Little Phatty CV inputs

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nikola
Posts: 153
Joined: Sun Nov 30, 2008 2:50 pm

Little Phatty CV inputs

Post by nikola » Sat Feb 06, 2016 4:03 pm

HI,

i am using moog expression pedal on CV filter input, and i don't get nice smooth sweeps with it, there is some kind of noise interduced when i am opening or closing filter cut-of with the pedal, like it has a lack of resolution or something, doesn't sound smooth at all!!

and that brings me to my question, are CV inputs processed by midi and then applied to filter parameters, or is cv filter input directly attached to filter circuits? I hope that is not the case and i just need a better expressen pedal...

Nikola
was i pushed or did i fall ?

EMwhite
Posts: 1651
Joined: Sun Jun 21, 2009 12:22 pm
Location: Middlesex

Re: Little Phatty CV inputs

Post by EMwhite » Sun Feb 07, 2016 5:56 pm

Could be the attenuator on the Moog expression pedal is not dialed in right and you are getting very little sweep effect coupled with a dirty main pot.

I'm not sure if you said which EP you had and if it was new or if you purchased it 2nd hand but you should open it from below, see if everything is moving smoothly and consider blowing some compressed air and possibly faderlube if you have any.

Some of the Deoxit products will actually do more harm than good but these pedals have inexpensive Alpha type potentiometers (about $2) so if you can solder, it's a trivial repair, assuming this is the problem.

To answer your 2nd question, the filter is directly attached (albeit electronically) to the cutoff pot. One of the very revolutionary things that the LP never got good credit for doing is the way that it managed RAC (real analog control) which allowed it to capture, at high resolution, the current setting of any of the four controls, and when selected, the ability to sweep smoothly according to different modes (snap, etc).

But it's an analog pot, not an encoder and it isn't quantized to a course resolution that would result in stepping or loss of control. When settings are eventually saved to a patch, they are stored in as a 12-bit value [0..4095] (if my memory serves me, so to speak) so you could argue that you are losing the slightest bit of resolution when a pot position is stored but I challenge anybody to take 270 degrees of potentiometer travel and be able to move it to the same position within any appreciable margin.

But back to your first problem, If you have a CP-251 or a way to generate a voltage of 0..5, you can test your LP out directly to see if it's the jack/circuit or if it's the expression pedal.
'76 Minimoog, Taurus 3, Oberheim FVS + Son of 2-voice; Sequential ProOne; Juno 106; Moog Model 15; Kurzweil 250; Hammond M3; and a handful of Fender Basses Flickr!

nikola
Posts: 153
Joined: Sun Nov 30, 2008 2:50 pm

Re: Little Phatty CV inputs

Post by nikola » Mon Feb 08, 2016 3:49 am

Hi EMwhite,

thanks for answering, it is new Moog pedal EP-3, i did opened it, and everything is moving smoothly, so i don't know.., i ques i should make a test like you suggested, i could do it with my A4.

I hope its pedal, i like LP a lot and I knew about RAC, I thought it is special little thing going on inside that nobody talks about :) But what I was wondering is are the CV inputs processed by some kind of MIDI processor, and than aplyed to parameters as midi information, but probably not..
was i pushed or did i fall ?

EMwhite
Posts: 1651
Joined: Sun Jun 21, 2009 12:22 pm
Location: Middlesex

Re: Little Phatty CV inputs

Post by EMwhite » Mon Feb 08, 2016 12:23 pm

As far as I'm aware (and can remember), it's pure voltage applied to the analog circuits. Granted, my Phatty was a Tribute, with the 2.0 upgrade (subsequently running the latest code) but it should be the same. If you are having a problem getting a good test together with your other gear, PM me and I can mail you a simple potentiometer wired to a 1/4" TRS plug (e.g. turn pot to simulate an expression pedal); all it does it does is attenuate the voltage down from full voltage on the ring (which should be 5V as sent by the Phatty) back into the tip of the same jack.
'76 Minimoog, Taurus 3, Oberheim FVS + Son of 2-voice; Sequential ProOne; Juno 106; Moog Model 15; Kurzweil 250; Hammond M3; and a handful of Fender Basses Flickr!

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stiiiiiiive
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Re: Little Phatty CV inputs

Post by stiiiiiiive » Fri Jun 16, 2017 4:38 am

Hey Nikola, any update about that problem ?
Have you managed to determine where the stepping effect came from?

On a side note, about RAC (I’m not EE): what is the difference between the Voyager’s pots and the LP’s ones?
Does the Voyager have DAC/ADC between the circuit and each pot?
How RAC manage the change of controlled parameter?

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