Modding the AI003 Looping ADSR to go 0-10V

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patched
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Modding the AI003 Looping ADSR to go 0-10V

Post by patched » Mon Dec 02, 2019 8:18 am

Hey all, I need your :help:

Currently, the AI003 goes between 0-7.5V. This becomes a problem with VCAs that expect 0-10V. Is there any easy way, like switching some resistor, to make this go up to 10V? I have looked at the schematic but can't say I understand much of what it does...

Schematic: https://aisynthesis.com/wp-content/uplo ... 1/adsr.pdf

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Navs
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Post by Navs » Mon Dec 02, 2019 10:55 am

At a quick glance I can't read that schematic, but what I was looking for was a resistor that sets gain on e.g. the output buffer. I imagine that would be the easiest way of amplifying the signal. Maybe ask the designer?

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Post by abelovesfun » Mon Dec 02, 2019 2:10 pm

Not that I am aware of. You need either a scaler module or a different VCA. Euro doesn't have "standards" for such things, so on the negative side - not all things work with each other as one might get in other systems (MOTM, MU). On the plus side, you get stranger circuits, in small part like this one where you can have an ADSR using just a few op-amps and diodes.
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Post by EATyourGUITAR » Mon Dec 02, 2019 3:12 pm

In eurorack some of the doepfer EG or VCA is 0v to +8v. This seems to be more popular than 0v to +10v. A lot of stuff is 0v to +5v. You can definitely whack on another opamp and another PCB but it is a klugde job. You might want another utility module in your rack anyway. That might be better to have them side by side.
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Post by patched » Mon Dec 02, 2019 6:44 pm

Thanks for the answers!
abelovesfun wrote:Not that I am aware of. You need either a scaler module or a different VCA. Euro doesn't have "standards" for such things, so on the negative side - not all things work with each other as one might get in other systems (MOTM, MU). On the plus side, you get stranger circuits, in small part like this one where you can have an ADSR using just a few op-amps and diodes.
Interesting... some forward voltage drop shenanigans going on that makes the voltage levels "hard coded"? I have a very hard time trying to follow the schematics, did you design it yourself or did you draw inspiration somewhere? Would be interested in reading some discussion of how it works :)
EATyourGUITAR wrote:In eurorack some of the doepfer EG or VCA is 0v to +8v. This seems to be more popular than 0v to +10v. A lot of stuff is 0v to +5v. You can definitely whack on another opamp and another PCB but it is a klugde job. You might want another utility module in your rack anyway. That might be better to have them side by side.
Fair enough, my setup isn't very large yet and all scaling utility I have is a dual attenuverter/offset generator, so sadly no way to make the AI fully compatible with the befaco HexVCA atm :( any recommendations for diy scalers with amplification?

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Post by Orgia Mode » Mon Dec 02, 2019 6:57 pm

EATyourGUITAR wrote:In eurorack some of the doepfer EG or VCA is 0v to +8v. This seems to be more popular than 0v to +10v. A lot of stuff is 0v to +5v. You can definitely whack on another opamp and another PCB but it is a klugde job. You might want another utility module in your rack anyway. That might be better to have them side by side.
I think the reason for this is because a lot of popular/cheap op amps like the TL072 clip at 10v with a supply of 12v, but not 'exactly' 10v. So 8v is perfectly safe with just about anyone's crusty makeshift +/-12v psu. :razz:

And yeah, a utility to amplify the output of one module to where you want it may be a better choice than modifying.

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Post by SphericalSound » Mon Dec 02, 2019 7:37 pm

Maybe you can modify your dual attenuverter/offset generator. It should be easy to do it some aplification too, let´s say 1.2x, changin just the last feedback resistor

It´s a diy version? Do you have the schematics?

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Post by Orgia Mode » Mon Dec 02, 2019 7:57 pm

It won't be as simple as changing a few resistors to get the voltage range you want. For example, I have an env generator that has a 6.3v capacitor that is charged and discharged to make the envelope shape, but I amplify the signal at the output. So there are other issues to consider here.
In my case, I amplify it to a range of 0-8v, not 0-10v. A VCA isn't "expecting" 0-10v.
While a VCA may accept that range, any VCA doing its job is still going to work with 0-7.5v.

