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I'm trying to build a guitar delay effect based on this schematic:

Schematic(https://i2.wp.com/cdn.makezine.com/uploads/2009/09/echobenderrev02.jpg)

I designed and oredered a pcb : https://easyeda.com/editor#id=7e588f25fbf742a5b97965476faa0c72|5b4e3f8fb2d04a0993a5a7e7a2797ad2

After waiting for few weeks, and hours of soldering I can't get it to work... All I Can hear is noise, nothing close to guitar. I double checked (I think) every component and its pinouts.. Can you help me somehow? It's my first project with pcb's...

The soldered PCB

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2 Answers 2

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It's very hard to see much anything in that image, but... frankly yeah, your soldering is terrible. That's all about practice though (much like in music!).

Generally speaking, to debug an electronic circuit, you should hook it up to power and check the potentials at different spots in it – first DC levels with a multimeter, then feed in an audio signal and see how it propagates, and where it fails.

I'd first make sure the operating voltages of all the ICs are right. The +5V should be pretty exact thanks to the stabiliser, the 9V depends on your power supply, and the unstabilised 4.5 V should at least be in between 4V and 5V.

If that's ok, see whether the OP-amps have any excessive output biases. With no input signal, their outputs – i.e., pins 7 and 1 – should also be about 4.5 V. If not, the problem is either that OP, or the parts immediately around it.

Specifically here, you'll likely find that IC2b won't be working correctly, because the input signal comes through an electrolytic capacitor with wrong polarity. See if C21 actually still works (it might well be damaged from the wrong charging). I would replace C21 and C22 with 100 nF unpolarized foil caps and R16 / R17 / R18 with 50 kΩ / 56 kΩ, respectively.

If the DC levels are right, make yourself an audio probe. That's easiest done by soldering a 100 nF / 220 kΩ high-pass RC filter into a 1/4" jack, with ground connected to 0 V and the other end of the cable to a guitar amp (Hi-Z input). Then check that at least the “dry” signal passes through.

About the PT2399 and its surrounding I can't tell you anything.

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    \$\begingroup\$ Everything leftaroundabout says here is spot on. I used to make a lot of guitar effects (still do occasionally) and in the beginning there are so many mistakes you can make you just need to learn troubleshooting steps and how to estimate expected voltages/current at each point. Useful data sheet: electrosmash.com/pt2399-analysis \$\endgroup\$
    – Rory Alsop
    Dec 3, 2018 at 22:16
  • \$\begingroup\$ Thanks for tips, I'll do my best to do something out of it! \$\endgroup\$
    – Brunon
    Dec 4, 2018 at 17:30
  • \$\begingroup\$ well, I checked the dc levels and everything was fine, the op outputs were diferent, 1 was 7,5v and 7 was 4,5. I changed the cappasitors and resistors as you suggested, and dc everywher is the same, exept for pin 7 which changes for 7v ... \$\endgroup\$
    – Brunon
    Dec 4, 2018 at 19:11
  • \$\begingroup\$ Even when both DRY and WET are turned down all the way? What about pin 2? \$\endgroup\$ Dec 4, 2018 at 20:06
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    \$\begingroup\$ Well, the probe is hopeless when the DC levels aren't even right. So, you have pin1: 7V, pin2: 7V, pin3: 4.5V? That would mean the OP-amp is broken. Can happen quite easily with too high solder temperature. \$\endgroup\$ Dec 4, 2018 at 20:31
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Besides @leftaroundabout 's awesome answer, I would like to suggest you a new approach.

I don't know if you skipped the explanation of some steps in the question, but looking at a schematic, designing a PCB and soldering is very risky, I would bet 1000 dollars against it. So, I will share what I think would be an ideal experience of getting a PCB to work.

  1. The project: calculate and design the circuit (in your case, this was already done)
  2. The simulation: Use a circuit simulation software, for example OrCad, draw your circuit in there and test it with different inputs. At this point you may already catch some project mistakes, but I wouldn't expect it to be the case here.
  3. The prototype: Use a Protoboard and build you circuit there, with the actual components you plan on using. This is where you could debug it and notice and correct all that @leftaroundabout said. (without waiting weeks and spending hours soldering yet)
  4. The PCB: After you get your prototype to work, then do exactly what you did. Chances of getting it right are 1000% higher now :D
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