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fine CV control for Malekko VCA in Exp Mode?
 
 
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matttech
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PostPosted: Thu Dec 08, 2011 3:42 pm    Post subject: fine CV control for Malekko VCA in Exp Mode? Reply with quote Add User to Ignore List

hi all

am wondering if there's a solution that will allow me greater control over the exponential cv input for the malekko vca. it's notoriously sensitive, and the line between no sound and total obliteration if very fine - so much so that you end up adjusting the cv input with TINY increments (even when using, say, an RS60 which has its own CV output control)

so....am wondering if there's a way of adding VERY fine attenuation

i have made some attenuators myself a while back - could these be modified so that they have a very narrow range? maybe by using a different value pot?

the only other way i can think of is to combine the ADSR in a mixer along with an a176 Control Voltage Source (this has coarse and a fine controls for doing stuff like adding fine tuning to oscs)....but this seems like a bit of a long way round the issue

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dogoftears
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PostPosted: Thu Dec 08, 2011 3:49 pm    Post subject: Reply with quote Add User to Ignore List

Active voltage into attenuator into cv input. Now u have two attenuators. Run thru more attenuators for finer and finer control. Foni cv mixer is good for this.

Keep in mind an exponential slope by nature is very responsive.

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msprigings
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PostPosted: Thu Dec 08, 2011 3:52 pm    Post subject: Reply with quote Add User to Ignore List

Isn't there some kind of trim on the back?

I can't remember exactly what it does.
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matttech
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PostPosted: Thu Dec 08, 2011 3:58 pm    Post subject: Reply with quote Add User to Ignore List

dogoftears wrote:
Active voltage into attenuator into cv input. Now u have two attenuators. Run thru more attenuators for finer and finer control. Foni cv mixer is good for this.

Keep in mind an exponential slope by nature is very responsive.


ok....will try that in a bit. so you'll be attenuating the already attenuated cv source (eg: you'll be getting, say, 50 % of 50% of the original signal)

that sounds like it should work. have built 2 boxes with 8 attenuators in, so that'll be no problem


re: trimming - that just determines the maximum that the exponential CV input will open the VCA to (to avoid clipping). i don't see that it would solve this issue - it would just mean that i couldn't get ANY distortion (rather than allowing me to control it more finely)

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msprigings
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PostPosted: Thu Dec 08, 2011 4:02 pm    Post subject: Reply with quote Add User to Ignore List

ahh that makes sense.
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matttech
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PostPosted: Thu Dec 08, 2011 4:18 pm    Post subject: Reply with quote Add User to Ignore List

actually the solution dogoftears suggested doesn't work. the useful range of the exp cv input knob is only between about 2 o'clock and full.

if you attenuate the voltage coming into it, it doesn't open the vca at all

the only other way of doing it would be to combine the attenuated voltage in a mixer with an offset (say, a138b or Maths)

still fiddly

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matttech
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PostPosted: Thu Dec 08, 2011 4:20 pm    Post subject: Reply with quote Add User to Ignore List

actually, that doesn't work either, as the offset means that the vca never closes completely

damn

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artisokka
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PostPosted: Thu Dec 08, 2011 4:23 pm    Post subject: Reply with quote Add User to Ignore List

matttech wrote:

damn


+1. sad banana

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Dr. Sketch-n-Etch
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PostPosted: Thu Dec 08, 2011 4:33 pm    Post subject: Reply with quote Add User to Ignore List

I don't actually know what is "inside" the Malekko VCA, but if it's anything like the expo-linear VCAs I've designed, then changing a single resistor value will change the sensitivity of the exponential response. I'm thinking that there is probably a CV summer in the circuit which is controlling the exponential CV to the VCA, and if the feedback resistor on this summer is decreased, then the CV control range is decreased. The beauty of surface-mounted resistors (I'm assuming that Malekko stuff is surface-mounted) is that you can simply stack another resistor on top of the existing one to decrease its effective value, without having to desolder anything. For example, if the feedback resistor is, say, 100k, then soldering another 100k resistor on top of it reduces the effective resistance to 50k (i.e., half), and this would halve the control range as well, in this case.

