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Analogue outputs (0-10) suitable to control Eurorack?


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That's not an easy one for the Zero88 chaps to answer - after all these products are designed to drive thyristor dimmers not analogue synths!

So you might have to make your own assessment of the electronics unless there is another forum member who has tried this.

Is there a specific desk you have in mind?

Often the output drive will be an op-amp follower with diode as shown below. This will give a low-impedance output which will give a good quality control signal that might suit your application:

image.png.edf4e70289e1af210b3ebe588b5503e3.png

Some desks, like the Mk1 Level series use a simpler circuit that has a higher impedance output. However this might still be fine.

You'll have to do your own investigations/experiments with the kit you have. If there is a specific desk you have in mind, then the Zero88 guys might be able to help you out with the specific output drive circuit used.

One issue you might have is needing to common the 0V of the lighting desk and the synth. This may or may not be ok. For example MIDI uses an optoisolator to ensure there is no common electrical path between each musical instrument. I'm not familiar with synth CV electronics so this may or may not have a similar requirement and if it does, you will need some interface electronics.

Good luck!

Kevin

 

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Thanks for you prompt answer – I have Sirius 24. I did some preliminary testing and it looks to be working fine. The input impedance on the modules I am using is 100kΩ. The common (0V) is now shared between Sirius and synth through the patch cables (not connected to chasis or ground) - I might use a separate thicker wire for that later. 

One thing that I run into is that I have slight offset on voltage outputs of Sirius - insted of 0 I get 0.24V. Any ideas what might be causing this or if it is whithin specs?

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52 minutes ago, hlmm said:

One thing that I run into is that I have slight offset on voltage outputs of Sirius - insted of 0 I get 0.24V. Any ideas what might be causing this or if it is whithin specs?

Probably within spec. Likely to be caused by that series diode and that the output opamps are probably quad LM324 single rail types so can't go all the way down to 0V. In lighting control this slight offset would be masked by dimmer preheat for tungsten filaments.

If you're using as the CV for a synth, I take it you would be using this more around middle-C so the CV is likely to be around the 2V-8V region? Although I'm intrigued how you use a lighting desk that "fades" channels with a synth - some kind of theremin emulator?!

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5 hours ago, kgallen said:

If you're using as the CV for a synth, I take it you would be using this more around middle-C so the CV is likely to be around the 2V-8V region? Although I'm intrigued how you use a lighting desk that "fades" channels with a synth - some kind of theremin emulator?

I took a picture of the board to make sure we are talking about the same thing. It would be nice if I could get them to 0V as I was hoping to use it also for level control (through Voltage Controled Amplifier). I wonder if simply placing another diode in series with first one could drop the voltage down (?). 

Regarding the use of this: I have several ideas I would like to try, one of them is to hook it up to Mr Rossum's Assimilator (it actually even has 24 CV inputs). But that is just an example. In a way, sound or music develops through time in the same way as light scenes.

I stumbled upon this desk rather by accident, liked the look of it and was thinking "What could I do with it". I have to say it is very nicely designed and built. Plus the fact that I can find people giving me tips on its maker's website forum after all those years is amazing. Thank you!

s24-1.jpg

s24-2.jpg

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Yes, we're talking about the same piece of circuitry.

From the left of your picture, output terminals, diodes (1N4148 or similar), then there is a transistor and resistor pack (base current limit?), then the row of chips is a mix of LM324 quad op-amps and 4051 8-channel analogue demuxes. Fairly standard time-division multiplex output stage from a processor-based desk outputting analogue control channels.

There is that transistor in there and I don't have an example schematic with that component in the mix. If you ask @KWR88 (Keith) really nicely he might provide that sheet of the Sirius schematic so you can see what's going on.

However since you're after this golden 0V output then you are probably going to need to design/implement an offsetting circuit. It sounds like you only need one channel of CV? An op-amp with an offset comparison voltage to take out that 240mV you're seeing. You will need +/- supply voltage rails so you can generate -240mV and your op-amp can drive down to 0V. Analogue electronics is not my speciality but if you google around the above ideas you will find "stuff". Come back and share here if you want. It's the sort of thing you could implement on a piece of Veroboard, no need for a custom PCB.

(Random point - your desk was built in March 1996, but those 4051 chips have a 1997 date code (9735, 35th week 1997), so they've been replaced at some point).

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17 minutes ago, KWR88 said:

And yes the initials on that label are mine, 😀 

Fantastic! I will be looking up the initials on the made/test label in all of my kit now and hope I find some "KR"s 😄

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Unbelievable... message sent.

Here is the device after the modifications - CV outputs ported to front on 6.3mm jacks (vertically aligned with faders in group of 6) and added wood panels (so it can be stored in vertical position).

 

s24cvout.jpg

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