Well, the best way it is, to avoid the use of the mains earth and thus this additional components.
In case of dual monaural constructions the RCA input connector is now mounted without isolation to the chassis envelope.
Unfortunately most transformers require mandatory the use of the mains earth for safety reasons.
This means at the same time, I have to introduce components between the metal chassis envelope and the GND from main board/star GND from power supply (to avoid double grounding).
I observe a wide range of different ways in commercial amp products - each manufacturer chooses other components resp. values resp. topologies.
Sometimes only a resistor (10 ohms until 1000 ohms) is present, somtimes only a MKT cap (10 nF until 1 uF), and sometimes both of them (the attached gainclone example with LM3875 e. g. uses a 100 ohms resistor and a cap with 0,22uF).
Also the wattage and the kind of the cap are highly variable (very small until very large).
The choosen position at the chassis and at the PCB are also different. Sometimes near the input GND, sometimes near the output (loudspeaker-terminals) and sometimes at the power caps (star ground).
Also, the thickness and the length of the connecting cables between the main-PCB GND and the chassis (over the mentioned components) are very different. In any cases I did observe an extremely thin wire.
Follow question rises up:
How did I calculate this devices between chassis/mains earth and secundary GND for lowest possible hum (highest possible signal to noise ratio) so as highest possible reliability and where are to find papers and test reports in this matter?
In case of dual monaural constructions the RCA input connector is now mounted without isolation to the chassis envelope.
Unfortunately most transformers require mandatory the use of the mains earth for safety reasons.
This means at the same time, I have to introduce components between the metal chassis envelope and the GND from main board/star GND from power supply (to avoid double grounding).
I observe a wide range of different ways in commercial amp products - each manufacturer chooses other components resp. values resp. topologies.
Sometimes only a resistor (10 ohms until 1000 ohms) is present, somtimes only a MKT cap (10 nF until 1 uF), and sometimes both of them (the attached gainclone example with LM3875 e. g. uses a 100 ohms resistor and a cap with 0,22uF).
Also the wattage and the kind of the cap are highly variable (very small until very large).
The choosen position at the chassis and at the PCB are also different. Sometimes near the input GND, sometimes near the output (loudspeaker-terminals) and sometimes at the power caps (star ground).
Also, the thickness and the length of the connecting cables between the main-PCB GND and the chassis (over the mentioned components) are very different. In any cases I did observe an extremely thin wire.
Follow question rises up:
How did I calculate this devices between chassis/mains earth and secundary GND for lowest possible hum (highest possible signal to noise ratio) so as highest possible reliability and where are to find papers and test reports in this matter?
Attachments
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Rod Elliot has an article about this. Basically it's like this:
The power resistor should be large enough to prevent currents flowing that would cause a ground loop hum, but small enough that if there is a primary-secondary short, enough current will flow to mains earth to blow fuse/trip breaker. It should be of sufficient wattage that it will survive a direct 240v to earth short for long enough to ensure the fuse/breaker trips.
The capacitor is seen as a short at high frequencies, for RFI purposes.
Generally, 10 Ohm/5W resistor and 100nF 275V X2 rated capacitor do the job. If the transformer is an EI type, or has an internal electrostatic shield, it should be connected directly to mains earth.
There's a few variants on this. Rod shows the use of a 35A rectifier connected as back-to-back diodes between mains earth and 0V. Nelson Pass has used a 10 ohm NTC thermistor instead of the 5W power resistor. A lot of amps dont even have a loop breaker - they just connect 0V to mains earth.
The power resistor should be large enough to prevent currents flowing that would cause a ground loop hum, but small enough that if there is a primary-secondary short, enough current will flow to mains earth to blow fuse/trip breaker. It should be of sufficient wattage that it will survive a direct 240v to earth short for long enough to ensure the fuse/breaker trips.
The capacitor is seen as a short at high frequencies, for RFI purposes.
Generally, 10 Ohm/5W resistor and 100nF 275V X2 rated capacitor do the job. If the transformer is an EI type, or has an internal electrostatic shield, it should be connected directly to mains earth.
