Synth DIY Projects

Technical openness and excellent documentation are core values for North Coast, and this page gathers schematics, build guides with Bills Of Materials (BOMs), and other SDIY information for all our products. Click through to the product pages for our commercially available modules if you want to buy a ready-to-use assembled module or kit; but you can also build from the plans linked here at no charge if you're willing and able to do all the component sourcing yourself. This page also covers some projects that we don't sell as commercial modules. Most of the information here is free under the GNU GPL; check the individual documents for details of their licensing terms.

Commercial modules

We offer complete kits for SDIY hobbyists, with all parts needed to build each module - or fully assembled and adjusted modules for those who prefer not to do the assembly themselves. Kits eliminate the waste of minimum order limits, the drudgery of searching multiple suppliers for a specific part, and the environmental and safety hazards of home PCB manufacture. Nonetheless, for those who prefer to strike out alone or just want technical information, the links below give complete details of each North Coast Synthesis commercial synth module.

MSK 007 Leapfrog VCF

MSK 007 Leapfrog VCF schematic Five-pole leapfrog-topology active filter, default configuration as a near-elliptic VCF with response peaks at DC, 0.667f, and 1f, then a very sharp slope, and response nulls at 2f and 3f, where f is the frequency chosen by control voltage. User/build manual with schematic (PDF); source package including PCB design (ZIP); audio demos; shop page.

MSK 008 Dual VC Octave Switch

MSK 008 schematic This module can add an octave switch function to an oscillator or other device that doesn't have one built in, but it also does several other things. Two channels in an 8HP module. Each channel contains an octave-level quantizer (that is: it rounds input to the nearest whole volt between -2 and +2), a precision adder, and a three-position toggle switch. Flip the switch manually to add or subtract an octave from your pitch control voltage; feed a control voltage into the quantization input for automatic octave switching; or use two control voltages with the adder for transposition. Each channel can also be configured by PCB solder jumper to subtract instead of adding; the default configuration does this with one of the two. User/build manual with schematic (PDF); source package including PCB design (ZIP); audio demos; shop page.

MSK 010 Fixed Sine Bank

MSK 010 schematic Eight fixed-frequency sine LFOs. Two big advantages over conventional LFO designs: the sine wave are pure, coming from sine-core oscillators without the glitches of waveshaping; and there are eight of them, independent of each other. Having many smooth independent LFOs is critical to large drone patches, modulating Clouds and other complex effects, and so on; and it couldn't be done in the analog realm with the more complex circuitry and HP consumption of variable-frequency LFOs. User/build manual with schematic (PDF); source package including PCB design (ZIP); audio demos; shop page.

MSK 011 Transistor Mixer

MSK 011 Transistor Mixer schematicMinimalist four-knob utility mixer, for audio or control voltages. Just six discrete transistors in traditional Class A circuits. AC and DC coupled outputs. Can be used as a distortion unit by offsetting the signal into the clipping region. User/build manual with schematic (PDF); source package including PCB design (ZIP); audio demos; shop page.

Plans-only SDIY projects

These date from before North Coast was a commercial operation, when I was just releasing free module designs for my own amusement. Be aware that they are not as polished as the commercial designs above.

MSK 002 "Asuka and Shinji" Distortion Amplifier

MSK 002 schematicThis project originated in a search for a worthy use of some new-old-stock germanium transistors that came into my possession. I also designed it around a pile of 0.47µF ceramic disc capacitors I had. It's a fuzz/distortion amplifier with a topology similar to the classic Fuzzrite guitar pedal, reworked into a Eurorack module. Depending on the knob settings, it can do extreme clipping-type distortion, a milder foldback similar to what tubes do, or just amplify with relatively little distortion (useful for boosting line-level signals to modular level). The PCB design is jumper-configurable for NPN or PNP transistors and can even combine one of each in a single channel. Each channel uses two transistors and there's some value in testing different individual transistors for best sound; but they are best not matched as such, but rather selected (the best combinations involve two transistors that don't match). In my prototype I built two channels into an 8HP Eurorack module and called them Asuka (the germanium PNP transistors) and Shinji (recent NPN silicon types). User/build manual with schematic (PDF); package containing Gerber and FPD designs for PCB and panel (ZIP); audio demos.

