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Modding the AI003 Looping ADSR to go 0-10V
MUFF WIGGLER Forum Index -> Music Tech DIY  
Author Modding the AI003 Looping ADSR to go 0-10V
patched
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/uploads/2016/11/adsr.pdf
Navs
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?
abelovesfun
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.
EATyourGUITAR
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.
patched
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 smile

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?
Orgia Mode
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.
SphericalSound
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?
Orgia Mode
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.
patched
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%20attenuverter/Atenuverter_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.
Orgia Mode
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%20attenuverter/Atenuverter_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.
SphericalSound
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
Orgia Mode
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.
EATyourGUITAR
https://www.befaco.org/docs/Hexmix_VCA/Hex_Mix_VCA_V4_Schematic.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
Navs
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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