Newly built Anushri - everything works except VCO
  • Hello,

    Finally finished my Anushri. Everything seems to work ok except the VCO.

    The subosccilator works when in DCO mode, but not in -1 or -2 mode.

    The filter, LFO, ADSR, drums, midi, sequencer stuff all works.

    Did the power troubleshooting and everything seemed fine.

    Any ideas?

    Regards
    jonkers

  • Ok so im trying out the signal tests.

    I get DCO audio on point K and U as expected, no VCO points generates audio signals but i get the correct voltage ramping up and down on most of the places.

    One interesting point is point E, its is always at -4 V which is not correct:
    “E: VCO reset pulse. 0V, with a short pulse close to +5V at each period of the VCO.”

    The power test is ok at all points.

    Any suggestions?

    Regards
    jonkers

  • Ok i just noticed something:

    Point F ramps from 0 to 2.5 Volts every 45 seconds.

    In some settings, i get a square wave from point H when point F is between1,2 – 1,8v .

    So every 45 seconds theres something going on with the square. No audio from point F or saw.
    The LFO needs to be set very high in order to get the square audible .

  • Update:
    When setting PW Mod max clockwise i get the square every 25 seconds for maybe 20 seconds, synchronized with ramp up on point F.

    It only works when sync is off, when sync set to on the square goes completely away.

    Im looking at old threads, and in this one Pichenettes says:
    “Basic sanity check: what is the voltage on IC6 pin 11 for different notes (should be positive, low for high notes; high for low notes ; absolute value above 2.5V)?”
    http://mutable-instruments.net/forum/discussion/3588/no-vco-it-disappeared/p1

    I have a constant voltage of 4.2V there regardless what note i feed it (via midi).
    Does anyone know what that means?

    Regards
    jonkers

  • IC6 pin 11 stuck at 4.2V means that the VCO will work at ridiculously low frequencies. This is consistent with the sluggish ramp you observe.

    Check the soldering and resistor value (by reading the coloured rings!) of R58, R59, R60, R57, R61.

    Check the soldering of R61.

    Check the soldering of IC7 – all pins.

    Post a high-res photo of your board around IC6 and IC7.

  • Wow – thanks for helping me!

    The resistors you mention are all the right values according to the build instructions.
    I resoldered all resistors and IC6 and IC7 but its still the same problem.

    High rez image 1:
    http://extrazoom.com/image-44751.html?heuln50x50

    High rez image 2:
    http://extrazoom.com/image-44752.html?heuln50x50

    Not very pretty after resoldering :/

  • Correction: i resoldered all the resistors you mention, and a couple on the other side of IC6

  • Testing indicates that the square wave im hearing is extreme LFO modulation of the pulse width, bringing it up into audible range. That explains why im not hearing the saw and is more proof that the VCO is ultra slow.

  • Can’t look at the images…

  • Ah, the image hosting was only valid for 24 hours.

    Here:
    http://imgur.com/k11F7Yp
    http://imgur.com/WIDkfv4

    I dont know if it helps but the voltage seems to actually come from pin 1 of IC 7.

    If i remove IC7 the voltage is gone both on IC6 pin 11 and in IC7 socket 1.

  • Looking at the schematic, what is the component marked in the attached image?

    anushschemq2.jpg
    610 x 428 - 42K
  • That’s the trimmer R75

  • Can you post a picture of the other side (components?)

  • Ah: http://imgur.com/ZL53Top

    Using the “beeeep” function on my measuring instrument i realize theres no connection between pin 1 och R75 an IC6 pin 11 / IC7 Pin 1

    It should be according to schematic. Could that be the problem?

    The soldering iron is heating up now :)

  • pin 1 OF R75

  • There should be continuity between IC7 pin 1 and R75 pin 1.

    If R75 is not correctly connected to the op-amp, the op-amp acts as a comparator and produces either very high or low voltages – so the oscillator is either stuck at a very low or very high frequencies.

    Check this image of the PCB tracks . Do the tracks connecting IC7 pin 1 and R75 pin 1 look damaged?

  • aha, yes actually the pcb wires between R75 pin1 and the first little hole in the track looks maybe damaged.

    There is connection between “the hole” and ic 7 pin 1.

    Can i just solder a small wire from R75 pin 1 to the hole?

  • > Can i just solder a small wire from R75 pin 1 to the hole?

    Yes! Note that the copper is exposed only inside the hole, not on the surface of the PCB.

  • It worked!!!! hahaha im soooo happy now!

    I was so eager to test it the first time that i forgot to put the IC´s back in place, worked better with them :)

    It now seems that i have a 100% working anushri, thank you so much for your help with this!

    Now to munching victory candy and tweak anushri :)

    Again, ninetyninehundred thousand million thank you´s!

  • This was fantastic. Good stuff! Enjoy your Anushri.

  • Thanks cold_fashioned, i´m enjoying it immensely :)