Studio Electronics Tonestar complete synthesiser voice Eurorack Module

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ARP 2600-inspired synth voice 31 years in the shaping.

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Manufacturer: Studio Electronics

Category: Keyboards & Synths



TONESTAR is an ARP 2600-inspired synth voice 31 years in the shaping, pre-patched like Pearlman's prodigy, and fully #OutsToOuts in-the-box modular, allowing for highpass/bandpass/notch filter tones, and bristling X-mod effects. Connect CV / gate and twist 'n' switch, or pull its tones and voltages apart one 3.5mm cord at a time. 26 knobs, 7 switches, and 21 jacks make for complex and satisfying signal flow, color and collisions. If it gets reedy, route the triangle wave 'round the VCF, and push dat Sub.


Envelope FYI: The Tonestar Sustain control replicates the behavior of the 2600 and Odyssey: after the initial Decay, it continues to move (sink) very slowly, adding a little extra texture to the sound. It's technically a flaw, but after digging out my Odyssey, it is for sure a desirable "quirk", and the perfect companion to the 4072 filter (which we mistakenly titled a 4075 in the Boomstar Modular line).

Another bit of fun: The LFO is voltage controlled, so you can envelope, LFO, or otherwise modulate both the rate and the depth; the ADSR amount is also voltage controlled, so it can be manipulated by MIDI dynamics, MIDI volume, an LFO, etc. Greg [St. Regis] has decreed that anything must be patchable to anything, so some technically wrong patchings (for example, pulse wave out to ADSR out) may often produce unexpectedly interesting, x-mod/notch filtering—quite pleasing effects.

Additional Info

Additional Info

All Controls—arranged in order of signal flow—and Patch Points

FREQUENCY – Oscillator frequency attenuator.
PULSE WIDTH – Variable pulse wave width control.
OCT – +1/-1 octave switch.
LFO (^) – Triangle wave low frequency oscillation to pulse width control.
FREQ/PW – Oscillator frequency, or Pulse (square wave) width to ADSR modulation routing switch. Center off.
GLIDE – Slew generator control.
TRIANGLE*/NO VCF – Triangle to VCA switch—bypasses VCF.
MOD (ADSR) – Oscillation modulation via ADSR control.
SAWTOOTH* – Sawtooth wave attenuator.
SQUARE* – Square wave attenuator.
SUB – Square wave Sub Oscillator attenuator.
TRIANGLE* – Waveform output.
SAWTOOTH* – Waveform output.
SQUARE* – Waveform output.
MIX – Composite waveform output.
1V/O – One volt per octave control voltage input.
TUNE – Master fine tune (approx. -5/+ 5 semitones).
MOD IN – Modulation CV input. Normaled to ADSR; ADSR is replaced when alt. source connected.
* symbol


NOISE – White noise generator output.
LEVEL – Noise attenuator.


FREQUENCY Frequency, or cut-off attenuator
RESONANCE – Resonance, or Q attenuator.
TRACK – Keyboard/voltage tracking attenuator.
DRIVE – Oscillator output to filter input attenuator.
FREQ/RESO – Filter Frequency, or Resonance to LFO modulation routing switch. Center off position.
ADSR – Filter to ADSR envelope attenuator.
MOD (LFO) – Filter to LFO attenuator.
EXT IN – External audio input.
FIL OUT – Filter audio output.
MOD IN – Frequency or Resonance modulation CV input.


TRIANGLE/SQUARE* – Waveform select switch (triangle core).
DPTH (OSC) – LFO to Oscillator control.
– Speed or rate attenuator.
DEPTH – Control voltage Input.
TRIANGLE* – Triangle wave output.
SQUARE*– Square wave output.
SPEED – Speed or rate CV input.
* symbol


ATTACK – Attack stage control.
DECAY– Decay stage control.
SUSTAIN – Sustain stage control.
RELEASE – Release stage control.
DRONE/MASTER – Indefinite/instant sustain, and master mode for ADSR routing switch. Center off.
ATTACK – Attack stage control
RELEASE – Release stage control.
MOD IN – Allows for dynamic modulation of the ADSR, eg., if you want the amount of modulation added to/determined by a external source, jack in; or if you prefer, modulation input to the ADSR routing—use with velocity, or a sequencer: the sequencer could isolate the ADSR amount the amount to a single step in the phrase for example. Exciting. A second external envelope can provide an interesting effect, or the AR (in the box patching).
ADSR OUT – ADSR output.
AR OUT – AR Output.


FEEDBACK – Oscillator/filter feedback loop control.
VOLUME – Master volume control.
VCA/CV – Amplifier control voltage output.
– VCA mix input switch switch (normalled jack). When set to IN, external audio replaces filter output to VCA; when set to mix MIX, filter output is fed along with the filter audio to VCA.
VCA IN – Audio input.
OUTPUT – Main output.


PCB Mounting Scheme - Through-hole.
- Discrete, voltage controlled, 24/db/oct cascaded transconductance low-pass filter, employing six pairs of hand-matched transistors.
- 32hp.
Depth - 35mm including connectors.
Power Usage - 130mA, 80mA (+12 / -12)

PDF Redux

Outs to Outs and Other Interesting TONE☆ Patches

Optional DIY Adjustments

The tweaking and fine tuning process of a new SE offering can be seemingly endless. Many of the decisions we make are akin to choosing between chocolate, or chocolate with almonds (Fair Trade Organic of course), both tasty and worthy of consumption. At a certain point you have to step away and let your little baby go—but sometimes after flipping back and forth on preferences, we implement a few minor changes after the official production release. The following tweaks fall into the subjective "with or without nuts" category:

Units #2-15 / Noise - The noise on the Tonestar leans to the Pink side, a little dark and moody. Some may like it, some may want the more bright and sizzled white variety. One resistor or capacitor change will shift it to the white spectrum.

Units #2-22 / Feedback - The Feedback loop is big, bold and deep on the low end; maybe a bit too much so. One resistor change will reign it in, but still allow enough chaotic madness at maximum level.