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Reliable source for creating ground loop/mains hum?
MUFF WIGGLER Forum Index -> Music Tech DIY  
Author Reliable source for creating ground loop/mains hum?
artilect99
Anyone know of a reliable way to get ground loop/mains 60-cycle hum from a dedicated circuit? I realize this is usually something people want to get rid of like the plague, but I'm looking for a dedicated patch point which produces it rather than having to fuck with a patch cable with one end hanging, etc... ideally this would be a buffered signal not susceptible to loading/impedance issues.

I've tried mixing noise and a ~60hz squarewave to simulate it but it doesn't seem to be as "rich" a signal... am I crazy?
fitzgreyve
I've read in a number of sources that what you hear is mostly the first harmonic - for you that would be 120Hz



Sorry, Doesn't help with actually generating it, however a mix of fundamental and first harmonic (sines) has a good sound to it ?
fuzzbass
If you have a spring reverb unit, try feeding 0V from its send through the reverb pan and back via the return line. This has proven reliable in the past.
Grumble
60Hz (or 50Hz where I live) hum is usually NOT a rich (you mean a lot of harmonics?) signal, that why it's called hum in the first place Mr. Green
You get a lot of harmonics (which make the "hum" sounds fatter) when using dimmers and the signal from that is picked up by your sound system.
Dimmers just cut-off the sine wave when enough energy is detected as the control is set for and you will find the first harmonic usually the most powerful frequency in that situation because the sine wave of the power line is cut twice, once in the positive and once in the negative half of the sine wave.
One sure way to get the 60 (50) Hz into your system is to connect a coil to the input of an amplifier.
joem
Easy!



(Don't actually don't do that, please. Dead Banana )
windspirit
i was on a noise forum awhile agoand someone literally had a step down transformer that plugged into the wall with an audio jack on the other end. Be very careful if you attempt this (and obviously I claim no responsibility if you mess anything up including your life).
ndf
A loose guitar pickup works great. Something like the attached photo - add some gain (eg using MI Ears) and you have hum - and noise and whatever else.

artilect99
Damn, and I thought this wouldn't get any replies!

That actually explains a lot, thanks Fitzgreyve... I'll try more first harmonic.

I do have a spring reverb, but it's usually being used for more important stuff (e.g. reverb) ... it would certainly work though, it's a bastard for hum depending on where it's positioned!

ndf -- what am I looking at there, just a guitar pickup soldered to a 1/4" jack..? I'm guessing the trick is lots of gain... hihi
artilect99
Grumble -- I just meant that I wasn't able to synthesize it convincingly. Looking at Fitzgreyve's spectrograph there is a lot of harmonics above the fundamental, and a lot of energy below. It's much more buzzy and complex than a pure 60hz fundamental.
artilect99
Found this, which gives a convincing simulation in software... no wonder I found it hard to replicate this kind of complexity on a synth. Maybe some kind of 40106 squarewave generator with specific tunings and passive filters would get me close...?

EDIT: whoops, forgot the link

60hz Hum
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