Grounding.

[dudelove]

i've been very confused by this term grounding. can someone please enlighten me with a few links or some good information?

well i dont really know what to ask because its all so confusing to me. hahaha..

i mean things like when i plug my guitar, pedalboard to play. and i want to play along together with a song, so i plug my ipod into a set of speakers. once i plug it in, there's loud hum coming from my amp. remove the ipod, the hum goes away. and, when i like touch any metal part on my pedals, or my cable, the hum stops too.

i'm using humbuckers, an isolated power supply and my amp has been grounded.

i hope to understand the whole issue abt grounding and stuff. i've experienced alot of other wierd issues as well.

 

[lightice]

Hum usually comes from two sources.

Firstly, its grounding issues like you've mentioned.
Secondly, its magnetic/RF interference due to high powered AC supply or a strong transformer nearby interacting with the guitar's pickups causing 60 cycle hum.

Strong transformers and florescent light can even cause humbuckers to get the 60 cycle when pointing the pickups directly at the source.

As for grounding, you should take note of ground loops and NPN/PNP grounding.

Lets first discuss the signal chain grounding:

From you -> guitar -> cable -> stompboxes -> cable -> amp -> speaker

Here's how it starts:

You ground the strings because the human body, which is mostly composed of water, is an excellent conductor. As a result it acts as an antenna, amplifying any noise present to a sometimes deafening degree.

By grounding the strings you ensure that when you touch them you are yourself grounded to the circuit, which then bleeds off that amplified noise to ground. You can test this by setting up your guitar in front of the amp and cranking the volume. Then move a few feet away and slowly move up against the guitar. You'll find that the noise and buzzing from the pickups will increase as you get closer to them, only vanishing when you finally touch the strings.

If you don't ground the strings you'll find that the noise and buzzing from the pickups will actually increase when you touch them.

All electronics and signal components in the guitar are grounded commonly.
The electronics are connected to the output jack ground, which connects to all cable shielding/ground, which is in turned connected to all stompbox chassis and amp chassis and the speaker is also grounded commonly with all grounds in the signal chain.

Why ground loops occur:

According to Randall:
A ground loop is a situation where you may be inadvertently grounding a device in multiple places at varying potentials.

It just means that 1 device is grounded to different grounding paths.

Here is a diagram: http://alexplorer.net/guitar/basics/grounding.html

For ground loops in the signal chain, it can be due to power supply mixing NPN and PNP devices. Because NPN uses negative ground, PNP uses positive ground.

Also, having 1 signal into 2 amps plugged into the same mains outlet can also cause ground loop. this can be solved by lifting the ground or not grounding 1 amp to mains.

There's a lot more info available on the net, but as a basic this is it. I hope you understand what I've written, if in any case you have doubts please list them down. I'd be glad to explain as best I can.

 

[gsonique]

ipod not grounded :mrgreen:

I bet your speakers are the powered type with built in amp.
i bet too that it runs on supply from an adapter type with no ground reference
...