grounding

[Guest massi]

Hi everybody ,my second posting here,I have to say ,midibox forum works GREAT :)

I ve a question about ground:wich pin or way to plug the metal chassis to the core?and what else has to be grounded to the chasiss?please tell me all the ground connection I have to do except the knobs and faders of course.

thanks in advance

massi -italy  (midibox 1.0 thorsten rule!)

[pay_c]

Mainly only the chassis. Take any ground connection (e.g. just solder a wire under the core on some ground - the big stuff is always the ground).

Take care of isolating the power supply good from the chassis (could bring in some short). The other plugs don´t need to be grounded anyhow (MIDI conns, Banksticks and so on).

I think thats it...  :)

[Guest massi]

Thanks again Pay_c :)

Ive solved the previous ainx problem,was a short

So just ground the core,no need for ainx or dinx..

best regards maximilian

[pay_c]

Errr... just btw: (am a little  ??? cause of your answer)

The ground, no matter if the GND of the core or of the AIN or whatever is everywhere the same! So it doesn´t matter wether you take the ground for the chassis from the AIN or the Core or whatever.

The only thing you shouldn´t do: Making ground "circles" - this means e.g.:

CoreGND---DIN1GND---DIN2GND---whateverGND---chassisGND---andbacktoCoreGND

This *can* bring in ground humming into all your signals if the circle is getting very long.

Greetz

[moebius]

Hi,

Analogue Devices Application Note AN-347:Shielding and Guarding is a great resource for "more technically" minded people. Giving detailed information about noise pickup and how to avoid it.

www.analog.com -> "Technical library" dropdown menu ->Application Notes.. and there it is somewhere ;)

Bye, Moebius

[Fx3_hdrive]

i have a relevent Q about grounding the core with mains grounding. because i am using an internal PSU (i know ;D, kool) and here in britan a we have a 3 pin mains plug (live, neutral, ground)

The Q is can the mains ground be connected with core groung ? will it not interfere?

you can read on if you like...

I had a wire form my radiator to ground myself while i was working with PIC (good point this), and i touched a serial port of my PC and i got an 80 volt shock. why? what? were? how? i was asking myself and belive me, it wasnt pleasent :(.

Strange things...

by the way i know it wasn't 220v because i'm still here and it did feel more like 65 to 80v, belive me i've been shocked dosens of times so i've grounded my midibox so by brother woudnt have to expirience it too.

/edit: just spelling

[moebius]

The Q is can the mains ground be connected with core groung ? will it not interfere?

Yes, you should probably connect it. At least with all metal casing.

(With mains powered equipment with conductive parts to be touched by user, this provides protection agains hazardous faults (ie. short circuit from "live wire" to chassis) as it provides "return path" to ground, blowing the fuse)

Only thing to look out is creating ground loops - there should be only one path to the ground.

why? what? were? how?

I know the feeling.  :o (Got it from an old coax ethernet cable and a radiator).

There's a different potential between a "mains grounded" (?) computer case and the radiator.. so radiator really isn't a ground point, more like voltage source ;) Don't ask me why .. :D

Bye, Moebius

[Fx3_hdrive]

thanx for your reply.

i asked if i can connect the core GND to the mains GND because i was afraid that the core ungrounded might get some noize, i have grounded the mains strait away and its the choice between connecting the core and not connecting the core. will core get noize if its not conected to the metal case?

P.S.

why? what? were? how?

its more like : Ahhh! you mother f-f-f-f... !!!

[moebius]

Yes, just ground the core. As long as everything is connected to one common ground (point) external and internal interferences should be "sucked" to it. (Or, if this is MBSID, you can experiment: "With or without" - can you hear, what happens to SID noisefloor)

its more like : Ahhh! you mother f-f-f-f... !!!

Yup.. but it's so much more pleasant to be able to curse than That 220v total blackout(CH!!) ;)

Bye, Moebius

[pilo]

the case should be wire to the midibox ground by only one wire, taken from the Psu for example. Try to avoid ground loop.

For the radiator stuff, maybe you're computer is not plug to earth, is it? if not, then you have the answer :)

I think it's the same here, we've got neutral and phase on all plug, and earth on some.

As far as I remember neutral is the earth of the stuff that give you the current (nuclear plant), but as it comes from far away, it's not the same voltage as the earth in your house. That's why there is another earth on your plug :) putting the case to ground I think is for CEM stuff (is it the same word in english?), and then the best is to put it to earth.

take care that some IC that need heatsink has not always their metal parts wire to gnd... I remember when building a gain clone with LM3886 in non isolated package, which was internaly wire to -V (-35V!), and then a jack fall on it... makes beautiful smoke :)

Maybe I wrote wrong things here, and I would be pleased if someone can correct me, that's  the questions I always want to ask but always forgot....

