TK. Posted October 11, 2005 Report Share Posted October 11, 2005 Today I did the first experiments with a CEM3378 filter, which someof the germans purchased in a collection order from synthtech.comA top view of the workbench:Right side: A AOUT_LC module based on the schematics from Karl Dalen.It mainly consists of 2 * 74HC595 and not less than 36*10k resistors to realizea 12bit DAC, which controls the Cutoff frequency.The final version I'm planning will consist of 48*10k resistors for an 12bit DAC(CutOff) and 4bit DAC (Resonance) (I guess that the resolution is enough, especiallybecause I have to build 4 of them ;-)In addition this module has an OP-Amp to control the gain and offset of theoutput CV - for the filter it turned out that this is a very important featureBottom: the CEM3378 circuit (based on the datasheet) + a +/- 5V voltage regulator.Both, the filter and the AOUT_LC circuit are powered with this low biased voltage.In addition, the CEM3378 needs +12VLeft side: ok, my beloved MBSIDAnd here the first demo - MBSID in TB303 mode, controlled via MIDI (internalsequencer not used) - filter/envelope parameters tweaked in realtimehttp://www.ucapps.de/mp3/midibox_sid/mbsid_demo11.mp3IMHO the filter sounds very good, especially on filter sweeps it can be noticedthat the volume doesn't get lower even when resonance is close to self-oscillation.During the first tests I also noticed, that key-tracking is a must for such a filter.Therefore I implemented it into the firmware (CC#6) - now I have to find a wayto store this value, because the SysEx data structure is completely allocated :-/Best Regards, Thorsten. Quote Link to comment Share on other sites More sharing options...
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