I was wondering how ground loops are dealt with in commercial audio equipment that is always perfectly safe to use because it passes regulations and is CE certified etc (so this equipment must be earthed properly). And yet it must not have ground loop hum problems, so I assume they have built in some kind of ground loop breaker.
The most common ground loop breaker I've seen is the 10 Ohm 5 watt resistor in parallel with a 100nF cap connected between circuit ground (zero volt line) and earth. But is this safe to do? (if it can get CE certified, then it is definitely safe). But if the resistor has 250 volts across it, then it would have to dissipate 6 kW 😱. Using diodes sounds less safe to me because they could go open circuit like a burned out resistor?
Another option that doesn't seem to be talked about much would be to put a resistor in series with the audio interconnect ground connection like 1k. Surely this would be able to reduce ground loop currents much more than a 10 ohm in the safety earth line? I'm not sure what effect this will have on sound quality (is there a reason why no one does this?)
So hopefully someone can offer some insight in to how it is dealt with "properly".
The most common ground loop breaker I've seen is the 10 Ohm 5 watt resistor in parallel with a 100nF cap connected between circuit ground (zero volt line) and earth. But is this safe to do? (if it can get CE certified, then it is definitely safe). But if the resistor has 250 volts across it, then it would have to dissipate 6 kW 😱. Using diodes sounds less safe to me because they could go open circuit like a burned out resistor?
Another option that doesn't seem to be talked about much would be to put a resistor in series with the audio interconnect ground connection like 1k. Surely this would be able to reduce ground loop currents much more than a 10 ohm in the safety earth line? I'm not sure what effect this will have on sound quality (is there a reason why no one does this?)
So hopefully someone can offer some insight in to how it is dealt with "properly".
The best way, aside from using audio transformers, is to design the equipment in double insulated chassis meeting Class II specs so that you don't have to use that !@#$% third pin safety ground.
That's the cause of most ground loop problems. And if you look at most mass market consumer gear, you'll see that they use two prong power cords. They avoid ground loops by not creating them in the first place.
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That's the cause of most ground loop problems. And if you look at most mass market consumer gear, you'll see that they use two prong power cords. They avoid ground loops by not creating them in the first place.
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The incoming AC power is grounded by the safety ground wire connected directly to chassis. Only the audio circuits go through the network.
Why do some components use only 2 prong AC connections while others require a safety ground? My preamp and digital source both use 2-prong AC power cords while my monobloc amps both use 3-prong ac cords, which have the ground wire internally attached directly to the chassis.
Why is ground needed in the amps and why not in the preamp/source?
Why is ground needed in the amps and why not in the preamp/source?
" ... safety ground? My preamp and digital source both use 2-prong AC power cords while my monobloc amps both use 3-prong ac cords ..."
'Cause they can is a part of it. Commercial & industrial rules don't apply in many cases (here in the states, anyway).
Also it is a matter of total power / wattage, pre-amp verses power amp. I'm not sure what the cut off point is anymore as the consumer v. commercial rules are bent regularily (here in the states, anyway).
For my money I welcome the return of late of the two prong power cord, pre-amp or power amp, DVD player, whatever. As reported above, doubly insulated chassis, etc., make for better sounding gear. If you are sensable about it, two wire designs can work better, sound better, run cooler ...
'Cause they can is a part of it. Commercial & industrial rules don't apply in many cases (here in the states, anyway).
Also it is a matter of total power / wattage, pre-amp verses power amp. I'm not sure what the cut off point is anymore as the consumer v. commercial rules are bent regularily (here in the states, anyway).
For my money I welcome the return of late of the two prong power cord, pre-amp or power amp, DVD player, whatever. As reported above, doubly insulated chassis, etc., make for better sounding gear. If you are sensable about it, two wire designs can work better, sound better, run cooler ...
It looks like the double insulated PSU is the best way of doing it. But easier said than done for DIY. Can it just be as simple as adding an extra layer of heatshrink tubing over the mains carrying wires and solder joints?
If the fuse doesn't blow, then yes. But a reasonably sized fuse will pop before the resistor has time to burn out since it has a much smaller thermal mass. Do use something like a carbon comp resistor, not a film unit.
As a practical matter, double insulation is very difficult to do correctly for diy. If you're installing stuff in your own system and the ground loop breaking resistor makes you nervous, you can put ground lift switches or plugs in each unit, connect the whole thing, then lift different grounds until the hum stops. As long as there's electrical connection between all signal grounds (i.e., no isolating input or output transformers) and at least one unit has the signal and safety ground connected, the system will be safe.
