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Chassis Ground/Signal Ground/Circuit Ground

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crutschow

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A Signal Ground is the common or return line for any signal. Typically it's the same as the Circuit Ground.
A Circuit Ground is the signal common (return) connection for all the devices in a circuit. It's just a convenient reference point. Typically in a circuit you have one or more power points and a Circuit Ground (zero volts) point. It may or may not be connected to earth ground (typically not).

A Chassis Ground is whatever the chassis of a device is connected to. It may be earth ground, Circuit Ground, or both.

See http://en.wikipedia.org/wiki/Ground_(electricity) for examples of the circuit schematic symbols for the various types of grounds. (But what they call the earth ground symbol is also often just used for circuit ground, with no connection to earth). If you look at any circuit schematic you will typically see one of them. If there is more than one of the same symbol in a schematic it just means they are all the same ground point and are connected together in the circuit.
 

RCinFLA

Well-Known Member
It is just different names used for separate common connections.

Some circuits need to avoid ground loops that can cause unwanted feedback signal.

For example. A power amplifier output stage that draws high current can raise its ground potential slightly due to resistance in wiring. The low level audio input to the power amp should get is own common grounding between its source and destination (power amp). You don't want the input low level signal to have an output signal superimposed on input due to ground common loop of the amplifier's high current output.

It is not always easy to identify these ground loops. This is why differential signals are commonly used since they are relatively immune to ground loop modulation.
 

Leadfree

New Member
Can you please clarify how to avoid ground loops in amplifiers? Im planning on using a TEA2025 amp but have not yet designed PCB.
Should i basically run two wires back to the negative terminal of battery, one from a separate ground for the mic input circuitry, and the other wire from all the earths on the TEA2025 amp and associated amp circuitry?
 
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Robert_G

New Member
Can you please clarify how to avoid ground loops in amplifiers? Im planning on using a TEA2025 amp but have not yet designed PCB.
Should i basically run two wires back to the negative terminal of battery, one from a separate ground for the mic input circuitry, and the other wire from all the earths on the TEA2025 amp and associated amp circuitry?
Hopefully this will be of some help, pretty good explanation, maybe it could be useful in your design...

YouTube - Ground Loops
 

Leadfree

New Member
OK thanks will watch it (dammit i hate capped internet speeds, will go have a snooze and wait for it to load)
 

crutschow

Well-Known Member
Most Helpful Member
Can you please clarify how to avoid ground loops in amplifiers? Im planning on using a TEA2025 amp but have not yet designed PCB.
Should i basically run two wires back to the negative terminal of battery, one from a separate ground for the mic input circuitry, and the other wire from all the earths on the TEA2025 amp and associated amp circuitry?
The general principle is to use a single-point ground, with the single point carefully selected. You don't want the high ground current flow from the power stages to travel though the ground for the input stages. So the single-point power return to the supply should be close to the power stage. The grounds from the input stage should go to the single-point by a path that doesn't include the power path for the output.

Running two wires is not a good idea since then the ground path from the input to the output would be through the high current line from power stage. Thus the input ground would bounce around due the the current going through the output stage wire resistance, which you don't want.
 

audioguru

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The output power from the TEA2025 IC is so low that there will not be a problem with a ground loop fed back from the power supply ground to the input ground unless you use extremely small traces on your pcb.

The TEA2025 uses wide ground traces on its pcb to cool it.
 
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Dean Huster

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