I have been thinking (never good) about grounding amplifiers.I always do the safety earth to chassis, but then the active and line go thru the transformer and I use the line as negative. So the Line is isolated from the Earth.
Should the Line be connected to Earth after the transformer, as I assume they are connected back at the power station etc. It sounds dangerous...
Some thoughts on Grounding, Earth and Line
Should the Line be connected to Earth after the transformer, as I assume they are connected back at the power station etc. It sounds dangerous...
Some thoughts on Grounding, Earth and Line
Hi bullpeters,
your use of "active" and "line" is a bit confusing to me but then English is not my first language.
I assume, you are wondering how to ground your power supply after the transformer?!?
The ground of your power supply is basically identical with signal ground.
It is a good idea to have a single point where this potential is referenced to safety ground level. This is a single connection to your chassis but does not necessary have to be at the same spot where safety ground is connected.
In most cases, it is adventitious to have some distance between the two connections.
I have read, that many people use the input as point for grounding the signal circuit.
I have very good experience using the negative terminal of the last filter cap of the power supply as point for a star ground and having a single wire going from there to the chassis. This chassis connection is separated by some distance from the safety ground connection (green/yellow here in Germany; connected to the chassis by a low resistance bond i.e. star washer, etc.). This way you are sure, your signal is actually referenced to ground level.
There are a few threads about avoiding ground loops etc here on the forum.
So, I am sure you will find a plethora of information if my advice is too convoluted.
Cheers,
Martin
your use of "active" and "line" is a bit confusing to me but then English is not my first language.
I assume, you are wondering how to ground your power supply after the transformer?!?
The ground of your power supply is basically identical with signal ground.
It is a good idea to have a single point where this potential is referenced to safety ground level. This is a single connection to your chassis but does not necessary have to be at the same spot where safety ground is connected.
In most cases, it is adventitious to have some distance between the two connections.
I have read, that many people use the input as point for grounding the signal circuit.
I have very good experience using the negative terminal of the last filter cap of the power supply as point for a star ground and having a single wire going from there to the chassis. This chassis connection is separated by some distance from the safety ground connection (green/yellow here in Germany; connected to the chassis by a low resistance bond i.e. star washer, etc.). This way you are sure, your signal is actually referenced to ground level.
There are a few threads about avoiding ground loops etc here on the forum.
So, I am sure you will find a plethora of information if my advice is too convoluted.
Cheers,
Martin
Neutral may be connected to earth at the substation, but you should not connect it at home as huge currents could flow especially under fault conditions. You should regard neutral as being potentially almost as dangerous as live. It may have highish voltage, or it may get swapped with live.
Live and neutral go to the transformer primary, via switch and fuse. Ground/earth goes to the chassis (and the transformer frame). The signal ground will also connect to the chassis somewhere.
Live and neutral go to the transformer primary, via switch and fuse. Ground/earth goes to the chassis (and the transformer frame). The signal ground will also connect to the chassis somewhere.
Kind of, Neutral should be viewed as a live conductor (The names are cannonically Line, Neutral and Earth, with both line and neutral being considered to be live conductors).
The way this is supposed to work is that both line and neutral are isolated from your chassis and connect via a fuse and possibly switch and filter, to the primary side of the transformer. You do NOT make any connection between these conductors and the case (No not always strictly true, but if you are asking the question you dont want to go there).
The safety earth is connected directly to your chassis and (directly or otherwise) to the main neutral bar back at the utility substation, in normal use it carries no current to speak of, but if there is a fault to chassis then a large current can flow blowing the fuse quickly.
Neutral must never be connected to chassis unless you **REALLY** know what you are doing as it can become live under fault conditions (Hence why it is viewed as a live conductor).
It is instructive to consider what would happen if the neutral was connected to chassis and the neutral and earth came adrift in the socket, current would then flow from the live, through the transformer and would then flow to the chassis, making it live relative to earth, this condition would be potentially deadly.
