the chassis ground is the Safety Earth where the Mains Protective earth wire (the third wire) connects to the chassis. It is there for Safety ONLY.
It does not improve the quality of the Audio.
The Audio Ground is a separate issue and should be located where it best serves it's AUDIO purpose.
Once each of these have been located then to complete the SAFETY requirement, one must connect the Audio Ground to the Safety Earth to take fault current to PE and ensure the mains fuse ruptures quickly removing the danger due to the fault.
It does not improve the quality of the Audio.
The Audio Ground is a separate issue and should be located where it best serves it's AUDIO purpose.
Once each of these have been located then to complete the SAFETY requirement, one must connect the Audio Ground to the Safety Earth to take fault current to PE and ensure the mains fuse ruptures quickly removing the danger due to the fault.
I think I've asked this question before, but I can't for the life of me find that post.
http://sound.westhost.com/earth-f4.gif
Is there any benefit to increasing the resistor value?
http://sound.westhost.com/earth-f4.gif
Is there any benefit to increasing the resistor value?
Ground lifting.
What ever happened to "lifting" the ground on one end of one of the interconnects shield to stop a ground loop?. the equipment is still grounded properly and the cable is still shielded. is there some safety reason not to do that?
I have always just added a "lift" switch and just grounded the star ground right to the chassis/safety ground.
What ever happened to "lifting" the ground on one end of one of the interconnects shield to stop a ground loop?. the equipment is still grounded properly and the cable is still shielded. is there some safety reason not to do that?
I have always just added a "lift" switch and just grounded the star ground right to the chassis/safety ground.
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each circuit needs a flow and return. It is a circuit (a circular route) after all.
The Signal Hot is the flow and the Signal Ground is the return.
The coax shield can be the return route of the circuit, or a second line wire inside the shield can be the return. A twisted pair can be the flow and return without a shield, some twisted pairs have a shield. This shield is not a return, so can be disconnected at one end and still act as a shield.
If the amplifier has a well orgainised zero voltage reference, then the shield can go direct to the zero voltage reference, but it is much more common to take the shield to the RCA gound (barrel) and then to the Signal Ground at the input to the amp PCB.
You are confusing the different circuits.
There is a mains circuit. There is a signal circuit. There is a speaker signal circuit. There is a Transformer secondary circuit. There is a rectifier to smoothing cap circuit, etc.
Each circuit has a flow and return.
Shorting a Power rail to Signal Ground connects two circuits. If you then look at where the currents flow you can see whether a fuse will blow or a resistor will overheat. But you must look at the actual circuits work out the easiest route for the actual fault current to flow.
Once that flow has established, will the amplifier draw more power? Will that cause another circuit to pass more current? Will that cause a fuse to blow?
There is a mains circuit. There is a signal circuit. There is a speaker signal circuit. There is a Transformer secondary circuit. There is a rectifier to smoothing cap circuit, etc.
Each circuit has a flow and return.
Shorting a Power rail to Signal Ground connects two circuits. If you then look at where the currents flow you can see whether a fuse will blow or a resistor will overheat. But you must look at the actual circuits work out the easiest route for the actual fault current to flow.
Once that flow has established, will the amplifier draw more power? Will that cause another circuit to pass more current? Will that cause a fuse to blow?
The resistor may blow, but the bridge will conduct enough current to blow the appropriate fuse. That's why you don't use just a resistor.
Gnd loop problem in stereo amp...
Hi
I have a similar arrangement to post #5,except:
- 2 channels power amp
- One main power supply (with transfo #1) for output stage of the 2 amps
- two regulated power supply (from a single transfo #2) for the front end of each amp
- Chassis is not yet connected so far(but will be eventually)
So far, I have one single star ground for all power supplies
When only one channel is connected I get no hum but when the 2 are connected I get big hum.
What do you suggest?
