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Powered CV In jacks Effects Pedals, Units & Accessories
Old 9th April 2019
  #1
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Powered CV In jacks

Hi, I'm an almost complete newbie into the modular (actually semi-modular) world, and I have what's maybe a very stupid question. I searched the forum but didn't find a precise answer.

I have a Moog Little Phatty with the CV Out upgrade. I also have a Moog CP-251 CV controller and a few other synths with CV connections (Microbrute, Karp Odyssey).
Several CV In jacks on the Little Phatty and CP-251 are "active", meaning they supply power so a passive expression pedal can be directly plugged in them to control the related parameter.

For example, that's what the manual of the LP states:
CV Inputs:
The Pitch, Filter and Volume CV jacks supply power and will accept an expression pedal such as the Moogerfooger EP-2 (ring = +5.5 supply to the pedal, tip = variable CV return), or a control voltage from –5 to +5 Volts. The KB Gate Input accepts a footswitch (a momentary, normally-closed footswitch like the Moog FS-1) or a +5 Volt Gate Signal.


And this is the relative part of the CP-251 manual:
Eight of the CP251's jacks are held with red nuts. These input jacks are equipped with power for expression pedals. You can plug an expression pedal directly into any of these jacks - or use the jacks as conventional inputs.


Ok, so it is written that these jacks CAN also be used as conventional inputs. But isn't this in contrast with the fact that they are powered? If you plug a CV source in them, isn't this basically connecting an Out to another Out, which if I'm not mistaken is the only thing to really avoid with modulars?
Or given that an expression pedal uses a TRS cable, maybe the jack connection is wired in a way that connecting a mono TS jack avoids the control current? So if I use mono TS cables I can just connect anything without worries?

Sorry for the dumb post, I just wanted to make sure that I can freely use all the CV jacks in my equipment without frying anything!
Old 9th April 2019
  #2
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Derp's Avatar
Good question. I've messed with expression inputs and CV before, and didn't have any problems. That's just my experience and I could have just gotten lucky, so somebody else may want to chime in to confirm this.
Old 10th April 2019
  #3
Lives for gear
Quote:
Originally Posted by Spider76 View Post
Or given that an expression pedal uses a TRS cable, maybe the jack connection is wired in a way that connecting a mono TS jack avoids the control current? So if I use mono TS cables I can just connect anything without worries?
Yes
Old 10th April 2019
  #4
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Thanks for the replies!
I dug deeper into the manuals and, while there's no further info about the Phatty, the CP-251 tech notes add the following sentence that I had overlooked:

"Plugging a conventional two-circuit phone plug (tip-sleeve) into any of the red jacks will not adversely affect the operation of any part of the CP251. Such a phone plug will short that jack’s pedal supply to ground, causing a current of about 2 milliamperes to flow through the plug’s barrel."

So yes, the control voltage for powering expression pedals is supplied at the ring of the TRS connector, and plugging a TS plug will simply bypass the control current, functioning as a normal passive jack.
Now I can breathe easier and go patching!
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