There's a few variants on this. Rod shows the use of a 35A rectifier connected as back-to-back diodes between mains earth and 0V. Nelson Pass has used a 10 ohm NTC thermistor instead of the 5W power resistor. A lot of amps dont even have a loop breaker - they just connect 0V to mains earth.
Post 1
The pic shows the Audio Ground connected to the Safety Earth via a Disconnecting Network of 100r//0u22F.
TEST that arrangement.
I bet
1.) the Disconnecting Network blows up.
2.) that the mains fuse may remain intact.
3.) that if the mains fuse remains intact that the potentially fatal result will be MAINS voltage on the Chassis.
Tief, you have made a grave mistake placing that dangerous schematic on the Forum where every Member can see it.
Please ask to have the dangerously wired pic removed before someone gets killed.
The pic shows the Audio Ground connected to the Safety Earth via a Disconnecting Network of 100r//0u22F.
TEST that arrangement.
I bet
1.) the Disconnecting Network blows up.
2.) that the mains fuse may remain intact.
3.) that if the mains fuse remains intact that the potentially fatal result will be MAINS voltage on the Chassis.
Tief, you have made a grave mistake placing that dangerous schematic on the Forum where every Member can see it.
Please ask to have the dangerously wired pic removed before someone gets killed.
this does not work safely
If a direct wire connection is made between Chassis and Audio Ground then that is usually sufficient to meet that crucial safety requirement that the fuse blows in event of a mains fault.
If a Disconnecting Network is substituted for that direct wire connection then That DN must survive up to a few kA of fault current.
If you are not sure then TEST it.
I have and I know that the DN in the ESP site which is basically copied from this Forum works. Beware there is an ambiguity in the ESP schematic.
He shows the PE connected to the DN and then going to Chassis.
That pic is wrong !!!!
The PE goes direct to Chassis.
The Audio Ground goes to Chassis either direct or via a DN. This Chassis connection can be many inches, cms away from the Safety Earth where the PE connected to Chassis.
Disconnecting Network
The DN must use inverse parallel diodes to pass the Fault current from Audio Ground to Chassis. The other components in parallel to the high power diodes are all optional.
These can be
a.) a switch, of low current capability
b.) a resistor, of low power dissipation.
c.) a capacitor, of low power/voltage
d.) an NTC, of low power.
I have not tested a high power NTC as the main fault current carrying element.
It may be that a High Power NTC can be used instead of the inverse parallel High power Diodes.
Would some Member/s like to carry out thorough safety testing of this NTC substitution for 110/120Vac and for 220/240Vac mains supply systems?
The DN must use inverse parallel diodes to pass the Fault current from Audio Ground to Chassis. The other components in parallel to the high power diodes are all optional.
These can be
a.) a switch, of low current capability
b.) a resistor, of low power dissipation.
c.) a capacitor, of low power/voltage
d.) an NTC, of low power.
I have not tested a high power NTC as the main fault current carrying element.
It may be that a High Power NTC can be used instead of the inverse parallel High power Diodes.
Would some Member/s like to carry out thorough safety testing of this NTC substitution for 110/120Vac and for 220/240Vac mains supply systems?
"gnd loop breaker" safety issues may be practically improved by using anti-parallel power diodes rated for enough current to blow fuses or breakers
allows a good fraction of the diode's Vf to be "blocked" by the high impedance to reduce hum but carries the 10s-100 of A for the time required to blow fuse or open breakers in the event of a fault to the mains with only a few V clamping V
may not satisfy some safety agency rules - they aren't all consistent or flexible
in Intrinsic Safety rules that cover chemical plant safety 2x parallel diodes rated with continuous current equal to any fusing in the system are considered "safe" - the diodes may be assumed to only fail shorted in the safety analysis
I don't buy line xfmr that don't meet double/reinforced insulation standards, 4kV Hipot for domestic mains V - then the output side can safely float
allows a good fraction of the diode's Vf to be "blocked" by the high impedance to reduce hum but carries the 10s-100 of A for the time required to blow fuse or open breakers in the event of a fault to the mains with only a few V clamping V
may not satisfy some safety agency rules - they aren't all consistent or flexible
in Intrinsic Safety rules that cover chemical plant safety 2x parallel diodes rated with continuous current equal to any fusing in the system are considered "safe" - the diodes may be assumed to only fail shorted in the safety analysis
I don't buy line xfmr that don't meet double/reinforced insulation standards, 4kV Hipot for domestic mains V - then the output side can safely float
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Please let me know which post # and the URL (or mean you post #1 here? - for that case please note: this schematic isn't from me.)
