Eurorack Reference

Bastl Instruments / bastl-instruments/kastle

Kastle (v1.5)

Kastle v1.5 is a mini modular synthesizer with a headphone output, 2 in/out ports for interfacing other gear, running on 3 AA batteries or USB power. It features a complex oscillator with 6 synthesis modes, a voltage-controllable LFO, and a stepped waveform generator inspired by the Rungler circuit. [12]

Specifications

HP
—
Depth
—
+12V
—
−12V
—
+5V
—
Last verified
2026-05-02

Capabilities

  • Complex Oscillator complex-oscillator
  • LFO lfo
  • Stepped Voltage Generator stepped-voltage-generator
    Rungler-inspired stepped generator producing 8 voltages, updated twice per LFO period. Mode set by BIT IN: low=8-step, disconnected=16-step, high=random. [12]

Jacks (17)

Inputs (11)

NameSignalVoltageDescription
+ mixed — Provides a high/positive voltage reference. Can set MODE to high state, offset modulation signals, or set BIT IN high. [12]
- mixed — Connects directly to ground. Can set MODE to low state, set BIT IN low, or connect grounds between instruments. [12]
BIT IN cv — Controls the shift register input for the stepped generator. Low = 8-step pattern; disconnected = 16-step pattern (inverted bit); high = random pattern. [12]
I/O L mixed 0V to 5V Left channel of the I/O CV port stereo jack. Can carry modulation, audio, or clock signals in or out. External input signals are rectified; Kastle responds only to 0-5V. [12]
I/O R mixed 0V to 5V Right channel of the I/O CV port stereo jack. Can carry modulation, audio, or clock signals in or out. External input signals are rectified; Kastle responds only to 0-5V. [12]
LFO RST trigger — Resets LFO phase to the highest point of the triangle, then the triangle begins to fall. Useful for creating complex modulation curves or synchronizing with external clock. [12]
MODE cv — Selects synthesis mode for both OSC OUT and SECONDARY OSC OUT. Disconnected = phase modulation / phase distortion; high = track & hold / formant synthesis; low = noise / tonal noise mode. [12]
PITCH MOD cv — CV input for pitch modulation; amount controlled by the PITCH MOD knob. [12]
RATE MOD cv — CV input for LFO rate modulation; amount controlled by the RATE MOD knob. [12]
TIMBRE MOD cv — CV input for timbre (modulating oscillator pitch) modulation; amount controlled by TIMBRE MOD knob. [12]
WAVESHAPE cv — CV input to modulate the WAVESHAPE parameter (3rd sound parameter); also sets pulse width of OSC PULSE output. [12]

Outputs (6)

NameSignalVoltageDescription
LFO PULSE gate — Outputs LFO pulse wave in sync with the triangle wave. High when triangle is rising, low when falling. Useful for synchronizing external equipment. [12]
LFO TRIANGLE cv — Outputs the LFO triangle waveform. Can be altered by modulating LFO RATE or triggering LFO RST. [12]
OSC OUT audio — Main oscillator output. Can be used as a signal source; when another output is patched here, it passively mixes with the oscillator signal and routes to the OUT jack. [12]
OUT audio — Main output of the complex oscillator, can drive headphones or a speaker system. [12]
SECONDARY OSC OUT audio — Alternative waveform output from the secondary modulating oscillator, adjustable by WAVESHAPE. Can modulate internal parameters, mix with main oscillator via OSC OUT, or output via I/O jack. [12]
STEPPED cv — Outputs stepped voltages from the Rungler-inspired generator. Produces 8 different voltages in random, 8-step, or 16-step patterns depending on BIT IN. Updates twice per LFO period. [12]

Parameters (7)

NameTypeRangeMin FWBehavior
LFO RATE knob — — Sets the speed of the LFO modulation. Modulation speed is displayed by an LED near the knob. [12]
OSC PITCH knob — — Adjusts the pitch of the main oscillator. [12]
OSC TIMBRE knob — — Adjusts the pitch of the modulating (secondary) oscillator. [12]
PITCH MOD knob — — Controls the amount of modulation applied from the PITCH MOD input socket to the main oscillator pitch. [12]
RATE MOD knob — — Sets the amount of modulation applied from the RATE MOD input socket to the LFO rate. Especially useful for creating complex modulation curves. [12]
TIMBRE MOD knob — — Sets the amount of modulation applied from the TIMBRE MOD input socket to the modulating oscillator pitch. [12]
WAVESHAPE knob — — Controls the 3rd sound parameter (function depends on synthesis mode) and also sets the pulse width of the OSC PULSE output. [12]

Firmware history (0 versions)

No firmware history recorded.

References (2)