MXR 117?

[shawnee]

Since this project is in the works, I have a question: The vintage MXR flangers that I have seen have a GND pin on the power cord. How can you ground the case on the AC side if the case is part of the negative for the DC side?

[stecykmi]

turns out it doesn't matter. the AC input is rectified (ie turned into DC), but this actually only uses the live and neutral rails. The ground is (almost) only for safety reasons.

[shawnee]

Thank you for the reply. OK that makes sense. I wonder if it could introduce noise into the DC side of the circuit? (I guess it doesn't or they wouldn't have added an AC ground). So my next question is: would you add a ground to an AC powered pedal that didn't have a ground wire to start with?

[stecykmi]

only way that I could see noise added is if you didn't filter the rectified power enough.

for switching over to a 3-prong cord, it depends on the circuit that's already there. I'm not familiar enough with rectifier circuits to say exactly what to do, but it might be as simple as attaching the ground wire to the enclosure. but chances are you don't really need to play with it as long as it's already working.

[shawnee]

OK. Thanks for the input. I guess I should leave it off since it wasn't there before. I already wired in a 3 prong cord and thought that it may not be a good idea to ground the case that has DC negative on it already. I can pull it and put a two prong cord on it.

[stecykmi]

you can also just leave the 3rd prong floating, there's no harm in that as long as you tape the end so it doesn't short.

[shawnee]

Yeah that's probably the easiest thing to do since it's already soldered in. Thanks.