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Obsidius Whooshing Sound

mikeperez83

New member
I ordered and built 2 Obsidius boards, one works perfectly as intended, the other also works...kinda. In bypass mode its very quiet, engaged, the pots all work as well as the effect and toggles EXCEPT if i move the Grunt switch up or down, especially UP I get this loud whooshing sound even with the volume completely turned down on the bass. i can play over the noise, but its also very apparent. All my solder joints look solid, i used an audio probe and deiced to swap out Both IC 1 and IC 3 which is the CD4049, still getting the same issue. i can't really tell what i'm missing, is there some sort of groundloop i somehow have before the first IC? The signal travels through the whole board getting more and more amplified. (I also changed out the 1N5817)
 

Nostradoomus

Well-known member
If you socketed the J201s in each board swap them into the same positions and see if the behaviour changes on your board that’s acting up.
 

Chuck D. Bones

Well-known member
Does the noise get louder if you turn DRIVE up? If so, it's most likely the JFETs or a noisy capacitor. Did you use any ceramic caps? If the noise is loud even with DRIVE set to zero, then it's probably the CD4049. CD4049s are noisy, some more than others. Try swapping the 4049 between boards and see if the noise moves with the chip. I have found that the TI chips are noisier than RCA or Fairchild. Unfortunately, only the TI chips are currently in production.
 

mikeperez83

New member
Does the noise get louder if you turn DRIVE up? If so, it's most likely the JFETs or a noisy capacitor. Did you use any ceramic caps? If the noise is loud even with DRIVE set to zero, then it's probably the CD4049. CD4049s are noisy, some more than others. Try swapping the 4049 between boards and see if the noise moves with the chip. I have found that the TI chips are noisier than RCA or Fairchild. Unfortunately, only the TI chips are currently in production.
I have swapped out the 4049 and the first op amp. None of the caps are ceramic, they’re all either monolithic or film. I’m starting to suspect the jfets, as their smd and despite me being extremely careful, I may have fried one.
 

mikeperez83

New member
Does the noise change when you vary DRIVE?
No, it’s just a constant sound, like hearing an airplane fly overhead while inside your house, and of course raising the gain and volume increase it, but it’s a constant. Again, even if I turn the volume all the way down on the instrument, it’s still there.
 

mikeperez83

New member
Does the noise get louder if you turn DRIVE up? If so, it's most likely the JFETs or a noisy capacitor. Did you use any ceramic caps? If the noise is loud even with DRIVE set to zero, then it's probably the CD4049. CD4049s are noisy, some more than others. Try swapping the 4049 between boards and see if the noise moves with the chip. I have found that the TI chips are noisier than RCA or Fairchild. Unfortunately, only the TI chips are currently in production.
swapped out the jfets to remove them as a possibility, noise is still present. the only major components i haven't swapped out are the 3rd and 4th op amps. May have to set this guy aside til i get more parts in.
 
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