[moebius]

For the radiator stuff, maybe you're computer is not plug to earth, is it? if not, then you have the answer :)

Had to check this out. Extension cable has "ground", but livingroom wall outlet doesn't: Between extension cable "ground" and the radiator: Nice 110VAC, Ouch! (Of course I HAD to touch it)

take care that some IC that need heatsink has not always their metal parts wire to gnd...

..like 78xx vs. 79xx regulators. (Gotta remember that when building AOUT module..?!)

Pilo, Thanks..

Good tips and points out there,

Bye Moebius

[Mickey_Sadler]

Years ago I worked in an area with electronic equipment, computers, teletypes used as computer consoles (now you know how old I am) in an area wired by "licensed electricians". I was touching one piece of equipment and leaned over and touched a teletype I was reading information from and got a dandy shock. Seems like the "electricians" had miswired ground in the shop and there was around 68 volts between grounds. Some equipment in that room ran on 120 volt, some 240 volt (both single phase) some on 208 volt three phase (all 60 cycle), some on 220 volt single phase 400 cycle, etc. Made my day go a bit slower till I found what was ok to touch and what was not!

Mickey

[moebius]

Mickey

I have a growing respect towards LIVING electricians ;)

A friend told me that as he was with his father, who was doing service/ installation work at a big factory, how his father insured that cabling was powerless.. by just swinging a knife with insulated shaft, cutting through cable carrying 220v.. and same time checking which fuse that line was connected..

I did another check at my cabling. It's still 110VAC between ground point of the extension cable and the radiator, even without anything connected, so it must be parasitic inductance.

Bye, Moebius

[uclaros]

Hi all!

I have a question about grounding too!

Suppose the following setup:

A wall outlet with three terminals (including ground),

a (how do we say in english the T used on outlets to provide 2 or 3 outlets out of a single one, u get the point),

a pre-amp with a 3 terminal plug,

a power-amp with 3 terminal plug.

OK, we connect them alltogether, plug in our instrument and play.

The question is : Haven't we made huge ground loops between the pre, the poweramp, the outlet and the audio signal cable's ground??

Wouldn't it be better to ground only the power amp and provide ground to the pre over the signal cable??

Thanks, uclaros!

[arumblack]

You may be right, from an audio point of view. but from a safety point of view the way you currently have set up is correct. Guitar players have died from this ( so I've heard, though i believe a damp stage was also involved...), and you could geta nasty shock. though it could work just fine.

[moebius]

Well..

This is JUST a thing I am wondering about. If all the equipment are provided with grounding (or "grounding", like in my case, but anyway same potential for "ground") from power, and from audio connections.. forming a ground loop.

What to do? Nothing? Making "ground lifted cables" (no ground connected)? DI boxes (with transformer) boxes with a "ground lift" option?

Bye, Moebius

[moebius]

arumblack:

Really, only one path to the ground point is needed.. whatever it is. (Electrical potential between the players guitars ground point and the stage caused this.)

Bye, Moebius

[pilo]

yes it makes big ground loop, and sometimes you have too use DI box.

I think that ground loops can be a problem if they are near a tx or something like that.

I remember the first time I plug my gain clone (yes again :)) in a party (I never used it with 2 speaker before! lol) and the only sound we can hear was a big buuuzzzzz... because of ground loop (and this is when I knew what a ground loop was!! hehe)

the 79xx voltage regulator are not wire to gnd (the case)?? if 78xx are used like 79xx there is this problem, but I though that 79xx has got the case wire to gnd... have to check before putting the heatsink on my last psu then! lol

[moebius]

pilo,

and everybody else, we are learning from each other! ;) And probably having some fun..

79xx have V input at the center pin, connected to case (metal).. (Only if I knew why?!)

Bye, Moebius

[pilo]

lol yes you're right!!! I just checked (but I though I did it before)...

well, this time no smoke :) have to remember this when I'm going to put the heatsink ;)

Thanks moebius!

[doc]

Hi everybody,

... just reading your ground discussion with a big fear in my eyes !!

Just some things to remember (in Germany we have rules for this called VDE. Don't know what you have!):

Some things you are doing with MAIN VOLTAGE are very very dangerous !

Please be careful with this things. Only some things to remember:

Some things to remember, when using a psu inside a metal case:

-  you MUST ground the case.

-  you have to take care of the distance beetween leading cables and metal case (at least 12 mm).

