Sub Phatty Pitch CV IN behavior

[kingfriday]

Using the LFO Doepfer Dark Energy to modulate the pitch on the Sub Phatty (via the Pitch CV In jack) is producing some really bizarre results. The LFO on the DE has 3 modes, and in "high" mode, it can get very very fast. Applying this to pitch should produce standard analog FM, however this is not what I am getting. If you use slow LFO rates, the pitch modulation sounds as normal as can be, but when you push it up into the audio range, it starts sounding really wacky. I don't quite know how to describe it, but it is definitely not doing what it is supposed to. It sounds like it the osc pitch just jumps around randomly and there is no actual FM going on.

Audio rate FM on the filter using this same LFO sounds totally normal (Well, as normal as filter FM can sound )

Amos (or anyone), is there some sort of "limit' on the pitch CV in on the Sub... or something that is causing it to not respond to the LFO CV in the normal way when fed audio rate modulation? Or is there a certain type of audio rate LFO that I need to use? I figured standard Eurorack modules would work, no problem.

[mico]

The resolution to this may be as simple as increasing the LFO range for your given patch. Remember that the Sub Phatty's LFO rate is chopped into pieces and selectable through Shift mode's hidden parameters.

Let me know that pans out for you. It may be surprising to think that this could restrict CV input behavior, but such may be the case.

[kingfriday]

Didn't even think to check that. I'll give it a go when I get home and let you know what happens.

Also, is anyone else getting this behavior when trying to apply an external LFO to the Pitch CV in? I tried using the LFO on my CP-251, but it doesn't go fast enough to make the wonky stuff happen.

[mico]

Didn't even think to check that. I'll give it a go when I get home and let you know what happens.

Also, is anyone else getting this behavior when trying to apply an external LFO to the Pitch CV in? I tried using the LFO on my CP-251, but it doesn't go fast enough to make the wonky stuff happen.

I'm nearly positive your issue will be remedied with what I've detailed above.

[stiiiiiiive]

Guys, I have no Dark Energy nor SubPhatty here, but I'm confused.
Mico, are you sating the LFO speed setting of the Sub would alter the way a CV in signal modulates the Sub's oscillators pitch?

[kingfriday]

mico, you are a genius, sir. Increasing the LFO range did indeed fix the resolution problem. Now the high speed LFO on the Dark Energy is imparting proper FM to the Sub's Pitch CV in.

Guys, I have no Dark Energy nor SubPhatty here, but I'm confused.
Mico, are you sating the LFO speed setting of the Sub would alter the way a CV in signal modulates the Sub's oscillators pitch?

Yup, this is what mico was saying, and he was correct.

The only thing that I find weird now is that the FM is only happening up to the sustain stage of the sound. If there is any release on the amp, the FM disappears during the release phase and you hear osc as you would with no FM. Very strange, but now that I'm thinking about it in terms of the mod buss, maybe this has something to do with the Keyboard Gate IN? mico, what do you think?

[stiiiiiiive]

Guys, I have no Dark Energy nor SubPhatty here, but I'm confused.
Mico, are you sating the LFO speed setting of the Sub would alter the way a CV in signal modulates the Sub's oscillators pitch?

Yup, this is what mico was saying, and he was correct.

Amazing, but I'm glad you've worked it out

[Portamental]

There's something that you should be aware when using an external LFO into the pitch CV input of the SubPhatty

- An LFO swings from minus voltage to plus voltage. (-2.5/+2.5 for full strength LFO from the CP-251)

- A vintage Moog or Phatty or Voyager accepts minus voltages as pitch CV from -5v to 5v

- The Minitaur and SubPhatty are limited to 0 to 5 volts on pitch and filter CV inputs.

When an external LFO is injected into the pitch CV jack on the Minitaur, it can only modulate half a cycle (the positive), the negative portion equals 0. That leads to bizarre pitch modulation indeed.

Same for the filter. Case verified on my Minitaur and CP-251. Sub Phatty manual page 8 says the range of filter and pitch CV is 0 to 5v too, same as the Minitaur

Even if you were to use the CP-251 to offset the voltage, you would have to adjust the cutoff accordingly.

External pitch or filter modulation the traditional Moog way is not possible with the Minitaur or the SubPhatty.

Another oddity to add to the list. Old school people are not thrilled with either (MT, SubP).

[kingfriday]

Hallelujah. I did not know any of that but now things are really starting to make sense (RTFM dummy!). This is ever so slightly disappointing but good to know. Why on earth did Moog choose to set up the CV ins like this?

So the workaround is to use the CP-251 attenuator to offset the negative voltage part of the LFO cycle into the positive range and then rescale your pitch or filter to where you want it. Makes sense. I'll give this a whirl tonight and see how it goes.

Thanks for that info Porta!

[kingfriday]

Ok, so even after running the LFO into the attenuator on the CP-251 and attenuating the signal "all the way positive", I believe it is simply attenuating the signal in both direcitons. I think what I need is an actual voltage offset module to get the results I'm looking for. I still have to wonder why moog set up the CV inputs this way. It seems to really limit how they can be used.

After some hours of messing around with the CV ins on the Sub it seems like there is definitely some kind of weird limitation on the pitch modulation bus. When using an external oscillator or audio range LFO to impart FM, the FM cuts off after the rate goes too high. As you increase the frequency of the modulating signal, it simply stops; the FM effect of the modulator ceases to increase. When using the built in LFO at high rate, the modulation literally disappears after you play past a certain point with the keyboard LFO tracking turned up to 200%

[Portamental]

That's not how it works. The attenuator is just what its name indicates, an attenuator, it does not change the shape of the signal. At +5, the output is the same a the input.

You have to use the mixer section to make an offset that is added to the signal. The mixer attenuates too if the master level is anything below 10.

Read manual very carefully.