You should probably ask Malekko about it. I'm sure they can suggest an easy mod to get closer to what you want, or even do it for you.

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matttech
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PostPosted: Thu Dec 08, 2011 5:16 pm    Post subject: Reply with quote Add User to Ignore List

Dr. Sketch-n-Etch wrote:
I don't actually know what is "inside" the Malekko VCA, but if it's anything like the expo-linear VCAs I've designed, then changing a single resistor value will change the sensitivity of the exponential response. I'm thinking that there is probably a CV summer in the circuit which is controlling the exponential CV to the VCA, and if the feedback resistor on this summer is decreased, then the CV control range is decreased. The beauty of surface-mounted resistors (I'm assuming that Malekko stuff is surface-mounted) is that you can simply stack another resistor on top of the existing one to decrease its effective value, without having to desolder anything. For example, if the feedback resistor is, say, 100k, then soldering another 100k resistor on top of it reduces the effective resistance to 50k (i.e., half), and this would halve the control range as well, in this case.

You should probably ask Malekko about it. I'm sure they can suggest an easy mod to get closer to what you want, or even do it for you.


it's not really the overall range that i want to decrease....it's the USABLE range of the knob that i need to "zoom in" on. if i reduce the range of the exp input, then i'll lose the distortion near the top. what i need to be able to do is to end up with a knob that lets me move in very fine increments between 2 o'clock and full (there are lots of different tones of distortion in that area, but it's very hard to select them, as the amount you have to move the knob is absolutely TINY)

hmmmm...maybe i should just get a dedicated distortion module

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matttech
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PostPosted: Thu Dec 08, 2011 5:39 pm    Post subject: Reply with quote Add User to Ignore List

bodge solution:

take the DC generated by ch. 2 of Maths into the input of ch. 3.

set ch. 3 to about 1-2 o'clock (so that it is heavily attenuating ch. 2's DC signal)

then send the output of ch. 3 into a mixer.

send the ADSR into another channel of the mixer.

you now have fine control over the CV input, and when you sweep over the entire positive half of ch. 2's knob you get a very gradual increase in CV gain into the VCA

fucking messy though........can't see me bothering to do this often

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Jason Brock
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PostPosted: Thu Dec 08, 2011 6:04 pm    Post subject: Reply with quote Add User to Ignore List

I must say this is the biggest thing about Eurorack that bums me out. Within a system that is made by only one manufacturer, all of these levels and response curves would ideally be calibrated and tailored to match one another and provide the maximum usable range when turning a knob.

I've got a similar situation to yours, and I also have an rs-60 envelope. That envelope rocks because of that built-in attenuverter at the bottom. So handy. But when I use it to drive my Intellijel Azimuth as an output VCA, I get similar results to what you are describing. There is a "sweet spot" when turning up the output level on the rs-60 (about half way up) where it sounds "right" to me, i.e. close to unity gain coming out of the Azimuth and the envelope shape sounds nice. But it is a fine line, because if I bump up the level just a bit I get clipping, and if I turn it down just a bit I can hardly hear any audio coming out. I'm wondering if Intellijel's new uVCA will play nicer with hotter signals, since it uses the SSM chip. I also remember being fairly happy with my Doepfer 132-3, since it seemed to take any sort of envelope signal you could throw at it and it wouldn't clip.
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Dr. Sketch-n-Etch
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PostPosted: Thu Dec 08, 2011 6:34 pm    Post subject: Reply with quote Add User to Ignore List

Jason Brock wrote:
I'm wondering if Intellijel's new uVCA will play nicer with hotter signals, since it uses the SSM chip.

The uVCA will allow you to define any response between pure exponential and pure linear, and will give clean 2x unity gain in any mode. Indeed, the uVCA would actually solve Matttech's problem, because it has independent controls for CV and CV Bias as well as Mode. This means that not only could Matttech dial in exactly the range of the CV that he wanted with the CV control, but he could locate the centre of that range anywhere he wanted with the Bias control, and could select the optimum sensitivity to that CV range by dialling in a custom response with the Mode control.

