GND Scheme questions

[merlin]

So, every connector, XLR, jack... needs his own connection to chassis, right? I can't tie all the shields together and bolt on chassis, no?

For inputs and transformer-balanced outputs yes you can do that. It is not 'best' but it is OK if you have to.

And the circuit GND needs to tie chassis no? It's correct if a use a metal stand off that contact the GND circuit to chassis? Or where is the best place to tie the GND circuit?

Yes, circuit GND needs to tie to chassis (sometimes through a resistor or diodes rather than a direct connection). You can use a metal standoff if you wish.

 

[CJ]

Intuitive experimentation can sometimes be the quickest way to get a good ground scheme.

 

[sahib]

And the circuit GND needs to tie chassis no? It's correct if a use a metal stand off that contact the GND circuit to chassis? Or where is the best place to tie the GND circuit?

Here is a ground scheme I use.

I note that ccaudle comments on soldering not being permissible. This is probably the case in his jurisdiction but there are PCB mount IEC too where the earth tab is soldered along with live and neutral. There are also equipment perfectly compliant where the earth wire is soldered to the IEC earth tab.

I solder the earth wire to the eyelet but then also crimp it to lock-in.

 

[rock soderstrom]

As I mentioned in my first post, the whole story is nationally regulated. Some things may be allowed in one country and prohibited in another.

Here some things were mentioned, which are forbidden in Germany. We have quite strict rules on this subject. Some examples: The PE connection to the chassis is exclusive, you are not allowed to attach any other grounding to it. Here is a diagram showing the structure of such a connection.


The PE of the supply cable must have at least the same cable diameter as the other supply cables and must be longer than these, so that if the supply cable is torn out of the strain relief, the PE conductor is the last to lose contact. PE soldering is not allowed AFAIK. There are further rules on this subject here in Germany, a final test of the protective grounding with a test device designed for this purpose is mandatory.

All the regulations on this topic are also subject to constant changes and harmonization with the rules of other countries, e.g. within the EU.

Therefore, for the germans, in case of doubt, research the current legal rules in Germany. My knowledge is essentially based on my basic training over 30 years ago.

 

[Bo Deadly]

Here is a ground scheme I use.

I would not do it this way. You should only have one wire from the supply to the chassis bolt. Using the chassis bolt as a star ground is acceptable in a guitar amp as a practical matter. But in pro-audio you can do better which is to have all 0V references converge at the 0V of the last filter capacitor. Because you have two separate PCBs in this particular scenario, you would have to just pick a 0V terminal of one of the PCBs. Then run a short and thick wire between the 0V terminals of the two PCBs. I would probably use the bipolar supply PCB for 0V refs since that's likely feeding the circuit with the most gain but one could also argue that 0V refs should converge on the 48V pcb because return currents are running over the chassis and through the 0V pcb / chassis interconnects. But it should not matter if the 0V interconnects are short and thick. Ideally, the bipolar and 48V are all on the same PCB and all 0V refs converge next to 0V of the same filter cap. So at least put the 0V ref point near the chassis bolt so the one wire connecting the 0V refs to the chassis bolt is short.

 

[Newmarket]

This is probably the case in his jurisdiction but there are PCB mount IEC too where the earth tab is soldered along with live and neutral. There are also equipment perfectly compliant where the earth wire is soldered to the IEC earth tab.

I solder the earth wire to the eyelet but then also crimp it to lock-in.

yeah - but it's the connection to chassis that is the focus here as I see it. The connection to a power connector is not the same although you could argue whether it should be.
Crimping "Purists" might criticise soldering before crimping. Due to making the joint brittle and also possibly compromising the "gas free joint" idea.
imo with a large diameter cable it's not really an issue and tinning bare copper may add some environmental protection.
Worth checking out if you need to be certain of compliance.

 

[Newmarket]

As I mentioned in my first post, the whole story is nationally regulated. Some things may be allowed in one country and prohibited in another.

Here some things were mentioned, which are forbidden in Germany. We have quite strict rules on this subject. Some examples: The PE connection to the chassis is exclusive, you are not allowed to attach any other grounding to it. Here is a diagram showing the structure of such a connection.
View attachment 101132

The PE of the supply cable must have at least the same cable diameter as the other supply cables and must be longer than these, so that if the supply cable is torn out of the strain relief, the PE conductor is the last to lose contact. PE soldering is not allowed AFAIK. There are further rules on this subject here in Germany, a final test of the protective grounding with a test device designed for this purpose is mandatory.

All the regulations on this topic are also subject to constant changes and harmonization with the rules of other countries, e.g. within the EU.

