XL LFO 2 rate modulation question.

[A Lyttle Folk]

Hello there. It's my first full day with my new instrument, so please forgive my ignorance.

I think I'm right in saying that you can't slow down the rate of LFO 2 with an input into the Rate CV jack. So anything going into that jack will change the rate above, but never below, the panel setting. Seems fairly reasonable, given that its slowest rate is so low anyway, just using the panel control, but I wanted to make sure that it was supposed to be like that. Is anyone able to confirm that it's supposed to be like this please?

Thanks very much for your attention.

[latigid on]

Check the manual -- does it accept a negative CV? As far as I know this is a digital LFO, normally you should not send negative voltage to microprocessor pins, but it depends on how Moog has designed the circuit. It's common practice to add protection diodes to clamp input voltages within a safe range.

[A Lyttle Folk]

Hello again - thanks for the response. The manual seems to ignore that particular aspect of LFO2 entirely. I've only done a quick search on the PDF version, but going by that - nothing. So - if I understand you correctly - using LFO 1 to modulate the speed of LFO 2 would be a bad idea, as the negative part of the LFO 1 signal would be an unhealthy input for LFO 2. I suppose that would make sense if we were to assume that it was designed to just reject the negative part of the input signal entirely. Which presumably would mean either a period where no modulation was occurring. I think, on listening / experimenting further, that's what is happening. So, in my example above, the rate of LFO 2 is going - fast - normal - fast - normal. Hmmm. Interesting!

Thanks for your help - much appreciated.

[Cpt Beardheart]

Check out the manual addendum published for LFO2, which is here: http://www.moogmusic.com/sites/default/ ... 2_midi.pdf

In it, they explain that the input range for LFO2 ext CV rate is 0v to 5v, and that it is additive to the LFO2 rate panel control.

So basically, yes. You're right. You can't reduce the LFO rate by sending a CV signal, and that input does not accept negative voltages.

The way I deal with this (the pitch CV is the same way) is to set the panel control at your lowest desired level (in this case, the slowest rate you intend to use), and then use CV to go up from there.

[latigid on]

Hi, no problem!

LFO1 is bipolar from memory, so its range is -2.5 to 2.5 V. You can send it at a slow frequency to the LFO2 RATE input and see what happens:

Code: Select all

/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\

or

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/\__/\__/\__/\__/\__/\__/\_

Of course it will be a little more complicated as you are essentially frequency modulating the frequency of LFO2. The above is meant to indicate the _effect_ (or modulation amount) on LFO2 RATE.

If it sounds like the bottom range of LFO1 is clipped (no effect on LFO2 rate at this point of the cycle) then that is the protection diodes clamping the negative voltage to about 0 V.

In that case, there is no opportunity to slow down LFO2, sorry (maybe in software though).

[A Lyttle Folk]

Ahh...thanks. Captain - that was a very useful read and Latigid - I think that the second graphic shows what's going on very nicely. I'm curious as to why you say that LFO1 would be 2.5 to -2.5. Could it not be +5 to -5? Sorry if that's a stupid point or demonstrates that I haven't studied the manual properly. (Guilty).

Thanks again.