Hi folks.
Does anyone know if the circuit discribed here is legal to implement in the UK, for a valve poweramp (Dynaco ST70):
http://sound.westhost.com/earthing.htm
I have an earth loop but I don't wish to disconnect any of the safety earths, and this looks like an ideal solution, short of converting all my gear to balanced signal interconnects!
Many thanks,
- John
Does anyone know if the circuit discribed here is legal to implement in the UK, for a valve poweramp (Dynaco ST70):
http://sound.westhost.com/earthing.htm
I have an earth loop but I don't wish to disconnect any of the safety earths, and this looks like an ideal solution, short of converting all my gear to balanced signal interconnects!
Many thanks,
- John
Hello again John,
You mean the bridge rectifier I take it, for lifting ground impedances. Is it legal ? I am 99.99999% sure the answer is no, for the reason that the earth connection has to be "direct" and meet absolute requirements for minimum impedance etc in the event of a fault. It would fail on all counts.
The earth connection has to be able to carry the full fault current ie live to earth short until the fuse blows, and to be able to do it repeatedly time after time.
That said in practice it probably would be O.K. If a fault occurred diode bridges usually fail short circuit under overload but IT CANT BE GUARANTEED. Do you see the problem. If it failed open circuit the protection would be removed.
You mean the bridge rectifier I take it, for lifting ground impedances. Is it legal ? I am 99.99999% sure the answer is no, for the reason that the earth connection has to be "direct" and meet absolute requirements for minimum impedance etc in the event of a fault. It would fail on all counts.
The earth connection has to be able to carry the full fault current ie live to earth short until the fuse blows, and to be able to do it repeatedly time after time.
That said in practice it probably would be O.K. If a fault occurred diode bridges usually fail short circuit under overload but IT CANT BE GUARANTEED. Do you see the problem. If it failed open circuit the protection would be removed.
As soon as the earth cable enters the unit take it to a good solid ground point on the case (...assuming a metal case of course). If you have a multi-part case make sure each part of the case conducts to that point (...just resistance test it).
The rest is up to you. 'Lifting' the audio ground to break a loop is common practice. The ESP circuit looks comprehensive. Substituting two 1N4007 diodes reverse strapped across each other is usually as good as the bridge though.
If your mains transformer has a steel case remember to ground it to the amplifier case.
The rest is up to you. 'Lifting' the audio ground to break a loop is common practice. The ESP circuit looks comprehensive. Substituting two 1N4007 diodes reverse strapped across each other is usually as good as the bridge though.
If your mains transformer has a steel case remember to ground it to the amplifier case.
Mooly said:
Refering to Figure 3. on the ESP site (http://sound.westhost.com/earthing.htm) then the ground is made to the case immediately upon entry, which is fine. If there is a subsequent fault the worst case scenario is a power short to chassis ground, which would connect directly to the grounded earth point and the fuse / ELCB would trip in the house distribution board.
If there is a more minor fault on the audio circuit board then the resistor will conduct and the ELCB in your home's distribution panel should trip. If the current is so great as to create a 1.4 Volt drop across the resistor then the diodes of the bridge will conduct.
Admittedly it's been lots of years since I looked at the regs, but I think this set-up should be fine.
Gordy's right - but just top make this really clear, the problem really rests with the ambiguous way the word 'ground' is used.
If your equipment has conductive cases they must be bonded to the mains Earth to minimise shock*
Tha 0v side of the circuitry within that case does not have to also bonded to mains earth, but in any system it should be, once, for safety. You can control how and where this is done. If you have only one such Earth-0v bond in a system, you have no 'earth loops' by definition, but you must ensure that any interconnects can carry the propsective fault currents and/or fuse the secondary side of circuit supplies to ensure disconnection in the case of a fault to Earth.
The purpose of ESP circuit is in this latter link, to separate the circuit 0v side from the Mains earth, but in a manner that can carry fault current.
* unless 'Double Insulation' standards are adhered to. Without stringent testing this is not a suitable DIY technique
If your equipment has conductive cases they must be bonded to the mains Earth to minimise shock*
Tha 0v side of the circuitry within that case does not have to also bonded to mains earth, but in any system it should be, once, for safety. You can control how and where this is done. If you have only one such Earth-0v bond in a system, you have no 'earth loops' by definition, but you must ensure that any interconnects can carry the propsective fault currents and/or fuse the secondary side of circuit supplies to ensure disconnection in the case of a fault to Earth.
