SOLVED Octarock Not Turning On

[Pufftones]

Hey, so my title pretty much says it. This is my second build. When turned off, signal passes through the pedal and I get a clean sound. When turned on, the light on the footswitch does not turn on and everything goes silent. Here are some photos. Let me know if you see anything suspicious or if more photos would be helpful.

 

[Pufftones]

I know this has been quiet for a bit but circling back because I was out of town and then sick for a bit and just got troubleshooting last night.

I replaced the small board on the back of the switch and it's still behaving in exactly the same way. In some sense this is a good thing because it would at least indicate that this isn't the problem. Fresh solder and much cleaner connections and still the same behavior. I also ran power to it and started testing voltage around the board. Two of the ceramic capacitors read a voltage on one side and 0V on the other. I've tried reflowing them as well as testing the voltage on both sides of the board (meaning both on the bottom at the connection and directly on the capacitors) and still get the same result. I'm and ME by trade and so my understanding of circuits and components is OK but not great. Is it possible for capacitors to just be dead? That's what seems to be the case so I think I'm going to just order some new ones, replace those and see if that fixes anything?

Does anyone have any specific tips for testing voltages around the board? Are there specific things I should be doing in terms of like following traces and trying to narrow this down to the specific components? I've just been kinda going around with the DMM testing things and seeing what happens and this jumped out at me as "huh, that seems wrong."

 

[Pufftones]

Alright, here's a more detailed update on what it is and isn't doing. I've made a video in hopes that maybe someone has run into this or another pedal doing something similar and can give me some advice about what might be going wrong here. I also just took these photos and tried to get them to focus a little better than the first ones. It's kinda tricky since I want to get as much detail and be as close to the board as possible but that also narrows the field of focus on the camera. Thank you in advance to anyone who watches or has any further ideas.

PedalPCB OctaRock as of 05/01/2023

7 new items added to shared album

photos.app.goo.gl

 

[Pufftones]

Ok, I have no idea whether anyone's reading this but I'm going to write it if only to think through the status of this pedal and what I suspect is going on. Currently, everything except the octave down is working. That knob does absolutely nothing and if you turn it all the way up with everything else turned all the way down, the pedal is silent.

Observations/Notes:

• I cleaned the flux off the pcb with a soft bristle toothbrush and acetone.
• All connection to the octave down pot are good.
  • The DMM reads the same voltage on lug 3 of the octave down pot and the mids switch. This indicates that current is traveling from the switch to the pot.
  • The resistance read on R46 can be adjusted using the octave down pot. Again, this indicates that the connection there is good.
  • Lug 1 of the octave down pot reads about 18V when the pedal is turned on.
• I did a continuity check on Q2 and read the expected diode drop. This pretty much rules out that transistor.
• I tested the legs on every one of the IC's. I get voltages on all the legs that I should and get 0 where it is grounded. So at very least the connections to the IC's are all good.
• Since IC2 is the last one before the octave down pot and IC's 1 and 2 are the same, I tried swapping IC1 and 2 around to see if maybe IC2 was damaged in some way. The pedal functioned exactly the same.

Based on these findings, my best guess is that, assuming all my connections are solid and I haven't shorted anything out in that section the circuit which doesn't seem to be the case, my culprit is probably IC3 or IC5 because those two only go to the octave down. Do these deductions seems reasonable based on the schematic and my observations? Thank you to anyone who may have any input on the subject.

Here's another quick video demonstrating what it does and doesn't do.

 

[giovanni]

It’s likely that you have a short that’s causing the signal to go to ground when you turn the octave down on. Have you used an audio probe to trace the signal? Also the octave up sounds pretty noisy to me. I haven’t built one of these but I have the original which is quiet like a mouse.

 

[Pufftones]

I haven't tried an audio probe. Just looked up how to make one and this seems super straightforward. I'll definitely be throwing one together this week and giving that a try. No idea what's going on with the noise on the octave up nor was I sure that it was atypical. I kinda dug the fuzzy nasal sound of it but if something's malfunctioning there too it's worth knowing. Thanks for the tips!