If there's any chance of plugging and unplugging which would leave something floating, don't do it this way, use ground breaking resistors and/or transformers.
" ... It looks like the double insulated PSU is the best way of doing it. But easier said than done for DIY. Can it just be as simple as adding an extra layer of heatshrink tubing over the mains carrying wires and solder joints? ..."
A whole lot more required ... starting with a plastic case / chassis or well insulated interior parts.
For DIYer's this may not be a deal breaker. The important thing for our safety and those we love = keeping the primary side well insulated and fused and in the case of power amps, keeping the secondaries insulated and output isolated from a metal chassis, etc. ... Well thought out designs with lots of kabitzing between knowledgable folks who have good ideas and practical experience will help.
SY and Kevin know about this stuff and so do many others here at DIYAudio.com ... it is advisable to ask and there are no dumb questions when it comes to safety and fire hazards ... think of shocks that can put you in the hospital =
A whole lot more required ... starting with a plastic case / chassis or well insulated interior parts.
For DIYer's this may not be a deal breaker. The important thing for our safety and those we love = keeping the primary side well insulated and fused and in the case of power amps, keeping the secondaries insulated and output isolated from a metal chassis, etc. ... Well thought out designs with lots of kabitzing between knowledgable folks who have good ideas and practical experience will help.
SY and Kevin know about this stuff and so do many others here at DIYAudio.com ... it is advisable to ask and there are no dumb questions when it comes to safety and fire hazards ... think of shocks that can put you in the hospital =
Thanks for your input guys. There is much to think about. I've looked into ground lift switches and it does not really appeal to me. I really like the idea of double insulation because it has no draw backs that I can see - if it can be done of course! If all low power stuff like the source and preamp etc is double insulated, then there will be no need to go to all the trouble of double insulation for the power amp.
But what would be the best way of going about double insulation? If the wires are insulated and there is heatshrink over the solder joints, then that would be the 1st layer of insulation. But the 2nd layer is a little more tricky.
If the chassis is metal, then maybe the easiest way of doing it would be to install the transformer, mains wires, IEC inlet, in a plastic box and mount that inside the metal chassis? Would the transformer need to be inside the plastic box?
BTW, I was thinking about shocks that can put you in the ground 😉
But what would be the best way of going about double insulation? If the wires are insulated and there is heatshrink over the solder joints, then that would be the 1st layer of insulation. But the 2nd layer is a little more tricky.
If the chassis is metal, then maybe the easiest way of doing it would be to install the transformer, mains wires, IEC inlet, in a plastic box and mount that inside the metal chassis? Would the transformer need to be inside the plastic box?
BTW, I was thinking about shocks that can put you in the ground 😉
Hi,
just to complicate the picture.
Ground loop problems occur just as often when two channel sources are connected to two channel receivers.
That receiver can be anywhere in the audio chain not just the power amp.
The ground lift switch DOES NOT disconnect the safety ground from the chassis.
The ground lift switch should (but only in commercial equipment maintained and used by appropriately trained personnel) short out the disconnecting network between audio ground and safety ground. It must not break the audio ground link to the safety ground, otherwise you are exposing the users to a very real danger of electrocution if an internal fault allowed mains to touch any part of the audio circuit.
Simply putting the mains transformer inside an insulating box does not stop mains voltage leaking to the secondary side if the transformer suffered a catastophic failure.
Do not think that producing ClassII equipment can be DIYed by untrained designers and HOW CAN A DIYER TEST CLASSII EQUIPMENT to prove it meets the standard?
I suspect many do not appreciate what is happening in the few uS before a fuse breaks in a faulty appliance that sends mains voltage to earth.
just to complicate the picture.
Ground loop problems occur just as often when two channel sources are connected to two channel receivers.
That receiver can be anywhere in the audio chain not just the power amp.
The ground lift switch DOES NOT disconnect the safety ground from the chassis.
The ground lift switch should (but only in commercial equipment maintained and used by appropriately trained personnel) short out the disconnecting network between audio ground and safety ground. It must not break the audio ground link to the safety ground, otherwise you are exposing the users to a very real danger of electrocution if an internal fault allowed mains to touch any part of the audio circuit.
Simply putting the mains transformer inside an insulating box does not stop mains voltage leaking to the secondary side if the transformer suffered a catastophic failure.
Do not think that producing ClassII equipment can be DIYed by untrained designers and HOW CAN A DIYER TEST CLASSII EQUIPMENT to prove it meets the standard?
I suspect many do not appreciate what is happening in the few uS before a fuse breaks in a faulty appliance that sends mains voltage to earth.
