Adding CV to existing things/mod Nebulophone into a eurorack module.

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foot
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Adding CV to existing things/mod Nebulophone into a eurorack module.

Post by foot » Fri Jul 24, 2020 1:46 pm

Hey all!
Just getting my start into the Eurorack world (recently picked up a Neutron, and DIYing a skiff). I had the thought of trying to modify some of my existing noise makers to allow CV control, specifically the Bleep Labs Nebulophone you can see here:
https://bleeplabs.com/product/nebulophone/
I built mine using their kit, and had the thought that if I can CV control some of its parameters that I may be able to use it as a module, or at the least as a semi-modular like the neutron. I know about using vactrols, so I’m going to make up one and try it. Anyone have any experience doing something like this ? I’ve built many guitar pedals, but nothing in the eurorack realm (as of yet), so CV etc is pretty new to me.
Thanks!
-Kevin

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Eloc
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Re: Adding CV to existing things/mod Nebulophone into a eurorack module.

Post by Eloc » Fri Jul 24, 2020 3:04 pm

Well, looking at the schematic, the three pots are used to send a voltage between 0-5V to the ATmega. So if you want to keep it simple you could send your CV to those same pins with some input protection (using a zener diode or a couple of 1N4148 diodes for example and a resistor) and then you would have CV control over those parameters.

If you want to go a little more complex, you could scale and offset you're CV and sum it with the voltage from the pots using a couple of op-amps so that you could have a CV attenuator and use of full +/-5V CV etc

You could probably also do something with transistors to get gate/trigger control of the 'Arp Switch', 'Glide' and 'Shift' as those pins are just shorted to GND or left floating

Depends how much control you want. And also I don't know anything about the Nebulophone so I don't know how useful any of those would be

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StrongWrong
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Re: Adding CV to existing things/mod Nebulophone into a eurorack module.

Post by StrongWrong » Fri Jul 24, 2020 4:07 pm

This video shows a sync mod for the Neb and a Volca...might work for modular... :hmm:

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foot
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Re: Adding CV to existing things/mod Nebulophone into a eurorack module.

Post by foot » Fri Jul 24, 2020 6:52 pm

Eloc wrote:
Fri Jul 24, 2020 3:04 pm
Well, looking at the schematic, the three pots are used to send a voltage between 0-5V to the ATmega. So if you want to keep it simple you could send your CV to those same pins with some input protection (using a zener diode or a couple of 1N4148 diodes for example and a resistor) and then you would have CV control over those parameters.

If you want to go a little more complex, you could scale and offset you're CV and sum it with the voltage from the pots using a couple of op-amps so that you could have a CV attenuator and use of full +/-5V CV etc

You could probably also do something with transistors to get gate/trigger control of the 'Arp Switch', 'Glide' and 'Shift' as those pins are just shorted to GND or left floating

Depends how much control you want. And also I don't know anything about the Nebulophone so I don't know how useful any of those would be
Thank you so much for looking into this so deeply!! What I think I’ll do is try all of these, and see if it’s worth while or not, and then transition it to a eurorack plate. I’ll definitely post my results!

foot
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Re: Adding CV to existing things/mod Nebulophone into a eurorack module.

Post by foot » Fri Jul 24, 2020 6:53 pm

StrongWrong wrote:
Fri Jul 24, 2020 4:07 pm
This video shows a sync mod for the Neb and a Volca...might work for modular... :hmm:

Oooo, that looks interesting! I’ll check it out thanks!

foot
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Re: Adding CV to existing things/mod Nebulophone into a eurorack module.

Post by foot » Mon Jul 27, 2020 1:13 pm

Tried messing with the ARP, and WAV knobs using a patch cable coming from the Neutron LFO and 2 4148 diodes with limited success. Mostly just made noises in time with the LFO rate. These knobs have a pretty specific function where they change between completely different sounds (and speeds) depending on where you are in the travel of the pot, so I'm wondering if it needs to see a very specific voltage to work right.

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Eloc
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Re: Adding CV to existing things/mod Nebulophone into a eurorack module.

Post by Eloc » Mon Jul 27, 2020 2:46 pm

In addition to the two diodes, you will need to at least use some resistors to passively sum the voltage from the pot and your CV together, or preferably use an op-amp to actively sum those two voltages together. If you just inject a voltage directly into the ATmega you could be shorting your CV directly to GND or 5V depending where the pot is set.

If the pots select between completely different sounds (like a software based rotary switch) I would personally actively sum the CV (through a pot as attenuator) with the original pot's voltage. Then you can dial in the CV amount and use the orig pot as the 'initial' setting. Something like this:
DC Sum.JPG
Theres a little DC mixer PCB you can get Ken Stone's 'CGS04' from various places that has one of the circuits on it
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