Reliable source for creating ground loop/mains hum?

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artilect99
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Reliable source for creating ground loop/mains hum?

Post by artilect99 » Wed Jun 05, 2019 6:38 pm

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?

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fitzgreyve
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Post by fitzgreyve » Thu Jun 06, 2019 4:36 am

I've read in a number of sources that what you hear is mostly the first harmonic - for you that would be 120Hz

Image

Sorry, Doesn't help with actually generating it, however a mix of fundamental and first harmonic (sines) has a good sound to it ?
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fuzzbass
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Post by fuzzbass » Thu Jun 06, 2019 6:46 am

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.
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Grumble
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Post by Grumble » Thu Jun 06, 2019 6:52 am

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 :mrgreen:
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.

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joem
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Post by joem » Thu Jun 06, 2019 4:27 pm

Easy!

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(Don't actually don't do that, please. :deadbanana: )

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windspirit
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Post by windspirit » Thu Jun 06, 2019 10:55 pm

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).

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Post by ndf » Thu Jun 06, 2019 11:22 pm

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.

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artilect99
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Post by artilect99 » Sat Jun 08, 2019 11:40 am

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:
Last edited by artilect99 on Sat Jun 08, 2019 12:32 pm, edited 1 time in total.

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artilect99
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Post by artilect99 » Sat Jun 08, 2019 11:48 am

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.

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artilect99
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Post by artilect99 » Sat Jun 08, 2019 12:19 pm

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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