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Scaled Voltage Reference 1V and 83,3mV steps
MUFF WIGGLER Forum Index -> Music Tech DIY  
Author Scaled Voltage Reference 1V and 83,3mV steps
Haralds:Werk
This module provides high precision CV outputs in 1V (octaves) and 83,3mV (halves) steps. The 1V output goes from 0 to 8V. The 83,3mV steps goes from -5 to plus 5 steps (halves). This module is thought for all who are missing octave switches in some modules. Especially in VCO. With this module you can switch octaves and halves as well.
Specs and features
High precision output 0-8V in 1V steps (octaves)
High precision output in 83,3mV steps, +/- 5 steps (Halves)
Runs on +/-15V and +/-12V

The Documentation for download can be found in my website.



The precision voltage is derived from the REF102. The negative voltage is provided with the INA105. It is crucial to match the resistors in the voltage dividers as good as you can. The outputs of the voltage dividers are buffered to avoid loading of the dividers. The resistors around the OpAmps must be matched as well. The one volt and the 83,3mV steps are added together with IC4A. The three outputs are individual buffered.



Haralds:Werk
Just added the Gerber files for this module to the site.
TheSlowGrowth
I see you used "in the loop" protection resistors on the outputs. This can lead to ringing on transients and to instability when capacitive loads are connected to the output. Have you measured the transient response of the circuit when a long cable is attached (or better: with a cap to GND)? It may be a good idea to add compensation caps between the opamp outputs and the inverting inputs to compensate this.

Also it may be a good idea to add a CV input to the mixer section, for those that don't know how to do it.

EDIT: One more question: The load on the reference is quite low. Could it be enough to feed both resistor strings from the same reference? This would save one of the references.

Otherwise this is a really cool circuit that will be very helpful to many!
MickMad
This is excellent for tuning VCOs! Good job smile
roglok
Thanks a lot for sharing! I second the motion that a CV input would be a useful addition, especially since there is a spare opamp and multiple outputs.
Haralds:Werk
TheSlowGrowth wrote:
I see you used "in the loop" protection resistors on the outputs. This can lead to ringing on transients and to instability when capacitive loads are connected to the output. Have you measured the transient response of the circuit when a long cable is attached (or better: with a cap to GND)? It may be a good idea to add compensation caps between the opamp outputs and the inverting inputs to compensate this.


Yes, I know that. If I have to design for a Eurorack module I surely have added those capacitors. I am running an all banana system, so long cables with capacitive load are not an issue here. BTW. when starts a cable to be "long"?

TheSlowGrowth wrote:
Also it may be a good idea to add a CV input to the mixer section, for those that don't know how to do it.


Yes, I already have one with CV input and negative and positve V/Oct output. Not yet published though.

TheSlowGrowth wrote:
EDIT: One more question: The load on the reference is quite low. Could it be enough to feed both resistor strings from the same reference? This would save one of the references.


This might work. There are some other points to save monye as well. You can replace the INA105 with an OP27 and trimming or omit the buffers after the switches and the following OpAmps. But I want to stay save and when building one offs part count and costs are not a big problem. The faceplates are more expensive.

TheSlowGrowth wrote:
Otherwise this is a really cool circuit that will be very helpful to many!


Thanks
Haralds:Werk
MickMad wrote:
This is excellent for tuning VCOs! Good job smile


Thanks. And I use it a lot in the calibration process for VCO's and VCF's.
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