Good points Andrew, but if he can source a Class-II rated transformer and implement the appropriate physical construction it's not as hard as first thought. The difficulty is finding out the appropriate physical construction.
When I worked in pro audio, I spent over a week just reading the relevant British Standard. That was full time.
When I worked in pro audio, I spent over a week just reading the relevant British Standard. That was full time.
Class II transformers
I thought that since the primary and secondary windings are isolated electrically, then a catastrophic failure was so unlikely that it was not worth worrying about. But it looks like there are Class II transformers as well. There is some info on this here.
So Class II transformers fail safely by shorting themselves out. But can a regular toroidal transformer be used with a fuse in the live wire for protection. So it should also fail safely? Can it be done without a Class II transformer?
AndrewT said:
I thought that since the primary and secondary windings are isolated electrically, then a catastrophic failure was so unlikely that it was not worth worrying about. But it looks like there are Class II transformers as well. There is some info on this here.
So Class II transformers fail safely by shorting themselves out. But can a regular toroidal transformer be used with a fuse in the live wire for protection. So it should also fail safely? Can it be done without a Class II transformer?
Hi Mr Duck,
Just asking the question indicates to me that you should not be considering designing any mains side equipment and even less so a classII product (=no earth protection).
you must always correctly fuse the primary of the equipment. No if or but.
Just asking the question indicates to me that you should not be considering designing any mains side equipment and even less so a classII product (=no earth protection).
I don't know the ClassII regulations but this senario does not sound safe for any product.
AndrewT said:
Hi, Andrew. I mean that since class II transformers are designed to fail safely, would it be possible to use a non class II transformer with a fuse to meet the same specs? Because toroidal transformers are preferable in audio equipment because of low magnetic fields.
I didn't think those mains adapters (wall warts) had fuses in them. So they must use class II transformers which do not need fuses (according to that website).
Yes that does not sound quite right. Maybe they mean the transformer goes to the equivalent of open circuit like a fuse would do.AndrewT said:
Class-II transformers usually have thermal fuses in at the very least. It would not be acceptable to simply user-add a fuse to any transformer as it could be at some point bypassed or wrongly replaced by an idiotic future user.
Also a Class-II rated part will have been designed and made to greater creepage and clearance distances.
Also a Class-II rated part will have been designed and made to greater creepage and clearance distances.
I've been searching the web to have a look inside commercial CD players to see how they do it. I could not find any great pictures that show the double insulated PSU in detail, but the only difference I can see is that they left the earth connection off. In some cases the transformer was clearly just bolted to the metal chassis. I checked to make sure it had the double insulated symbol on the back:
So I am at a loss as to how double insulation is supposed to be done 😕 Is there some more detailed info somewhere where I can read up about it? Any recommended reading? I do not really want to spend a full working week of reading about it if I can help it, but I do want to get the gist of it at least.
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So I am at a loss as to how double insulation is supposed to be done 😕 Is there some more detailed info somewhere where I can read up about it? Any recommended reading? I do not really want to spend a full working week of reading about it if I can help it, but I do want to get the gist of it at least.
If you have to ask these questions you are not safe to attempt Class II construction and the very least of your worries will be that your house insurance will be invalid. You simply do not know enough to be able to make the judgement about whether what you are doing is safe.
Stick to a Class I properly earthed conductive enclosure (that's a metal chassis to you and me) and avoid ground loops by not connecting your 0V signal earth to chassis on more than one chassis.
Stick to a Class I properly earthed conductive enclosure (that's a metal chassis to you and me) and avoid ground loops by not connecting your 0V signal earth to chassis on more than one chassis.
Hi, I would say playing with mains voltage is never safe. But I am very careful and quite meticulous by nature, so I trust myself that I won't kill anyone by doing this. A few days ago I didn't really know anything about double insulating, I've learned a few things already and I have imagined how it could be done. But taking a look at commercial stuff, it looks different from how I imagined it would need to be. So I need to learn more. I wouldn't attempt it unless I knew what I was doing. That is why I ask the questions to make sure.
If someone wants to teach it to me that would be great but I would not expect anyone to want to do that. So if there is some web page that goes into some detail about how it is done then please link if you know of one. Otherwise, are there any good books on the subject?
If someone wants to teach it to me that would be great but I would not expect anyone to want to do that. So if there is some web page that goes into some detail about how it is done then please link if you know of one. Otherwise, are there any good books on the subject?
This stuff is documented up to the eyeballs for a reason. If you don't want to read British Standards and the like I'm sorry but you may as well just stick to earthed constructions.
If you can't even buy a Class-II transformer you are stuck before you even start anyway.
If you can't even buy a Class-II transformer you are stuck before you even start anyway.
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