Does this sound normal/distorted?
  • I have yet to attach my LCD and I wanna make sure that everything is fine before I do. However, the last potentiometer on the right makes a really weird and distorted sound whenever it gets turned past a certain point and then it just stops making sound. I attached sound. So basically does it sound like it should?
    Dont listen with headphones.

  • Just adding a bit more info because the first post might be lacking. It’s an SMR4 filter board.
    This is my 2nd MOBO board, so I am fairly certain the problems on the filter board. After following the audio route, it seems like the problem starts from the oscillator itself.
    Again I’m not sure what sound exactly I should be hearing, but the last potentiometer on the right, produces this really strange noise, while the other three just seem to adjust their respective parameters.
    The last time I checked the power supply was operating normally with +/- 5.
    Any help would be greatly appreciated, I am completely lost on how to solve this. I don’t want to attach the LCD until this is fixed, because I did that on my last MOBO and I wrecked it trying to get the LCD off :/

    Cheers from Dublin :)

    Linked: pictures of the two boards:

  • Not sure whats happening here. What did you do to produce the sound? It sounds like you were sending a fast sequence of random MIDI notes to the Shruthi (is that right?) while adjusting the cutoff frequency.
    I don’t know what preset the shruthi was operating in. It could very well be the normal sound for that preset.

  • I used the “Jam” mode on the synth
  • Here I just sent two midi notes to it, and just adjusted the last potentiometer.

  • Hi, normally the 4th Pot had nothing to do with the sound of the filterboard . But it can be that one control PWM can’t work – because of a short on the filterboard . Or do you have made a MIDI loop ??

  • Thanks for the reply, Yes the MIDI is looping as I turn the 4th pot all the way from the left to the right. I am planning on attaching the LCD soon, at the moment I have no soldering iron, and I hope that the LCD might be able to explain things a bit better.

  • Update:
    When I plug it in and send MIDI for one second it sounds pretty normal then suddenly just gets quieter and starts to sound all fuzzy and distorted. It stays like that until I plug and unplug it, then does the same thing.

  • Sounds like overheating. What’s the wallwart that you use?

  • I’m using 9V at 400mA

  • Can you check the temperatures on the 7905 and 7805? And the voltages at the outputs of both of them after it got quiet and distorted?

    Sound getting quiet and distorted is a pretty strong indication of bad power conditions.

  • 5.05V on 7805
    -4.95V on the 7905

    I don’t have a thermometer but neither were really that hot, I could easily touch both of them. Left the synth on for about 10mins

  • From what I’ve read on other posts, this seems to be pretty normal?

  • Perfectly normal and within specifications.