Pendulum troubleshooting

drew_t

New member
I built a Pendulum, tried it out briefly before boxing it up, and it seemed to have a very nice, almost Univibe-y sound. I initially had the wrong value pot for the speed control, and I think I may have damaged something either changing the pot or putting the board in the enclosure. It now sounds like a very plain trem with all the high end removed. The high pass and low pass LEDs blink in an alternating fashion, and the rate indicator LED seems like it does what it's supposed to do. I replaced the high pass LED and the LDR (I used the Tayda ones) and the electrolytic next to them (C101), and swapped the two ICs around, but the sound didn't change. Have looked at the back of the board for solder bridges or misc debris and didn't see anything. Can someone advise how to troubleshoot this; specifically, how to tell if the higher frequencies are being lost at some point?

Schem is here: https://forum.pedalpcb.com/threads/missing-build-docs-schematics.3784/page-9#post-52417
Pendulum build document: https://docs.pedalpcb.com/project/PedalPCB-Pendulum.pdf
 

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I built a Pendulum, tried it out briefly before boxing it up, and it seemed to have a very nice, almost Univibe-y sound. I initially had the wrong value pot for the speed control, and I think I may have damaged something either changing the pot or putting the board in the enclosure. It now sounds like a very plain trem with all the high end removed. The high pass and low pass LEDs blink in an alternating fashion, and the rate indicator LED seems like it does what it's supposed to do. I replaced the high pass LED and the LDR (I used the Tayda ones) and the electrolytic next to them (C101), and swapped the two ICs around, but the sound didn't change. Have looked at the back of the board for solder bridges or misc debris and didn't see anything. Can someone advise how to troubleshoot this; specifically, how to tell if the higher frequencies are being lost at some point?

Schem is here: https://forum.pedalpcb.com/threads/missing-build-docs-schematics.3784/page-9#post-52417
Pendulum build document: https://docs.pedalpcb.com/project/PedalPCB-Pendulum.pdf
Edit: Did you use a plastic dust cap on the Volume Pot ???
If not, it is common for the Pot to short on the Solder tits!!!


Check Pads for Continuity with matching Colours:
Pendulum Continuity Check.jpg
 
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Thanks for the response.

I do have continuity at the indicated points.

I used a PedalPCB pot insulator ( https://www.pedalpcb.com/product/pot-insulator/ ) on the volume pot.
OK, You need to check all your Resistor values are correct.
Here is a Resistor Calculator, Click on Bands for 5 Colours
Look for things like 47K resistor installed instead of 4k7:


I'm signing off now but will be back later!
 
One additional clue I forgot to mention: if I put a piece of cardboard in between the LED and the LDR on the high pass filter side (in other words, blocking the LDR from being able to "see" the blinking LED), the sound is unaffected.

Also, I check each resistor with a meter before I solder them in, so it's unlikely (not impossible) that one of them is a wrong value.
 
Edit: I'm curious if you have continuity on Yellow Circles!
Check all these new Circles for Continuity:
Pendulum Continuity Check.jpg
 
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Those all check out, too, and I tested a few more things around R4, R5, and R6 and C2 and C3.

Another thing I've noticed is that with the volume knob more than around a quarter of the way up, output gets really loud and kind of distorted.

I think I'm going to put this down for a day or two and then come back to it and look at all the resistors through a magnifying glass.
 
Those all check out, too, and I tested a few more things around R4, R5, and R6 and C2 and C3.

Another thing I've noticed is that with the volume knob more than around a quarter of the way up, output gets really loud and kind of distorted.

I think I'm going to put this down for a day or two and then come back to it and look at all the resistors through a magnifying glass.
Check this out : https://northcoastsynthesis.com/news/beware-fake-parts/
R5 -12K is the only one that I can't be sure of in the Picture you posted.
The other is your Cap values, Check those again !!!
 
Another thing I've noticed is that with the volume knob more than around a quarter of the way up, output gets really loud and kind of distorted.


I built a pendulum with TL074s that were probably counterfeit (from AliExpress) and had this effect with the output before swapping them out with genuine ones. If you think yours are legit I'm at a loss because everything looks alright - I compared your resistors to mine and they match as well.
 
I replaced C2, and that seems to have fixed it. I'm not sure if I had a bad solder joint, or the cap got bent back and forth too much, or maybe both.

Interesting note about the fake chips -- seems like it would be like making counterfeit pennies or something equally stupid. I got mine from Tayda, and their appearance matches those of the ones pictured in the article.

Anyway, thanks for the help, guys.
 
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