What means "via a Disconnecting Network" (maybe a ground lift switch?)??
BTW - for me all kinds of wiring (resp. all audio devices with such wiring) with additional mains earth are absolutely dangerously wired. Until now I don't understand, why there are not only 2-wired manis connectors without earth and additional double insulation standards by transformer and wiring by commercial products. The main deficiency is actually the absense of double insulation standards by transformer at most models from vintage and currently models.
Imagine what happens, if the mains earth connection is interrupted within the amplifier or whatever by shorting the hot mains wire "L" with the cabinet at the same time (e. h. when an insulation fault is present on the transformer), and your child grasps with one hand on the amplifier and with the other to a water tap ...
And please note: what happens in such cases is independend from the question of this topic here.
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Originally Posted by AndrewT
How much extra would each of these cost?
Would they still sell?
The standards available for safe manufacture of electrical equipment cover many and every type of device. The manufacturer chooses the type of safety protection appropriate to the device they manufacture.
That range of standards must include both for Class I and Class II and others.
We, as amateurs, without the resources to design and build and test and guarantee double insulated equipment, have no choice but to do our best with Class I protection. We connect all external parts to Safety Earth and we connect that Safety Earth to Protective Earth (PE).
imagine buying an isolation transformer powered 3 bar room heater or a isolation transformer powered hair straightening tongs or a etc.....
How much extra would each of these cost?
Would they still sell?
The standards available for safe manufacture of electrical equipment cover many and every type of device. The manufacturer chooses the type of safety protection appropriate to the device they manufacture.
That range of standards must include both for Class I and Class II and others.
We, as amateurs, without the resources to design and build and test and guarantee double insulated equipment, have no choice but to do our best with Class I protection. We connect all external parts to Safety Earth and we connect that Safety Earth to Protective Earth (PE).
I don't understand the marked terms. First, my English is too poor for it, and secondly I talk about "protection class II" transformers and don't talk about additional isolation (insulation) transformers.
However - both professionals and amateurs should use transformers in those kind as the following URLs shows:
Toroidal Lighting Transformers
http://www.tauscher-transformatoren.de/assets/pdf/R_16.pdf
HAL-TRAFO 60VA - Halogentrafo 60 VA, 230V - 11,6 V bei reichelt elektronik
HAL-TRAFO K60VA - Halogentrafo 60 VA, 230V - 11,6 V, Klemmen bei reichelt elektronik
Then protection class II is present (tools in protection class II are completely insulated by a special insulation). Such transformers do not require earthing (only 2 wires for mains lead are necessary).
What about the costs? Not significant larger than by the use of class I transformers.
check out also this URL for basic informations concerning the various kinds of protection class
http://www.rohrlux.de/Html/gb_schutzarten.html
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Yes. I don't understand, why I should remove. Where is mentioned from me, that this is the right wiring kind?
OTOH, this kind of wiring you will find by a wide range of commercial products. For this reason I have posted this schematic as an example.
This schematic I have found several times online (have a look to various service manuals/schematics - e. g. Cyrus "ONE" and "TWO").
But in this case the uploaded schematic is to understand in context with the topic here, but under no circumstances as my favorite diy instructions.
Nevertheless I will send one of the moderators a PM to delete this schema because I cannot carry out this because I am not a moderator.
BTW - you don't read my posts carefully. Please explain this term:
"a Disconnecting Network"
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