Super Heterodyne - Divebomb sound with no input

[airbud]

Hi all, just finished this about an hour ago after the delivery was delayed due to the big storm in the northeast. While I'm playing it sounds cool and I believe is working correctly, but if I don't play or even unplug the input, it'll make a kind of divebomb sound falling in pitch, like a whammy bar dive.

I tried a different opamp and CD4069 (based on another thread I had some intuition it might've been those), and checked the soldering on both those two spots specifically (the last two pics) and overall. I didn't see anything that screamed out at me, any thoughts on what to try next?

The sound reminds me of when I had GI Joe's as a kid, and some made crappy little noises designed to annoy parents, and this one was the divebomb noise.

Thanks for any advice!

 

[airbud]

here's the thread: https://forum.pedalpcb.com/threads/super-heterodyne-noise-but-not-the-good-kind.21346/

 

[airbud]

reflowed some joints and swapped out the CD40106, still getting the noise. i think it might be early on in the signal path, since whatever noise issue is getting converted to an oscillator (maybe somewhere in this section of the diagram? not sure).

any advice on what to try next? this is one of my first pedals with these chips so i'm still developing my understanding of how they work.

thanks!

 

[airbud]

another round of messing around with knobs and looking through the circuit, there's some type of noise no matter which oscillator is isolated each oscillator makes a different noise, so whatever issue is upstream from the oscillator section, and then getting processed by each oscillator if my hypothesis is correct, the issue is something with grounding in the power supply, or an issue in front of the blue arrow in the attached image.

too tired to keep hacking at it tonight but hopefully i get there soon! i'm having a ball with the bit commander and i want to put them together and see what nonsense transpires.

thanks!


(apologies for multiposting but it's easier to follow my debug process this way).

 

[airbud]

i had R23 as 5.6M since i didn't have 10M, i just tried chaining two 5.6M's. still the same issue. also swapped the CD4046.

still raging about putting the transformers in wrong on the bit commander and octave clang

 

[jwin615]

Are you running it solo or on a pedal board?
Try a dedicated power supply?

 

[jwin615]

I'd also try cleaning your flux off. That's a lot of flux. Are you adding flux?

 

[airbud]

I'd also try cleaning your flux off. That's a lot of flux. Are you adding flux?

i've been running on a dedicated supply solo.

no added flux, just from the solder. maybe i cleaned up some spots with desolder braid, that might've had a little bit.

still no dice, thanks for the advice, i was unsure when flux started needing to be cleaned up.

 

[chris.knudson]

i've been running on a dedicated supply solo.

no added flux, just from the solder. maybe i cleaned up some spots with desolder braid, that might've had a little bit.

still no dice, thanks for the advice, i was unsure when flux started needing to be cleaned up.

I like to clean as much flux off of the board as I can when I'm troubleshooting. It makes it easier to spot problems.

 

[airbud]

I like to clean as much flux off of the board as I can when I'm troubleshooting. It makes it easier to spot problems.

I used alcohol and a qtip and got so-so results; what's your weapon of choice? Still some residue I couldn't gently remove with isopropyl. It was diluted, FWIW (I use it for houseplant pests).

 

[chris.knudson]

I used alcohol and a qtip and got so-so results; what's your weapon of choice? Still some residue I couldn't gently remove with isopropyl. It was diluted, FWIW (I use it for houseplant pests).

I don't use diluted alcohol. I generally use 91% (mostly because I can get it at the grocery store), but a lot of people use 99% isopropyl. My weapon of choice is a soft bristled tooth brush. I dip it in alcohol, scrub the board, clean the brush on a paper towel and repeat until the board looks clean. There are probably better ways to do it, but I try to avoid wiping the board with a Q-tip or tissue or anything thats sheds fibers.

 

[airbud]

I don't use diluted alcohol. I generally use 91% (mostly because I can get it at the grocery store), but a lot of people use 99% isopropyl. My weapon of choice is a soft bristled tooth brush. I dip it in alcohol, scrub the board, clean the brush on a paper towel and repeat until the board looks clean. There are probably better ways to do it, but I try to avoid wiping the board with a Q-tip or tissue or anything thats sheds fibers.

yeah i'll try straight-from-the-bottle isopropyl in the morning. the fibers definitely made themselves known and assured me that the qtip is not the right choice.

 

[jwyles90]

Do you have an audio probe at all? Might be worth taking it to the board and checking the different chip outputs to see if you can isolate which section it starts/stops at.

 

[airbud]

Do you have an audio probe at all? Might be worth taking it to the board and checking the different chip outputs to see if you can isolate which section it starts/stops at.

I don't but I've been overdue to get one.

is it like a transistor tester where a cheap one is fine? or does quality really matter?

thank you for the suggestion!!

 

[jwyles90]

I don't but I've been overdue to get one.

is it like a transistor tester where a cheap one is fine? or does quality really matter?

thank you for the suggestion!!

I don't think the quality matters a ton, but I could be wrong. I know there are diagrams out there for building your own as well. If you've got some wire, alligator clips, audio jacks, and a couple of caps and resistors (I don't remember which values, though), you can put one together yourself.

I wound up buying one from Rattlesnake Cables that has been great and wasn't too bad price-wise.

 

[Fuzzonaut]

I don't but I've been overdue to get one.

is it like a transistor tester where a cheap one is fine? or does quality really matter?

thank you for the suggestion!!

Audio Probe? Easy to DIY: You need one 1/4″ mono plug, one 100nF capacitor, an alligator clip and some wire.

 

[Giorfida]

Audio Probe? Easy to DIY: You need one 1/4″ mono plug, one 100nF capacitor, an alligator clip and some wire.

View attachment 73284

Only suggestion I’d make, if space permits, use a 600v or 1kv cap instead- that way if you are working on something that has higher voltage present (like a tube amp) you are good

 

[airbud]

ok coming back to this after a weekend working on the brewery renovation (the floors are looking good!), i confirmed the component values are correct. i had to pillage the A500k pot, i have some arriving today so i'll be able to test again after that.

if i still am not having luck i'll go pick up an audio probe from big box (i don't have any alligator clips) and start with that whole jam. thanks for the help guys, if you see anything else in the photos let me know.