 

[Pufftones]

Ok, so I made an audio probe and haven't definitively figured out what's going on but I think I'm close. I've narrowed it down to the section of the circuit between The first pin on IC1 and lug 2 on the octave down pot. At pin 1 on IC1, I hear the frequency an octave down. On the second leg of resistor 16, it is still an octave down but there is a massive drop in volume. It is still audible however very quiet from there through IC1 pin 5. It gets a touch louder on pin 7, the output of IC1. It then continues downward in volume until the mids switch. The signal is audible on the mids switch but just barely. On the second lug of the pot and R46, I can actually hear a perfectly clear signal at the original frequency. Still, the octave down signal is dead silent out of the output jack. Anyone got any ideas about what's going on? It's odd that at no point does it seem like the signal cuts out entirely. I was expecting that at some point I would just hear complete silence and that would be where I was shorting out. I'm wondering that maybe C9 isn't grounding properly or something isn't functioning correctly with IC1. Would that make sense to someone who understands a little more clearly what that section of the circuit is actually doing? Thanks so much for any feedback or ideas anyone might have.

 

[giovanni]

Hard for me to say without seeing the schematic. For example if IC1 is a buffer I wouldn’t expect its output to be louder. I would triple check all components past that point. Did you do some continuity checks on the pots? If the entire pedal goes quiet when you turn the low octave up I would guess you have a short somewhere in there and maybe you can find it by checking continuity between the pot pins and ground?

 

[Pufftones]

Ok, so here's the full schematic.

https://docs.pedalpcb.com/project/Schematic-Octarock.png

Here's the section of it that I suspect is the culprit.

The "OCTAVE -" line all the way to the right runs directly to lug 1 on the octave down pot. Lug 2 on the octave down put runs to R46.

The direct and octave up signals still work regardless of where the pot on the octave down is set. On the other hand, no matter what, octave down is always silent.

Also, I just realized that everywhere that I was saying IC1 in my last post, I meant IC2.

 

[giovanni]

So you get signal at the output of IC2.2?

 

[Pufftones]

Just barely. It is very quiet. It is an amplifier. Intuitively it seems like the output should be significantly louder than the input signal.

 

[giovanni]

IC2.2 is a buffer. The volume should be the same. If it’s not there is something wrong with that stage.

 

[Pufftones]

Got it, I need to go back and double check but I feel like it changed across IC2.2. Going to circle back and test this tomorrow night.

 

[DGWVI]

Can you compare the output signal between the junction of R40/R41 to the output at pin 1 of Q2? It should be loud and kinda harsh, but this will tell you if the JFet is at fault or if something else downstream is killing your signal

Also, verify the values used in the Sallen-Key filter (IC2.2). With the parts values used in the build doc, its cutoff frequencies are ~150hz and 470hz, which will give the impression that some volume has been lost

 

[NickC]

I just finished my octrarock everything works perfectly except the low octave, strangely I tried to remove and replace the second jrc and for a few seconds and then faded I heard the lower octave as it should sound, so if you got these components like me on banzai music the problem could be this.

update: I'll tell you more, I noticed that if I touch pins 3 and 4 with a screwdriver the low octave returns and then slowly discharges until it vanishes again.

another thing, if i switch from 9 to 12 V, for few second the octave down works and than if fades away, so i think its the jrc.

 

[Pufftones]

I just finished my octrarock everything works perfectly except the low octave, strangely I tried to remove and replace the second jrc and for a few seconds and then faded I heard the lower octave as it should sound, so if you got these components like me on banzai music the problem could be this.

update: I'll tell you more, I noticed that if I touch pins 3 and 4 with a screwdriver the low octave returns and then slowly discharges until it vanishes again.

another thing, if i switch from 9 to 12 V, for few second the octave down works and than if fades away, so i think its the jrc.

I've been meaning to update this for a while. I ended up just starting over and the second one worked like a charm straight out of the gate. I had to remove and replace a bunch of things with the first build and I'm pretty convinced that I damaged a trace or a solder pad somewhere along the way the first time.

 

[NickC]

solved i have changed the banzai music 2n5457 with some old 2n5458 in my stok, it works!