Using the MP-201 as a "regular" expression pedal.

Beethree · Post by **Beethree** » Fri Dec 04, 2009 11:54 am

I am thinking of adding an MP-201 to my pedalboard that I use with multiple keyboard configurations for live performance.
In addition to it's midi-centric chores, would I be able to use the CV out, after setting max and min voltages, to act as an expression pedal with say, a Nord electro 3 directly into its 1/4 in. control pedal jack?

I am obviously not well versed in using control voltage in controlling gear....

Amos · Post by **Amos** » Fri Dec 04, 2009 12:49 pm

Yes, this was the original idea behind the MP-201: four regular CV expression pedals.

Obviously, it kind of got out of hand from there...

But this basic function still works very well.

DontBelievetheHype · Post by **DontBelievetheHype** » Wed Jan 27, 2010 4:05 am

Aside from all the added functionality over any regular kind of expression pedal, the MP-201 has the best feeling treadle of any expression or volume pedal I've tried- the extra weight and size also gives it a solid base, and the whole package really lends itself well to expressive and precise manipulation/modulation/etc.

ark · Post by **ark** » Mon Feb 08, 2010 1:16 am

Amos wrote:Yes, this was the original idea behind the MP-201: four regular CV expression pedals.

I must be missing something. The CV outputs of the MP-201 are voltages, right? An expression pedal is a potentiometer that you move with your foot, right? How can one substitute for the other?

Portamental · Post by **Portamental** » Mon Feb 08, 2010 2:27 am

With an expression pedal, the host device feeds some current through the ring of the plug, this goes through the pedal potentiometers, acting as a potential divider. One portion of the divided voltage appears on the tip of the jack, that's the CV. An expression pedal without the current source is a dead device. That's the design that has been prevailing for years, and it will neither change or go obsolete. It's a simple device.

The MP-201 uses a different approach. It contains all the circuitry and logic to generate the CV directly at the tip of the plug, without the requirements of the ring current or potentiometers.

In the end, the sleeve is the ground, and the tip is the CV on both devices, they are functional equivalent.

ark · Post by **ark** » Mon Feb 08, 2010 11:10 am

Portamental wrote:The MP-201 uses a different approach. It contains all the circuitry and logic to generate the CV directly at the tip of the plug, without the requirements of the ring current or potentiometers.

OK...so now what happens if I connect the MP-201 to a device that expects just a potentiometer? There is no way to know what voltage that device would be supplying, so idn't there the possibility of breaking something?

Portamental · Post by **Portamental** » Mon Feb 08, 2010 8:29 pm

ark wrote:There is no way to know what voltage that device would be supplying, so idn't there the possibility of breaking something?

No. If you use a TS patch cable (no ring), the ring supply is shorted to ground and it is safe by design.

On that subject, Moog often uses the word 'shorted' in it's literature to describe the situation. It is a poor choice of word IMO and the word 'shorting' is indeed scary to most people. This is not what is happening. Upstream from the plug's ring is a circuit designed to let flow a small amount of current (1 ma at 5 volts). Without a plug, this circuit is open, with a TS plug, it is fully closed, like an off-on switch. Same goes for products of any other company. It's all safe

So now is the time to have fun and leave the worries behind

blewis · Post by **blewis** » Sat Feb 13, 2010 1:21 pm

Portamental wrote:
ark wrote:There is no way to know what voltage that device would be supplying, so idn't there the possibility of breaking something?
No. If you use a TS patch cable (no ring), the ring supply is shorted to ground and it is safe by design.

Upstream from the plug's ring is a circuit designed to let flow a small amount of current (1 ma at 5 volts). Without a plug, this circuit is open, with a TS plug, it is fully closed, like an off-on switch. Same goes for products of any other company. It's all safe

I'm a bit confused by this. I'm trying to use the MP-201 with my Digidesign 11R. The 11R expects to see an expression pedal across a TRS jack.

I can't get the MP-201 to work with the 11R if I push the MP-201's TS output all the way in, where the Ring & Sleeve of the 11R would get shorted.

However, if I pull the TS MP-201 output out _half way_ I can get it to work. It seems to me that the 11R is measuring a voltage across the Ring and Sleeve. In other words, it's expecting that the wiper of the expression pedal is the node where the expression voltage should be.

Measuring the output of the 11R, the Tip has about 3.27V and the Ring has about 3.25V, so I'd suspect there's a small resistor between the Tip and the Ring @ the output of the 11R. And a big resistor between Ring and Sleeve where almost all the voltage is dropped (on the output of the 11R).

Anyway, what I'm observing on this piece of equipment is different than what you described (I think). Have any ideas what the difference might be attributed to?

I thought having the MP-201 drive a it's output between the Ring and Sleeve of the 11R's TRS jack was basically faking out the 11R like the MP-201 was a pot (regular expression pedal)

The Digi guys are saying, "don't do it, you'll blow components", but I haven't sorted it out for myself yet.

Brandon

blewis · Post by **blewis** » Fri Mar 12, 2010 7:07 am