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~ E ~ L ~ E ~ C ~ T ~ R ~ O ~ S ~ O ~ U ~ N ~ D ~

V C O           V C F           V C S           V C A

G3400 "HORSE" - A MODULAR SYNTHESIZER FOR PEOPLE

"Unfortunately, as you probably already know, people"
- @Horse_ebooks

"or for that matter Marino Marini when he didn't pick the
rider as carefully
as the horse"
- Frank O'Hara, "Having a coke with you"

A complete instrument with  ample opportunity for interaction and
experimentation.

"Horse"  is direct  and  powerful, providing  four essentials  of
modular synthesis:  oscillator, filter, envelope,  and amplifier.
Each submodule  is independent,  and provides multiple  points of
manual and/or voltage control.

VCO  Sawtooth core  based on  silicon controlled  rectifier, with
discrete sync  and pulse  shaping circuits,  and temperature
compensated volt per octave input. This core is also used in
the Korg  PS3100, Roland  TB-303, and the  Formata Polivoks.
Erica Synths  notes the  addition of a  sync circuit  to the
Polivoks  VCO in  their  DIY  VCO 3;  this  sync circuit  is
employed here.

VCF  2nd order  nonlinear state variable circuit,  using unbiased
(class  B)   gain  cells  as  voltage   controlled  element.
Simultaneous Lowpass, Bandpass, and Highpass outputs, with a
unique waveshaping  characteristic. The  lack of  biasing in
the gain cells results in crossover distortion at two points
in the filter's signal path.  This results in a distinct and
aggressive tone not found elsewhere.

VCS  ADSR/LFO/Slew limiter, with voltage control over rise, fall,
and both. Full ADSR mode  when using the Gate input. Bipolar
LFO. Range  switch expands  range from  minutes long  LFO to
high audio  rate. The core  of  the circuit is present  in a
wide number  of modules and  synthesizers, but namely in the
Korg PS3100  and Serge  Dual Universal Slope  Generator. The
ADSR logic is novel, to the best of the designer's knowledge.

VCA  Biased   discrete  gain   cell  VCA,   with  novel   2-stage
wavefolding  circuit,  giving  up  to  40dB^  of  continuous
wavefolding. Mode  switches to change between  fold and step
functions expand  waveshaping capabilities further.  The VCA
portion  is standard  Blackmer  gain cell,  with biasing  to
eliminate distortion (unlike the VCF). The wavefolder uses a
novel  "step  cell"  nonlinearity, which  creates  deadzones
above  and below  0 volts.  The  step cell  allows for  more
complex  behaviors  with   fewer  complex  components  (e.g.
op-amps)

^ Most  wavefolders can be  described through the  number of
folds  they create  or the  number of  stages used.  The two
Gauche  wavefolders discussed  are  not  built like  typical
wavefolders, where these terms  carry enough information for
a user.  Gain, on the  other hand, clearly  communicates the
range of defined  behavior. This is also in  line with other
waveshaping  effects,  such  as overdrive  and  fuzz,  which
similarly utilize gain as the main control parameter.

> Release .. April 23 2026
> MSRP ..... 450 USD
> Format ... Eurorack
> Width .... ~40hp
> Depth .... ~20mm

> Power .... +12V @ ~60mA
-12V @ ~40mA
+5V  is not used

> Controls . VCO - Coarse/Fine frequency, Pulse width
VCF - Cutoff, Resonance
VCS - Full ADSR, Scale, range and mode switches
VCA - Input level, gain, DC offset, modes

> Inputs ... VCO - Sync, FM*, V/oct, PWM*
VCF - Aux*, Signal, CV*, Freq
VCS - Rise, Both, Fall, Sus*^, Gate^
VCA - Gain*^, Unity, In*
* has attenuator with matching name
^ has input normalling
100K input impedance, except:
Voct = 110K
Freq = 150K
+/- 5V  nominal levels, except:
VCS Gate input reacts to ~ +1V DC
VCA Gain is clipped at +5V DC

> Outputs .. VCO - Pulse, Saw
VCF - Lowpass, Bandpass, Highpass
VCS - Inverted output, Two jacks for main
VCA - Clean, First and second folding stages
1K output impedance everywhere
+/-5V nominal levels, except:
VCS in ADSR mode is unipolar
VCF at high resonance will exceed +/-5V

par: jw74rh1s4
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