StringTheory Owner’s Manual

StringTheory is a lo-fi, 4-note, paraphonic string synthesizer, based on the Solina String Synth emulation designed and coded by Jan Ostman.

Connecting StringTheory to your system


Use a 16-way IDC cable to connect StringTheory to your Eurorack power supply – be careful to observe the correct orientation of the connector. Note that when the keyed connector is inserted into the header on the back of StringTheory, the note “RED!” on the PCB indicates the position of the red-marked channel of the 16-way cable.


StringTheory relies on a MIDI connection. The front panel connection of StringTheory will accept a 3.5mm stereo (TRS) jack where

Tip = MIDI DIN pin 4
Ring = MIDI DIN pin 5
Sleeve = MIDI DIN pin 2 (shield)

This arrangement is known as “Type B” and is used on other devices such as:

Arturia Beatstep Pro
Novation Launchpad Pro
1010 Music Eurorack modules

You can use a 3.5mm stereo patch cable to connect these devices directly to StringTheory.

The supplied adaptor (only available with full DIY kits or pre-assembled modules) will convert a 5-pin DIN MIDI socket into a Type B 3.5mm stereo jack, allowing any MIDI device to be connected.

On the back of StringTheory a 2-pin header (J1) can accept a MIDI signal from other Eurorack devices (for example, our MidiIn, ThruBox Embedded and MidiAccess products). Such MIDI headers on all of our products have the pins labelled “4” and “5”, representing the equivalent MIDI DIN signal pins. To connect two products, use jumper wires to connect pin 4 of the sending device to 4 of the receiving device and pin 5 of the sending device to pin 5 of the receiving device.


The gate out socket will send a voltage of approximately 5V while StringTheory is receiving a MIDI note. This can be connected to the gate input of other Eurorack devices.

The gate LED will light while a gate signal is present at the output.

On the back of StringTheory, a jumper (J2) can be set to send the gate signal to the Eurorack gate bus. This can then be received by other suitably equipped modules on the same bus (for example, the Doepfer A140 ADSR). If you do not wish to use this feature, simple remove the jumper from the 2-pin header J2.


The out socket sends audio to other modules or to a mixer device.



The envelope knob controls a combined A-R (Attack-Release) envelope for the synthesizer. At the 12 o’clock position (marked “0” on the panel) the Attack and Release will both be set to zero, resulting in an on-off sound. Turning the knob clockwise will increase the Release time whilst maintain a short Attack. Turning the knob counter-clockwise will increase both the Attack and Release times.


This knob controls the string “ensemble” effect. At the zero position, the effect is off. As the knob is moved clockwise, a phaser-like effect is applied to the sound, thickening and widening it.


This knob applies a leslie-like lfo modulation/detune to the sound. At the zero position the effect is off. Turning the knob clockwise switches the effect on and increases its frequency.

MIDI Learn

Above the MIDI socket is a small hole in the panel. A paperclip or wire can be inserted into this hole and used to press the switch located beneath it; doing so puts the device into “MIDI Learn” mode. When the device is in this mode, the gate out LED will flash continuously.

When in learn mode, the device will listen on all MIDI channels for a MIDI note message. When it receives a note message, it will set the device to listen on that MIDI channel only. This setting is saved to StringTheory’s internal memory so that the channel setting will be preserved even when powered off/on again.

After the channel and reference note is set, StringTheory will wait for a second note to set the MIDI offset. This allows you to transpose the output from StringTheory – commonly, this is used to offset the module by one or more octaves.

So, for example, if you pressed note C2 to set the MIDI channel and reference, then pressed C4 to set the offset, note C2 will sound whenever you play C4 – this offset of 2 octaves will also be applied to all other notes.

If you don’t want to set an offset, simply press the same note again.