Case and Ground!

eruarou · Post by **eruarou** » 19 Apr 2012, 05:59

merlinb wrote:
eruarou wrote:for a proper earthing and grounding scheme... 3 cables are needed... but the guitar cable only has 2.. Ring and Sleeve... SO WT....F...
how to do there
Only mains powered equipment with a metal chassis needs a mains earth.

A guitar is not mains powered. A pedal is not mains powered (usually). These things do not need mains earth. The amplifier does, if it is mains powered.

What sort of 9V supply are you using?

im using this one
http://www.reichelt.de/Festspannungsnet ... 9f3d10d1d0

merlinb · Post by **merlinb** » 19 Apr 2012, 08:49

eruarou wrote: im using this one
http://www.reichelt.de/Festspannungsnet ... 9f3d10d1d0

That is a switching power supply- that is almost certainly your problem! It's not bad grounding, it's power supply noise! Switch-mode adapters are notoriously noisy, especially when used with transistor pedals like the Fuzz Face.

You need to buy a 9V regulated, linear adapter!

eruarou · Post by **eruarou** » 19 Apr 2012, 16:03

merlinb wrote:
eruarou wrote: im using this one
http://www.reichelt.de/Festspannungsnet ... 9f3d10d1d0
That is a switching power supply- that is almost certainly your problem! It's not bad grounding, it's power supply noise! Switch-mode adapters are notoriously noisy, especially when used with transistor pedals like the Fuzz Face.

You need to buy a 9V regulated, linear adapter!

boaaaaaaaaaaaaa xD whats the damn difference between this power supplies? xD

Nocentelli · Post by **Nocentelli** » 19 Apr 2012, 19:26

There's a simple test - Try the circuit out with a battery and if the noise disappears, the power supply looks more likely to be the problem.

eruarou · Post by **eruarou** » 19 Apr 2012, 20:20

Nocentelli wrote:There's a simple test - Try the circuit out with a battery and if the noise disappears, the power supply looks more likely to be the problem.

yeah when i dont have the poewr supply connected there is almost no noise.. i would say no noise!
so you guys think a LM7805 power supply would solve this thing?

phatt · Post by **phatt** » 22 Apr 2012, 12:22

merlinb wrote:
eruarou wrote: im using this one
http://www.reichelt.de/Festspannungsnet ... 9f3d10d1d0
That is a switching power supply- that is almost certainly your problem! It's not bad grounding, it's power supply noise! Switch-mode adapters are notoriously noisy, especially when used with transistor pedals like the Fuzz Face.

You need to buy a 9V regulated, linear adapter!

Arrh Yes ,, of course. Thanks Merlin Now I see the issue.

The Boss SMPU unit seems to be fairly quite but yes some are just a nightmare for the unwary.

Easy enough to tell the difference,,, REAL Transformers weigh a lot more that plastic wannabe transformers.
Phil.

eruarou · Post by **eruarou** » 13 May 2012, 10:56

one more stupid question
i have some noise hum but
Why When i touch the ground of my circuit... or the sleeve of the cable... the noise is gone??? :s

eruarou · Post by **eruarou** » 14 May 2012, 19:03

deltafred wrote:
Cub wrote:That's a good explanation, Pete ! Do you know if there is any audible difference in the amount of noise between these two methods ?
Using a resistor, capacitor, or a direct connection will make no difference.

If your case is not earthed and you touch it with your hand (a pretty high resistance to ground) that is usually enough resistance to silence it due to the very high source impedance of the interference.

why is this happening? how do you know the impedance of the interference? or which book can you recommend me to read about this?

phatt · Post by **phatt** » 15 May 2012, 03:55

The circuit *Common* and the *Chassis Ground* are at different potetials.
With high gain circuits this isuue is (just like your signal) massivly amplified.

Google ground issues in electronic circuits for clues.
Jensen transformer pages contain a whole list of PDF's that also might help you grasp the issue.

Also go seek out SNR (Signal to noise ratio)related topics.

Most hot rod pedals don't bode well when you look at the SNR specs.

Any hobby person can build a distortion circuit,,,,but building one with low noise is a whole other subject which is not easy to explain.

I'm no expert but at some point common sense tells you that you have to turn things down in most circuits and find a happy medium.