MSK 003 Unpowered Ring Modulator

MSK 003 schematicI'm now calling this an "unpowered" module because I want to discourage people from using the term "passive" for modules that contain active components like diodes... but the documents still say "passive" because that's what I called it when I first released it. Whichever term you use, the point is that it draws its power from the input signals without needing a connection of its own to the power supply. One of the first modules I ever designed: just a simple transformer-based ring modulator circuit using a true ring of diodes (not a four-quadrant multiplier made some other way) for the authentic ring modulator sound. I built mine with hand-matched germanium diodes. Two boards fit nicely into a 4HP module; the boards (one ring modulator per board) could easily be repurposed to other form factors too. User/build manual with schematic (PDF); package containing Gerber and FPD designs for the PCB and panel (ZIP); audio demo.

MSK 006 Exponential VCA

MSK 006 schematicExponential-response VCA built out of TO-92 discrete transistors (20 of them per channel!). The circuit is more or less that of an LM13700 operational transconductance amplifier chip, build out of single transistors for art's sake. It's not exactly hi-fi, but it imparts a warm and sweet crackling distortion that I rather like. It also provides a fair bit of output power and could be used for tasks like driving headphones or small speakers directly. User/build manual with schematic (PDF); source package including PCB design (ZIP); audio demo.

Other DIY modules, past and future

Not every module I build actually makes it to the level of a project I can share. Some are plans for the future; others represent experiments from the past. Here are a few from those two categories.

MSK 001 "Sekai" Universal Host

MSK 001 SekaiSingle-board ARM Linux machine, USB hub, two CVpals, and a LCD/pushbutton module all combined behind a 36HP panel. I use this for controlling my Eurorack, with a USB-MIDI keyboard, by SSHing into it over the Ethernet connection, and with homemade control software running directly on the module (including a program specifically for exploring fractal chord progressions). Unfortunately, it's a one-off and pretty much stuck as a one-off because it was designed around components I can't get in quantity. This particular single-board computer is no longer made, the USB hub I used was a cheapo no-name brand one with some tricky modifications, and so on. Also, the Sekai requires massive amounts of +5V power, delivered by a separate wall-wart power supply that plugs into the front panel.

MSK 004 "Octothorpe" Octuple VCO

MSK 004 schematicEight VCO cores sharing a common control system. They have independent outputs but they're meant to be used as a single unit, for chorus and cloud effects, with adjustable detuning and some extra features, including an adjustable-coefficient temperature compensation system. The oscillator cores are based on 555 timers, but they're sawtooth cores, not similar to the Thomas Henry 555 triangle VCO core. Lots of neat ideas in here, but overall, there were enough issues with it that I decided not to proceed further after the first prototype. The biggest thing was that the cores tend to synchronize, I think through crosstalk in the TL074 quad op amp chips, and that screws up some of the desired musical effects. The adjustable-coefficient tempco worked well but required a complicated and impractical adjustment procedure, warming and cooling the module to different temperatures to explore the adjustment curve. I still like the overall concept of a "super-saw" VCO, though, and may explore that further in the future.

MSK 005 "Snake Pit"

MSK 005 Snake PitSo called because it's full of adders. Three channels, each containing a precision adder and a manual slew rate limiter, plus some voltage references. After building this and playing with it for a while, I decided not to take the design further. The precision adder part is nice, and the idea of combining those with other functions ended up in the MSK 008 Octave Switch, but the slew rate limiters didn't turn out as I had hoped (in particular, they were meant to be linear and behaved more like RC circuits) and there were some issues with the physical design.

MSK 009 "Coiler" multimode filter

MSK 009 Coiler schematicClassic OTA-based two-pole state-variable multimode filter (low-pass, band-pass, and high-pass outputs from a single input) with a twist: instead of voltage on capacitors to represent the state variables, it uses current through inductors, with negative resistance to compensate for their non-ideal behaviour at low frequencies. This one may actually make it to the commercialized product stage. I've built a breadboard test version, and it sounds great, but it's terribly badly behaved. Tracking is more or less random, including going in the wrong direction at some voltages. Oscillation is frequent and hard to control. In many ways it's the opposite of the clean and precise MSK 007 Leapfrog VCF. Even if people think they want unpredictable filters, I need to make it at least repeatable enough that I can be sure each one I build will at least sort of work (however variably) and that's the main challenge to commercializing it.

MSK 012 Transistor ADSR

MSK 012 Transistor ADSRAn ADSR envelope generator built from discrete transistors - no op amps or other ICs! Planned for commercial release some time after the Transistor Mixer.