Sources of Noise

[John Dyson]

22 minutes ago, Speedskater said:

AC line noise often comes from:

a] Other hi-fi components, like big power amps with linear power supplies.

b] Other hi-fi components with SMPS power supplies.

c] any nearby wall-worts.

d] nearby appliances.

e] nearby hi-tech lighting systems.

f] HVAC

g] other entertainment, computer or network units.

 

 

Back in the old days, florescent lights with the associated ballast was often a big source of noise (pretty much covered by 'nearby appliances' in the list above.)   I dont' know of those pollution prone mini-florescents are bad at all though.

 

John

 

[John Dyson]

6 minutes ago, Speedskater said:

Now that's confusing. What do you mean by earth/ground? The words have so many different meaning and so many incorrect meaning.

Yea -- all of those terms are used interchangably and can be confusing when actually doing the circuit layout if taken literally.  The goal is to make sure that there are no digital currents intermixed through an analog common return path.   So, don't hook the 'ground' or '0V' pin of a digital chip onto the analog common return path.  There is an adage -- keep the digital and analog grounds separate, and that is a good 1st order guideline, but doesn't solve the interference problem entirely.   'Ground noise' as it is sometimes called, is usually a prominent noise source, but not the only one.   When dealing with chips with 100amp sub-ns wide spikes -- that is a huge opportunity for developing a voltage across a very short wire.   Thems digital chips are the culprits (even though usually only CPUs are the evil 100amp sources, but still -- even more normal digital parts can be pretty noisy.)

 

PS -- also need to be careful about where bypass capacitors go.

 

John