Vco problem

Moevot · Joined: Oct 16, 2019 Posts: 14 Location: Poland

Hello. I am a beginner in this field, so please bear in mind Smile

In general, everything seems to be OK, except that the oscillator all the time makes the last sound even when the CV drops to 0. After removing and restoring voltage, it still "remembers" the sound. At CV = 0, he should rather be silent. I replaced all the chips, but the problem persists.

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gabbagabi · Posted: Tue Oct 22, 2019 9:34 am Post subject:

Hi and

to our little mad world Very Happy

if you scroll down the vco page:
http://yusynth.net/Modular/EN/VCO/index.html

you will find:

TUNING

Disconnect the CV source from the V/OCT input.
Turn the FREQUENCY potentiometer to 0 (fully counter-clockwise position)
Turn the FINE TUNE potentiometer to 0 (mid-range position)
Adjust T1 in order to read a frequency of 16.2 Hz
Plug a CV/GATE keyboard (starting at C, and giving 0V for lower C)
Press A3 key, and check that the pitch is A3 / 220Hz. If not adjust T1.

that means if you dont apply any CV to the VCO, it will still swing on 16,2Hz (if you did tthe tuning rigth) (with T1 u set the minimum frequenzy)
--> its not a bug its a feature Very Happy

Moevot · Joined: Oct 16, 2019 Posts: 14 Location: Poland

I have already understood this topic. Unfortunately, I have a problem already on 1 octave, with each subsequent one is even worse. I replaced Lm394 with AS394, OPA 2134 with TL072 and no changes. What elements have a major impact on tracking accuracy? I would check them first.

flagada · Joined: Dec 15, 2016 Posts: 39 Location: Amsterdam

Did you use a 1K tempco for R12?

PHOBoS · Posted: Thu Oct 24, 2019 7:35 am Post subject:

the tempco should only have an influence on temperature related drift not on the tracking itself.

Moevot · Joined: Oct 16, 2019 Posts: 14 Location: Poland

I changed the R50 to 90k for a 5v pull-up, but it only leveled the top of the sine wave. All components have 1% tolerance which eliminates their error almost to zero. I have finished the second oscillator which I assembled, measuring each resistor for certainty, I used the same parts. Rather, I was sure that I did not make a mistake while mounting the first oscillator so I kept looking ......
And the reason was incorrect calibration.
The calibration method described on the website is accurate but at first it made no sense to me. And here I made a mistake. After following the instructions carefully, I was able to get 4 octaves and an acceptable 5. As a start I am happy but I was counting on more for using quite good quality parts.

Initially, I calibrated the VCO using Arturia KeyStep which turned out to be a tragedy because it requires calibration itself. As it turned out, voltage levels are tragic.

Thank you for your help, I will probably have many, not always wise questions. Very Happy

Until now, I was dealing only with digital electronics and automation with an emphasis on programming microcontrollers and PLC, so everything analog is a discovery that requires learning for me. Cool