Therefore, for the germans, in case of doubt, research the current legal rules in Germany. My knowledge is essentially based on my basic training over 30 years ago.

Good info'. Question: are you saying that German specific regulations require anything that is not included in the relevant EU Standards relating to the Low Voltage Directive (LVD) ? Would seem odd since EU trade requires countries to accept goods from other EU member states without further qualification.
So I'm guessing the above (assuming currently correct) applies across EU.

 

[ruffrecords]

The basics:

Cheers

Ian

 

[spoontex]

This is what I'm building:

JH. Subtle Chorus

If you see the schematics in this page:

"Main board schematics, page 2"

http://jhaible.com/legacy/subtle_chorus/subtle_chorus_main_board_sch_dwg2.pdf

You see the "interface" connection that is confused for me.

I want to build it with XLR and unbalanced connections.

http://jhaible.com/legacy/subtle_chorus/sc_audio_balanced.pdf

If you see the unbalanced scheme and compare to "only balanced connections", you see that one pin of "interface" are tied to gnd if you use balanced, and unconnected if you use unbalanced.

http://jhaible.com/legacy/subtle_chorus/sc_audio_unbalanced.pdf

http://jhaible.com/legacy/subtle_chorus/sc_audio_balanced_only.pdf

anybody understand this 3 pin interface what is doing, apart of switching between stereo and mono? and how to wire it properly?

 

[sahib]

I would not do it this way. You should only have one wire from the supply to the chassis bolt. Using the chassis bolt as a star ground is acceptable in a guitar amp as a practical matter. But in pro-audio you can do better which is to have all 0V references converge at the 0V of the last filter capacitor. Because you have two separate PCBs in this particular scenario, you would have to just pick a 0V terminal of one of the PCBs. Then run a short and thick wire between the 0V terminals of the two PCBs. I would probably use the bipolar supply PCB for 0V refs since that's likely feeding the circuit with the most gain but one could also argue that 0V refs should converge on the 48V pcb because return currents are running over the chassis and through the 0V pcb / chassis interconnects. But it should matter if the 0V interconnects are short and thick. Ideally, the bipolar and 48V are all on the same PCB and all 0V refs converge next to 0V of the same filter cap. So at least put the 0V ref point near the chassis bolt so the one wire connecting the 0V refs to the chassis bolt is short.

With all due respect you are convoluting the issue with unnecessary information. This is what we use on our 500 racks and it is a pro audio.

You do not pick one regulator board as your 0V point. No matter how many regulator boards you have your 0V point is chassis stud point where the safety earth from IEC is connected.

As for the argument that the +48V ground point should be picked as 0V point, I do not think you know what you are talking about.

I have designed boards with triple output and 48V sharing the same ground plane but that has nothing to do with ideal. It is just economy.

yeah - but it's the connection to chassis that is the focus here as I see it. The connection to a power connector is not the same although you could argue whether it should be.

I know that very well.

If you have so stupidly high current circulating in your safety ground that it will melt the solder, the eyelet on the chassis stud point is the last of your concerns.

Crimping "Purists" might criticise soldering before crimping. Due to making the joint brittle and also possibly compromising the "gas free joint" idea.

They sure may. But done properly it does not compromise anything. I have not counted but the number of safety earth connections I made over the years will run into thousand if not thousands.

imo with a large diameter cable it's not really an issue and tinning bare copper may add some environmental protection.
Worth checking out if you need to be certain of compliance.

You may have a point. But lead free will take care of the environmental protection issue.

 

[Newmarket]

You may have a point. But lead free will take care of the environmental protection issue.

I could have been clearer there. I didn't mean pollution of the environment. I was meaning protection of the copper conductors from airborne contaminants etc.

 

[sahib]

Well, 50% you and 50% me. My apologies. I should also have read it a bit more carefully.

 

[ccaudle]

If you have so stupidly high current circulating in your safety ground that it will melt the solder, the eyelet on the chassis stud point is the last of your concerns.

Of course you must be right about allowing solder connections, some equipment does have PCB mounted IEC inlet connectors. Perhaps I was confusing practice in some high power equipment I have worked on with general requirements.

 

[JohnRoberts]

If you have so stupidly high current circulating in your safety ground that it will melt the solder, the eyelet on the chassis stud point is the last of your concerns.

the purpose of a safety ground bond is to sink enough current long enough to trip the fuse/breaker without a dangerous voltage rise from IxR... My recollection from last time I had to deal with this (last century) was something like 50A with less than 10V rise.

