Author: reprola_wpadm

Surprisingly Cinematic Sounds

In this video, the Rantbot Ctrl-Surf module generates a MIDI data stream played by the Rantbot MIDI-Lappi module. Timing signals for the Ctrl-Surf are generated by a Make Noise René module.

The Ctrl-Surf eurorack module provides four clock/gate inputs. They are:

ARP CLK – This signal advances the current arpeggio by one step.

CHORD STRIKE – Ctrl-Surf sends out MIDI commands to play the current chord once for each chord strike pulse.

ACCENT – When this input is high, MIDI commands are generated to play notes louder. It does not affect the volume of previously played notes that may still be ringing.

PRESET ADVANCE – Moves the current arpeggio, arpeggio program change (instrument sound), chord, and chord program change to the next one of four available presets.

The combination of these four basic inputs in various timings gives rise to entertaining compositions and moods that belie their simple roots.

Using the Accent input

The Accent input is a eurorack 3.5 mm gate input that applies a volume accent (louder) to all outgoing notes while the input is true. Rantbot was pleased to hear the subtle effect. Now four out of five inputs are utilized: Arpeggio Clock, Chord Strike, Preset Advance, and Accent. These can be heard in operation in the video below. The joystick was also used for pitch bend.

Rantbot battles featuritis

Rantbot has built one Ctrl-Surf module using the 1st version printed circuit board, without a faceplate. Experiments were done to 3D print a faceplate, but it was too ugly. The decision was made to use a PCB frontplate to better match the lovely MIDI-Lappi modules. Translucent illuminated switch caps for the sixteen pushbuttons will be 3D printed. They have been tested, and function nicely.

The combination of MIDI-Lappi and Control Surface (Ctrl-Surf) modules has been very fruitful. Ctrl-Surf currently has three eurorack gate inputs: Arpeggio, Chord, and Preset. Each of the four illuminated Preset switches is associated with individual chord and arpeggio notes chosen from the twelve illuminated “piano keyboard” switches. The Mode knob selects Arpeggio or Chord display and note entry functions. The left half of Mode knob rotation selects Arpeggio, and the right half selects Chord.

The arpeggio input clocks notes in an ascending pattern. The chord input strikes and releases notes together. The Preset input advances to the next one of four presets, in a circular fashion.

The two knobs at the top of the module select the 127 built-in sounds using MIDI program change messages compatible with the MIDI-Lappi. The arpeggio and chords can have independent sounds.

The joystick is used for pitch bend and transpose functions.

All of this is operating on the 1st version of Ctrl-Surf module hardware. It is so interesting to use that Rantbot produced a CD called Crex Meadows featuring MIDI-Lappi and Ctrl-Surf in a eurorack environment.

The 2nd version of Ctrl-Surf looks like this in KiCAD:

Rantbot has added a 4th eurorack input, and LEDs for each input. The temptation, of course, is to add more features. As soon as Rantbot added the 4th input, it wanted a 5th, but not sure if it is possible without expanding the module.

Here is another visualization from FreeCAD:

Control Surface

In order to wring out the tones of MIDI-Lappi, I have been using a bread board circuit that I program to send a variety of MIDI messages to the MIDI-Lappi module. I’m generating Note On, Note Off, Program Change, and Pitch Bend messages.

It would be nice to have these features (and more!) in a rack-mounted eurorack format, so I drew a schematic and routed a board in KiCad:

I will do some final physical and electrical checks before ordering boards from OSH Park. Then, while waiting for delivery, I’d like to layout a face plate for 3D printing. That is the plan so far.

Finally ordered three boards from OSH Park, and made this little video to show the design in 3D. Face plate art will have to wait until programming is done and the functionality is fully programmed. For now, it is running on a breadboard circuit, without the illuminated push buttons. The colors will be different, probably with a black faceplate.

Fender Blender

Rantbot sold and shipped one very nice original 1970’s Fender Blender on Schematic shows five transistor craziness from after the age after tubes but before op-amps. Transaction went smoothly, is awesome, but Rantbot’s ancient servoes grieved a bit to see Fender Blender go. It was so great on kick drum mic.

Inside the Fender Blender

Doing burn in testing of MIDI-Lappi modules #1, 2, & 3. Rantbot connected Arturia BeatStep Pro to MIDI-Lappi. Rantbot is reminded of 1980’s percussion sounds. Rantbot tasked with finish testing and procure shipping materials and stop procrastinating.


All three modules completely wired, all operated correctly on power-up. Created Rantbot seller account and sold one Mu-Tron Phasor pedal. Very happy with from Rantbot’s perspective, and got 5 star buyer satisfaction. One vintage Fender Blender pedal to sell before listing MIDI-Lappi serial numbers 1, 2 and 3.

Entering final assembly

MIDI-Lappi serial numbers 001, 002, and 003 are entering final assembly phase. In this step, the DIN connectors and 3.5 mm audio jacks are wired with discrete wires back to the printed circuit boards.

They will be offered on for somewhere around $249 each. If enough units are eventually sold to cover development cost, Rantbot will open source all design files. including KiCad boards and schematics, FreeCAD 3D files, and bill of materials.

Three units are built, and work nicely on first test. Rantbot is using antiquated skills to work on a brief instruction manual, to be included on this website.

MIDI-Lappi eurorack module

MIDI-Lappi module is built by Rantbot. It is based on VS1053 chip from VLSI company in Finland. It accepts MIDI input and produces audio output from General MIDI sound set.

MIDI is a technical standard that describes a communications protocol, digital interface, and electrical connectors that connect a wide variety of electronic musical instruments, computers, and related audio devices for playing, editing and recording music, per Wikipedia.

Lappi is Finnish cheese that is named so because it was developed in the Lapland province of Finland. It is produced from partially skimmed cow’s milk, making it nearly identical to Swiss cheese, except that the milk is pasteurised. In addition, the cheese is mild in flavour and firm-textured with small holes. The smooth, rich, creamy cheese is sweet to taste and preferred by those who like mild tasting cheeses and are allergic to gluten.

Lappi works well in fondues, adds flavour to smoked turkey and goes well with a dessert wine such as a Riesling, according to

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