The PropSynth D Digital 6 Voice DIY Synth

This one spotted and sent in via swissdoc. You can find the project page in German here [archived here] and a Googlish translation here [archive link]. Some info from that translation:

"Hello to all music fans electronics engineers.

After Hammond and Steicherkeyboard simulations based on a Parallax Propeller step to build a synthesizer was the logical consequence.
This new development is a classic polyphonic 6 voice synthesizer to the universally known model: known oscilator filter VCA, geimein as subtractive sound generation.
This time it was not about to emulate a specific synthesizer, but to develop a "normal" tone generator can not be more than many other synths in me - but with a standard processor - which was not designed for this purpose.


features:

2 Ozillatoren per voice / 6 voice polyphony
10 wavetables for Ozillatoren
Filter, (4-pole lowpass, 2-pole lowpass / highpass / bandpass) with resonance
ADSR generator Filterhülkurve
ADSR generator envelope amplifier (VCA)
LFO to filter modulation
LFO for vibrato
Noise generator
diverse chorus effects
Hall device
3-band EQ
"Half-Analog" operation with potentiometers in a parameter matrix
Preset memory, 32 Programs
LED display
Control via Midi Controller
stereo outputs

Controlled by MIDI propeller than enough for a 6 voice polyphony. The motherboard is only 200 * 100mm in size and contains all components inc. The operating element. The single-sided board and is very selbstbau friendly because only components were used which are easy to obtain, SMD components (which we unfortunately can not do without) are installed via adapter, and leave with 1.27mm pin spacing easily solder by hand."

See the links at the top of this post for additional pics and details.