reSEMble all-in-one Eurorack synthesizer module

Build a single-panel, single-voice Eurorack all-in-one synth module that’s inspired by the Oberheim SEM

Summary

Conceived by musician Randy Piscione, this is a set of PCBs and a Eurorack panel to build a single-panel, single-voice Eurorack all-in-one synth module that’s inspired by the Oberheim SEM.

These are not clones. Randy asked Tom Oberheim about doing an SEM clone for Eurorack, and he referred him to a friend of his who has been helping him since the 1970s. They had a long phone conversation and his take is that Tom would rather see us develop something new, even if it is based on his work. So, that was our goal.

There are 12 sub modules that comprise the completed voice.

How it works

The number one benefit over individual Eurorack modules is that 90% of the standard patching that is required to create a usable synthesizer voice is built in.

The 3 VCOs, VCF and two EGs are based on vintage synthesizer concepts and in particular the functionality of the SEM. But, in addition to a 3rd VCO, there are a few other enhancements, including an expanded LFO, Noise, sample and hold, a wavefolder and more modulation and routing options.

Each “module” can be built and tested as a standalone Eurorack module but when they are all complete they come together behind the reSEMble panel. There is no point-to-point wiring. All connections are made with ribbon cables that run from the back of each module to a single bus board.

As part of the design we have provided numerous patching options without using patch cables. The combination of toggle switches and expanded module functionality replace approximately 80 patchcords.

VCOs

These are full featured SAW Core VCOs. Sine, Pulse, Saw waveforms available with multiple modulation inputs and oscillator sync.

• Saw core VCO
• Pulse, sine and sawtooth waveforms
• 1V/octave input + variable Linear FM CV and variable Exponential FM CV
• Adjustable pulse width and variable PWM CV input
• Hard sync input
• Easy to calibrate and customize
• Only 3 ICs
• Accurate tracking and excellent temperature stability

MOD

This is a versatile modulation controller combining a dual range LFO, Sample and Hold and Noise. The LFO can be calibrated to give a smooth range across the two ranges or be set to give ultra low speeds if required.

The LFO has three switchable waveforms.

The sample and hold has a mix control that allows the source to come from VCO3 or the on-board noise.

WAVE SHAPER

This is a combination wavefolder and ring modulator, with inputs for the folder (Z) and X and Y for the ring modulator.

The module takes a sine wave and can literally “fold” the incoming sine wave in either a soft/triangular effect or a hard/square/crunchy effect. Electric guitar sounds are easily within your reach.

The attenuated input for folder modulation allows the Mod section to dynamically control the fold amount.

There is an onboard mixer, providing the ability to fold an input sine wave, the output of the ring modulator or a combination of the two.

• Wavefolder
• Ring modulator
• Separate folder and ring modulator outputs
• CV input for fold amount
• Built in mixer/fader for panning between ring modulator and a third sine wave input

VCF

This is a state variable filter which has a very simple design and is easy to build. The filter behaves similarly to vintage filters of the 1970s and 1980s and this is further reflected in the presentation of the controls. The two pole filter has -12dB per octave roll-off for high pass and low pass and a -12 db wide (-6dB either side) bandpass output.

It has voltage control of cutoff frequency (F). F and Q (resonance) are adjustable with panel controls and the frequency is also adjustable from other modulation sources within the reSEMble. The response of the filter can be switched in or out of bandpass mode. When bandpass mode is off the filter can be continuously swept between Low Pass, Notch and High Pass responses.

ENVELOPE GENERATORS

Nice vintage style envelope generators (EG) that use all discrete components (no ICs or IC sockets) so it’s fun and easy to build.

The EG can be switched between ADSR and ADSD mode with a front panel push button. In ADSD mode the Delay pot controls the delay and the release parts of the envelope just like some popular synths of the 1970s and 1980s. The EG can be triggered from the input gate or the LFO, resulting in complex waveforms for modulation of the VCF or the VCA.

This EG outputs an exponential curve and has a re-triggerable gate.

OUTPUT MIXER

The output stage has a number of key inputs from the reSEMble and a VCA controlled by the adjacent envelope generator or the LFO.

Conclusion

Depending on how many components you already have, assuming and hoping you are not doing this as a first build, you have a project to keep you busy all winter, and you come out of it with a super SEM for less than 1/5th the price of an actual SEM, if you can find one.

Demos

The following videos, courtesy of Randy Piscione, show the reSEMble in action:

A demo of the reSEMble - see and hear the module's many capabilities

A visual and audio comparison of the reSEMBle and the SEM

A few insights and individual module highlights

Documentation

Comprehensive documentation and parts lists are provided in the documentation link for building, testing and calibrating the modules.

The documentation is organized so that each sub-module can be built independently.

Time lapse reSEMble asSEMble demonstration

https://www.tindie.com/products/pmfoundations/resemble-all-in-one-eurorack-synthesizer-module/