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Malekko Quad LFO brings on larger newbie questions
Old 25th November 2019
  #1
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Malekko Quad LFO brings on larger newbie questions

I've just started building my first eurorack mono synth. I have a SE Tonestar 8106 synth voice and I got the Strymon Magneto as a delay but I wanted to add a modulation source. I found the Malekko Quad LFO for a good deal so I scooped it.
First I used it to replace the internal LFO and it was awesome. I have way more control over shape and I love using the automation and messing with the distortion.

But then I wanted to use it to create a tremolo effect so I took one of the lfo outs and plugged it into the VCA In (I also tried the Mod In for the VCA). I quickly found that, no matter where I placed the Level knob, it was going completely silent during part of its phase.

I'm guessing I need some kind of CV compressor or attenuator but I'm really hoping there's a workaround that doesn't require another module because I have limited space in my Waldorf KB37 and I still wanna get a separate filter module.

I guess VCA just doesn't work like a filter where the modulation adds on to the level it's already at...

Sorry I don't have better language to describe the issue. Does anyone get what I'm getting at? Thanks.
Old 25th November 2019
  #2
Lives for gear
Attenuators are your friend.

So are Attenuverters.

The (passive) 4hp Quad Attenuator from SSF / WMD is about $60 and a popular choice.

IMO every rack needs one or two similar modules.
Old 25th November 2019
  #3
Lives for gear
For starters, you should be going into the VCA CV, not the VCA IN... the VCA IN is an audio input allowing you to put external sound sources through the VCA.

There may be other problems afoot, but start there.

Just in general, as your journey continues, you will likely want some attenuators at some point in order to tame signals - kind of what you are after when you say "compression". These are sometimes built into modules on inputs or outputs... in the case of an LFO output, might be called something like "depth" for example. Another issue that will come up as well is whether signals are uni- or bi-polar, in other words whether the CV being generated is only in the positive range, or whether (as is often the case with LFOs) that the wave has peaks in both positive and negative ranges - ie centered around 0 volts. VCAs mostly only respond to positive voltages, so there's a possibility that half your LFO wave shape will be closing the VCA completely as the negative part will basically be ignored. So you have to shift the wave up by means of an "offset". Sometimes knobs related to CV inputs function in this way rather than as attenuator as mentioned above saving you a dedicated module. There is a bit of a controversy as to which way knobs should behave, but as attenuators are generally easier to come by (they can be passive) many people prefer the offset model, which you describe as "like a filter". Just be aware that this isn't always the case. While we're here, also look out for "attenuverters" - they are like attenuators, but instead of ending with a completely flattened wave, they continue through the 0 point and then give you an inverted version of the input shape. In other words the "0" position or flat wave is at the 12 o'clock position.

Anyway, a quick look at your LFO makes me think the "level" control will have you covered for attenuation, and you may find the "volume" knob will give you the offset you need once you have the right jack input.... Otherwise a Disting is always a very handy tool in any small system!
Old 25th November 2019
  #4
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Ok. Yeah I think the uni vs bi-polar situation is pretty clutch here.
For the record, I was using the VCA CV, I just wrote vca in by accident.
With level all the way down on quad lfo, no sound is heard regardless of volume knob on 8106.
So, with an offset this seems like the tremolo effect could be made.
With an attenuator, I’m guessing the no sound thing would be the same, like the level on the quad lfo, it would still disregard the original level of the 8106 and instead of going from 0 to X with X being the level setting, it would go from 0 to (X minus the attenuation amount), right?
Is there a way to make my quad lfo uni-polar?
If not, what uni-polar lfos do people like.
And also, what small width offset modules do people like?
Old 25th November 2019
  #5
M32
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A unipolar lfo is essentially a looping envelope.

I have a mutable stages which can be 6 looping AD envelopes with morpheable waveforms/slopes. I like using that for unipolar modulations.
It can also be a sequencer, sequential switch, sample and hold, any kind(sometimes multiple) of envelope, ad, adsr, hahdsr, ...
it's one of those mutable modules that is underestimated and overlooked a bit

Xaoc Zadar is pretty sweet too, and the new Intellijel Qaudrax is also very versatile and powerful. One of those two is certainly going to end up in my rig at some point.

i just got a Noise Engineering Sinc Defero multiple attenuater module, super handy to have easy control of the modulation amount. Featurewise, Mutable blinds seems perfect, but it is quite big. I have a Veils VCA and a smaller 8hp clone, anyone know if there's someone out there making 8hp blinds clones?
Old 26th November 2019
  #6
Gear Guru
 
Derp's Avatar
This definitely sounds like attenuation is what you need, but you have multiple options. You can buy dedicated modules that range hugely in price, size, and power requirements, but there are also cables with attenuators built in. Perfect Circuit has them for about $12 a pop.

Old 17th December 2019
  #7
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monomer's Avatar
 

Quote:
Originally Posted by dwbkeys View Post
Is there a way to make my quad lfo uni-polar?
Basically you need to add a DC signal to your LFO signal.
The problem with that would be that the DC signal would need to be exactly as much as the LFO's amplitude if you want a proper unipolar signal.
So if you change the level on the LFO module you will also need to adjust the DC signal to compensate.

But the thing is, you probably don't actually need a normal unipolar LFO.

You still need a DC offset somehow.

Here is the simplest option without a unipolar LFO.
Use a mixer module to feed the VCA cv.
Put a DC signal in the mixer.
This will decide the basic level of your sound but it needs to be set so the VCA is opened only about half-way.
Then also patch an LFO into that mixer.
The level of the LFO will then decide the amount of tremolo.

There is just one little problem with this setup. Since the LFO is bi-polar and the DC signal already opens up the VCA, at some point (when increasing the LFO level) you will hit the max on the VCA.
You can adjust the DC signal so the LFO then doesn't top out the VCA. And you probably want to fiddle with the LFO level after that.
All in all, this is workable but a little fiddly.

A nicer way to do this is to use (indeed) an unipolar LFO. But the thing is, it needs to be a negative unipolar signal. You could do this by mixing an LFO with a negative DC signal. Using a negative DC signal has the same problem as above, it needs to match the LFO's amplitude to get a proper unipolar LFO. But i guess it's not all that important for this application.

If you already have a positive unipolar LFO (which i think is not an option on your LFO) you could just use an attenuverter to make it negative.

But in your case with a bipolar LFO the easiest thing would be to leave the level of the LFO module at max and mix in a negative DC signal that pushes the LFO into the negative side.

Anyway, once you have your negative unipolar LFO you can then use another DC signal to open up the VCA to around it's max, and then mix in the negative LFO. The LFO will only make the sound less loud, without upward overshoot on the VCA cv.
This way you can dial in the amount of tremolo you want without fiddling with the balance between the DC signal and LFO level. You just adjust the LFO signal on the mixer (so after making it negative unipolar) to have less or more pronounced tremolo.

I just hope i made it clear enough without making drawings.
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