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midiDAC calibration issue
MUFF WIGGLER Forum Index -> Oakley Sound Systems  
Author midiDAC calibration issue
jean_schön
Hi,

I'm trying to trim V/oct, and when i send midi note 127, the highest voltage i can get on pin 1 on U1 is -9.7 V. what might be wrong?

i've checked all the resistors around U1 and U8. i'm getting +/- 15 V to the module.
Synthbuilder
Are you definitely sending note number 127? For some reason a lot of modern controllers don't go up that high. Check with midiox or record the note into a DAW and see what note the controller is actually sending.

Tony
jean_schön
Yes I sent it through midiOx, which says I’m sending note G10. I’m using an old Alesis quadrasynth as midi controller -> midiOx -> midiDac. I also tried the app sendmidi and explicitly stated send note 127. Still only 9.7 volts. And the lowest note yields 2.5 volts!
jean_schön
Sorry that might be wrong, FL Studio says the note is G8. i'm gonna try to transpose with midiOx..

edit: Yes, i transposed and now i'm getting the correct values. thanks!
jean_schön
Another question though:

I'm calibrating this midiDAC as the first thing in my system. Since i do not have a calibrated VCO, how should i go about this? Should i just set midi note 127 to produce -10.58 V and then plug in my VCO and do the INIT calibration with that, or do i calibrate the midiDAC to actually produce 1 Volt per octave out of the pitch jack, which would entail tweaking both v/oct and init trimmers until this is obtained while measuring the pitch jack?

if i just set the v/oct to -10.58 i do not get 1 volt per octave, the C's rather produce 9.9V. 8.8V, 7.7V, 6.6 etc...

Sorry if these are dumb questions but i'm new to this and couldn't quite get the hang of this.
Synthbuilder
jean_schön wrote:
if i just set the v/oct to -10.58 i do not get 1 volt per octave, the C's rather produce 9.9V. 8.8V, 7.7V, 6.6 etc...

Something has gone wrong here.

Before you measure pin 1 of U1 make sure that the tune pot's wiper voltage is 0.00V. Then with note G9 you should get 10.58V at pin 1 of U1 (or 10.00V with C9). INIT does not affect either the wiper voltage or the voltage on pin 1 of U1. However, INIT, along with TUNE and V/OCT, affect the voltage that is present on the midiDAC's PITCH (Key CV) socket.

So long as pin 1 on U1 is doing the right thing then you are fine. To check this, play down the keyboard. You should be finding that the voltage on pin 1 is going down one volt per octave. C9 = 10V, C8 = 9V, etc. It won't be perfect since neither the 12-bit DAC used in the midiDAC or your voltmeter is perfectly accurate, but it probably should be within +/-10mV. The lowest note, midi note number 0, at C-1 is 0V.

If this is all correct then you can set INIT to suit any other midiCV convertors you may have. I use the standard of C4 (midi note number 60) = 5V. So INIT is basically set so that PITCH follows the voltage on pin 1 of U1.

Tony
jean_schön
Synthbuilder wrote:
jean_schön wrote:
if i just set the v/oct to -10.58 i do not get 1 volt per octave, the C's rather produce 9.9V. 8.8V, 7.7V, 6.6 etc...

Something has gone wrong here.

Before you measure pin 1 of U1 make sure that the tune pot's wiper voltage is 0.00V. Then with note G9 you should get 10.58V at pin 1 of U1 (or 10.00V with C9). INIT does not affect either the wiper voltage or the voltage on pin 1 of U1. However, INIT, along with TUNE and V/OCT, affect the voltage that is present on the midiDAC's PITCH (Key CV) socket.

So long as pin 1 on U1 is doing the right thing then you are fine. To check this, play down the keyboard. You should be finding that the voltage on pin 1 is going down one volt per octave. C9 = 10V, C8 = 9V, etc. It won't be perfect since neither the 12-bit DAC used in the midiDAC or your voltmeter is perfectly accurate, but it probably should be within +/-10mV. The lowest note, midi note number 0, at C-1 is 0V.

If this is all correct then you can set INIT to suit any other midiCV convertors you may have. I use the standard of C4 (midi note number 60) = 5V. So INIT is basically set so that PITCH follows the voltage on pin 1 of U1.

Tony


This is the thing, when the wiper voltage is 0 V, and i tweak the v/oct trimmer to have G9 = -10.58 V, i get 9.9 V at C9, 8.8 at C8, 7.7 at C7, etc etc. lowest note gives me -1.4 V.

any clue as to what might be causing this?
Synthbuilder
Is the bend depth pot set to its minimum when you are measuring pin 1 U1? It shouldn't make much of a difference if the device is working properly but it is best if the bend pot is set to zero. What's the voltage on pitch bend socket's signal lug? It should be very close to 0V. If not you may have a problem with the resistor values R23, R24, R25.

What about the voltage on pin 1 U12? This is the raw pitch voltage from the DAC. It should not ever go negative - although it won't be 1V/octave. Note G9 will produce a voltage of around 10V. Midi note 0 (C-1) should produce 0.00V.

Tony
jean_schön
bend depth is set to minimum, bender socket signal lug is 0.0028 V.

pin 1 on U12 gives me 8.9 V from G9, and lowest note gives me 3.0 V!
Synthbuilder
jean_schön wrote:
pin 1 on U12 gives me 8.9 V from G9, and lowest note gives me 3.0 V!

Do you know what the midi number of your lowest note is? Is it C-1 ie. midi note 0?

Pin 1 of U4 should closely follow the voltage seen at pin 1 U12. If not there may be a problem with U5.

Do you have a scope? If so, have a look at the waveform on pin 1 of U12. It should be a constant voltage once you have pressed a note. There should not appreciable AC content - that is, you shouldn't be seeing any ripple on top of the DC voltage.

Tony
jean_schön
Hey,

thanks for all your help. It was my midi controller that was wrong, and midiOx told me the wrong midi notes for it. when i sent midi out through my DAW, all values are now correct.

thank you again!
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