Distorted sound

Hi again, having built up my Shruthi 4 pole mission and overcome several problems with the help of this group, I have now come up against a new problem - very distorted and quiet output. I have to turn the gain up on my sound card considerably just to hear the Shruthi but am then swamped with noise. I am just about to try the audio test points as mentioned elsewhere but was just wondering if anyone else has encountered this and found the fix?
All voltages check out ok - 7v in from wallwart and 4.96 (+ and -) on the board and going to all chips (checked ok as per other posted help)
Everything else appears to be working ok and the display and led’s all fine and functioning as they should. I have checked all solder joints on both boards and they appear ok.
This sounds to me like an amplification problem? I will check the audio test points and post results in the next hour or so.

And you have set the filter type to 4pm? … Because I completed a polivoks yesterday and only got noise, until I remembered to set the right filter type. :slight_smile:


I am getting some synth sound through which change accordingly when I select a new patch its just they are all very quiet and distorted.

Audio test points is way to go…

And board photo please!

Okay - have checked all solder joints all ok. Just as an experiment I removed IC1 the tl072 and the output increased considerably but was more distorted than ever. I take it this IC is just a buffer to reduce the signal from the osc before the filter stage?
Also, would the gain transistor Q2 affect the overall gain of the circuit and produce these effects if defective ( I am going to change it anyway as it was sourced from china and I am a little dubious of its quality)
Haven’t been able to take any photos yet.


The IC1 is a dual opamp. It forms the input stage for the filter as well as the last output stage after the VCA.
What you are doing here is making some really wild guesses. In the end all parts come from china so i wouldn’t worry about that. Changing parts is also risky, you might damage the pcb.
How did you test that all you solder joints are ok? I sometimes get a fine connection on the multimeter but not good enough for audio to go through.
You should do the signal flow test on the audio points described on the build page for the 4PM.

Thanks Shiftr after everything it turned out to be a duff Jack socket - wonderful volume now I have replaced it.
Thanks everybody for your help