MF-101 as VCA trick

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PHC
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MF-101 as VCA trick

Post by PHC » Mon Jan 19, 2015 8:39 am

Hi

I know the MF-102 as VCA concept, but I've lately come up with another workaround for the VCA topic.

Maybe this has been posted before, sorry if I'm being captain obvious here, but it lately occured to me.
Consider the following configuration:

1. Audio is fed into MF-101 Low-Pass Filter that is fully closed and the MIX knob is at 100%. The resulting outpul is silence.
2. As above, but MIX is 0%, the result is full volume of the incoming signal.

Now as we turn the MIX knob, we fade between silence and full volume, effectively performing the same function as a VCA would.
If we control the MIX via CV we get a VCA (the incoming CV has to be swapped in polarity - via CP-251 mixer or a patch cable with swapped leads, because: MIX goes down, volume goes up).

Example:
A. For the above configuration, plug a triangle LFO into the MIX on MF-101 and You get tremolo
B. As above, but plug in an envelope from the CV-out modded Little Phatty and You get Envelope controlled VCA

Note:
I haven't tried this technique with processing CVs, as they are to hot an will clip MF-101 input, but I imagine that if I reduce them in level (eg. via CP-251 attenuator), it should work. Then You might want to "re-amplify" them using the CP-251 multiple and mixer trick.

Tell me what You think.

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_DemonDan_
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Re: MF-101 as VCA trick

Post by _DemonDan_ » Mon Jan 19, 2015 11:01 am

I think that's a very clever alternate use for an MF-101. Kudos!
Last edited by _DemonDan_ on Mon Jan 19, 2015 11:56 am, edited 1 time in total.
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PHC
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Re: MF-101 as VCA trick

Post by PHC » Mon Jan 19, 2015 11:44 am

I've come up with this while giving a lecture on synthesis.
We made a synth using CV outs of the Phatty.

Freqbox as VCO controlled via LP Pitch CV Out, MF-101 filter, second MF-101 as VCA + envelopes from Phatty CV Outs to both MF-101s + LP Mod Bus out for vibrato (summed with Pitch CV in CP-251 mixer).

We also observed the voltages on a analog oscilloscope.
Great fun, might do a video for knobz.net someday :-)

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stiiiiiiive
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Re: MF-101 as VCA trick

Post by stiiiiiiive » Mon Jan 19, 2015 11:47 am

Very smart indeed. I'm eager to know how good it works, even if I don't have any 101.

PHC
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Re: MF-101 as VCA trick

Post by PHC » Mon Jan 19, 2015 11:58 am

It works quite nicely, in fact the whole described synth worked good, haven't checked how well the Freqbox tracks the keyboard, as I would be expecting some drift. One thing I noticed is that the LP Pitch CV out outputs raw key pressed voltage with no regard for the pitch wheel, which doesn't allow for a 3 Osc lead (plugging Freqbox Osc Out to LP Audio in to act as a 3rd oscillator).

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_DemonDan_
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Re: MF-101 as VCA trick

Post by _DemonDan_ » Mon Jan 19, 2015 12:15 pm

PHC wrote:One thing I noticed is that the LP PITCH CV OUT outputs raw key-pressed voltage with no regard for the PITCH Wheel, which doesn't allow for a 3 Osc lead (plugging FreqBox's OSC OUT to LP AUDIO EXT IN to act as a 3rd oscillator).
Although the FreqBox's OSC won't track the Little Phatty's PITCH Wheel, that *can* be used as a performance feature.

This link will take to to 3:55 of a Solar Phatty video doing just that:

https://www.youtube.com/watch?feature=p ... IOhI#t=235

Notice how you can play the pitch-bent Phatty notes against the non-bent FreqBox note (at 5:17).
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PHC
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Re: MF-101 as VCA trick

Post by PHC » Mon Jan 19, 2015 12:40 pm

Yeah, You are right. I guess I'd get best results by setting bend range to a fifth or octave.

Nice video BTW

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Re: MF-101 as VCA trick

Post by EMwhite » Thu Jan 29, 2015 10:25 am

PHC wrote:One thing I noticed is that the LP PITCH CV OUT outputs raw key-pressed voltage with no regard for the PITCH Wheel, which doesn't allow for a 3 Osc lead (plugging FreqBox's OSC OUT to LP AUDIO EXT IN to act as a 3rd oscillator).
I thought that they addressed this in later versions of the CV OUT mod (perhaps the units that were built this way out of factory)?

I had a Tribute with CV OUT and unfortunately, pitch bend and glide didn't affect the CV OUT voltage but I thought that was because mine was one of the first produced. I'll cross post this in Phatty Forum...

Thanks.
'76 Minimoog, Taurus 3, Oberheim FVS + Son of 2-voice; Sequential ProOne; Juno 106; Moog Model 15; Kurzweil 250; Hammond M3; and a handful of Fender Basses Flickr!

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