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 Forum index » DIY Hardware and Software » MusicFromOuterSpace.com designs by Ray Wilson
understanding ground in schematics..help please
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circlingcrane



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PostPosted: Sat Oct 22, 2011 5:07 am    Post subject:  understanding ground in schematics..help please Reply with quote  Mark this post and the followings unread

just getting into synth diy and have built a couple kit modules. I'm now starting to learn about converting schematics to actual working modules and have ground question. I always see the ground symbol coming off allot of designated parts in a schematic and wonder where does this ground get attached to? To the faceplate? to the neg side of the power supply? can someone help me understand ground as it relates to synth module?

much appreciated in advance for the help.
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Blue Hell
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PostPosted: Sat Oct 22, 2011 5:30 am    Post subject: Reply with quote  Mark this post and the followings unread

Ground basically is a historic mistake, the word should be banned for electronics Laughing

Anyway, as it is used for electronics circuits it really is just the zero Volt supply voltage, and it is the reference to which all other voltages are usually measured.

For ease of drawing in a schematic usually the supply voltages are not drawn to be connected, but such is implied. So all the ground symbols are connected together and then go to the zero Volt out of your power supply.

There are many possible scenarios, but what you'll see mostly is either a single ended or a dual power supply.

For the single ended one, like a battery for instance, you'll see a + and a - terminal and usually the the - terminal will be used as the zero Volt line.

For a dual power supply you'll have three terminals, where usually the "middle one" is considered to be zero Volts, and then you'll usually have another terminal that's positive relative to that and the third one being negative relatively.

It's maybe good to know that there is no such thing as an absolute Voltage - Voltage is always a difference between two potentials, and so you can arbitrarily define one potential to be Zero, and that really just means that this is your reference against which all other points are measured.

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circlingcrane



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PostPosted: Sat Oct 22, 2011 5:57 am    Post subject: Reply with quote  Mark this post and the followings unread

thanks so much for the help. So in the below example, Ray is using a dual supply (+12v) (-12v) in this schematic and all the ground icons represent wires / traces that should all go back to the 0v point on the pcb? At what point do you know which grounds just get hooked to the front metal panel and don't go back to the 0v point on the pcb? is there a rule of thumb here for understanding this? again thanks so much for helping me understand this, I've been stuck trying to understand this.


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Blue Hell
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PostPosted: Sat Oct 22, 2011 6:56 am    Post subject: Reply with quote  Mark this post and the followings unread

circlingcrane wrote:
[...] in this schematic and all the ground icons represent wires / traces that should all go back to the 0v point on the pcb?


Yes.

Quote:
At what point do you know which grounds just get hooked to the front metal panel and don't go back to the 0v point on the pcb? is there a rule of thumb here for understanding this?


Hard to answer that in general, as it depends on the actual construction .. but you can try to connect the front panel to the PCB at the same point where the zero volts of the supply is connected to it, that's not a bad choice usually.

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circlingcrane



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PostPosted: Sat Oct 22, 2011 7:08 am    Post subject: Reply with quote  Mark this post and the followings unread

Blue Hell wrote:
Hard to answer that in general, as it depends on the actual construction .. but you can try to connect the front panel to the PCB at the same point where the zero volts of the supply is connected to it, that's not a bad choice usually.


thanks for the teaching. I now have a better understanding of the ground symbol, as it relates to modular synth schematics. Much appreciated and grateful.
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sompost



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PostPosted: Sat Oct 22, 2011 8:27 am    Post subject: Follow-up question
Subject description: ...regarding power supplies.
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I have a follow-up question to "understanding ground in schematics".

I am building a 19' rack unit synth with its own power supply fed from the mains power. I want to 'earth' the metal case of the unit (i.e. connect it to the earth plug from the mains connector).

My question: does the earth (from the mains power) need to be insulated from the ground (of the circuit) or are they the same? Note that the front panel will be connected to the ground (via jacks, pots and stuff) and also to the earth (via the metal case).

Thanks for your advice.

