Moog Werkstatt: adding a VCA CV input jack

I’ve already blogged about the reasons you might want to mod your Werkstatt, and have posted a list of mods here, so to complete the VCO/VCF/VCA trio, here’s the VCA input at last!

How it Works

This is a very simple mod, and just replicates the existing patch header input. All you need is a 10k resistor, some wire, and a jack socket.

Werkstatt VCA CV input mod schematic

Werkstatt VCA CV input mod schematic

The easiest point to solder to on the board is JMP62. This is located just above the Decay pot. This point is where incoming VCA CV signals are passively mixed. It’s probably best to solder the new parts to this jumper on the underside of the PCB, which you can see on the photos of the wiring:

Werkstatt VCA input JMP62 location

Werkstatt VCA input: JMP62 location

Werkstatt VCA input JMP62 on underside of PCB

Werkstatt VCA input: JMP62 on underside of PCB

Werkstatt VCA input soldering

Werkstatt VCA input: soldering

Werkstatt VCA input panel

Werkstatt VCA input: side panel


10k resistor
Jack socket

Further thoughts

As the Werkstatt already has a pin for VCA modulation on its patch header, you might think this mod seems less immediately useful than the VCO or VCF CV inputs. The main issue is that there is no way to simply switch off the Werkstatt’s own VCA – you can select EG shaping, or ‘on’ for drones, but you can’t bypass it for use with an external envelope. What does this mean in practice, and why bother adding a CV input for it?

If you’re using the Werkstsatt with a modular, you’ll have more interesting envelopes than the attack-decay type on the Werkstatt. You might well also have something that will give an offset. It should be possible to use a negative offset to counteract the Werkstatt’s ‘on’ VCA CV, and mix in a more interesting envelope signal; setting the Werkstatt’s VCA to ‘on’ and feeding this CV input with that mix will then allow you to contour the Werkstatt’s VCA as you like.

It would also allow you to use the Werkstatt’s own patchbay to feed the VCA with its LFO, and simultaneously blend another LFO in with this CV mod. Mixing different LFOs gives a lot of movement to a sound, and can be very enjoyable to play with. You can also sequence the VCA level this way, while retaining other modulation via the pin header.

As always, my mods are not definitive – the best thing to do is experiment, and adapt, and find out what works for you and this excellent little synthesizer. Enjoy!

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9 responses to “Moog Werkstatt: adding a VCA CV input jack”

  1. Hans says :

    Why have you choosen to use a resistor? This input doesn’t differ from the one the Moog branded Expander, does it? I checked some images and this expander doesn’t has any components other than connectors soldered. So why not just solder the jack connector directly on the pcb side of the patch panel? Hope to hear from you, can’t wait to get soldering 🙂

    • synthnerd says :

      Hi! This is a very good question, and I think the answer is buried in one of these blog posts… You’re right, it is possible to just solder a jack socket to the patch header without a resistor. However, if you do this, anything you plug in to the socket will not be isolated from any connections you make with the patch header. This would mean you might short two outputs directly together, which isn’t recommended. If you attach Moog’s expander board, that covers up the small patch header, replacing it with jacks. My mods don’t replace the existing patch header, they work alongside it. With the resistor in place, soldered to the point I suggest, there is no danger of shorting things together, and all the inputs work side by side. You can use my mods *and* the onboard patch header just as usual.

      Hope that helps 🙂

      • jasper komassa says :

        Finally did the gate mod and it works great! I’m wondering if adding this VCA input would be fun to do even though I have the patch header? Would it add more functionality with patching?

      • synthnerd says :

        Glad to hear it! Personally, I find the modded inputs more convenient, but it’s a matter of personal taste I think. Lots of people would be perfectly happy with just the patch header.

  2. Hans says :

    That helps a lot! Very clear answer, thanks.

  3. jasper komassa says :

    Finally did the gate mod and it works great! I’m wondering if adding this VCA input would be fun to do even though I have the patch header? Would it add more functionality with patching?

  4. Timon Kurz says :

    Hi Synthnerd 🙂 First thank you a lot for your work. I just did the CV and the Gate mod and i love it! I recognise some very high pitched noise as soon as i plug a gate input in. Would it be possible to use a bypass cap or a cap in any other configuration to get rid of the high pitch noise? thank you and cheers, timon

    • synthnerd says :

      Glad you like the site! Lots of people have found my Werkstatt Gate mod very useful, but you’re the first to mention noise. Unfortunately, noise comes in many flavours, and you’re going to need to do some logical problem-solving to find out exactly what’s causing it before you can implement a solution. A buzz when you connect the Gate input sounds like you might have a ground loop problem. There are lots of articles on the internet about ground loops – I can’t give you a definite answer on this though as it’s going to depend on how you have everything set up.

      Here’s a link to Sound On Sound’s search results for ground loop prevention:

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