Modification of a Hohner PK 250 midi (synthesizer/keyboard)
By manipulating the circuit, it is possible to freely adjust parameters such as filter frequency, resonance and the envelope (ADSR), an option that was not originally intended.
The built-in CEM3391 chips make it possible.
The additional potentiometers serve as voltage dividers which influence the values, and the switches can be used to toggle between expansion and factory settings.
A project in cooperation with Eduard Brandmair, who also provided the device; October/November 2023
Photos: Eduard Brandmair
An optimized toy piano.
The pulses of the LFO (square wave) can be used as triggers for notes, with the knob the frequency is changed. The 3.5mm jacks are used as input for external trigger/gate signals, using the toggle switches to switch between input and internal frequency. The contacts made with the metal pins and clips determine the pitch of the notes played. The LEDs indicate each pulse, internal or external.
A toy car with additional functions:
Inputs for control voltage to trigger the sound samples, so the device can be played rhythmically with a sequencer.
The two knobs are used for sound control, a kind of gate function. They determine whether a sound is triggered and how long the "tone" is held.