pedal SHIELD MEGA - NOT WORKING AT ALL

4 years 8 months ago #1972 by Memos
Hello to everyone, newbie here so be please be patient :silly:

I followed the building instructions step by step.
I followed the troubleshooting step by step - but it seems that the most of you at some point you have guitar sound with a lot of hiss.

I can't hear any guitar sound!!! ONLY HISS

I did the led screen and the blink tests and uploaded all the codes and it seems that the pedal recognises the effects.Also signal generator is working fine. Buttons are working fine too...but still no guitar sound..

Maybe you can help me with some tips what is going wrong?! :unsure:

Thanks in advance

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4 years 8 months ago #1973 by Ray
Hi Memos,
It is normal to have some background hiss in the system, but the guitar signal is always much louder than the noise, in fact when you play the guitar you should not hear any hiss.

I did the led screen and the blink tests and uploaded all the codes and it seems that the pedal recognises the effects.Also signal generator is working fine. Buttons are working fine too...but still no guitar sound..

If the signal generator is working thats good, because the output stage is working. So probably your issue would be located on the input stage.

Did you check the voltages on the op-amp? anything out of specs? you should have something like:




Im sure that you already did it, but did you tried adjusting the VR1 potentiometer?
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4 years 8 months ago #1974 by Memos
Hi Ray! Thank you for your quick response!

I checked the voltages and the measurements are fine except one (op-amp 1.39V instead of 2.6V) as you can see in the photos below.

But still, no guitar sound. :unsure:

Please let me know what's the next move...




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4 years 8 months ago #1976 by Ray
Thanks for the images.
I can see that you have 1.39V instead of 2.5 at the op-amp pin5, but that should be fine its a high impedance point and multimeters have a hard time measuring that.
The first thing I would try is to retouch with a soldering iron all the points of the input stage, many users fix like that all their problems.
I'm not sure if you did that already.

Also, did you try just the simple "clean" code and try go to bypassing and non-bypassing and see if at least the bypassing is working?

And remember that input/outputs are mirrored from a "normal" guitar pedal.

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