several unlabeled pots control the oscillators impact on each other and then two signals are mixed at the final stage. Just as a note I get these pots by buying damaged internal boards of Mackie mixers. With a little time you can remove these great center detent pots for pennies. A schematic isn’t available right now but I will get something together and post soon.

There were a couple problems that I didn’t really notice until after the circuit was wired up. I used a pot to control the balance of the two signals going into and additive mixer at the output. This causes large swings in output volume depending on how far from center the pot is. When jamming it all in the box with a battery something happened  and one pot has no impact on the sound. These problems aside, the tone generator makes some great chirps, bleeps, bloops, and squeals.

I’ve recorded a string of the sounds you can generate with this tone generator, chopped it up into a couple dozen samples and included them for your use. If you end up using them in something I’d love to hear what you do.

You can see the complete set of photos here on Flickr