Trouble with Mr. Squishy

adamwithanh

New member
Hey, newbie here. I've built 4 or 5 perfboard circuits so far, and only 1 has been successful. I seem to keep having the same issue, which is that true bypass is working, the led comes on, but no sound when the effect is activated. I've triple-checked all component values, orientation for polarized components, and layout (this current one is from effectslayout - http://effectslayouts.blogspot.com/search?q=squishy). One thing I notice is that when plugged in, my DMM registers continuity between ground wires and positive wires, but not when circuit is unplugged. I'm just not sure how to troubleshoot from here. Help?

IMG_4396.JPG IMG_4395.JPG IMG_4394.JPG IMG_4393.JPG IMG_4396.JPG IMG_4395.JPG IMG_4394.JPG IMG_4393.JPG
 
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BuddytheReow

Breadboard Baker
Since you are a real DIY'er I would suggest building and using an audio probe. Trace the circuit with the schematic to find out where your problem spot is. Instructions how to build a quick and dirty one are here.
 

adamwithanh

New member
Since you are a real DIY'er I would suggest building and using an audio probe. Trace the circuit with the schematic to find out where your problem spot is. Instructions how to build a quick and dirty one are here.
Okay first of all, you’re a genius and thank you for explaining how to make an audio probe in a way that makes sense. Here are my findings:
1. There is a signal up to the first pin on the 220pf cap, but it doesn’t make it to the other side, even when the cap is replaced. Should it?
2. There is signal from the anode of 4148 diode, through 2.1k R, through neg of 4.7uf cap, to pin 3 of pot, but no further in that direction. It does however go to pos of that 4.7uf cap, to 220k R and pin one of 4558 chip. No other points on the board have signal.
3. If I crank the amp with the effect turned on, I can actually hear a faint signal through it, along with a loud hum, and none of the pots impact the signal at all.

Is any of this helpful? Thanks so much again!
 
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BuddytheReow

Breadboard Baker
I would suggest a few things to help you. Here is the schematic from Effectslayouts. I have highlighted the signal path where your audio probe should go. I've also highlighted in red where your should check with your probe. Many of the items your are referring to with no signal are grounded so it makes sense why you aren't hearing anything. Also, check your voltages on pin 8 of the 4558 chip and the drains on Q1 (that's the top pin).
1642090937778.png
 

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adamwithanh

New member
Okay, SO immensely helpful. Here are my findings with the probe:

- Good signal to pin 3 of gain pot, and there's some signal to pin 2 of that pot, but it's significantly weaker and more distorted.
- Very weak, buzzy signal at pin 3 of 4558, still weak but less buzzy at pin 2, and much louder and far less buzzy at pin 1.
- Strong signal at pin 3 of level pot, but NONE at pin 2 (output).
- Strong signal between 2K1 and D1, but NONE on the neg side of D1.
- No signal on source of Q1 or Q2. No signal on any pin of Q1.
- As mentioned, no signal on drain of Q1. Very weak buzzy signal on drain (and gate if that matters) of Q2.
- Voltages for all IC Pins:
1. 4.70
2. 4.70
3. 3.80
4. 0
5. 0
6. 8.83
7. 8.83
8. 9.41

Hopefully you can help decode some of this for me. This gets complicated fast. Again, thanks so much for taking the time.
 
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BuddytheReow

Breadboard Baker
OK. A couple of things. Let's get the top half of the circuit working before we tackle the bottom portion.

-Did you crank the gain pot all the way before testing? Pin 2 and 3 should be identical.
-Your volume pot has a short somewhere. Check your solder joints/connections between pins 1 and 2.
-Your IC voltages look ok. To give you a quick overview of this chip:
introduction-to-jrc4558-2.png

Pins 5, 6, and 7 are acting as a buffer here.

Once you've got that working I would start checking for shorted connections on the bottom half of the circuit. Visual inspection is key here. Check to make sure you have no solder bridges anywhere where they shouldn't be. You may have to use a solder sucker and reflow the joints.
 
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adamwithanh

New member
SUCCESS! I reflowed lug 2 of the gain pot and that fixed the signal there. You were right about the volume pot, it was f-cked. I switched it out twice before I got one that worked properly (I guess the potentiometer kits from amazon are a crapshoot), and viola, sound emerges!

