Dear KK Ho sir,
Nice to meet you in today’s UCD Class D power amplifier demo. The machine is good!
In this topic of “grounding”, I would like to express my opinion and refresh the purposes of grounding as below:
The primary purpose of electrical grounding is for "safety to human being". Nothing is more important than safety and classified as mission critical importance. Regarding the noise problem caused by improper grounding in audio system, it is classified as functional critical to the system.
In America, it is called “ground”. In British, it is called “earth”. In general, the purposes of electrical grounding are: (Ref: http://www.epanorama.net/documents/groundloop/why_grounding.html)
1) Protection to human being in case of equipment damage (safety critical issue).
2) Protection to the electrical system (overvoltage protection to property)
3) Voltage stabilization (same reference point in whole electrical system)
In audio system, improper grounding will cause noise problem. It usually refers to “ground loop” problem (ref: http://www.epanorama.net/documents/groundloop/). It can be divided into two parts:
1) interconnect cable
2) electronic device unit
In part I, digital signal is not sensitive to ground loop while analog signal is sensitive to ground loop. (ref: http://www.epanorama.net/documents/groundloop/digital_audio.html
) Both unbalanced and balanced analog signal cable exist ground loop problem. The basic requirement of cabling is:
1) Unbalanced analog signal cable: 1 conductor plus shield
=> (+) signal connect to center of conductor and (-) signal connect to ground and shield
2) Balanced analog signal cable: 2 conductors plus shield
=> (+) signal (hot) connects to Pin 2, (-) signal (cold) connects to Pin 3 and ground connects to Pin 1 and shield.
The simple solution to solve ground loop problem is to connect one end of cable with shield connect to ground and lift up another of cable with shield not connect to ground. Which end of cable should not connect to ground? Normal practice is the end “input” to next electronic device. Hence, the grounding depends on previous level of equipment and any problem in grounding will not transfer to next layer of device. If you argue about to lift up at “input”, but not “output”, it is a normal practice, there is not research support that you cannot do at “output” end.
In part II, it refers to the circuit design of grounding in PCB or something else in electronic device unit.
=> Circuit design for grounding:
1) i.e. grounding in digital vs analog circuit
2) i.e. grounding in high voltage (HV) vs Low voltage (LV) circuit
http://www.epanorama.net/documents/groundloop/in_circuit.html
http://www.epanorama.net/documents/groundloop/audiocircuit_grounding.html
=> Star grounding (commonly used technique)
http://www.aikenamps.com/StarGround.html
http://www.geofex.com/Article_Folders/stargnd/stargnd.htm
Finally, noise problem is not solely caused by improper grounding, but also due to other reasons such as RFI and EMI issues. (ref: http://www.epanorama.net/documents/groundloop/othernoise.html)
B. regards,
alant |
[複製鏈接]
