NGF-E Project: 24dB LP / HP VCF

This is my take on the 24dB LP / HP VCF. This filter type is widely used in many synthesizers. Because this one is for my Next Generation Formant project i started with the original Elektor Formant schematic and added my changes to the design. All parts are updated to today (2017/7) available parts. The connections are the same as in the original to keep the possibility for internal wiring. If you don’t need those features just leave them out. This PCB provides all basic functions as in the original Elektor Formant. The additional functionality is put on an add-on board. The CA3080 are replaced with LM13700. The LP/HP switch is replaced with DG419 to avoid wiring problems. The signal level is raised to 10Vpp for a better signal to noise ratio. The exponentiator for generating Iabc for the OTA’s is temperature compensated. The additional function on this PCB is the linear TM input and the sign changer for the ENV input for easier use when the filter is switched to high pass mode. All other additional functions are on the add-on board. The add-on board provides voltage control for Q and the volume indicator.

The documentation for download can be found in my website.

NGF-E Project: 24dB LP / HP VCF schematic

NGF-E Project: 24dB LP / HP VCF PCB

NGF-E Project: 24dB LP / HP VCF rear view with AddO PCB