Some lessons I've learned from this experience that weren't obvious to me:
1. Lugs 1 and 2 of pots should be the same. It makes sense now, but I hadn't specifically read that anywhere. Maybe it's obvious to most people. Oops.
2. Soldering is EVEN more likely to be the problem than I previously believed. It says it in every troubleshooting guide, but I really felt like I'd gotten it down. Some of my pot lug wires were sorta splayed out within the joint, which also wasn't keeping a good connection.
3. How to create and use an audio probe. Holy crap this one is huge. Absolutely could not have done this without that. Invaluable, thank you.

Things I'd like to understand better in the future:
1. How to know what values each pin of the IC should have. I understand that there's a lot to learn about how these work, and so far everything I've read or watched has gone over my head really quickly. But how do people on here use the voltage values of each pin to determine whether or not the IC is working properly? And the same for transistors? Is this just one of those things that takes years to even begin to understand?
2.

Thanks so much for all the help, BuddytheReow. Seriously, I was getting close to thinking it just wasn't gonna be possible for me to continue doing this as a hobby.
 

BuddytheReow

Breadboard Baker
SUCCESS! I reflowed lug 2 of the gain pot and that fixed the signal there. You were right about the volume pot, it was f-cked. I switched it out twice before I got one that worked properly (I guess the potentiometer kits from amazon are a crapshoot), and viola, sound emerges!

Some lessons I've learned from this experience that weren't obvious to me:
1. Lugs 1 and 2 of pots should be the same. It makes sense now, but I hadn't specifically read that anywhere. Maybe it's obvious to most people. Oops.
2. Soldering is EVEN more likely to be the problem than I previously believed. It says it in every troubleshooting guide, but I really felt like I'd gotten it down. Some of my pot lug wires were sorta splayed out within the joint, which also wasn't keeping a good connection.
3. How to create and use an audio probe. Holy crap this one is huge. Absolutely could not have done this without that. Invaluable, thank you.

Things I'd like to understand better in the future:
1. How to know what values each pin of the IC should have. I understand that there's a lot to learn about how these work, and so far everything I've read or watched has gone over my head really quickly. But how do people on here use the voltage values of each pin to determine whether or not the IC is working properly? And the same for transistors? Is this just one of those things that takes years to even begin to understand?
2.

Thanks so much for all the help, BuddytheReow. Seriously, I was getting close to thinking it just wasn't gonna be possible for me to continue doing this as a hobby.
OK. Great to hear you've got the opamp part working. Have you checked to see if the bottom part of the circuit is working?

This will help clarify about potentiometers. Definitely worth a read. https://www.coda-effects.com/2015/12/potentiometers-and-guitar-effects.html

How good are you at reading schematics? This will help you troubleshoot in the future.

For IC voltages you'll need to learn what pin does what. The 4558 opamp is grounded at pin 4 for most circuits so it will measure 0 99% of the time. Pin 8 is the input voltage so it should be 9v or whatever the power supply is. For the others you'll need to read up on voltage dividers and how resistors change the voltages in a circuit. This part is EE 101. Here is a good link to learn most of the basics. https://www.allaboutcircuits.com/textbook/. You can find other items in the "resources" thread in the Test Kitchen.
 
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adamwithanh

New member
The transistors are getting voltage now, and they weren't before. So that's good, yes?

I've read that coda-effects page, but it was very helpful to review it again.

And this other link you sent is AWESOME. I keep asking people how I can go about understanding circuits better and ending up with articles or youtube channels. Very helpful, but not comprehensive.

I've been getting better at reading schematics, though there are a few things that still confuse me, like whether it matters if commons are connected in series (like, daisy-chained) or if they should all string back to one singular point (star grounding or something like that?)
 
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giovanni

Well-known member
I think the grounding thing is more of a next level topic that doesn’t come up until you really understand circuit design, noise, and a bit of electromagnetism.

As far as how to understand circuits, it can take some studying to get there. I studied EE and that foundation is really helpful. Not that you should know all of that, but at least you need to understand ohm law and its extension to the frequency domain, and how common components work (resistor, capacitor and inductor to begin with). Next, I would look into how ideal op amps work (much different from actual op amps) and ideal voltage sources (also much different than a guitar pickup). That’s a lot of topics and I haven’t even mentioned transistors (which are building blocks for op amps, among other things).

In college I used Sedra-Smith as a textbook for this stuff, but I find it kinda meh. The art of electronics is famous but really not beginner friendly. Others on the forums have recommended other books, you should be able to find better references. And I’m happy to help if you have questions.
 
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