I recently picked up a small usb DAC on fleabay and noticed that the earth pin on IEC socket doesn't connect to the chassis, instead it is wired to the ground of the r-core transformer.
I tested with a continuity meter and there's no connection between the earth pin and the chassis at all. Isn't this rather unsafe? Or is it ok given the transformer is in fact grounded to the IEC socket?
On another note, the ground shield of the RCA output sockets were also not grounded to the mains earth. There was some slight humming, but this disappeared when I soldered some hookup wire from the shield/ground of the RCA sockets to the earth pin on the IEC socket - I assume it is safe to leave it like this now, or should I have grounded the signal ground to the mains ground via a resistor, capacitor or some diodes?
I tested with a continuity meter and there's no connection between the earth pin and the chassis at all. Isn't this rather unsafe? Or is it ok given the transformer is in fact grounded to the IEC socket?
On another note, the ground shield of the RCA output sockets were also not grounded to the mains earth. There was some slight humming, but this disappeared when I soldered some hookup wire from the shield/ground of the RCA sockets to the earth pin on the IEC socket - I assume it is safe to leave it like this now, or should I have grounded the signal ground to the mains ground via a resistor, capacitor or some diodes?
Fleabay products aren't going to have passed the regulatory tests so they're a bit of a crap-shoot as regards electrical safety. I agree its probably unsafe - the IEC earth pin should be bonded to the chassis first and foremost. Maximum safety comes from hard-wiring the RCA commons to the chassis, all other options will be less safe to varying degrees.
If it has an IEC 3 pin socket and no mains earth to chassis, then it is dangerous and illegal! You may have an equivalent of Trading Standards over there that youy can report it to if you wish.
I would be worth adding a connection to mains earth. 16AWG wire terminated with crimp eyelet to an M4 bolt with star washers either side of the eyelet and nyloc nut is what I do.
I would be worth adding a connection to mains earth. 16AWG wire terminated with crimp eyelet to an M4 bolt with star washers either side of the eyelet and nyloc nut is what I do.
I tend to think it is also the best option for the integrity of the input and output signals.
I do find it interesting that most of the Chinese gear on fleabay has floating earths, how we don't have more reports of injuries is quite amazing! Unless they are double insulated I guess (how do we test this?).....
It certainly was a relief to find that when I grounded the RCA shields to the earth pin the buzzing completely disappeared, but now I'm not entirely sure I should continue using the DAC until I've connected the earth pin to the chassis.
Will it be ok to use until I can get the drill out to add another hole?
The sound of the unit itself is fantastic!
Abraxalito - I know you use a lot of DACs which only use single rail 5v supplies, out of interest, do you ground the -ve side of the supply to the chassis?
It certainly was a relief to find that when I grounded the RCA shields to the earth pin the buzzing completely disappeared, but now I'm not entirely sure I should continue using the DAC until I've connected the earth pin to the chassis.
Will it be ok to use until I can get the drill out to add another hole?
The sound of the unit itself is fantastic!
Abraxalito - I know you use a lot of DACs which only use single rail 5v supplies, out of interest, do you ground the -ve side of the supply to the chassis?
For a metal case there are two safe options: grounded case, or double insulation. I suspect your unit had neither.
Dealing with hum is a separate issue. The RCA outer is part of signal ground, not safety ground. However, for safety reasons there should be a connection somewhere between these two - even though this can often increase hum.
Dealing with hum is a separate issue. The RCA outer is part of signal ground, not safety ground. However, for safety reasons there should be a connection somewhere between these two - even though this can often increase hum.
A metal chassis should be connected to PE. Connecting signal GND directly to PE is not obligatory with low power devices (at least here). It introduces problems.
Please see here for dutch class II regulations with low power devices (page 3). Please note the lack of connection between signal GND and PE. It works best for me to build my audio devices like this except for the power amp which has signal GND connected to PE ("lifted" however).
http://www.elektormagazine.nl/articles/zelfbouw-en-veiligheid/6539
Please see here for dutch class II regulations with low power devices (page 3). Please note the lack of connection between signal GND and PE. It works best for me to build my audio devices like this except for the power amp which has signal GND connected to PE ("lifted" however).
http://www.elektormagazine.nl/articles/zelfbouw-en-veiligheid/6539
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If the equipment is double insulated and displays the concentric squares symbol then there should be no PE wire and thus no PE connection.
The fact that there is a PE wire seems to indicate it is not double insulated and thus the rule regarding PE to Chassis must be adhered to.
