This guide will help you to find and fix any issue with the pedalSHIELD MEGA hardware.
As an introduction, I have to say that 99% of the problems are due to silly mistakes that you can be fixed with a careful visual inspection (take your time).
Before doing any serious troubleshooting just try to re-touch with the soldering iron ALL the solder joints, it is pretty easy to get a (disconnected) cold joint, especially in the header or op-amp socket (also try unplugging and plugging the op-amp). Take some time an re-heat the components joints to have perfect smooth connections.
Guitar connects to the right and the amp to the left hand side jack connector, like:
Make sure that the RV1 trimmer is in a good position. This trimmer resistor adjusts the level of the guitar signal going into the pedal. Having it in the middle position (the notch facing up) is a good starting point for any guitar, then you can go a bit clock/anti-clockwise to get a louder signal but not clipped.
Electrolytic Caps or op-amp placed wrong: Have a look to a good PCB in high resolution and check that you have yours in the right orientation.
Check any short circuit between nearby pads and check that all solder points are good.
Once all the things above are checked, take again your soldering iron and re-solder again all the joints (you can apply some extra solder if needed). This will fix any dry joins. This action takes a minute and solves a lot of problems. Don't forget the pin headers and also un-plug and plug the op-amp into the socket again.
Now, the best way to troubleshoot the pedalSHIELD MEGA PCB is following these 4 steps:
1. Check the power supplies: There are 3 test points on the PCB labeled as GND, +2.5V, and +5V. Using a multimeter make sure that you have there the right voltages at those points. Also, check that the op-amp is correctly powered (GND on pin 4 and +5V on pin 8 ). Additionally, check that you have the voltages of the image below:
2. Check the output stage: You can load the sine-wave generator program. It only uses the output stage independently if the input stage is wrong. If it works you can be sure that the second 1/2 op-amp area is good.
The sinewave generator code is here: www.electrosmash.com/forum/pedalshield-m...rduino-mega-2560-adk
3. Check the input stage: Be sure that the trimmer VR1 is in a "medium" position, you can adjust it better later. Load a clean/volume pedal and check if you are able to get it working. Note that it is mandatory to have the sinewave code working before trying the Clean pedal.
The Clean pedal code is here: www.electrosmash.com/forum/pedalshield-m...5-clean-guitar-pedal
As a tip I can to say that 99,9% of the errors are due to some connection is wrong or some component is misplaced. From previous experience building dozens of pedalSHIELDs they always work straight away from soldering correctly, but we are all humans and we all make mistakes.
If all the above fails, just carefully component by component that it is well placed and orientated, don't take anything for granted.
If you can borrow another pair of eyes to have a look at it, do it. Sometimes others can easily see things that we are passing over.
If you have an oscilloscope and a signal generator (I use Visual Analyzer) you can trace a sinewave from the input jack -> op-amp input -> op-amp output -> input ADC. You can also trace the output signal from the Pi Zero PWM outputs to the op-amp, etc...
- In the first video, I can hear that the sound has improved with the 9V battery pack that you use. The power supply noise is maybe the biggest factor of noise in this project.
The noise is still noticeable so I wonder if maybe the gain that you are using at the amp is a bit too high, there is no guitar signal to compare. I don't know if I am explaining myself clearly but if the amp gain is pretty high, it is "normal" to have some background noise as the general guitar level and noise will be playing over it.
In terms of sound quality I think that the DUE shield sounds better, but just by a small margin, they are not completely different animals.
- In the second video, the signal generator can be heard even with the effect disconnected, this can be fixed by software by adding
after the sentence:
digitalWrite(LED, LOW);// switch-off the LED
Basically, it will stop the signal generator when the effect is off.
This again could be seen if the gain of the amp after the pedal is too high, although in theory the effect is completely disconnected due to the action of the 3PDT footswitch, a tiny portion of the signal could be coupling into the audio path through the switch and the amp could be amplifying it...
Just in case... could you check (with a multimeter (if you have one)) that your 3PDT connects the pins like the image below?:
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