Bastl Instruments Kastle 2 Alchemist

Bastl Instruments has introduced the Kastle 2 Alchemist, a compact hybrid synthesis instrument that fits in your pocket but delivers surprisingly deep sound design capabilities. Running on three AA batteries for up to 18 hours or via USB-C power, this device brings patchable synthesis to truly portable contexts.

The philosophy behind the Alchemist is distinctive: rather than writing melodies directly, you set up behaviors through patching that allow melodies to emerge organically. The device stays within your chosen musical scale while generating unexpected melodic ideas through the interaction of its modulation sources.

Five Synthesis Modes

The Alchemist's sound engine spans five distinct synthesis modes, each with its own character. The Filter mode offers classic subtractive synthesis with three detuned oscillators feeding a resonant lowpass filter. FM mode delivers phase modulation inspired by digital classics like the DX7, producing bell-like tones or atonal textures depending on oscillator ratios.

Supersaw mode provides the thick, detuned sound familiar from trance music, while Hypersine creates unique digital timbres through ring modulation and track-and-hold processing. The Glitchnoise mode ventures into unpredictable territory with noisy, experimental textures.

Each mode is controlled by a main Timbre knob that sweeps from harmonic sine waves to full-spectrum sounds, refined by a Ratio control that adjusts oscillator detuning and waveform mixing. An ENV macro knob affects both the envelope characteristics and the synthesis behavior, letting you morph between modes when turned counterclockwise.

Patchable Modulation System

The patchbay enables patch programming through 0-5 volt compatible connections. Two pitch modulation inputs—Note and Play—work together to create arpeggios and melodic sequences. The Note input quantizes to your selected scale and updates on triggers, while the Play input generates thirds, fifths, and octaves above the base note, triggering envelopes when the voltage changes.

This interaction between the pitch inputs creates what Bastl calls "melodic inspiration beyond classic arpeggios." By patching the LFO triangle wave to Play while feeding CV to Note and Gate to the trigger input, you generate scale-quantized arpeggios with harmonic rhythm.

The built-in LFO offers triangle and pulse outputs with reset input and attenuverting modulation. A pattern generator provides gate and CV outputs running on 16-step sequences, always synced to tempo. The rhythms and scales are customizable through a web-based editor accessible via USB-C.

Effects and Sound Shaping

A dual effects section adds the finishing touch to the Alchemist's sound palette. Turn the FX knob left for a tempo-synced delay that smears arpeggios into echoed harmonies. Turn it right for a chorus-flanger-distortion-combfilter chain custom-tuned for each synthesis mode.

The Pitch Slide macro applies pitch envelope and portamento, creating gliding rubber textures. In FM and Glitchnoise modes, the rightmost FX setting creates a resonant delay line (comb filter or Karplus-Strong resonator) with frequency aligned to pitch—useful for exploring extreme sound design territory.

Connectivity and Integration

Despite its compact size, the Alchemist offers comprehensive connectivity. Stereo audio input accepts signals up to 6Vpp and can be mixed with the Alchemist's output or routed through its effects. Stereo output drives headphones up to 250 ohms.

Analog sync input and output enable clock synchronization with other instruments. The right channels of the sync jacks provide modular I/O connections for additional control voltage routing.

USB MIDI flows bidirectionally, allowing the Alchemist to receive clock, notes, CCs, and pitch bend, while sending MIDI data to DAWs or other instruments. This makes it function as both a sound module and a MIDI controller/sequencer. The device processes audio at 44kHz/16-bit in stereo.

Who Benefits and When

The Kastle 2 Alchemist serves several musical contexts effectively. For traveling musicians and live performers, the battery operation and pocket size make it an always-available sketchpad for ideas. It excels in modular setups where its pattern generator and LFO can sequence external gear while receiving modulation in return.

Electronic music producers working with portable setups will find it pairs naturally with devices like the Teenage Engineering PO series (particularly with proper sync cable routing), Korg Volca series, Critter & Guitari Organelle, or other Bastl instruments like the Kastle Drum or Softpop SP2.

In educational contexts, the visual patchbay makes modular synthesis concepts tangible without the space and cost requirements of Eurorack. The web editor provides a clear entry point for understanding scales and rhythmic patterns.

Sound designers exploring generative techniques benefit from the semi-autonomous melody generation. Set up a patch configuration, let it run, and capture the emergent musical ideas. The combination of quantized pitch and pattern-based modulation creates structured randomness that stays musical.

Studio musicians can integrate it via USB MIDI, using it as a unique voice alongside software instruments or as a hardware sequencer generating MIDI data for other synths. The effects section makes it useful as a desktop processor for adding character to other sources.

Ambient and experimental musicians will appreciate the drone modes (activated at both extremes of the ENV knob), the morphing between synthesis modes, and the unpredictable sweetspots in Glitchnoise mode.

Technical Details

The Alchemist runs on three AA batteries (rechargeable or standard) drawing 100-150mA, providing 15-18 hours of operation. USB-C provides alternative power and enables firmware updates, MIDI communication, and access to the web-based editor for customizing scales and rhythms.

The device includes 10 patch cables and a quickstart guide. A comprehensive manual details the button combinations, patch programming techniques, and MIDI implementation. Memory reset and firmware update modes are accessible through button combinations at power-on.

The Alchemist represents the third firmware variant for the Kastle 2 hardware platform, with full cross-compatibility across the Kastle 2 series.

Whether you're sketching ideas on a train, building a portable performance rig, or exploring generative composition at home, the Kastle 2 Alchemist offers a distinctive approach to melody creation in a truly portable package.