Bastl Instruments Kastle 2 Alchemist

Pocket-sized, patchable hybrid synthesizer for evolving melodies

• A patchable hybrid-synthesis synthesizer—monophonic but capable of generating melodies and harmonies
• 5 synthesis modes: FILTER, FM, HYPERSINE, SUPERSAW, and GLITCHNOISE
• ENV macro that affects both the synth and sequencer and allows for continuous morphing between modes
• Dual FX section: spacious delay and a macro chorus/flanger/distortion/comb filter tailored to each mode
• CV and GATE pattern generator, synchronizable LFO, and quantizer with selectable scales
• Customizable rhythms, scales, and number of steps via a web app, with options for polyrhythms and polymeters
• USB MIDI input and output, allowing it to be used as a controller and sequencer
• Powered by 3 AA batteries or via USB-C, with stereo audio input and sync in/out

The Bastl Instruments Kastle 2 Alchemist is a fully patchable, pocket-sized hybrid synthesizer that guides you in discovering melodies and even harmonies, despite being monophonic. Sequences programmed via patches and sent to the two PITCH MOD inputs open up a world of melodic inspiration that goes beyond classic arpeggios, while always staying within the scale you choose. The approach is clear: don’t write the melodies—let them emerge from the behavior you create by making the different modulation sources interact.

Five hybrid synthesis modes in a pocket-sized synth

The Alchemist offers a wide, carefully calibrated range of timbres, distributed across five synthesis modes: FILTER, FM, HYPERSINE, SUPERSAW, and GLITCHNOISE. You cycle through them using the main TIMBRE knob and fine-tune them with the RATIO control, which adjusts the detune ratios of the oscillators and the waveform blending ratios. Under the hood, you’ll find four oscillators, FM with feedback, raw waveform mixing, ring modulation, track-and-hold, stereo noise with track-and-hold, a stereo filter, and a transient shaper.

ENV macro and mode morphing

The ENV knob is a macro that affects multiple parts of the synth and sequencing engine to maximize musicality. Turned to the right, it sets the decay and focuses the TIMBRE on the transients; turned to the left, it adds attack and decay and shifts the timbre toward the body of the sound; at either extreme, it enters DRONE mode. With long envelopes, it slows down the arpeggio, and on the left side, it allows for continuous morphing between synthesis modes, creating truly unique sounds. The envelope is also available on a patchable output.

Dual FX and Pitch Slide Sections

The timbral palette expands with the dual effects section: on the left, a wide delay that transforms arpeggios into echo-reverb harmonies; on the right, a macro chorus, flanger, distortion, and comb filter specifically tuned for each synthesis mode. The PITCH SLIDE macro applies a pitch envelope and portamento for smooth, rubbery textures.

Patchable Sequencer, Quantizer, and Modulation

All main parameters can be precisely modulated and sequenced by the CV and GATE pattern generator—synchronized to the tempo and programmable via patch—along with an LFO featuring triangle and pulse waveform outputs, a reset input, and modulation via an attenuverter, which can be synchronized or free-running. Tempo is controlled via tap tempo, a divider, and an external clock input.

NOTE and PLAY inputs for scaled arpeggios

The PITCH knob covers ±3 octaves from the base note, and the PITCH MOD with attenuverter feeds two inputs. NOTE generates a quantized pitch on the selected scale, updated with each trigger. PLAY adds a third, fifth, and octave above the note, triggering the envelope on each change with time quantization on the PLAY GRID: perfect for arpeggios. Use the BANK button combinations to change the scale, root note, fine tuning, and octave.

Web app for scales, rhythms, and sequencer steps

Through the web app, you can create custom scales, program rhythmic patterns for the gate generator, and choose the number of sequencer steps: in addition to classic lengths, you’ll find a whole array of options for those who love polyrhythms and polymeters. Starting with firmware 1.7, you can apply Humanize and Swing to the CV and GATE outputs, and assign the LFO modulation destination in the advanced settings.

Portable, Synchronizable, and USB MIDI-Ready

The Kastle 2 Alchemist is compact and powered by 3 AA batteries—rechargeable or non-rechargeable—or via USB-C, so you can play anywhere: with a power consumption of approximately 100–150 mA, the batteries last up to 15–18 hours. The analog sync in and out ports let you sync it with other portable instruments, while the right channel of the sync jacks provides modular I/O connections.

Stereo Audio Input and Effects on External Sources

The stereo input, with gain up to +12 dB and signals up to 6 Vpp, allows you to mix external sources into the Alchemist’s output or route them through the built-in effects. The stereo output directly drives headphones up to 250 ohms.

USB MIDI In and Out

The Kastle 2 isn’t just a sound generator—it’s also a MIDI controller and sequencer: it sends MIDI clock, notes, and CC via USB to your DAW or a USB MIDI instrument, and receives clock, notes, CC, and pitch bend, for seamless studio integration.

Package Contents

• Kastle 2 Alchemist
• Quick Start Guide
• 10 patch cables
• Sticker
• Batteries not included, for environmental reasons

Technical Specifications

• Brand: Bastl Instruments
• Model: Kastle 2 Alchemist
• Type: Patchable, hybrid-synthesis, monophonic pocket synthesizer
• Synthesis modes: FILTER, FM, SUPERSAW, HYPERSINE, GLITCHNOISE
• Hybrid synthesis: 4 oscillators, FM with feedback, raw waveform mixing, ring modulation, track and hold, stereo noise with track and hold, stereo filter, transient shaper
• Effects: delay (left), chorus/flanger/distortion (right)
• Audio processing: stereo at 44 kHz / 16-bit
• Pitch: ±3 octaves from the base note, PITCH MOD with attenuverter, NOTE and PLAY inputs
• Quantizer: selectable scales, user-defined scales via web app
• Timbre: TIMBRE with RATIO, TRIGGER input, TIMBRE MOD with attenuverter, MODE input with attenuator
• Envelope: ENV macro with DRONE mode and morphing, ENV MOD with attenuverter, ENV output
• LFO: triangular and pulse, reset input, modulation with attenuverter, synchronized or free-running
• Tempo: tap tempo, divider, external clock input
• Pattern generator: tempo-synced, GATE and CV outputs, programmable via patch
• Customization via web app: rhythmic patterns, scales, sequencer step count
• Firmware 1.7: Humanize/Swing on CV and GATE, assignable LFO MOD destination
• Audio input: stereo, gain up to +12 dB, up to 6 Vpp
• Audio output: stereo, headphone drive up to 250 Ohm
• Sync: analog input and output, modular I/O on the right channel of the sync jacks
• USB MIDI In: clock, notes, CC, pitch bend
• USB MIDI Out: clock, notes, CC
• USB-C: firmware updates, USB MIDI, editor functions, power
• Power: 3 AA batteries (rechargeable or non-rechargeable) or USB-C
• Power consumption: approximately 100–150 mA, battery life up to 15–18 hours with 3 AA batteries
• Contents: Kastle 2 Alchemist, quick start guide, 10 patch cables, sticker (batteries not included)