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 Forum index » Instruments and Equipment » Modular Synthesis
Adding CV in's to Doepfer A-104 Trautonium Formant Filter
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Infrablue



Joined: Dec 29, 2011
Posts: 123
Location: Utah

PostPosted: Fri Jun 08, 2012 10:04 am    Post subject: Adding CV in's to Doepfer A-104 Trautonium Formant Filter Reply with quote  Mark this post and the followings unread

I'm hoping to add CV inputs to control frequency independently on each filter on the Doepfer A-104 Trautonium Formant Filter.

The pots for the frequency are A50K pots. I'm pretty new to modding stuff, would this be as simple as routing CV to the middle pin on the pot?

Is this safe to just try out? Would I need additional components? I'm mainly going to use Silent Way software to modulate these so I can provide offset and fine tuning of the CV.

Thanks!
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elmegil



Joined: Mar 20, 2012
Posts: 1516
Location: Chicago
Audio files: 14

PostPosted: Fri Jun 08, 2012 3:00 pm    Post subject: Reply with quote  Mark this post and the followings unread

I can't provide a definitive answer, but...

Are the pots hooked up as power, wiper, ground? In other words, three separate connections? That's a typical voltage variance, and it might work to just put the voltage in (though it seems to me you'd want to use a normally closed jack to disconnect the pot when you're doing cv in).

If it's actually more like one side and the wiper together going to one point and the other side somewhere else, then that's just a variable resistance and it certainly won't work to just plug a voltage in there. I'm not experienced enough to explain what the alternatives are for that scenario, but there are some.
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Infrablue



Joined: Dec 29, 2011
Posts: 123
Location: Utah

PostPosted: Fri Jun 08, 2012 3:20 pm    Post subject: Reply with quote  Mark this post and the followings unread

thanks for the fast info Smile
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ndkent



Joined: Jan 03, 2006
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Location: new york

PostPosted: Sat Jun 09, 2012 9:27 pm    Post subject: Reply with quote  Mark this post and the followings unread

If you look at the doc for the A-101-9 you can see how to wire the A-104 pots up to a vactrol (CV in with variable resistance out).

I would think a lot of people would have modded one if it were a matter of simply soldering in a CV. I think the official Doepfer line is if you want CV you'd buy the A-127 while this one adds the 4th filter and follows Sala's Trautonium tradition of not having a VCF
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Infrablue



Joined: Dec 29, 2011
Posts: 123
Location: Utah

PostPosted: Sat Jun 09, 2012 11:54 pm    Post subject: Reply with quote  Mark this post and the followings unread

ndkent wrote:
If you look at the doc for the A-101-9 you can see how to wire the A-104 pots up to a vactrol (CV in with variable resistance out).


Wow, great info. The manual for the A-101-9 is quite a resource for other things as well with all the module schematics.

I did just order an A-127, but the Vactrol module is so useful I may just get that as well.

I did try just tests of low volt CVs on the pots and it did have effects but more just changing overall volume and not frequency as wanted. So vactrols are the answer. And in the case of the A-104 it does take a double vactrol to modulate frequency as the manual shows. And the A-101-9 is also valuable since dual vactrols are being banned from production for some environmental reason.

Thanks so much for the info.

I'll be using the A-127 for real time enunciation/filtering of a live analog Steiner EVI or at times a ribbon controlled VCO and then use the A-104 to build a complex static formant body for the overall sound.
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ndkent



Joined: Jan 03, 2006
Posts: 66
Location: new york

PostPosted: Sun Jun 10, 2012 4:08 am    Post subject: Reply with quote  Mark this post and the followings unread

If you find the Vactrol module interesting you might want to put it high on your list to get since as you said there is currently a Vactrol shortage plus I've heard that it has sold badly. My guess is because of the soldering complexity perhaps the few who want to do the mod often consider a totally DIY solution without a special module - http://bridechamber.com/VC_Res_PCB.html for instance. Anyway Doepfer tends to discontinue modules for very low sales and parts issues and that one is both.
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