Trouble with CV!

[SimonChr]

Hi.
I have read the manual for the MP-201 and for my Low pass filter MF-101.
I use "stereo" jacks to connect between the CV1 output on MP-201 to the Cutoff input on my MF-101.
If I use unipolar mode (0 to +5 volt) - as I should according to the MF-101 manual - the full range of the Cutoff doesn't respond, it's like half of the range.
I have turned the knob on the MF-101 fully counterclockwise.
If I set the MP-201 to bipolar mode (-5 to +5 volt) and set the Cutoff knob of the MF-101 to 10:00 A.M., then the whole range is there!
Please guide me, I'm lost here.
Thanks
Simon

[SteveD]

Hi Simon -

The CV input on the MF-101 is less than full range with a 0 to +5V input. So this is normal.

When we introduced the moogerfooger MF-101, we figured a large number of users would be guitar players, and they would want to use expression pedals for filter sweeps, sort of like a wah. The range of sweep possible on the front panel is much larger than typically musically relevant for most classic guitar setups - most electric guitars don't produce frequencies from 20Hz to 16KHz, and many guitar amps don't reproduce that kind of frequency range very well.

However, on your own you discovered the work-around - set the cutoff knob close to center and feed a -5V to +5V CV into the Cutoff CV. That's one of the reasons we included bi-polar mode on the MP-201, because there are a number of Moog CV inputs that can benefit from CVs less than 0V. Another example is using a negative CV to slow down the LFOs on the Ring Mod, Phaser, or Voyager more than is available from their LFO rate control knobs.

Hope that helps!
SD

[SimonChr]

It did!
But still a bit strange, though I can understand why.
Thank you.
Simon

[gutbag]

Interesting... could you clarify a couple of things? I seem to remember that the internal reference voltage that is presented on the tip is about 5.6V. Is that the absolute maximum for a CV? I mean, would it stop producing a change if I drove the input above 5.6V?

Also, does a CV input below 0V have any effect?

I should say that I'm particularly interested in the Ring Mod and LPF.

Thanks.

[SteveD]

Howdy -

The "~+5.6" reference on moogerfoogers, Voyager and LP CV jacks that accept Expression pedals is presented on the ring - then sent to one end of a pot with the wiper returning to the tip, you have basically a 0 to +5V CV at the input (Don't worry - you don't have to be super precise w/ the math for this application).

So *TYPICALLY* things that are Frequency related - LFOs, VCOs, Filter Cutoff, MF-103 "Sweep", etc... Can work with -5V to +5V CVs. *Typically* VCA type things (Mix, Amount, etc), or anything that is turned into MIDI (for instance MOD1 and MOD2 on Voyager) use 0 to +5V CVs.

These are not hard and fast rules - but they depend on the circuit - and each circuit may deal w/ CV inputs a little different depending on how they get used in each product. Best way to learn is to try it out!

Hope that helps -
SD

[gutbag]

Thanks Steve. I mixed up tip and ring - oops.

[jazzymike]

SteveD thank you very much for the info(s).
However I have a question. Let's say I would like to achieve a full sweep via CV with the physical knob set near or counterclockwise.
Let's say I amplify the CV signal (with the common peak being 5v) to a value of f.e. 8-12V
Would there be a risk of damaging internal components? If not, would I actually achieve a full sweep, or is there a voltage limiter?

Kind Regards,
Mike


p.s.:
I've also just realized, that you might not want to encourage users to apply voltages higher than specified, even if there's a tolerance headroom. In that case, I would still appreciate a PM. I promise to be discreet

[jazzymike]

my question has been answered here:

http://www.moogmusic.com/forum/viewtopi ... =3&t=11448

[calaverasgrande]

Wouldn't using TRS/stereo plugs be incorrect? I am under the impression you only use those for CV pedals like the EP2. The MP201 is only mono plug compatible from what the literature tells me.