Adding CV in's to Doepfer A-104 Trautonium Formant Filter

Infrablue · Joined: Dec 29, 2011 Posts: 131 Location: Utah

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!

elmegil · Posted: Fri Jun 08, 2012 3:00 pm Post subject:

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.

Infrablue · Joined: Dec 29, 2011 Posts: 131 Location: Utah

thanks for the fast info Smile

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

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

Infrablue · Joined: Dec 29, 2011 Posts: 131 Location: Utah

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

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.