I hear your pain, Jason Brock, and I design all my modules to a specific standard (0 to 5V CV, 0 to 10V envelopes, -5V to +5V VCO and LFO waveforms, and VCAs that will gladly accept any of these three into any input and still give good results without clipping or bottoming out). Not to denigrate other designers, as there are certainly equally good and equally valid alternatives, but sticking to this standard has worked very well for me.

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matttech
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PostPosted: Thu Dec 08, 2011 6:38 pm    Post subject: Reply with quote Add User to Ignore List

it'ss a fucking pain isn't it? that malekko would be great apart from this "feature". i'm almost inclined to keep the a132-4 i'm selling, as that is much easier to do controlled distortion with. (i am actually after distortion, rather than a clean sound...but i need to be able to control how much)

i strongly recommend the Oakley CLassic vcas - i have two and they are excellent. you do still need to trim the CV inputs if you're sending hot ADSRs (MFB, RS60) into it....but it's no biggie. it doesn't really distort if you send the cv in too high, but you don't get such an extreme exp curve to it. with rs60 on full, the cv inputs just need to be set to 2'o clock and they're fine.

the a132-4 is pretty cool, as you can trim CV input 1 on each channel of it so that it never clips, but CV input 2 has no trimmer, so you can then use that for distortion, which is fun (doesn't sound much different from the malekko if i'm honest). when set clean, it sounds identical to the CEM 132-3s that i've got

oakleys are the best all-round one for me though. the 2 audio inputs, and 2 CV inputs - one lin, one exp - ....along with the output gain, is a nice feature list too

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PostPosted: Thu Dec 08, 2011 7:04 pm    Post subject: Reply with quote Add User to Ignore List

matttech wrote:
that malekko would be great apart from this "feature".


well I got used to it now, a little fiddly but I can dial pretty much what I want as distortion, and I love it's sound in exp mode. strangely I have a harder time with my envelators with it, but the deopfer adsr work like a charm, with a lower sustain stage I got a distortion peak before the decay, just perfect. I just use a tiny bit of it's crispiness in fact not full on distortion. It clicks a little more than I would like but that maybe unavoidable to a degree in exp mode vcas.

Anyway that vca helped me understand how important they are in the final sound. That makes me want to try lots o them now -and at first I taught that was a pretty much "transparent" module that would not really matter witch I use in terms of sound. I am going nuts over envelopes and vcas now... I wish I could have got the cwjeman vca-adsr and the 4-mx vca... but I may find what I want in the intellijel u modules (waiting for vc-adsr!) or other brands anyway


Dr. Sketch-n-Etch wrote:

The uVCA will allow you to define any response between pure exponential and pure linear, and will give clean 2x unity gain in any mode. .


yeah that is really applause

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flashheart
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PostPosted: Thu Dec 08, 2011 7:26 pm    Post subject: Reply with quote Add User to Ignore List

Rather than just an attenuator you really need an offset + attenuator - then you can use the offset to get into the range. Essentially what you done with the Maths. Seems poor that the useable range is so small though.

Funny as well that the Doepfer seems to be easier to deal with versus higher end VCAs...
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Jason Brock
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PostPosted: Thu Dec 08, 2011 8:34 pm    Post subject: Reply with quote Add User to Ignore List

Dr. Sketch-n-Etch wrote:

The uVCA will allow you to define any response between pure exponential and pure linear, and will give clean 2x unity gain in any mode.


Cool, thanks for the reply. I'm pretty sure I'll be trying one out as soon as they hit the shops.
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matttech
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PostPosted: Fri Dec 09, 2011 7:22 am    Post subject: Reply with quote Add User to Ignore List

flashheart wrote:
Rather than just an attenuator you really need an offset + attenuator - then you can use the offset to get into the range. Essentially what you done with the Maths. Seems poor that the useable range is so small though.

Funny as well that the Doepfer seems to be easier to deal with versus higher end VCAs...


yeah, well i have to heavily reduce the range of the offset knob to give me the precise control that i'm after. otherwise the problem just moves to a different knob

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