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Blue Hell
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PostPosted: Sat Oct 22, 2011 9:22 am    Post subject: Reply with quote  Mark this post and the followings unread

Oh .. thats like opening a can of worms ... I'd not ground the case to safety ground, but make sure the mains wiring is well fixed and insulated. Such is allowed according to the rules in NL.
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varice



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PostPosted: Sat Oct 22, 2011 1:47 pm    Post subject: Reply with quote  Mark this post and the followings unread

Blue Hell wrote:
Oh .. thats like opening a can of worms ...

That’s true Exclamation Laughing Exclamation There are many opinions about that, ranging from “I lift every ground on all my equipment” to “I ground everything so that I don’t risk electrocuting myself or burning my house down”.

For safety reasons (when you bring the AC mains into the device enclosure), I would recommend earth grounding the case/front panel/circuit common. But unfortunately, that can increase the possibility of “ground loop” noise problems when connecting several earth grounded devices together. There are ways though to reduce any ground loop noise without sacrificing safety. One technique that has worked very well for me is to power all of my modest size home studio equipment from a single grounded AC power outlet in the room. Of course, I keep the total power load well below the safe limit and use power strips with circuit breakers/fuses.

But, if you still run into ground loop noise problems, then you have no other option than to start lifting the earth ground between devices. Just try to keep at least one device with an earthed common in the audio system.

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PostPosted: Sat Oct 22, 2011 3:22 pm    Post subject: Reply with quote  Mark this post and the followings unread

varice wrote:
“I lift every ground on all my equipment”


How did you guess Shocked Laughing

But yeah, safety is a real concern of course.

However, I'm from the school that says such can be accomplished without safety grounding when you pay sufficient attention to construction details (see how the Nords are made for instance).

Most important thing to ground lift would be your computer .. which for a laptop is ok to do, but for a floortop it may leave the case floating at half mains voltage ... YMMV Shocked

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varice



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PostPosted: Sat Oct 22, 2011 10:54 pm    Post subject: Reply with quote  Mark this post and the followings unread

Blue Hell wrote:
varice wrote:
“I lift every ground on all my equipment”

How did you guess Shocked Laughing

Laughing I really had no idea that you are in that camp. But, I have seen a recent post from Howard M. stating that he normally removes the earth ground prong from the power cords of his gear.

I’m glad that I have been fortunate enough (knock on wood) to not have experienced a bad ground loop problem that would cause me to take such measures. But, of course if I was forced to, I would lift those grounds just the same Exclamation

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PostPosted: Sat Oct 22, 2011 11:55 pm    Post subject: Reply with quote  Mark this post and the followings unread

ground loops is also a term that is misleading

what we call ground loops in reality occur because of resistance to ground
ie : a resistive ground connection can cause
a large potential difference between two items of equipement
this will mean their grounds will be different with respect to each other
this is exhibited as a voltage and can be measured it may also be heard as a hum or hiss or other
unwanted noise in an audio situation
all wire has an inherent resistance to it depending on type, guage
and length this will also cause potential differences to occur within a system
particularly larger more complex systems or over longer distances
IMHO removing the ground prong from any power cord is an insanity
more than a few people have died from the belief they are solving the problem when they are not and are actually just getting around a symptom
[sorry howard] but it's an old roadies trick that fried more than one guitarist /singer and they should have known better
yes grounding faults are a huge pain to find but better than the possible
alternative

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sompost



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PostPosted: Sun Oct 23, 2011 1:31 am    Post subject: Reply with quote  Mark this post and the followings unread

I've heard about sucht things like ground loop and humming noises, too, but my concern was actually closer to the ground, so to speak.

If you've got a center tap transformer, you use the center tap as your ground level, and have your positive and negative voltages based on that. But if the center tap is not actually 0V with respect to 'earth' level (could be anything, right?) and you connect both you would have a current flowing through the transformer into earth. Would that be a problem? Am I overthinking?

I tend to ground the case, and then see if there's a problem. If there is, I'd follow the advice given above to completely insulate the power supply ("box in box"-style: mains in - raw DC out) and keep the case unearthed.

Thanks for your answers so far.

