Bastl Instruments Kastle 2 Alchemist

The Kastle 2 Alchemist is Bastl Instruments’ latest pocket sized sound machine, a hybrid synth voice, pattern generator, and USB MIDI controller that punches well above its weight. It may be monophonic on paper, but thanks to its clever pitch logic, built in harmony tricks, and lush effects, it often feels far bigger than a single voice device has any right to be.

At the heart of the Kastle 2 Alchemist are five synthesis modes: Filter, FM, Supersaw, Hypersine, and Glitchnoise. These are swept through using the main Timbre control, with the Ratio parameter refining detune and waveform relationships per mode. This makes it easy to move from clean subtractive tones to noisy textures and fizzy supersaws without menus or hidden layers. The ENV control acts as a powerful macro, shaping amplitude, timbral focus, and even morphing between synthesis modes, allowing everything from sharp plucks to sustained drones with a single twist.

Rather than a traditional step sequencer, pitch is driven by a smart and playful system of inputs. The Pitch knob sets a base note, the Note input introduces quantized scales, and the Play input adds automatic harmonies such as thirds, fifths, and octaves locked to an internal grid. This encourages evolving arpeggios, shifting harmonies, and generative melodic lines using simple gates and CV. When deeper control is needed, scales and rhythmic behaviour can be customised via Bastl’s web based editor.

The effects section is equally flexible. A dual FX engine provides stereo delay on one side and a chorus, flanger, distortion, and comb filter macro on the other, with tuning that adapts to each synthesis mode. Simple patterns can quickly become smeared into lush echoes, gritty resonances, or wide stereo washes. External audio can also be routed through the effects using the stereo input, turning the Kastle 2 Alchemist into a compact processor as well as a synth.

With a clockable LFO, analogue sync in and out, and full USB MIDI input and output, the Kastle 2 Alchemist easily bridges hardware and software setups. It can drive a DAW, sync with other battery powered gear, or sit happily as a standalone sketchpad. Power it from three AA batteries or USB C, plug in headphones, and it is ready to go anywhere.

Rather than writing melodies step by step, the Kastle 2 Alchemist encourages you to set up behaviours such as scales, rhythms, and routings, then let it surprise you. It can be a small synth, a weird controller, or a generative idea machine, and it truly shines when you give up a little control.