VCO and VCF trouble
  • Hi,

    i have some problems with my Anushri built from a complete kit by MI.
    The main problem is the resonance control, even at the lowest setting, there
    seems to be quite a lot of resonance. Furthermore, the pulsewidth isn’t at 50%
    at the center position. I also experience tuning issues, but I guess I should
    figure that out after getting the filter and the VCO working correctly.

    I already resoldered all connections. The voltages I measured appear to be
    correct.

    Unfortunately I don’t have a better camera at hand right now, but I can try to
    make better pictures of certain areas if needed.

    Mainboard:
    http://www.brechpunkt.de/paste/Ne0TLtGx.jpg
    http://www.brechpunkt.de/paste/OhCS5MPp.jpg

    Square derived from Sawtooth at 50% PW setting:
    http://www.brechpunkt.de/paste/UCBl6J97.jpg

    DC corrected Sawtooth:
    http://www.brechpunkt.de/paste/ZeCYNc8B.jpg

    Sawtooth Core:
    http://www.brechpunkt.de/paste/6SDXZAk8.jpg

    Square Wave with Filter fully opened and 0 Resonance:
    http://www.brechpunkt.de/paste/p3WlskZu.jpg

    Thanks for your help in advance :)

  • Are you sure you have used the right pot (100kA) for the resonance control?

  • I am not 100% sure. Is it possible to measure the pot in circuit? (with the control board disconnected from the mainboard)

  • Yes, this is possible (quite an exception!). You should measure 100k between both extremities.

  • It is only 87k

  • Hmmm must still be good…

    Can you check the color codes of R51 / R52 / R53 / R54?

  • The resistors are 470, 4.7k, 4.7k, 33k, so they should be correct.

    What about the DC corrected sawtooth wave? Is it correct, as it appears somehow clipped?