The noise comes from a combination of many factors mostly the passives (and layout of same) which means use of actives claiming insanely low noise won't make one ounce of difference if you have not got the basic circuitry all sorted for best results.

Back to your Q.
I believe players like SRV used a splitter box which separated the guitar ground/common from the amps.
The box had it's own separate ground connection.

In other words you could drive a ground stake into the earth and connect the common of the guitar to that instead of amp common.

I won't say exactly how it was done because done wrong it could kill someone,, but it is a valid way to alleviate ground loops and such issues.

Keep asking as I'm sure better qualified folk here can explain it better than myself.
Cheers, Phil.

deltafred · Post by **deltafred** » 15 May 2012, 10:45

eruarou wrote: how do you know the impedance of the interference?

The impedance is very high, it would be pretty difficult to measure and also rather pointless as all you really need to know is how to suppress the interference.

.. which book can you recommend me to read about this?

I have never seen anything about it in a book although I am sure someone must have written about it.

As to the why, I have my own theory but it may be completely wrong and I don't want to mislead anyone.

eruarou · Post by **eruarou** » 15 May 2012, 17:23

Thanks for your replies...

but then the question how to supress the interference? just by having a grounded case?! ...
i cant understand that... why that happens...

deltafred · Post by **deltafred** » 15 May 2012, 22:29

eruarou wrote:Thanks for your replies...

but then the question how to supress the interference? just by having a grounded case?! ...
i cant understand that... why that happens...

The case forms a Faraday Cage as long as it is grounded (see extract from wikipeadia below for how it works).

*When it is not grounded It will act as an aerial and pick up any radiated signals (interference) and will retransmit them to the circuitry inside the box.

(*This is the bit I am unsure of so if anyone has a better explanation please feel free to post it. I am sure this is a very simplistic explanation and there is no doubt lots of maths involved in the proper one.)

Wikipedia wrote:A Faraday cage or Faraday shield is an enclosure formed by conducting material or by a mesh of such material. Such an enclosure blocks out external static and non-static electric fields. Faraday cages are named after the English scientist Michael Faraday, who invented them in 1836.[1]

A Faraday cage's operation depends on the fact that an external static electrical field will cause the electrical charges within the cage's conducting material to redistribute themselves so as to cancel the field's effects in the cage's interior. This phenomenon is used, for example, to protect electronic equipment from lightning strikes and electrostatic discharges.

Faraday cages cannot block static and slowly varying magnetic fields, such as the Earth's magnetic field (a compass will still work inside). To a large degree though, they shield the interior from external electromagnetic radiation if the conductor is thick enough and any holes are significantly smaller than the wavelength of the radiation. For example, certain computer forensic test procedures of electronic systems that require an environment free of electromagnetic interference can be carried out within a screen room. These rooms are spaces that are completely enclosed by one or more layers of a fine metal mesh or perforated sheet metal. The metal layers are grounded in order to dissipate any electric currents generated from external or internal electromagnetic fields, and thus they block a large amount of the electromagnetic interference. See also electromagnetic shielding.

The reception or transmission of radio waves, a form of electromagnetic radiation, to or from an antenna within a Faraday cage are heavily attenuated or blocked by a Faraday cage.

John Ricky · Post by **John Ricky** » 15 May 2012, 23:12

deltafred wrote:
The case forms a Faraday Cage as long as it is grounded (see extract from wikipeadia below for how it works).

*When it is not grounded It will act as an aerial and pick up any radiated signals (interference) and will retransmit them to the circuitry inside the box.

(*This is the bit I am unsure of so if anyone has a better explanation please feel free to post it. I am sure this is a very simplistic explanation and there is no doubt lots of maths involved in the proper one.)

Simplistic but accurate. What happens is radio waves induce eddy currents in the metal. When grounded these happily flow away, but if there is any impedance to ground that can allow a potential difference, you get reradiation. The dimensions of the box will define the resonant frequency.

Here's a practical example...

http://berkeley.intel-research.net/arahimi/helmet/

For a slightly more theoretical approach take a look at

http://www.analog.com/static/imported-f ... AN_347.pdf

Cheers
John

deltafred · Post by **deltafred** » 16 May 2012, 08:48

Thanks John, I'm glad I was on the right track as I didn't want to mislead anyone. I knew someone on FSB would know more about it than I did.

Love the article on the tinfoil hats!