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Thoughts on Semi-Modular Synths vs. Eurorack – Part 6

Soma Pulsar 23 semi modular percussion synth

Thoughts on Semi-Modular Synths vs. Eurorack – Part 6

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And a last article about a special semi modular synth, which supplies us with more uncommon modules: the Soma Pulsar 23. The domain of this semi modular desktop synth are drum sounds and other percussive sounds, even if it is well able to produce wide range of other kinds of sonic events too.

semi modular synthesizers soma pulsar 23

Before I start talking about the details I have to mention, that the Soma Pulsar 23 lacks one very important characteristic, which we counted as an advantage over pure modulars (Eurorack etc.): the quite comfortable price-per-module relation. The Pulsar 23 is expensive (far above 2,000 dollars at the moment of writing this article (April 2022). But anyway, it´s a semi modular synthesizer, and it delivers extraordinary modules, which are:

a master clock generator

an event looper (kind of sequencer)

a looper recorder

4 ASR envelope generators

a bass drum synth module (oscillator)

a bass synthesis module (oscillator)

a snare drum and clap synthesis module

a hi-hat synthesis module

a so called “Shaos” module (= shift register + random/chaos)

an effect processor module (delay, reverb, filter)

an LFO

A distortion module

4 attenuators

a MIDI to CV converter

an impulse converter

2 VCAs

2 inverters

soma pulsar-23 drumsynth


The Soma Pulsar 23 is equipped with 6 single voice audio outputs and a master audio output. There are 6 single voice outputs even if the machine has got only 4 voices, because we can connect each of the audio outputs to any module we want (e.g. the LFO running at audio rate, or the effect unit, where we have fed in external audio from another synth etc.).

The first thing we discover when we look at this semi modular synth is the unconventional way the patch points are led out: they are pins, not jacks! You need aligator clips cables to patch this synth (but you can patch a working connection only using your fingers as well). But there is a “pin to jack” module in the upper left corner of the front panel, where signals from the pins are converted to (e.g. Eurorack format) output and input jacks, from where we can feed them into our other semi modular synths (or into a purely modular system), or – the other way round – feed signals (audio, CV, gate etc.) from the outside world into the Soma Pulsar 23.



semi modular synthesizers soma pulsar 23

The Synth is equipped with a MIDI in connection, and using MIDI the pads can be played even with different velocities. Altogether there are 12 parameters that can be automated via MIDI: Triggers of the 4 synthesis modules, 4 freely assignable MIDI to CV converters, SHAPE, WARP, Portamento and Pitchbender functions of the BASS module. The synthesis modules and MIDI to CV converter automatically recognize the key and the continuous controller (CC). In case a MIDI keyboard key is assigned, the velocity value of the pressed key will be transmitted. If a controller is assigned, the position of the controller is transmitted.


Without any patching, Pulsar-23 is a drum machine with a sequencer with a conventional linear structure: clock generator -> looper -> sound modules -> FX -> output. The full capabilities of the Pulsar are revealed when you start connecting modules to each other, creating control and modulation channels. Since the number and depth of interactions are completely under your control, a smooth transition from classical analog drum synthesis to abstract noise and similar things is possible. The LFO and SHAOS modules can be used as sound generators, and in general any voltage source in Pulsar can be considered a sound source, processing it in various ways and mixing it into the common mix or using it separately. Just like any audio output, you can use it as a source of control voltage or modulation.

A number of Pulsar patch points are more than just CV control inputs. Some of the points commonly used for circuit bending have been brought out, which allows you to wedge into the circuit, changing its behavior on the fly. You can use single electronic components, such as a resistor, capacitor, diode or transistor, including them in a control or modulation circuit to get different behaviors and sound.

There is a crucial aspect to consider, when we want to use the Pulsar 23 in a setup of different semi modular synthesizers (or make it work together with e.g. Eurorack modules): The signal range is unipolar from 0 Volt to plus 10 Volt instead of the more common minus 5 Volt to plus 5 Volt range. Negative CVs e.g. are simply ignored! The effective range of an external bipolar LFO is cut in half this way (negative signals up to minus 20 Volt would not damage the machine though).

All in all Soma Pulsar-23 is more than a common percussive synth. It can be played even melodically with external pitch CV. It´s modules deliver a lot of unconventional combinations of functions, and if there weren´t the incredible price, it would be a perfect supplement to our semi modular synth collection/setup, which would close the gap between semi modular and the multicoloured world of Eurorack quite a good bit. In my next article (chapter 4) I´m going to talk about the workflow with semi modular synths compared to purely modular systems like e.g. Eurorack. See details in the 32 pages manual here: https://drive.google.com/file/d/1cb7AWZQGrgik55-PGLMCSMZO9X0T3C6N/view

to be continued

to part 1: https://www.dev.rofilm-media.net/node/336

to part 2: https://www.dev.rofilm-media.net/node/352

to part 3: https://www.dev.rofilm-media.net/node/354

to part 4: https://www.dev.rofilm-media.net/node/359

to part 5: https://www.dev.rofilm-media.net/node/366

to part 7: https://www.dev.rofilm-media.net/node/382

to part 8: https://www.dev.rofilm-media.net/node/387

to part 9: https://www.dev.rofilm-media.net/node/392



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