CEM 3320 + SID

[DrBunsen]

Looking forward to more news about your board, seppoman!  ;D

[NorthernLightX]

Hi,

here´s another link to the Fonik board: http://www.modular.fonik.de/Page27.html

I also took some inspiration from it. The schematic is not very far away from the reference design in the SSM datasheet. The Fonik board is definitely nice for modular synths and completey manual control. One thing all (except one) schematics I found are missing is a linearization for the resonance CV. The datasheet suggests a neg log pot, and Fonik simulates this by the resistor in parallel to the pot. So for manual control this probably works fine. Only for CV control, like with the MBSID/MBFM, the problem is that the response is still exponential. This means that in the lower quarter of the CV range, not much happens. Then it starts to have more and more influence and after about midway the thing goes off like a rocket.

The only implementation I found that deals with this issue is this one:

http://www.emulatorarchive.com/assets/PDF/SSM2033%20SSM2044%20Circuits.pdf

Here, a 3080 is used for linearization. As the 3080 is obsolete by now (still widely available, but nevertheless), I used a LM13700 instead and played with the values until it worked well. For MB applications, this is quite a benefit!

I don´t want to diss the Fonik board at all, but from my board you´ll get two channels on a similar PCB size (left out all the pot and additional CV stuff) and a (kind of) linear response of Q. Also, some values are adjusted for +/-12V instead of +/-15V supply. So it´ll be more suitable for Midiboxing (while being less suitable for modular stuff because of the missing direct control).

Seppoman

Hi Seppo, I would love to have cutoff and resonance knobs on my small SIDbox to directly control the external filter. Would it be better for me to build the fonik board for that and use 2 pots, or is there a way to achieve something similar with your board? I don't mind using encoders, as long as I only have to mount 2 of them. (I'm also builing Wilba's box so I want this small box to be a bit custom with minimal controls).

AOUT board looks good, rumours about more boards from you sound very good too :D

Cheers,  Alex.

[stryd_one]

That really comes down to a decision about whether you want to save the filter settings with the patch, and whether you want to be able to automate it (MIDI CC's). If you want either of these things, then it is best to use the AOUT board.

[seppoman]

Hi,

Gavin: I don´t know about differences between 13600/13700 and I don´t have 13600s so I can´t try it out. But I think I´ve read about the 13700 in most cases being a good replacement for 13600 cirquits. So when the board is finished, you could just try it. If it doesn´t work as good, just buy a 13700 for 50 cents or play around with the surrounding resistor values.

NLX: stryd is right, if you want to save filter settings and have envelopes controlling everything, you need an AOUT. The fonik board has CV ins, too. main difference is that you´ll have exponential Q CV response with it, i.e. for fixed Q values in a patch, you need to use other values (finer control over low Q settings, worse with higher Q). For Q envelopes/LFOs, the behaviour will be quite different.

My board won´t be having extra connectors for manual pot control, so everything´s controlled via the MBSID app. Adding them would be no big problem, but when you can´t save the settings with the patch, I don´t see much use for them anyway.

Seppoman

[drsyncenstein]

One of the post mentioned that

My preference right now (already given away above!), even though it is ONLY a 4-pole lowpass (no other modes possible) is the SSM-2044

But nearly any 4 pole vcf can be a multimode filter, there is nothing in the 3372 that makes it somehow into a multimode filter.

If you build a vcf from a SSM2044 or 2164 you could make it in a multimode filter the same way as any other 4 cell ota\vca\vcf chip. An example can be seen here: http://m.bareille.free.fr/modular1/vcf_multimode/extrapole.htm

It also has a link to the Oberheim Expander service manual which explains the theory behind it.

If you would like to build a nice filter, also look at this svf:

http://musicfromouterspace.com/analogsynth/STATEVARVCFFEB2006/STATEVARVCFFEB2006.html

[seppoman]

Hi Dr :)

there are a lot of nice discrete filters out there - The samples on the MFOS page surely sound cool. But both adding external multimode features or building discrete filters doesn´t match with the goals of the usual Midiboxer, like e.g. me ;) I personally never was interested in building modular synths - too much time, work, money, no interest in messing around with patch cords. If I wanted to build absolutely the best and most flexible filter in the world, I´d hang around not here but on Synth-DIY etc. The reason for me to be interested in the 2044 is: I just want to have a nice sounding analog filter that is easy to build, easy to calibrate, has a low parts count and complexity and therefore does use up little space, time and money. At the moment, I´m hoping to get two channels of 2044 filters on a PCB sized about 8x6 cms. The extention board from your first link looks like double that size for only one extention of one filter, i.e. we´d be talking about 4 or 5 times the total board space. That reason alone would kill the whole concept of using an integrated low parts count VCF for me. Please don´t feel offended - your comment and both your links are definitely interesting for all the modular guys out there - just I don´t see the application in usual Midibox projects.

Seppoman :)

[drsyncenstein]

Hi Seppo.

I was just reacting to what i read here, because i had the impression someone else was interested. I've got 4 pieces of 3372 waiting, but if i build multi mode out of it, the filter board alone will probably be bigger than the core and sid together.

Not to mention the extra logic that would need to be hooked into the software.

A quad filter and vca board for the MB-6582 might be interesting, but i guess they'd have to find another case to fit it  ;D