Ground lift, Class I, Short to Chassis, RCA shield, Safe?
I have built and external (inlet & outlet) Ground lift box with two diodes, resistor and a cap (Hum-X).
Connected the RCA plugs, turned amp On, hum was gone, hurray!
On second thought, is it safe?
What would be the least resistance path to a short to chassis?
If the line shorts to chassis, the least resistance path now is the flimsy RCA shields (to my audio interface
), till the PE diodes open.
The question is will the diodes open fast enough to conduct the high current to PE or the equipment connected to the RCA shield will also suffer from a short to chassis?
I have built and external (inlet & outlet) Ground lift box with two diodes, resistor and a cap (Hum-X).
Connected the RCA plugs, turned amp On, hum was gone, hurray!
On second thought, is it safe?
What would be the least resistance path to a short to chassis?
If the line shorts to chassis, the least resistance path now is the flimsy RCA shields (to my audio interface
), till the PE diodes open.The question is will the diodes open fast enough to conduct the high current to PE or the equipment connected to the RCA shield will also suffer from a short to chassis?
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PE is connected via diodes to amp chassis.
The amp PE is lifted via external box with diodes and a 10R resistor, so the only direct ground is through the audio RCA shield cable into the audio interface which is connected to a PC via firewire, and the PC is grounded.
If I maintain both grounds PC & Amp, I got a ground loop which I can hear through the speakers.
Simply lifting the ground from the Amp also works but it is dangerous.
My question is what happens during a short to amp chassis in the first micro second:
A. The huge current will flow through the RCA shield into the audio interface to PC to Ground.
B. The diodes are quick to open so the huge current will flow through the Amp PE.
I want to make sure the delicate digital equipment is safe using this diode ground lifting method.
Current flows through the least resistance path, in that case, the RCA shield to the delicate equipment.
The commercially available product called HUM-X does just that, it lifts the PE from chassis via diodes.
The amp PE is lifted via external box with diodes and a 10R resistor, so the only direct ground is through the audio RCA shield cable into the audio interface which is connected to a PC via firewire, and the PC is grounded.
If I maintain both grounds PC & Amp, I got a ground loop which I can hear through the speakers.
Simply lifting the ground from the Amp also works but it is dangerous.
My question is what happens during a short to amp chassis in the first micro second:
A. The huge current will flow through the RCA shield into the audio interface to PC to Ground.
B. The diodes are quick to open so the huge current will flow through the Amp PE.
I want to make sure the delicate digital equipment is safe using this diode ground lifting method.
Current flows through the least resistance path, in that case, the RCA shield to the delicate equipment.
The commercially available product called HUM-X does just that, it lifts the PE from chassis via diodes.
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Depending on your insurance, application and local regulations, you could be in just as much trouble with safety issues as any benefit you gain from dodging the basic problem. Note: the issues in the linked article are the same but several countries' standards are implicated in mains supply reference articles.
Audio Component Grounding and Interconnection - diyAudio
From my understanding of the ClassI regulation, you must change this.
The Chassis must be directly and mechanically fixed to the PE wire in the Mains cable.
I think you have no choice in this.
This applies to EVERY ClassI piece of equipment.
Each must use it's own PE wire to protect it's own Chassis.
Thanks Ian and Andrew.
I have done some measurements, and found that the source of the noise is the audio interface.
The audio interface ground (thus also the RCA shield/reference) is 50mV above PE of the PC and Amp.
The audio interface is connected to the PC via firewire cable, in one end of the cable its 50mV to PE, on the other it 0mV to PE.
What do you suggest?
I have done some measurements, and found that the source of the noise is the audio interface.
The audio interface ground (thus also the RCA shield/reference) is 50mV above PE of the PC and Amp.
The audio interface is connected to the PC via firewire cable, in one end of the cable its 50mV to PE, on the other it 0mV to PE.
What do you suggest?
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Sounds like at least one part is a double insulated device (ClassII).
The PE voltage of devices on the same socket outlet should be so close that interference on the meter tester probe/cables will obscure the tiny differences.
The PE wire should carry no significant current and thus should have no significant voltage drop from equipment to socket outlet.
The PE voltage of devices on the same socket outlet should be so close that interference on the meter tester probe/cables will obscure the tiny differences.