The last problem I had with this was winning UL approval for a small 2.5W commercial install amplifier design for office/factory intercom and background music. The SKU had a 3 wire line cord and screw terminals for audio in/out. UL's problem was that one of the screw terminals for the audio I/O was labelled "ground", so UL ground bond tested it at 50A. The PCB ground trace literally vaporized off the PCB from that much current. I had the option to finesse the problem by relabelling the screw terminal 0V or audio common instead of ground, but instead I sent the PCB design back to my layout guy and challenged him to beef it up enough to pass UL. He did and it did...

They sure may. But done properly it does not compromise anything. I have not counted but the number of safety earth connections I made over the years will run into thousand if not thousands.

some more or less than others while I didn't do that many myself personally (I had people for that).

JR

You may have a point. But lead free will take care of the environmental protection issue.

 

[spoontex]

This is what I'm building:

JH. Subtle Chorus

If you see the schematics in this page:

"Main board schematics, page 2"

http://jhaible.com/legacy/subtle_chorus/subtle_chorus_main_board_sch_dwg2.pdf

You see the "interface" connection that is confused for me.

I want to build it with XLR and unbalanced connections.

http://jhaible.com/legacy/subtle_chorus/sc_audio_balanced.pdf

If you see the unbalanced scheme and compare to "only balanced connections", you see that one pin of "interface" are tied to gnd if you use balanced, and unconnected if you use unbalanced.

http://jhaible.com/legacy/subtle_chorus/sc_audio_unbalanced.pdf

http://jhaible.com/legacy/subtle_chorus/sc_audio_balanced_only.pdf

anybody understand this 3 pin interface what is doing, apart of switching between stereo and mono? and how to wire it properly?

Anybody can help me? please?

 

[FIX]

I had an artist on my stage at the Bayou in DC, it was a national act, he said his amp was making a lot of noise lately. During sound check, he method was always to swing the guitar neck and touch the timing peg to the mic. He did that and both the high E and B string immediately became molten balls of nickel, spraying into where the audience would have been sitting. It did not blow the breaker. Turns out, his fuse holder was broken and the hot was sitting on the chassis. The AC hot was soldered to the rung and not the tip of the fuse holder, so the internal fuse was also useless. If he had started singing, it might have killed him.

So, start like this:

Have the stage wired so it is all on one phase. Then make sure the FOH and monitors are on the same phase. If you want the amps on the other phase, make sure the audio feeding them are balanced, and connect the shields at the AMP end and not the console. Then run a ground wire from the AMPS to the FOH console ground.

By doing so, you will just about eliminate all ground loops on the stage. Then all you have to worry about is bad fuse holders...

You can easily balance the AC load, regardless if it's dual phase power or 3 phase power. Have the electrician put lighting on the other phase. If it is 3 phase, it might be worth installing a 208 to 120VAC transformer, which would cost between $2-4K.

 

[sahib]

Anybody can help me? please?

I have checked the link.

He uses external transformer and I could not see any reference to a ground scheme. In fact, right before the demo files he says that he leaves it up to you to deal with power scheme etc. Pretty lazy. but I suppose he is covering his back.

I can't really make out what type of power connector he uses. But assume that you picked 5 pin XLR, and also decided to follow the external transformer scheme. All you have to do is to bring the safety earth (green/yellow wire) from the transformer box to the equipment case and tie it to the chassis using a say M4-M5 screw/bolt (chassis stud point). Use PIN 1 of the power connector for this to stay within convention. See the picture I posted. Also check the rock soderstorm's picture. In fact I do it exactly how his picture describes. Plus I use a second locking nut right at the end. but that is not necessary for you.

Tie the circuit ground directly to the M4-M5 screw point. Then tie input/output XLR PIN 1s to the chassis near the XLRs.

 

[CJ]

go wireless,

two prong cord safer than three prong in some instances,

(chassis is floating so git player is floating) (not on LSD, i mean electrical)
although i played some of my best stuff on acid, but the fret board started to melt, so i had to switch to shrooms which apparently they are now using to treat depression,

we had a 30 page argument about grounding a while back which alienated a few people , for some reason, grounding is an emotional topic,

 

[spoontex]

no one is answering my question.

My question is:

What is the third pin of interface connection? And why it need to short to pin 1 if use balanced and open with unbalanced?

 

[spoontex]

go wireless,

two prong cord safer than three prong in some instances,

(chassis is floating so git player is floating) (not on LSD, i mean electrical)
although i played some of my best stuff on acid, but the fret board started to melt, so i had to switch to shrooms which apparently they are now using to treat depression,

we had a 30 page argument about grounding a while back which alienated a few people , for some reason, grounding is an emotional topic,

I see... and I thinking about it.

In fact, the original Roland sdd 320 uses internal transformer with two prong cord.

But the question that I have is related to the interface connector.