Electronic – Is it possible to pick up noise in an audio circuit through the ground / earth wire

audionoise

In an audio circuit, such as a guitar's electronics (the only thing I ever dabble with!), I have always thought (probably simplistically) of every point along a continuous earth path being essentially all at the same voltage (a 'zero volt' reference voltage).

However, I was wondering – if you extend an earth wire from some point along that path, is it possible for that in itself to introduce noise to the circuit by changing the '0V' of the earth reference? (Possibly I am wondering "What is the difference between a long earth wire and an antenna" – but I don't know enough about antennas to know if that's what I'm asking 🙂

Best Answer

Yes, long ground connections can pick up noise, which means the ground in one place is a different voltage from the ground at another place. For single-ended signals, this ground offset voltage usually appears as part of the signal.

There are two common strategies for avoiding this situation:

  1. Use differential signals. The actual signal is encoded as the difference between two signals that are driven oppositely from each other. Ground offset then looks like a common mode signal, which can be largely ignored by the receiver.

  2. Pay attention to how things are grounded. Make sure all the grounds are tied back to one place without other connections to elsewhere, like the local power outlet ground. This ground net is then connected to real ground in one place only. Also avoid having deliberate current flow thru any ground connection. There should be separate returns for power current. Never use ground as a power return.

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