The PE wire should carry no significant current and thus should have no significant voltage drop from equipment to socket outlet.
I've used ground lifters on some of my designs.
In all cases the metal chassis are solidly connected to the power earth. It's the circuitry that's floatinf at +- 0.6 V around the ground point.
Interestingly I've been experimenting with non ground lifter hookups recently. I've got it to reasonably quiet, but not as quiet as when I use the ground lifter.
I will be doing some more work in this in the coming months . . .
In all cases the metal chassis are solidly connected to the power earth. It's the circuitry that's floatinf at +- 0.6 V around the ground point.
Interestingly I've been experimenting with non ground lifter hookups recently. I've got it to reasonably quiet, but not as quiet as when I use the ground lifter.
I will be doing some more work in this in the coming months . . .
almost all commercial audio is Class II (2 wire mains)
introducing some Class 1 permits shorter paths to earth through audio interconnects.
(this creates a ground loop through low level audio circuits a hum is often the result)
if you use a Class II rated XFMR there is no need to connect secondary circuits to PE /chassis. If your transformer has no such ratings then you must.
as always chassis is solidly connected to PE.
IDK why ppl blindly connect secondary circuits to PE chassis using class II rated components. fear uncertainty doubt comes to mind, whatever rant over
introducing some Class 1 permits shorter paths to earth through audio interconnects.
(this creates a ground loop through low level audio circuits a hum is often the result)
if you use a Class II rated XFMR there is no need to connect secondary circuits to PE /chassis. If your transformer has no such ratings then you must.
as always chassis is solidly connected to PE.
IDK why ppl blindly connect secondary circuits to PE chassis using class II rated components. fear uncertainty doubt comes to mind, whatever rant over
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All class I and dangerous!
My amps have loosely soldered Line and HT+ (tube) wires all over which just begging to touch the metal chassis.
What I need is a safest ground loop hum solution, not a law lesson.
The Amp has 0mV between Input Sleeve and PE, so it's fine.
The PC has 0mV between its chassis and PE, it's fine.
The audio interface puts a 50mV on the RCA sleeve in relation to PE, so this is clearly the noise source.
The only thing that connects the audio interface to the PC is a 3 foot firewire cable, in which I measure 50mV between ground ends of the firewire cable.
I tried adding a ground cable directly from the PE to the RCA sleeve, no success.
Solution?
Why would a pro audio interface generate a 50mV noise on its sleeve?
To make our lives harder and full of danger lifting the ground of a point to point wired tube amp.
My amps have loosely soldered Line and HT+ (tube) wires all over which just begging to touch the metal chassis.
What I need is a safest ground loop hum solution, not a law lesson.
The Amp has 0mV between Input Sleeve and PE, so it's fine.
The PC has 0mV between its chassis and PE, it's fine.
The audio interface puts a 50mV on the RCA sleeve in relation to PE, so this is clearly the noise source.
The only thing that connects the audio interface to the PC is a 3 foot firewire cable, in which I measure 50mV between ground ends of the firewire cable.
I tried adding a ground cable directly from the PE to the RCA sleeve, no success.
Solution?
Indeed.Bonsai said:
Why would a pro audio interface generate a 50mV noise on its sleeve?
To make our lives harder and full of danger lifting the ground of a point to point wired tube amp.
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the OP is homebrew tube guy posting in SS forum
use ground breaker line transformers
IDK usually go the other way to > II
use ground breaker line transformers
IDK usually go the other way to > II
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Wrong, Class 1 should ALWAYS be grounded!
Unless you have a ground loop and willing to trade safety for silence.
The best anti-hum solution is complete electric isolation the two appliances from one another.
Galvanic isolation via transformer or fiber optics will completely isolate the two systems.
I have tried an isolation transformer from ebay but is adds distortion even at lowest levels.
The Iso-Max by Jensen is just too damn expensive.
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distortion on line transformers indicates the levels are running too high, Eg approaches core saturation.
lower the levels by increased gain after the transformer, or get bigger stuff maybe the Jensen is too small for your levels too IDK. measure the levels and determine your gain 1st, then buy gear after.
core saturation is volt*seconds so high levels and low frequencies stress small cores
but you said low levels don't satisfy so something else is at play here? limit the bass and repeat tests
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