understanding star grounding

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#222
454Casull said:

Couldn't you just use the 0V line to connect them? That's the whole point of the circuit anyway, right? To separate earth and 0V.
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This is a fine point, but an important point. You want to separate earth from the system star ground, not from 0V.

Most grounding problems are caused by something that needs to be "grounded" connected to the wrong "ground" or the wrong place in the grounding structure. Therefore you need to be careful to identify the different "grounds" as to their use and make sure that their ground currents don't get mixed in "ground wires." The best way to ensure this is to use a system star ground like I outlined earlier.

Ground hygiene is like personal hygiene - sometimes you can cheat a little and get away with it - other times you won't. So it is good to develop and use practices that will always work.

In your specific case, if the 0V line is connected to the star ground in the amplifier, then you could probably double-use it to connect to the SLB in the power supply chassis. However. you could side-step this double-use by putting the SLB in the amplifier chassis.

Dave
 
#223
David Davenport said:
There are a lot of commercial appliances that do not have a fuse and will not burn the house down. If a fuse was needed for safety in an audio amplifier,.........



.............So, you are protecting the cable?

The cable should be designed such that it will withstand an overload long enough for the main component fuse to blow.
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this whole post seems to be an attempt to defend and promote the idea that a fuse protects a semiconductor based circuit.
That can never be the intention of a fuse.

You don't design a cable so that it can be protected with a fuse.
You select a fuse to ensure the downstream cable/s cannot not set fire to it's surroundings.
 
#225
The shield is usually connected to an outer ring around the pins. Can you post a picture of your connector, because I cannot imagine, how that could not make contact first. Especially, if it is a DIN connector.

It is also important to know that a shield is not the same as a PE. It is permissible to use the shield as PE, if its cross-section is big enough, but usually there is a separate wire, marked green and yellow to avoid confusion.
 
#226
hi guys i finished an mono amp using LM3875 chip and i have an small HUM 🙁 btw, i want to do the star ground to be safe with the voltajes.

Is ok to do in this way?

as its just an mono block, i need to connect Safety Earth to Chassis and to PG- and PG+ ?
 
#227
pacificblue said:
The shield is usually connected to an outer ring around the pins. Can you post a picture of your connector, because I cannot imagine, how that could not make contact first. Especially, if it is a DIN connector.

It is also important to know that a shield is not the same as a PE. It is permissible to use the shield as PE, if its cross-section is big enough, but usually there is a separate wire, marked green and yellow to avoid confusion.
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The threaded part with the outside barrel is connected to the shield. As you can see, though, the inner barrel which is directly adjacent to the black insulator in the receptable cannot touch the housing until it is fully inserted, at which point the pins will already have been seated. The threads cannot be relied on to contact before the pins.
 
#228
samsagaz said:
hi guys i finished an mono amp using LM3875 chip and i have an small HUM 🙁 btw, i want to do the star ground to be safe with the voltajes.

Is ok to do in this way?

as its just an mono block, i need to connect Safety Earth to Chassis and to PG- and PG+ ?
Click to expand...


Hi samsagaz,

A star ground is a good idea.

Yes, absolutely, connect safety ground to the chassis.

Sorry to hear about your hum. I have written an article on grounding and interconnection that might help you. The article is here:
http://www.raleighaudio.com/general_articles.htm

Dave
 
#229
454Casull said:
The threaded part with the outside barrel is connected to the shield. As you can see, though, the inner barrel which is directly adjacent to the black insulator in the receptable cannot touch the housing until it is fully inserted, at which point the pins will already have been seated. The threads cannot be relied on to contact before the pins.
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Hm, yes. That specific connector is designated as 'safe, only when connected', which means it is not designed for hot-swapping. The accepted solution to that is to add a label on amplifier and power supply to remind everyone that the PSU must not be connected to mains, when the connection from PSU to amplifier is not safely established.
 
#231
David Davenport said:



Hi samsagaz,

A star ground is a good idea.

Yes, absolutely, connect safety ground to the chassis.

Sorry to hear about your hum. I have written an article on grounding and interconnection that might help you. The article is here:
http://www.raleighaudio.com/general_articles.htm

Dave
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Thanks too much i was reading http://sound.westhost.com/earthing.htm and was great resource...

Your sumary are very nice too.

Let me see if i understand correctly....

will be OK to make the connections in that way?

As i say im working on two Diferents Mono Amps.


An externally hosted image should be here but it was not working when we last tested it.


Wich is the best way to make the connection?

Is OK to use Input and Output Gnd without connected? these are insulated from the Chassis
 
#232
samsagaz said:


Which is the best way to make the connection?
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Use the connection that is in the center diagram.


samsagaz said:


Is OK to use Input and Output Gnd without connected? these are insulated from the Chassis

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You have not said what the input and output is. If the input is single-ended and the output is directly from the amp chip, you will need to connect the grounds to make the circuit work. The input ground (cable shield) should be connected to the star. The amplifier ground should be connected to the star. The output ground should be connected to the star. Isolate the connectors from the chassis.

If the input and output are something else, tell me what they are.

Dave
 
#236
Okay, I'll give you two answers so you can make a choice.

First, the best solution is to galvanically isolate the computer from the amplifier with audio line transformers (one for each channel). I would suggest the EDCOR TPC10K/10K. While it is not the very best quality, it is very good and a good match for a computer sound card. It costs about $11 US each. For this solution:

- connect the signal and shield from the computer to the input of the transformer (each channel).
- connect the outputs of the transformers to the amplifier (signal and ground).
- connect the chassis to the safety ground.
- connect the chassis/safety ground to the star.
- connect the power supply common (0V) to the star.
- connect the amplifier reference to the star.
- connect the negative speaker lead to the star.

The second solution, while not as good as galvanic isolation, is less expensive and and the parts may be easier to get. That is to use a Safety Loop Breaker circuit. For this solution:

- connect the chassis to the safety ground.
- place the SLB between the chassis/safety ground and the star ground.
- connect the shield fron the computer connection to the star.
- conect the power supply common (0V) to the star.
- connect the amplifier reference to the star.
- connect the negative speaker lead to the star.

If you have only a computer and amplifier in the system, the SLB solution may work fine for you. However if you still have unaccepable hum then you will need to galvanically isolate the computer from the amplifier.

Dave
 
#237
Thanks too much for your time and share with my your knowledge 🙂

Looks like 2nd choice will be the one that i will take, or maybe can get some specs of the transformers and will try to make it in my country, the main problem is that will waste space using the trafos 🙂
 
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