In my (amateur) opinion, this equipment is hazardous and should be taken to your nearest authority and ask for it to be investigated.
They may decide to have it withdrawn from the market.
The fact that there is a PE wire seems to indicate it is not double insulated and thus the rule regarding PE to Chassis must be adhered to.
In my (amateur) opinion, this equipment is hazardous and should be taken to your nearest authority and ask for it to be investigated.
They may decide to have it withdrawn from the market.
The "consumer" programmes on our TV and Radio channels are full of reports of injuries due to unsafe equipment coming from abroad.
The problem seems to be far less for home produced equipment, maybe because we don't produce much, but more likely because the Authorities can more easily police our home manufacturers. Comply or go out of business.
Safety is a big issue for cheap foreign product.
The "out of the back door" product sellers don't care about the consumer. They only care about making a profit.
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All of you should read latest pulsing power supply principals.
Those does not require ground, isolation is made over the PCB by keeping primary and secondary in safe distance.
Therefore safety level it can not verified by visual inspection.
Those does not require ground, isolation is made over the PCB by keeping primary and secondary in safe distance.
Therefore safety level it can not verified by visual inspection.
pulsing power supply
Are they double insulated?
Do they declare on the equipment labeling?
Do they meet current standards?
Are they double insulated?
Do they declare on the equipment labeling?
Do they meet current standards?
It's you who needs to read up. You are talking about just one of the methods that double insulated equipment uses. By virtue of the equipment having a 3 pin IEC connector it cannot be double insulated and MUST by european law have mains earth connected to chassis.
you DC coupled RCA shield to IEC ground.
My opinion -> two capacitors in parallel instead: 0.1uF and 0.01uF -> this will provide AC coupling - should get rid of the hum but keep the mains earth, and the RCA (and other equipment connected in the chain) signal shield at the separate DC potentials.
Personally,I think the connection between IEC ground and the transformer, in what we could classify as double insulated apparatus, is sufficient and appropriate way to ground the DAC. Almost all consumer (reputable) HiFi products have mains IEC pin left floating, i.e. not connected to anything. Their PCB ground plains are connected to the chassis at (usually) multiple points where the PCB is screwed onto the chassis, using AC coupling: 0.1 / 0.01 / 0.001 uF caps - single, or combination(s).
Hard connection between IEC ground and the chassis is required if there are motors / heaters / pumps (and similar) inside the apparatus, whose metal frame(s) can be brought to mains AC potential in case of failure.
Of course, this is only my opinion. I am not specifically suggesting anything.
Nick
The only reason that DAC has IEC connector is to provide an easy match between a DAC and various mains plugs' standards, like US, UK, Europe, Japan, AU and what not... primaries can be wired for 110 or 230. This easily covers the whole world, so a DAC can be sold worldwide. Matching IEC mains cables can be very easily sourced, for $2 or less.
I've seen IEC connectors with only mains and neutral pin, installed in many DENON's and Marantz'es. These IEC connectors do not have earth pin. They usually have double insulated transformers, with winding insulation having to provide certain isolation levels between two windings, and between mains winding and transformer core.
In case of switching power supply, insulation is provided, as stated already by someone else in one of the posts above, by keeping a "distance" between the mains section and the rest of electronics, and by utilizing MOV's between phase and neutral, phase and ground, neutral and ground.
Nick
not if the insulation class, creepage and clearance distances fail the standards
separate bobbins for pri and sec do make it easier to meet the standards
but you don't have a guarantee that a R-core's windings meet the standards jus' because "R-core"
separate bobbins for pri and sec do make it easier to meet the standards
but you don't have a guarantee that a R-core's windings meet the standards jus' because "R-core"
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The thickness of the bobbins provides the DI isolation, as does the segmented bobbin in DI EI transformer ?.
I think it's a fair bet that modern R-Core transformers meet DI specs.
Dan.
I think it's a fair bet that modern R-Core transformers meet DI specs.
Dan.
Maybe in the past, manufacturers left the IEC earth pin floating, but anything made in the last 10 years at least MUST be CE marked, and to be able to apply the CE mark the equipment MUST have the earth pin connected to chassis.
Of course, it may be different in Australia to the EU. But I would imagine manufacturers just build to a common world standard.
Of course, it may be different in Australia to the EU. But I would imagine manufacturers just build to a common world standard.
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No, you don't need an earth pin to get a valid CE mark. You need either proper grounding, or proper Class II double insulation. Either will do. I am not aware that the mere presence of a floating unused ground connection in a chassis renders its otherwise impeccable Class II status invalid.
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