AOUT NG : only half expected voltage in bipolar

[robotfunk]

Can anyone confirm that the original AOUT module does actually output +/- 5V?

[latigid on]

Bumping this topic. As I am interested in re-routing the AOUT_NG board I would like to rectify this issue at the same time. An ideal situation would have unipolar mode from 0 to 10 V and bipolar as -5 to +5 V. What can be done? Should the offset control also include a buffer stage?

 

[NorthernLightX]

Last month illogik built my redesigned AOUT module and found some bugs in the PCB. While discussing possible solutions we came to the conclusion that it's probably much easier to have the AOUT only output unipolar 0 to 10 volt, and design a simple -5v level shifter board that can be used as an add-on (or separate module with hands-on access to the level shifting) to shift the output to -5 to +5 volt where needed.

 

Things to consider are:

- not a lot of equipment actually makes use of negative voltages

- equipment that needs bipolar CV input can be retrofitted with a fixed level shifter at the input to make it compatible with your other modules

- negative voltages can be used for CV modulation purposes (modulate one CV source with another) so it's certainly not useless

[latigid on]

Here is a different approach: inverting amp followed by an inverting mixer/unity gain buffer with switchable +5V offset

 

 

 

Two more op amps but probably a better design decision. A positive/negative voltage swing is often used to sweep above and below a set control e.g. an LFO modulating a filter frequency. As the new MBCV application will generate LFOs I think full scale CVs are still widely applicable.

 

 

Edited December 18, 2013 by latigid on

[NorthernLightX]

Two comments:

 

1. Do I see correctly that you take the +5v to shift the levels from the power rail? Is that precise enough? Maybe adding a precision reference is a better idea?

2. I would like to see the level shifter as a separate PCB, so MAX AOUT users could also benefit from it.

 

I agree with the usefulness of full scale CV for modulation purposes, like I wrote earlier :thumbsup:

[latigid on]

No, I have an offset wired from the +12 V buss, divided through a trimmer. The offset is mixed through an op amp summer, so load changes shouldn't be too much of an issue. This also uses a more stable inverting amplifier that needs to be inverted again for correct signal phase/polarity. The perfect place to introduce an offset voltage!