The purpose of ESP circuit is in this latter link, to separate the circuit 0v side from the Mains earth, but in a manner that can carry fault current.
* unless 'Double Insulation' standards are adhered to. Without stringent testing this is not a suitable DIY technique
IN4007 WILL explode under fault conditions. They are 1 amp devices. These were often used as bridge rectifiers in TV's VCR's etc . Seen it countless times. Two bits of wire where once lived a diode.
This is the problem of dubious advice. A huge bridge rectifier may survive or fail at least short so giving continued protection but as said NO GUARANTEES
This is the problem of dubious advice. A huge bridge rectifier may survive or fail at least short so giving continued protection but as said NO GUARANTEES
Just to add another voice that 1N series diodes would be completely unaccaptable. A creative portable appliance tester might find a way to test the equipment in such a way that the 20A test current is passed through the loop breaker, and if 1A diodes were used for this purpose then I hope it's now blindingly clear what the consequences would be.
The legal way to break ground loops on tube equipment with a safety ground to chassis is to put input transformers on every channel. Then twisted pair cable can be used. These are not cheap if they have high fidelity bandwidth. Stage band quality transformers usually do not.
A second way is to take tubes and make differential amps out of them, to reject the common mode voltage coming in from interequipment cables. there is usually not any way to take an existing amp chassis and come up with enough current to support all that. some organ power supplies have the B+ and filament current, but have entirely different function for the tubes.
A third way is to put a +-15 v supply in every power amp, and put in op amps to reject the common mode voltage caused by safety grounds on every chassis. This is what the market expects. Unfortunately tube transformers do not come with those voltages, and the sound of op amps may be different.
This problem comes up most often with vocalists singing into microphones, the system ground goes hot, and the mike starts shocking the vocalist.
In the mind of the safety people, they are much more worried about a baby crawling into a dark corner and touching a live chassis amp. The fact that the amp chassis, like a ST70, is at 100 deg after an hour of warm up, has nothing to do with regulation. The safety people assume the hazard will occur right at startup.
Personally, I keep my house empty of babies. The house has been childproofed, with a key lock. The amps have not been made safe for their presence.
A second way is to take tubes and make differential amps out of them, to reject the common mode voltage coming in from interequipment cables. there is usually not any way to take an existing amp chassis and come up with enough current to support all that. some organ power supplies have the B+ and filament current, but have entirely different function for the tubes.
A third way is to put a +-15 v supply in every power amp, and put in op amps to reject the common mode voltage caused by safety grounds on every chassis. This is what the market expects. Unfortunately tube transformers do not come with those voltages, and the sound of op amps may be different.
This problem comes up most often with vocalists singing into microphones, the system ground goes hot, and the mike starts shocking the vocalist.
In the mind of the safety people, they are much more worried about a baby crawling into a dark corner and touching a live chassis amp. The fact that the amp chassis, like a ST70, is at 100 deg after an hour of warm up, has nothing to do with regulation. The safety people assume the hazard will occur right at startup.
Personally, I keep my house empty of babies. The house has been childproofed, with a key lock. The amps have not been made safe for their presence.
The bible on grounding -
http://www.diyaudio.com/forums/diya...udio-component-grounding-interconnection.html
http://www.diyaudio.com/forums/diya...udio-component-grounding-interconnection.html
A minor technicality:
No Dynaco products I am aware of ever had UL listing in the USA and probably none in Europe either. And at least in the USA, they always had two wire power cords with a possible exception for the big model 400.
So it would be technically legal to run with a two wire power cord or do the ground bridge technique. The product should be grandfathered in - again this is true for the USA. Not sure if the EU grandfathers old non code compliant equipment.
No Dynaco products I am aware of ever had UL listing in the USA and probably none in Europe either. And at least in the USA, they always had two wire power cords with a possible exception for the big model 400.
So it would be technically legal to run with a two wire power cord or do the ground bridge technique. The product should be grandfathered in - again this is true for the USA. Not sure if the EU grandfathers old non code compliant equipment.
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