This one in via Grant B. via Elektor "FORMANT is an analog monophonic synthesizer published in the 70’s from Elektor magazine. It has a modular structure that allows it to be constructed step-by-step and expanded at will. It can be built at home and it is an excellent model to fully understand the operation of subtractive-type synthesizers.
This project presents a completely digital counterpart of the original FORMANT; let’s call it d-FORMANT. The basic idea is to replace the analog voltage that represents a signal with a digital 16-bits serial signal. The modular structure is fully maintained. Even the patching capabilities of the original FORMANT has been kept and the user can connect and disconnect cables while the d-FORMANT is working. All the knobs and switches can be implemented, although this first version of the d-FORMANT has a much simpler (and cheaper) user interface: A LCD, some buttons and a rotary encoder are enough to do the jobs of all the potentiometers and switches of the original FORMANT. The keyboard can be any MIDI device that sends simple “note on” and “note off” commands. The digital output passes through a DAC to produce an analog out.
The next post discuses some basic aspects that govern the entire project, while all the subsequent posts describe each module. Note that the structure of the analog FORMANT has been kept, so there are VCOs, VCF, ADSR and any module of the original design
Implementation
All parts except the DAC are through-hole. This makes the construction of the various modules very easy. The author has handled used the DAC also by hand, making a simple “adaptor”. All modules have been constructed in prototyping boards.
Further work
The design keeps its modular structure allowing expansion and modification. For example, a REVERB module, or a QUITAR FUZZY BOX can be added.
The user interface is very simple. However, its output is in RS232-type format. A possible enhancement could be to implement a user interface that is easier to use, either in hardware, or in software running on another machine (a tablet for example). The obvious benefit of the digital nature of the synthesizer is the existence of already stored sets of parameters.
The synthesizer is monophonic; however it is easier to expand the digital than the analog FORMANT to produce a polyphonic model.
The final design is cheap enough to implement it “just for fun”, and capable enough to have fun!"
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