SOLVED The Abyss Whooshing Noise

[punchy712]

I'm getting quite a bit of noise when turning on my Abyss, and it's likely related to the LFO as the whooshing noise produced is directly affected by the Rate/Intensity/Voice knobs. I was hoping someone could at least confirm if this kind of noise is expected from this circuit. I don't think so as the demos I've heard the sound was pretty clean, but I wanted to ask before I go too far with the debugging.

Attached is a picture of the guts (I just added the shielded wire on the output but it didn't make a difference) and here is a link showing the noise (starts with the pedal off).

I started a separate thread to discuss some potential ground issues as I wanted to eliminate that, but I don't think that's the cause here. I also apologize for all the questions, if it's better to merge them into a single thread please let me know.

 

[Erik S]

Is it possible that you’re missing a capacitor? I pulled up a photo of mine to check your cap orientations, and mine has 5 electro caps in the row between the two ICs where you’ve got four.

Could be that you have a board from an older revision, but If I zoom in on your photo it looks like there’s another cap circle on the screenprint in the center.



There are 5 on the current build doc.


Here’s mine.

 

[punchy712]

@Erik S good spot and sorry I should have mentioned this, but I didn't have enough room to mount all the caps on the same side so the missing one is on the other side of the board. I assume that's not an issue.

 

[Erik S]

Ah! That makes sense!

Are either of the big yellow caps tantalum’s? Are they oriented the right way?

Just listened to your sound clip. Mine definitely does not make that sound.

 

[punchy712]

Ah! That makes sense!

Are either of the big yellow caps tantalum’s? Are they oriented the right way?

Just listened to your sound clip. Mine definitely does not make that sound.

The big yellow caps are ceramic and not polarized.

Thanks for taking a listen and confirming that it's possible to build them without being noisy. I'll have to start probing around hopefully I can narrow down where the noise is coming from.

 

[punchy712]

I didn't expect this, but it looks like I may just have a bad pot. I probed pin 3 of the level pot and the sound was clean. Pin 2 of the pot is connected to the output and that was noisy. If I turn the pot all the way up then the noisy is gone. I never tried maxing out the level as I thought that would actually overdrive the signal and distort, but when just testing this out with a simple tone and through my audio interface it works well.

It's not the above, I'm not sure what happened with how I was probing, but the noise looks to be introduced as the signal is travelling through the different stages in TL074. Out of pin 8 and 14 the signal is clean. Out of pin 1 the signal is noisy and distorted. Pin 3 shows maybe a hint of noise, and pin 2 is definitely distorted, which would make sense as it's coupled to pin 1.

I swapped the TL074 for another one but with the same outcome.

 

[punchy712]

I'm really stuck on this one, and I'm not really sure how to debug it from here. I did a visual inspection and all the parts look to be correct, traced it for connectivity and that looks okay. The problem seems to be that as it's going through each stage of the TL074 with an LDR on each, the noise increases on the output pin of each stage/channel. Voltages as measured with my DMM look reasonable from what I can tell, at least based on the schematic.

This is a dumb question but is there any possibility of a LDR to actually introduce any noise? I wouldn't think so but thought I'd ask. Also, the build docs mention a 3mm red LED, but I don't see that on the schematic or PCB. Is it just the foot switch LED? That's been my assumption, but I haven't seen a size and color mentioned in other build docs.

 

[Synchrony Pedalworks]

For me, the “whooshing” noice depends on where I place the vibe in my chain. I like it in front of my drive pedals. See if changing it’s order of your pedal chain fixes the issue.

 

[punchy712]

For me, the “whooshing” noice depends on where I place the vibe in my chain. I like it in front of my drive pedals. See if changing it’s order of your pedal chain fixes the issue.

The noise is happening with the pedal being the only one in the chain, both in front of the amp and also just running it through my audio interface (where I feed it just a constant tone). From using the audio trace it just seems like the signal is getting distorted at some point through the circuit, but I can't figure out what could be causing it.

 

[ledtasso]

I am having very similar issue with the noise, any luck with figuring this out? "- related to the LFO as the whooshing noise produced is directly affected by the Rate/Intensity/Voice knobs."

 

[punchy712]

I am having very similar issue with the noise, any luck with figuring this out? "- related to the LFO as the whooshing noise produced is directly affected by the Rate/Intensity/Voice knobs."

Hey, sorry but no I haven't had any luck fixing it yet.

 

[punchy712]

For completeness, I'm going to mark this as solved not because I solved it but because I'm not going to get back to debugging the issue. Last time I looked at it, it seemed like I was somehow getting some noise through the ground lines from the separate circuit that controls the internal LED. I just received another board this week so I started from scratch and the new build works great.