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PostPosted: Sun Oct 23, 2011 4:48 am    Post subject: Reply with quote  Mark this post and the followings unread

sompost wrote:


If you've got a center tap transformer, you use the center tap as your ground level, and have your positive and negative voltages based on that. But if the center tap is not actually 0V with respect to 'earth' level (could be anything, right?) and you connect both you would have a current flowing through the transformer into earth. Would that be a problem? Am I overthinking?


I am also amateur but hear me out

I think this is were the fact that voltage is relative comes into play. I see it like this, it might be a flawed analogy, but If you imagine being one wire of the AC connection, you will see that the other wire is going lower than you feeding you electrons then higher sucking electrons. But looking at yourself you will be not moving. You can take any connection in the AC signal (the centre tap or either side) and it would seem that you yourself are static but everything else is moving. Thus if you make that (whatever one you want to be 0v) the common connection you can use circuitry to control which way current flows through your circuit.

This is why ground should really be called common

[this bit below is More of a guess than an answer! ]
Transformers do not let DC potential through, so if you connect the one point of a secondary side to another point of a different secondary side (via ground). I THINK current will not flow between those 2 points as they are isolated from each-other?? Once you start introducing DC through the use of diodes and smoothing caps things change.

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PostPosted: Sun Oct 23, 2011 1:24 pm    Post subject: Reply with quote  Mark this post and the followings unread

ground your case to whatever ground your AC supply has
hopefully the electrician who installed the building wiring did his job properly in the first place
attach your zero volt center tap of the transformer to the exact same point
also all your board and panel grounds should all come back
via the least resistive paths possible to this same point
think of this point as the centre of the universe
in theory if you could use superconductors for all ground wiring
and every connection had zero resistance you would never run into
the problem of noise or ground hum as no potential difference could exist
between the connected points.
reality however is obviously very different
the idea is to keep any potential differences to a minimum.

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PostPosted: Sun Oct 23, 2011 1:53 pm    Post subject: Reply with quote  Mark this post and the followings unread

wow - learnt a lot from this thread - thanks to all

do european connectors only have 2 pins? surely that would mean every object with an internal power supply / transformer is death trap - or is there some trick to make them safe?

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PostPosted: Sun Oct 23, 2011 2:05 pm    Post subject: Reply with quote  Mark this post and the followings unread

so called double insulation
no contactable metal parts can be live
done well it is safe unless the insulation breaks down such as due to lightning strike
done badly as in cheap knockoffs incorrectly manufactured = people die

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PostPosted: Mon Oct 24, 2011 12:14 am    Post subject: Reply with quote  Mark this post and the followings unread

Luka wrote:
do european connectors only have 2 pins?


There are two types, with and without safety grounding; like a washing machine will always have 3 pins, in general stuff for watery environments will have 3, but not equipment for dry rooms.

Double insulation is not only what it says, but also the construction needs be such that when a wire comes loose it can never touch accessible metal parts.

This is not just in Europe BTW, you'll see it in the US as well and probably other places. It is safe enough, but needs some attention to constructional details.

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PostPosted: Mon Oct 24, 2011 12:38 am    Post subject: Reply with quote  Mark this post and the followings unread

European connectors with earth have clips in the socket that connect with tabs on the plug.

http://www.piccolauniversitaitaliana.com/de/faqs/images/f_schuko_plug_and_socket.png

Items that power of wall warts never have saftey earth and is a way of getting around safety risks of taking mains into a unit. But they are a mess, with the chunky plugs we have in the uk you end up with a massive chunky brick of transformers!

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Luka



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PostPosted: Mon Oct 24, 2011 2:40 pm    Post subject: Reply with quote  Mark this post and the followings unread

ahh ok - that is the first one of those i have seen (not that ive been to europe)

weird how earth is the last connection to be made when you inset the plug - it looks like an afterthought addition

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PostPosted: Mon Oct 24, 2011 3:19 pm    Post subject: Reply with quote  Mark this post and the followings unread

Luka wrote:
weird how earth is the last connection to be made when you inset the plug


Actually its the first being made. Confused

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