Thanks
Hi
I have a similar arrangement to post #5,except:
- 2 channels power amp
- One main power supply (with transfo #1) for output stage of the 2 amps
- two regulated power supply (from a single transfo #2) for the front end of each amp
- Chassis is not yet connected so far(but will be eventually)
So far, I have one single star ground for all power supplies
When only one channel is connected I get no hum but when the 2 are connected I get big hum.
What do you suggest?
Thanks
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Hi
I have just read this thread and I am keen to make sure anything I build conforms to UK electrical safety requirements.
I am following the diagram provided earlier in this thread, and I have pick up the bits to make a ground break protection circuit.
Is there anything else I need to do to make it electrically safe?
I am currently building a P2P LM3875 amp and the schematic calls for a 100R resistor with a 0.22nf cap wired in parallel between the power ground star and the main chassis earth point. What is this used for?
Thanks
I have just read this thread and I am keen to make sure anything I build conforms to UK electrical safety requirements.
I am following the diagram provided earlier in this thread, and I have pick up the bits to make a ground break protection circuit.
Is there anything else I need to do to make it electrically safe?
I am currently building a P2P LM3875 amp and the schematic calls for a 100R resistor with a 0.22nf cap wired in parallel between the power ground star and the main chassis earth point. What is this used for?
Thanks
Both Chassis or what exists of them, MUST be PERMANENTLY connected to the Protective Earth wire, back to the third pin in the wall outlet socket.
The audio side must be connected to the Safety Earth.
This is usually (and best) done with a direct wire from Safety Earth to Audio ground (not signal ground). Signal Ground will have it's own connection to the Audio Ground.
This arrangement often gives symptoms of ground loop hum when connected to incompatible equipment.
I have found the easiest way to reduce, but never eliminate all measurable hum is to use a Disconnecting Network between the Audio Ground and the Safety Earth. It is worth adding a switch to short out the Disconnecting Network for those installations that do not benefit.
BTW,
I do not like the way the signal Ground in the amplifiers is connected. But, fortunately, that is not a Safety issue.
Some designers say that the Disconnecting Network is not a solution, it is simply plastering over the wound. I cannot disagree with that.
Look up other grounding details to find the experts and their solutions to grounding induced hum.
Look up ESP and Decibel Dungeon for Disconnecting Network details. The important parts are the two inverse parallel high current diodes. They MUST be capable of passing Fault Current until the mains fuse blows and the arc extinguishes. There's another reason for close rating the mains fuse. It blows more quickly.
The audio side must be connected to the Safety Earth.
This is usually (and best) done with a direct wire from Safety Earth to Audio ground (not signal ground). Signal Ground will have it's own connection to the Audio Ground.
This arrangement often gives symptoms of ground loop hum when connected to incompatible equipment.
I have found the easiest way to reduce, but never eliminate all measurable hum is to use a Disconnecting Network between the Audio Ground and the Safety Earth. It is worth adding a switch to short out the Disconnecting Network for those installations that do not benefit.
BTW,
I do not like the way the signal Ground in the amplifiers is connected. But, fortunately, that is not a Safety issue.
Some designers say that the Disconnecting Network is not a solution, it is simply plastering over the wound. I cannot disagree with that.
Look up other grounding details to find the experts and their solutions to grounding induced hum.
Look up ESP and Decibel Dungeon for Disconnecting Network details. The important parts are the two inverse parallel high current diodes. They MUST be capable of passing Fault Current until the mains fuse blows and the arc extinguishes. There's another reason for close rating the mains fuse. It blows more quickly.
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Thanks for the detailed reply
1. How would you improve on the signal ground layout?
2. The Bridge Rectifier is rated at 35A (KBPC35-04)
Bridge Rectifiers : Diodes : Maplin
that is very similar to the Disconnecting Network I wired across Live to safety earth to test that it did indeed survive sufficiently long.
I never did find all the bits of the fuseholder that blew apart when the fuses exploded. I think some of the fuse casing vaporised.