- You have to isolate the leading wires carefully

- The ground connection of the case must be unremovable

-  you are not allowed to operate on a open case except you use a special isolating transformer (in german: Trenntransformator, don't know the english word).

There are many other things to remember. If you are interested I can post a paper (in german) where all the main rules are listed.

So .... please be a little more careful. I don't want to read someday of a died midiboxer !

If you are not an expert in MAIN voltage you should use a (more safe) wall adapter with your projects !

greets

Doc

[moebius]

Yes, doc :)

I want to make some points clear:

Ground lifted MEANS:

NO ground connection on AUDIO cable! And definitely ON mains lead -> case -> internal electronics.

reason: If two audio equipment are connected with a ground point from MAINS, audio cable ground can cause hum from a ground loop.

reference:

http://www.epanorama.net/documents/groundloop/groundlift.html

YES, metal case SHOULD be connected to the MAINS ground. But when using transformer with a central tapped secondary (ie. bipolar supply)  (YOU MUST KNOW WHAT I MEAN), with audio equipment, then you might not want to connect that to the MAINS ground, but let it get it's ground connection from a audio line.

And some reference to the safety regulations:

http://www.epanorama.net/links/safety.html

---

You must know what you're doing. If not, just use a battery pack!

Bye, Moebius

p.s. And OF COURSE: If you're using internal power supply, you MUST use a FUSE with correct rating!!!!

[Fx3_hdrive]

hi

i just looked back couple of posts and i'm thinking that some people coud have missleading info. one thing is true: MAINS IS VERY DANGEROUS.

A true story: one time in my hame town one guy had a drill that had live wire touching the metal case (we in russia dont have earth pin on a plug) and he accidently touched the radiator (he was drilling at that time) he was dead instantly!

i myself dont know much about mains but i know to be extra careful !! make shure you see somone that can assure you that you creature (MidiBox) is safe, you might miss out the obvious thing.

P.S. you need to make a switch and make sure its on live wire (thus when you flick it off it breaks the live wire to the tranformer).

P.P.S. can i have some more info on the fuse? because i dont have an internal fuse but just the one on the plug. its about 5A.

another story quite irrelevent to midibox:

on internet i found a site which describes how to make a 10 to 40 KV generator using a special transformer (yes it is 40 000 v) and suprisingly that voltage is not fatal (it will give you a big sting though) because it has only 13mA (not enough to defiblilate a human heart) it is not fatal. but it hurts !!

the target of such big voltage is to create a spark or an arc of plasma (heated air to more than 1000 C) i've built one myself using a normal tranformer. it takes voltage not from mains but from a wall wart PSU and could be adapted to run from a battery providing it can squize 4 A. i dont want to give you the address of that site incase you'll try to build it..hehe.. :P

DONT try this at home if you didnt work with high voltage before.

thankx.

[jimhenry]

It has already been said but just in case this makes it easier for someone to understand the point, shielded cables should only have the shield connected at one end.

The idea of a shield is to provide a grounded enclosure for the wires inside but it should not conduct ground from one device to another. Each device connected by the shielded cable should have its own single connection to ground. Ground in each device could be at a different potential. So the wires will be inside the ground potential of one device with the shield extending the case of one of the devices and then inside the ground potential of the other device. You don't want to try to bring the two devices to the same potential by connecting their grounds, that will create a ground loop.

The wires themselves have to have a circuit that can deal with the possible lack of a common ground reference. A MIDI out is two wires. They go to an optocoupler where an LED is powered by those two wires only without any reference to the device the LED is in. Thus connected MIDI devices are completely isolated from each other as long as the shield is connected on only one end.

The two devices could be at quite different ground potentials, meaning metal cases could be at those potentials, and everything will work fine. But if you touch both cases at the same time YOU become the ground loop! :o Proper mains wiring is designed to keep all the ground potentials of properly constructed mains connected devices close to the same value. It is hard to do. It is much easier to use an approved wall power supply and leave the job of safely getting off the mains to that device.

[arumblack]

Firstly, sorry if I'm going slightly ot, but.... (this being mostly directed at Jim Henry's post) What to do for microphone wiring. the setup, mic jacks in one room running to my mixer in the other room. do i connect shield at both ends. I think yes, because the mic has no ground (unless you are holding  and touching something grounded?). what about other balanced conections , say from mixer to powered monitors? disconnect the shield on one end?. how are off the shelf cables wired?( all three pins wired right).

I am currently wiring up my studio and am trying hard to avoid hums and buzzes.

what about mains wiring....all outlets in the studio are on the same circuit, does it matter which plug to plug the gear into?

Thanks in advance!