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midiDAC V/OCT setup question
MUFF WIGGLER Forum Index -> Oakley Sound Systems  
Author midiDAC V/OCT setup question
Awazleon
Hello guys,

Just finished my first module "midiDAC" and fortunately it works from the first start. I'm very happy with that. Thx to Oalkey and Tony for the nice builder guide and the PCB quality It's peanut butter jelly time! It's peanut butter jelly time!

Now I'm doing the calibration and I would like to raise a fact and try to get answer :
When I calibrate the V/OCT by following the Tony instructions, I get -10.58V form pin 1 of U1, while I get 10.61V form the Pitch out jack when playing a G8 from my dawn.
If I play a C8 from my dawn, I get exactly -10v from pin 1 of U1 while I get 10,03V from Pitch out.
So, why I always have 0,03V difference between both test points ?
Is there better to calibrate by using the Pitch out ? I mean that in that case, I'll setup the V/OCT to get eg. 10V from Pitch out by playing the C8 ?

Thx in advance
Have a nice day

Pascal
Synthbuilder
Awazleon wrote:
I get -10.58V form pin 1 of U1, while I get 10.61V form the Pitch out jack...


The pitch out is not just the voltage on pin 1 U1 inverted. It also has the offset voltage applied from the INIT trimmer. It is the INIT trimmer that sets the difference in voltage between pin 1 U1 and the pitch output socket. Right now, you have a 0.03V difference but tweak the INIT trimmer and you'll see that difference change.

It is the INIT trimmer that sets the range over which the midiDAC's output will travel. But V/OCT should be set first before tweaking INIT.

Tony
Awazleon
Tony,

I understand now the purpose of the Init trimmer... d'oh!
Many thx for that.

Have a nice day and Merry Christmas to you w00t

Pascal
Awazleon92
Hello Tony,

I come back to this topic because I have an issue with my MidiDAC.
I decided (because some of my modules are 2 years old) to do a new setup of the MidiDAC, TSL and VCO.
Guess what : I play C8 as higher note (ok, I can play G8 but it's easier with C8 = 9V) and discovered on pin 1, U1 that I get more than -14Vcc
When I play a C3, I get around -7Vcc.

I guess that something failed into my MidiDAC. FYI, I also discovered that my PSU was delivering more than +/-22Vcc and that since some months. Now it is fixed and deliver +/-15.5Vcc.
Do you think that 22Vcc broke something ?
Do you have any advice ?

Have a nice day
Synthbuilder
Awazleon92 wrote:
Do you think that 22Vcc broke something ?


Quite possibly. That's 44V across the op-amps which is well above their maximum operating voltage of 36V.

The voltages you are measuring on the midiDAC are controlled by a voltage reference, U3. The +5V from this chip should not change with supply voltage. Measure pin 6 of U3 to make sure it is still reading exactly 5.00V. If not then U3 may well be damaged. Likewise pin 1 of U2 should be -5.00V. Pin 1 should always be the inverted voltage of the output of U3 - if not then U3 maybe damaged.

Tony
Awazleon92
Hello Tony,

You're probably right because I get +7.22V pin 6 of U3 and -7,22V pin 1 of U2.
I'll order a new REF-02 and keep you posted.
Thx for your help

Have a nice day
Pascal
Awazleon92
I changed the REF02 by a new one and got the same results. I still have around 7,25Vcc on pin 6 and -7,25Vcc on pin 1 U2.
I had a look on the schematic and can't find which other component can influence the REF02 or at least can add this extra voltage excepted the LT1013 which is in the out of the REF02.
Any suggestion ?

Have a nice day
Pascal
Synthbuilder
Do you have another voltmeter you can try? The output of a working REF-02 is 5.00V and nothing should be able to change that.

One other thought comes to mind. I have a voltmeter that starts to give the wrong results when the battery gets low. It has a battery low warning indicator but it gives the wrong readings even before the battery low light comes on.

Tony
Awazleon92
Tony,

When you think your best DVM friend will stay forever with you... and suddenly you discover that it is dead cry
After 15 years of use, it's finished.
Know, I have 5V out of REF02 and the MidiDAC works fine, I can even say always worked fine.
Conjuncture of 2 unattended things : PSU dead and DVM dead.

Have a nice week-end
Pascal
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