invisible lfo
  • floflo
    Hello at all. I first think that there are any prob on my smr, but when tuning it appears a strange thing: I set the 2 oscillator on none and the filter page on 50 63 0 0 on an init patch, I can hear a slow modulation as I am tweaking the res trimmer, so its impossible to tune it.. Very strange.. Has someone an idea?
  • pichenettespichenettes

    Are there any other modulation in the modulation matrix?

    Also, is your power supply good? It could be an unstable +5V rail polluting the expo converter circuit.

  • floflo
    I test 2 power supplies one from my echo soundcard and its the same?
  • floflo
    And no other modulation I just plug the ssm instead the smr and strange: the reso is low more and more with the time and it end up by disapear..
  • pichenettespichenettes

    On the SMR4:

    • Look at the +5V rail with a scope. Is it stable?
    • Look at the signal on pin1 of IC3. Is it stable?
  • floflo
    Thanks but I stop for now I am at a end of an electrical line and my family told me that electricity have high and low here so I ll wait to be on a new place.. Thanks
  • floflo
    Thanks but I stop for now I am at a end of an electrical line and my family told me that electricity have high and low here so I ll wait to be on a new place.. Thanks
  • floflo
    Hello at all.. I have discover a nex problem:
    Some soumd goes trough the audio out without jumper on the pole selector.. Can this be due to the power supply too?
    I have carefully look but can't see no short
    I hauent totally check for a swap yet bt was very careful when doing it
    Can it come from a damaged chip?
    Thanks to help me to find the best way to troublehoot it..
  • floflo
    My mind tell me that the cause of the problen is surely more a short than a bad solder .. I am exact..?in another post, [sound a bit distorded] pichenejtte say that the problem have chance to be around ic 5.. Is this the same case here?thanks
  • floflo
    Hello. I have just check all the resistor and look with a magnifiing glass that there is no short.. I see nothing wrong. There is a scratch on the solder mask between the low lead of the 1K between the two 3906 on the riht. It may cause short between the pad soldered and the pcb surface around it.may it be the problem?
  • pichenettespichenettes

    It doesn’t look like a problem with this part of the circuit (the 3906 and 1k are part of the circuit setting the cutoff frequency of the filter).

  • floflo
    Thanks. As my problem is very similar to the one on the other post, would it be good to probe as you recommend but without jumper in order to see when a sound appear a good idea? I have tempted to swap the ic on the board with no result.. Really can't see a short or a swap resistor.. Should it be possible it come from a faulty resistor? One in in the up of ic 5 has a strange form and is bad paint.. I will took photo as soon as ican... My problem seen perfectly described in the dendy post.. Shame he just find a workaround. Hope nnt be too boring..
  • floflo
    Hello I have done the probing you recommend to dendy but without the jumper . Until stage 6 I have a plain and loud signal. I think it go to the jumper at this point exact? At stage 7 I have a less loud signal which might be the consequence of a short between stage 6 and 7 is it right?thank
  • floflo
    It make me crazy I really can see any short..
  • floflo
    Can it come from the 3906 under stage 7?
  • pichenettespichenettes
    Even if the pole selection jumper isn't inserted, you should hear a small fraction of the resonance feedback through the VCA. This is part of the resonance loudness compensation circuit.

    So if the residual sound you hear is present only on patches with a high resonance, but totally absent when the resonance it set to 0, it looks like your problem is not a problem at all.
  • floflo
    Res to 0 and cut at 127 I can hear signal. If I turn the res it come pretty loud..and it s distorded with jumper..
  • pichenettespichenettes
    And what do you get at the middle pin of the pole selection jumper?
  • floflo
    Hello there is no sound at the middle tip...
  • floflo
    So I guess its a problem betwenn the jumper and stage 7?right
  • pichenettespichenettes
    Another theory: what you are hearing is as I suspected the signal from the resonance feedback path, and it's distorted because there's something wrong with the resonance VCA.

    To test this theory: does the signal at point 6 sound OK? Is it distorted? Can you hear that it has no resonance at all when resonance is set to 0 ; and a nice, self-oscillating tone when resonance is set to 63?
  • floflo
    At 6 when reso to 0 no resonance
    When I increase the res it lower the volume

    At res 63 I don't think its distorded

    I have just re-attempt to do the tuning and there is always the invisible mod I am on a new place...
  • floflo
    ...so I just finished to build a new smr board very carefully from a guy who never build his kit... And it react exactly as the first... And I finally found that sound is all right.and my preferred filter board. With the echo psu from my soumdcard the "invisible" lfo disapear...and no problem anymore to tune it... So you were finally right.. My problem was not a problem at all...sorry for your time but thanks anyway... I think I am going a little paranoid with all these little component around me..pretty new for me. Now my building shruthi adventure is over, will wait your next thing if it suit me, I never do solder before, you make me a junkie of that and I am now lurking on midibox sammich's and willzik xoxkit... I think to buy a" c++ pour les nul" too..and do music and patch at a time.. Will post the result here! Thanks for all and for giving me new interest! End of the first chapter!
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