Electronics > Beginners
Damage to a Guitar Pedal
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eev_carl:
Hi,

I was checking out the waveforms on some of my bass guitar effects pedals and think I damaged one.  I have a HomeBrew Electronics boutique overdrive / preamp.  I had plugged a bass in the input and broke out the output so that the tip and sleeve went to an oscilloscope.  I did this with several other pedals and was able to compare the different clipping waveforms.

Could a setup like this damage the pedal?  The pedal doesn't turn on anymore (other ones that underwent the same test do still function).  I used the same power adapter that I use during normal operation so I don't think there's a polarity problem with the supply.

Thanks,
Carl
Buriedcode:
It is unlikely that hooking it up to the scope like you said would damage the pedal, and even more unlikely that shorting the output would damage it.  Most overdrives only contain diodes, transistors or opamps, so not much to go wrong, although these can be killed given the right conditions.   The most common faults with guitar pedals are the mechanics - connectors, switches, broken knobs, stuff that takes the abuse.

When you say "it doesn't turn on" do you mean no signal output, or no indicator LED or both?  Most pedals these days are true-bypass, but are turned on by plugging in the input jack (the socket is stereo, so switches to ground). Also because of ground loops, DC jacks tend to be reverse polarity, which means if you use a DC socket that electrically connects to the metal case, the case can be at +9V rather than the 0V.  I suppose that connecting to a transistors base could fry one, but again its very unlikely thats whats happened, I'm just guessing.

A schematic and maybe even a photo would be helpful :)
floobydust:
What is your power supply for the pedals?
A (two-prong) SMPS wall-wart will float at ~60V due to the Y-capacitor.
Pedals usually get 9VDC power floating with respect to earth-ground. You can prove this by measuring ACV from guitar sleeve to earth-ground. It's not enough leakage current to give you a tingle but it can damage an IC if you hot-swap in the output jack to something earth-grounded like an oscilloscope.
The (pedal) tip touches earth-ground and a discharge occurs.

The other way to damage a (not well designed) pedal- shorting the tip to GND can do it if the output cap has a charge on it.
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