Good tutorials for CV controlled builds.

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Pahat_Kengat
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Good tutorials for CV controlled builds.

Post by Pahat_Kengat » Thu Apr 01, 2021 2:59 pm

Hello,

I feel like this is one of "those" topics that get posted in periodic cycles, but a quick search didn't bear much fruit, so here we are. I've recently been getting into DIY sound electronics, and would like to make the move from guitar pedals into more modular-oriented gear. I can find vero based tagboards for simple filters and such, but good 101 tutorials for building DIY modular gear seems to be hard to come by. Like guides going through how to build units that use and function with CV. I'd imagine finding resources is also made difficult by learning the ropes while also learning DIY vocabulary and lingo in a second language.

For example, currently I'm planning to build a "filter in a box" to go with electric organs. So in essence, a MS20 style HP and LP filters with cut-off and resonance controls and a variable shape LFO in one pedal sized package, with a very straight forward signal path. I've found schematics for both the filter and the LFO and have a general idea how to go about designing the lay-out. What I have trouble with is figuring out and understanding is how to include simple CV controllable elements into the equation, like CV in's for cut-off, resonance and LFO rate, and such. A trigger in for the LFO itself could be handy, but not necessary.

If anyone has any good online resources for CV building blocks to share, I'd be incredibly grateful! And while we're at it, any tips are also more than welcome. Thanks to everyone willing to help in advance! :party:

Pahat_Kengat
Learning to Wiggle
Posts: 27
Joined: Fri Dec 28, 2018 4:35 pm
Location: Helsinki

Re: Good tutorials for CV controlled builds.

Post by Pahat_Kengat » Thu Apr 01, 2021 3:00 pm

Here's a few examples of the issues I'm having with this particular project.

Image

For example with the filter I think I can locate the CV elements and think I understand how to build them as well.

Image

The LFO on the other hand doesn't seem to have CV controls on the board as it is, and I'm trying to learn how to implement elements that enable controlling the LFO rate with external CV.

...like I said, trying to word these things with limited vocabulary is quite challenging. Hopefully my point comes across regardless of this. :roll:

Sources for both tagboards:
http://guitar-fx-layouts.42897.x6.nabbl ... 31433.html
https://ua726.co.uk/2012/12/08/korg-ms- ... pboarding/

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joem
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Re: Good tutorials for CV controlled builds.

Post by joem » Fri Apr 02, 2021 4:25 pm

I'm not sure there are any general rules as far as adding CV control to something. You usually have to understand the circuit in order to know how to add CV control.

Take for instance the example of a control that currently uses a pot and you want to add CV control... That pot might be in use as a voltage divider, and if that's the case, replacing it with CV control is easy-ish. Adding CV control and keeping the pot control in a voltage divider case is easy-ish but more complicated than just replacing the pot (and you have to decide how you want them to work together -- do they add their voltages together? Or do you want the pot to become an attenuator when there's CV control?). If the pot is being used as an attenuator, replacing it with CV control will probably be more complicated and you will probably need to understand more of the circuit than just the pot-related stuff. If the pot is dual-gang, it's going to be very different to implement CV control when compared to a single-gang pot, no matter how the pot is being used. I'm sure I'm missing some cases, too, but hopefully this helps illustrate a bit how it's often not as simple as "I need to plug my jack in here in order to add CV control".

If you provide schematics instead of stripboard layouts, it'll make it easier for people to help, too, btw. Stripboard layouts are a bit like handing someone a math problem written out in a language (like in English: "five times x squared plus six times x plus 33 equals zero") whereas the schematic is a like the math problem written numerically (like "5x^2 + 6x + 33 = 0"). When parsing the language version (which might not be a language you're super familiar with) it's harder to immediately recognize that it's a quadratic equation.

Pahat_Kengat
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Re: Good tutorials for CV controlled builds.

Post by Pahat_Kengat » Sat Apr 03, 2021 7:47 am

Hey,

thanks for your response, it was very helpful! Next step is to get acquainted with CV and these different solutions. Right now I'm thinking I'll look into CV input overriding the pot completely, as that sounds like an easier solution for a beginner.

Thanks for the heads up on the stripboard layouts, as well! So far vero has been the base from which I've been learning, sort of building and soldering by numbers with limited understanding of what's going on on the board. I think this also contributes to the wording of my original post, as I was kind of imagining there being a combination of components that together turn a pot-based build into a CV registering build. Getting familiar with schematics and their own language is another thing to get familiar with.

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joem
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Re: Good tutorials for CV controlled builds.

Post by joem » Mon Apr 05, 2021 4:51 pm

Pahat_Kengat wrote:
Sat Apr 03, 2021 7:47 am
Right now I'm thinking I'll look into CV input overriding the pot completely, as that sounds like an easier solution for a beginner.
If the pot is being used as a simple voltage divider, then yeah, it should be easy. I drew up a quick little mspaint diagram to show how:
simple-cv-addition-for-voltage-divider.png
In this image, if the original circuit is connected like the way the pot is in this image (ignoring the jack and the green and purple connections) and the voltage on the pot is a constant voltage (there isn't a signal running through it), then adding the jack like in this image and permanently breaking the blue connection will do the trick. Note how the SWITCH and the TIP are shown on the jack... that shows that it's a jack where the SWITCH pin is normally connected to the TIP pin, and when you insert a cable it breaks that connection. This is what allows the original signal (the WIPER pin from the pot) to pass through to the TO CIRCUIT bit when no cable is inserted, and it's why you need to break the original blue connection -- the jack's connection replaces the blue connection.

As easy as this is, it's still a good idea to understand the circuit to be able to tell if the pot is being used as a voltage divider, and to tell if the voltage it's dividing is a constant voltage or if it's a signal voltage (which means it's acting as an attenuator for the signal). And to tell what voltage range the pot normally outputs. All important considerations when wanting to inject an external voltage (your CV input). And this is to say nothing of any potential impedance matching issues. But don't let this stop you from experimenting, as long as it's not an irreplaceable circuit!

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