EuroKastle is a Eurorack version of the Bastl Instruments Kastle or Drum Kastle Synth. This is the third PT Modular semi-kit I’ve purchased from Calsynth. It comes with a full populated PC board, two programmed ICs and panels for both the Euro Kastle and the Drum Kastle. The version depends on how the chips are flashed.

The Kastle has a unique digital lo-fi sound, and it can be melodic, rhythmic, as well as very noisy and droning, soft or harsh. It was designed to be fun on its own, but it thrives the most in an ecosystem of other modular gear.

The oscillator section has 3 sound parameters: PITCH, TIMBRE, and WAVESHAPE – all under voltage control, offering 6 different synthesis modes. It has a main output and a secondary waveform output. Both can be used independently or in combination. The 3 synthesis modes available through the main output are: phase modulation, noise mode, and track & hold modulation. There are 3 more modes on the secondary OSC output: phase distortion, tonal noise mode, and formant synthesis. Each mode utilizes one or two oscillators. The PITCH parameter controls the main oscillator, the TIMBRE sets the PITCH of the modulating oscillator, and the WAVESHAPE depends on the synthesis mode.

The build

Once again, the build is straightforward. You supply the pots, knobs, jacks and switches, plus a few headers and IC sockets. I was able to use a keyed header by filing one corner a bit to let it sit next to a component.

I placed black Bananuts on the outputs, using a red one for the LFO pulse output. I also used a dark red Davies 1900 clone knob for the LFO rate. The other three knobs each control one of the oscillator parameters.

LFO and Rungler

EuroKastle is a miniature synth voice, having a nice modulator built in. The LFO is voltage-controlled, having both Triangle and Pulse wave outputs. Internally the LFO drives a Rungler circuit that produces a step sequence. The Rungler has three modes: Random plus 8 step and 16 step repeating sequences. Rungler also has a CV input. The three CV outputs can be patched anywhere, including into any of the five CV inputs on the EuroKastle.

Each of the four knobs has a corresponding CV input with attenuator. The Pitch and LFO CV inputs are normalized from the Rungler, if nothing is patched into their CV inputs. Waveshape is normalized from the LFO triangle, and Timbre from the LFO square. Of course these can be overridden by patching.

NOTE: All of the outputs are in the positive voltage domain.

A demo for each mode

These recordings are in mono, taken from the Osc Out jack. (The Mix or Out jack carries a duplicate of Osc Out.) I haven’t done much experimenting with Osc Square Out yet. For these recordings I start out by manually twiddling the three parameters and then I turn up the pitch CV attenuator, which brings in the Rungler. I change the Rungler mode. Note that the LFO is used only to set the rate of the Runger.