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...
illogik Posted October 11, 2005 Report Share Posted October 11, 2005 sounds goood ;Dive modded a synth that has a similar cem ic, i like them >they have a seperate VCA too and all..low cost vcf aswell?cheers, marcel Quote Link to comment Share on other sites More sharing options...
raphael Posted October 11, 2005 Report Share Posted October 11, 2005 Promising ;D ;D ;D Quote Link to comment Share on other sites More sharing options...
Wisefire Posted October 11, 2005 Report Share Posted October 11, 2005 nice tb303 like sound.. it obviously isnt by any means exact.. but imho.. it sounds great.. but do i hear an echo? thats something i would like to have in my mbsid.. some kind of FX processor.. (delay and chorus/flanger) and bpm synced ofcourse :P Quote Link to comment Share on other sites More sharing options...
TK. Posted October 12, 2005 Author Report Share Posted October 12, 2005 low cost vcf aswell?It is - $10 + taxes + shipping is a fair price compared to the effort which is required to build a discrete filterYes, it's just the TB303 mode - not the typical TB303 sound. In fact I wasn't able yet to realize the same filter behaviour like on my moog-filter yet, I think that I have to optimize the OP stage at the end of the DAC, or the voltage divider at the CEM3378 filter CV input in order to fix this.However, the filter gave me some enjoyable hours today, it already makes a lot of fun to play with this toy :)Fx processor: there was a guy who realized a DSP project for such jobs, search for "miss parker" in the forumOn the other hand: I prefer the use of VST plugins. The usage is simple and more flexible.Best Regards, Thorsten. Quote Link to comment Share on other sites More sharing options...
SounDuke Posted October 16, 2005 Report Share Posted October 16, 2005 Good Thorsten, as it sounds I can say without doubt this is the chip used in Chroma polaris ;) -------> although CEM3372 I checked out the service manual of the old fender synth. Maybe some hardware could be taken as example for a mios polaris based synth :D Quote Link to comment Share on other sites More sharing options...
moogah Posted October 23, 2005 Report Share Posted October 23, 2005 Eh.. IMHO the application of the 3372 in the polaris is sub-par. That chip is capable of much more. I'll have to check the sheets, but I also think there are some differences between the 72 and 78. The 72 is also what was used for the massive multimode beast in the oberheim Martix-12 and XPander synths, the Xpander manual actually has a full app note about it too, check it out at bluesynths.com. Quite a nice chip really. Keep an eye out on ebay for SSM2044's too, those are nice (Mono/Poly, Wave 2, etc;) Quote Link to comment Share on other sites More sharing options...
Davo Posted October 23, 2005 Report Share Posted October 23, 2005 What additional controls are required for this filter? Does it connect only to the master core module? Quote Link to comment Share on other sites More sharing options...
moebius Posted October 23, 2005 Report Share Posted October 23, 2005 I'll have to check the sheets, but I also think there are some differences between the 72 and 78. The 72 is also what was used for the massive multimode beast in the oberheim Martix-12 and XPander synths...There are some differences, but it doesn't prevent using CEM3378 in similar multimode configuration as 3372.. all the gain cells have output taps. Keep an eye out on ebay for SSM2044's too, those are nice (Mono/Poly, Wave 2, etc;)Keep ya hands off of SSM2044s.. I might need some for my Polysix.. :DBye, Moebius Quote Link to comment Share on other sites More sharing options...
TK. Posted October 23, 2005 Author Report Share Posted October 23, 2005 What additional controls are required for this filter? Does it connect only to the master core module?You need a MBHP_AOUT_LC module (low-cost DAC)A schematic can now be found here: http://www.ucapps.de/mbhp/mbhp_aout_lc.pdfPCB Layout will also be provided (sooner or later)Best Regards, Thorsten. Quote Link to comment Share on other sites More sharing options...
Davo Posted October 23, 2005 Report Share Posted October 23, 2005 You need a MBHP_AOUT_LC module (low-cost DAC)A schematic can now be found here: http://www.ucapps.de/mbhp/mbhp_aout_lc.pdfPCB Layout will also be provided (sooner or later)Best Regards, Thorsten.I meant to ask what knobs or switches are required. Quote Link to comment Share on other sites More sharing options...
TK. Posted October 23, 2005 Author Report Share Posted October 23, 2005 I meant to ask what knobs or switches are required.no additional knobs or switches are required on the control surface, otherwise I would have mentioned it.See also this article http://www.midibox.org/forum/index.php?topic=5561.msg34212#msg34212Best Regards, Thorsten. Quote Link to comment Share on other sites More sharing options...
TK. Posted October 23, 2005 Author Report Share Posted October 23, 2005 MBHP_AOUT_LC layout: Quote Link to comment Share on other sites More sharing options...
TK. Posted November 3, 2005 Author Report Share Posted November 3, 2005 The PCB:Best Regards, Thorsten. Quote Link to comment Share on other sites More sharing options...
illogik Posted November 6, 2005 Report Share Posted November 6, 2005 can we have the .brd-file? i'm etching this weekend!by the way; is it (going to be) possible to put the s&h module with this?cheers, marcel Quote Link to comment Share on other sites More sharing options...
TK. Posted November 6, 2005 Author Report Share Posted November 6, 2005 Hi Marcel,link to the layout: http://www.ucapps.de/mbhp/mbhp_aout_lc_v1.brdlink to orderlist: http://www.ucapps.de/mbhp/mbhp_aout_lc_orderlist.txtYes, the SHX8 board can be used, but there is currently not firmware which supports this combination. And I'm sure that it won't be possible with MBSID or MBFM, but it will be supported by MB64 and MBCV (sooner or later...)Best Regards, Thorsten. Quote Link to comment Share on other sites More sharing options...
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