The safety earth serves two purposes really, firstly it provides an independent low impedance path to ensure that a live chassis fault will blow fuses or trip breakers in a fraction of a second, second it can limit the voltage reached by the case in the event of a live chassis fault, this connection is important. It is separate (within a consumer appliance) so that a fault in the neutral cannot cause a dangerous condition.
Regards, Dan.
The way this is supposed to work is that both line and neutral are isolated from your chassis and connect via a fuse and possibly switch and filter, to the primary side of the transformer. You do NOT make any connection between these conductors and the case (No not always strictly true, but if you are asking the question you dont want to go there).
The safety earth is connected directly to your chassis and (directly or otherwise) to the main neutral bar back at the utility substation, in normal use it carries no current to speak of, but if there is a fault to chassis then a large current can flow blowing the fuse quickly.
Neutral must never be connected to chassis unless you **REALLY** know what you are doing as it can become live under fault conditions (Hence why it is viewed as a live conductor).
It is instructive to consider what would happen if the neutral was connected to chassis and the neutral and earth came adrift in the socket, current would then flow from the live, through the transformer and would then flow to the chassis, making it live relative to earth, this condition would be potentially deadly.
The safety earth serves two purposes really, firstly it provides an independent low impedance path to ensure that a live chassis fault will blow fuses or trip breakers in a fraction of a second, second it can limit the voltage reached by the case in the event of a live chassis fault, this connection is important. It is separate (within a consumer appliance) so that a fault in the neutral cannot cause a dangerous condition.
Regards, Dan.
No, there is no contradiction. You are confusing "neutral" of your power line with "signal ground" of your power supply (at least that is what I think where the apparent contradiction comes from).
I was not aware of which side of your power transformer we are talking about. To make things clear:
On the primary side: As stated above by others, both "line" and "neutral" go to the transformers (via filter, fuse, power switch). ONLY safety earth is connected to the chassis here. Use a low resistance (star washer), fail-safe connection for that.
German law requires that line and neutral use shorter wires to go to the first connection than safety earth inside the chassis if you do not use an IEC plug. The idea behind that is, in case of an external force on the power cable and should the cable anchorage fail, safety earth will be the last cable to be disconnected.
No idea how the requirements are in other parts of the world.
Now, on the secondary side of the power transformer the situation is different.
Here, you would like to have your power supply 0-rail grounded (that's why it's called "ground"). That is what my first post was referring to.
I hope this makes things clearer.
In any case, I would strongly advice to pick up a standard textbook on electric installation and safety regulations of your country.
Internet forums (even excellent ones like this one) are just not a good source for information regarding safety issues.
Best,
Martin
I was not aware of which side of your power transformer we are talking about. To make things clear:
On the primary side: As stated above by others, both "line" and "neutral" go to the transformers (via filter, fuse, power switch). ONLY safety earth is connected to the chassis here. Use a low resistance (star washer), fail-safe connection for that.
German law requires that line and neutral use shorter wires to go to the first connection than safety earth inside the chassis if you do not use an IEC plug. The idea behind that is, in case of an external force on the power cable and should the cable anchorage fail, safety earth will be the last cable to be disconnected.
No idea how the requirements are in other parts of the world.
Now, on the secondary side of the power transformer the situation is different.
Here, you would like to have your power supply 0-rail grounded (that's why it's called "ground"). That is what my first post was referring to.
I hope this makes things clearer.
In any case, I would strongly advice to pick up a standard textbook on electric installation and safety regulations of your country.
Internet forums (even excellent ones like this one) are just not a good source for information regarding safety issues.
Best,
Martin
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Thanks Martin
I only ask this question after reading " building valve amplifiers.
Thanks for all your input. I have been previously attaching the ground to the chassis as close as I can, star washer etc. I then attach the neutral after the transformer to the earth at the first filter cap. I don't really "understand" why, hoping to learn why. Thanks for all your help
I only ask this question after reading " building valve amplifiers.