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Post by patched » Tue Dec 03, 2019 7:26 am

SphericalSound wrote:Maybe you can modify your dual attenuverter/offset generator. It should be easy to do it some aplification too, let´s say 1.2x, changin just the last feedback resistor

It´s a diy version? Do you have the schematics?
Yeah that's a good idea, I have the befaco dual attenuverter. Maybe get one of them to go to x2 would be useful. Here are the schematics (mirrored for some reason...): https://www.befaco.org/docs/Dual%20atte ... sch_V2.pdf
You think changing R2 to 200k would double the range?
Orgia Mode wrote:In my case, I amplify it to a range of 0-8v, not 0-10v. A VCA isn't "expecting" 0-10v.
While a VCA may accept that range, any VCA doing its job is still going to work with 0-7.5v.
I see you, but my problem is that the befaco hexVCA isn't fully open until 10V. This means that it will be very silent at 7.5V when I set it to give a fully exponential response.

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Post by Orgia Mode » Tue Dec 03, 2019 6:11 pm

patched wrote:
SphericalSound wrote:Maybe you can modify your dual attenuverter/offset generator. It should be easy to do it some aplification too, let´s say 1.2x, changin just the last feedback resistor

It´s a diy version? Do you have the schematics?
Yeah that's a good idea, I have the befaco dual attenuverter. Maybe get one of them to go to x2 would be useful. Here are the schematics (mirrored for some reason...): https://www.befaco.org/docs/Dual%20atte ... sch_V2.pdf
You think changing R2 to 200k would double the range?
Orgia Mode wrote:In my case, I amplify it to a range of 0-8v, not 0-10v. A VCA isn't "expecting" 0-10v.
While a VCA may accept that range, any VCA doing its job is still going to work with 0-7.5v.
I see you, but my problem is that the befaco hexVCA isn't fully open until 10V. This means that it will be very silent at 7.5V when I set it to give a fully exponential response.
oooh..it has an exponential response. That extra 2.5v will make all the difference then.

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Post by SphericalSound » Tue Dec 03, 2019 8:37 pm

Yeah, R2, R3, R10 or R13. Any of them. Not sure if you have to do 200k or 47K for the double. never remember these ecuations. Just look for inverting opamp

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Post by Orgia Mode » Tue Dec 03, 2019 8:44 pm

SphericalSound wrote:Yeah, R2, R3, R10 or R13. Any of them. Not sure if you have to do 200k or 47K for the double. never remember these ecuations. Just look for inverting opamp
Don't use R3 or R13. You'll end up doubling the offset too.

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Post by EATyourGUITAR » Wed Dec 04, 2019 10:10 am

https://www.befaco.org/docs/Hexmix_VCA/ ... ematic.pdf

on the hexmix vca you can decrease R10 as a bit of a fix. it is not ideal however. the ideal way would be to put all the log and exponential converters into a sim to get the best resistor values to change the range of cv to 0 to +7.5v
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Post by Navs » Wed Dec 04, 2019 10:50 am

abelovesfun wrote:Not that I am aware of.
What about IC1D, what is its function - a non-inverting buffer? Could it be modified/reconfigured to provide gain?

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Post by Orgia Mode » Wed Dec 11, 2019 2:48 pm

Navs wrote:
abelovesfun wrote:Not that I am aware of.
What about IC1D, what is its function - a non-inverting buffer? Could it be modified/reconfigured to provide gain?
I saw that too, but I also noticed it has what looks to be the attack segment on the inverting input so I was a little skeptical. It may still be worth a try, little by little.

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Post by abelovesfun » Wed Dec 11, 2019 8:28 pm

TBQH - if you want the AI003 to do 0-10V, I think the best way would be to add a separate scaler circuit to the output. Most Euro VCAs are 0-5V, and this module isn't designed to do 0-10V.

If it were me, I would add something like this https://www.stereoping.com/eurorack-diy ... r/?lang=en

Since all the PCBs are parallel to the panel, you can usually go deeper by adding a daughter PCB.

Or add a separate scaler module - they are VERY useful in a format that doesn't have "standards" the way an MU or MOTM system does.

Sorry I can't be of more assistance - I fully support stock builds, but can't afford to spend time walking through custom modifications (and I'm trying to prep for the shop to stop shipping while I'm on vacation - I leave Friday).
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Post by patched » Thu Dec 12, 2019 9:53 pm

abelovesfun wrote:If it were me, I would add something like this https://www.stereoping.com/eurorack-diy ... r/?lang=en
That looks like something that would be very useful, may also be a good project to learn how to make a homemade front plate :)

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