Abyss - Random explosive static

[Spiff4565]

I assembled the Abyss and originally it didn't work to well. Namely not at all.

So I measured voltages on the LRD's and found shit ton of variance on voltages or none at all. Plus the LED I used wasn't ideal

So I bought a bag of LRD's of the correct value (which the original ones were as well) and measured until I found four that were close to each other. And used a proper 3mm LED. After this it worked pretty well.I also reflowed all solder points.

However it will run fine for awhile awhile but then start making popping static explosions. Some times they occur several in a row followed by a minute and then start again. Doesn't matter if I'm playing or not.

My guess is one or more of the LDR's are the root cause. I've pushed the LDR's against the LED and pulled them away, each instance keeping the distance the same across all four.


Would the LDR's be a reasonable assumption for replacement? Any way to track down the component that could be the cause?

 

[GizzWizzKing]

Got any pics of the board? I'm no expert but that doesn't sound like an LDR issue to me.

 

[Spiff4565]

I opened it up to take pics. Pushed the LDR's back, checked everything over and took measurements on the IC's.

Here are my measurements on the IC's:

TL074:
1 - 4.52 Output 1
2 - 4.57 Inverting Input 1
3 - 4.58 Non-Inverting Input 1
4 - 9.13 Vcc+
5 - 4.59 Non-Inverting Input 2
6 - 4.59 Inverting Input 2
7 - 4.6 Output 2
8 - 4.53 Output 3
9 - 4.54 Inverting Input 3
10 - 4.55 Non-Inverting Input 3
11 - 0 Vcc1
12 - 4.55 Non-Inverting Input 4
13 -4.56 Inverting Input 4
14 - 4.62Output 4

TL072:
1 - 4.59
2 - 4.58
3 - 4.03
4 - 0
5 - 4.53
6 - 4.58
7 - 4.57
8 - 9.13

Near as I can tell these measurements look good.

I noticed the jack lugs were possibly near the base plate so I put some vinyl tape on the plate under the jacks.

Put it back together and less random noise, but still some occasionally.

 

[Nostradoomus]

Where are those black caps from? They seem rather small for some of those values

 

[Spiff4565]

Where are those black caps from? They seem rather small for some of those values

I don't recall where I got them. I've decided to replace the MLCC's with box film caps though. I'll report back once the parts have been swapped.

 

[Chuck D. Bones]

All of your opamp voltages are good. You're testing it with the box closed tight, right? LDRs are extremely sensitive and even the tiniest amount of stray light will mess up the performance of the pedal. It won't make explosive sounds though, it just won't sweep very well. The LED is flashing reliably? The LFO circuit is notorious for stalling when the SPEED is at max or min.

From the little I can see in the pic, your workmanship looks good. If the caps are the correct value, don't change them. Replacing parts at random is NOT the recommended troubleshoot procedure. It's inefficient and you run the risk of collateral damage. The one suspect part I see is the 8-pin DIP socket. That one has stamped metal pins and they are not reliable. The 14-pin socket has machined pins. Much more reliable. If you must use sockets, then used machine pin.

Pull the board out and inspect every solder joint under magnification. Look for cold or missing solder joints. Look for solder splashes and other debris. Make sure the IC leads are fully engaged. Sometimes a pin curls under and makes intermittent contact. Visual inspection is the #1 best troubleshooting tool.

 

[Spiff4565]

I used MLCC's rather than box film caps. I also used cheap electrolytics.

I have ordered a small inventory of quality component. I have already pulled those pieces out. They cheap MLCC's I used were wildly out of spec, at least the ones I've measured. Anymore I'll measure each component before installing. Spending a buck or two more on quality parts is a wise investment.

Yeah, I kept it dark for measure/testing. Good point on the socket. I'll investigate that next.

Thank you the compliment on workmanship. Over the course of several builds I can see a huge difference in the work. Still have room for improvement but each build develops more skill.

The next big leap is troubleshooting. It's great to have a community that is full of insight and encouragement.