Thanks for all your input. I have been previously attaching the ground to the chassis as close as I can, star washer etc. I then attach the neutral after the transformer to the earth at the first filter cap. I don't really "understand" why, hoping to learn why. Thanks for all your help
No! You are getting three quite different things mixed up.bullpeters said:
Neutral: part of the incoming mains supply - only goes to the transformer primary
Earth/ground: safety connection for the chassis
Signal ground: part of the circuit - will usually be connected in one and only one place to the chassis
Get the first two wrong and you have serious safety issues. Anybody who tells you to connect the incoming neutral to chassis is an idiot and must be ignored. If you have misunderstood what they say, then maybe you are not yet ready to build mains-powered equipment. It is not enough to blindly follow a rule; you need to understand what you are doing in order to keep you and your family safe.
Get the last one wrong and you get hum/buzz.
IEC socket EARTH (third prong) thats the pin you connect as close as you can to the chassis - its the pin that sits above/below the other two pins. Thats the safety ground earth ground whatever you want to call it. The other 2 pins, the hot and neutral (AKA ground in the USA) go to the transformer and only to the transformer via switch and on the hot side (line) a fuse. OK? Then after the transformer you can run a wire from the negative (ground/neutral) of your 1st or 2nd cap to your star ground point be it a bolt on the transformer (what I use) where you clean the chassis and add a star washer and another nut on top connecting your ground wire there. Signal ground (little tab on the insulated RCA jacks) gets connected the other tabs and that gets connected to the insulation or input wire SHIELD which can be connected to the ground circuit (neutral/negative) at the input where the signal gets connected to circuit in tube amp your driver tubes grid pins/volume pot-> grid pins. This is ASSuming you are using shielded wire for your signal going from your input jacks to your circuit.
Dont forget your fuse... dont forget to connect the safety ground to chassis..safety first (use a large gauge GREEN wire there) . Another good thing is a bleeder resistor..very handy when building power supplies and testing. It will drain those 450-550v caps safely down so you dont get a jolt of 450-500v connecting your DMM for testing. Also another thing, add an XY or X2 cap across the neutral and line (input AC voltage lines (not earth ground) this will help clean up any AC noise on the line. I do that right at the back of my IEC socket.
After building the power supply before testing, build yourself a dummy load (resistors that can handle the current) low ohms HIGH watts connect that across your B+/B- connect DMM with alligator clips across your circuit (B+/B-) turn on amp look for smoke then look for voltage. One hand near amp chassis at ALL times after power on first time.
Very important to use safe practice with everything you do all the time. NO shortcuts.
If you are unsure.. dont power on, take pics and post'em here or get someone local that works on HT (high voltage) to help you.
One thing to remember - your fuse is there to protect your home NOT your amp. Never trust it to protect your gear. It will protect your line in from melting and burning down your house, your transformer will burn up first and before the fuse blows (ASSuming slow blow fuse in use).
Cheers,
Bob
Shouldn't line filter be after fuse and switch? Though if you've got a fused, switched socket you're fine doing this.
For me, pictures help. If you go to the site below, and look at the assembly manual for their L2 line stage, you can see exactly how they arrange the grounds. There is also a short article on it there on that site.
Audio Note Kits - Welcome
Audio Note Kits - Welcome
Potato patato; I've seen it both ways, I like the easy way and just put the filter cap on top of the IEC socket hooked up to the line and neutral. I'm sure I could just as easily put it on top of the switch. The caps I have on hand have short leads and fit the IEC pin spacing perfectly... I doubt it makes much difference but hey give me a reason to change.
My point with suggestion to the OP was:
1) use em
2) use safe practice.
It's in the same vein as proper EARTH grounding... hum can be a bitch to track down once you've got it. Could be as simple as a florescent light causing it.. of course one would start to look inside the amp for cause.
Cheers,
Bob
A lot of modern equipment have the socket filtered to prevent noise getting out into the mains to pass the regulation tests.
When you turn the switch of you want the discharge to be filtered instead of getting out on your mains disturbing other apliances.
That´s one reason for the filter to be first in the chain.
All filter component should be X or Y type to prevent injury.
Yeah, I'm thinking this is an X situation (as no danger of making the chassis live) which means the cap may short on failure, but won't burn. So it would be nice to have a fuse before it.
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