This is a more explicit (I would argue the correct) way to notate the connections:
View attachment 128720
Ok, so you connect all the cable and connector shields to the enclosure and the enclosure to GND. I totally agree with that. Probably my diagrams are more ambiguous or less explicit (probably because they're made for my own use) but the way you draw is the way I build
I appreciate what you mean and you're right: things should be expressed and depicted as accurate as possible.
It is in the sense that many people use terminology very loosely and use the word "ground" to refer to many different things. That is why I like to use explicitly accurate words like "shield connection," "shield conductor," "chassis connection," "circuit reference node" in contexts where it is not overly cumbersome and doesn't just make a muddle of the text.
Well, I sincerely think there's a language factor. My native language is spanish and we use "tierra" (earth) and "masa" (mass) for ground, chassis connection, earth, etc. Anything that ends up connected to GND basically. We use "pantalla" (shield) for cable shield only for instance, not for enclosure. Language....
You have mixed up the concept of circuit reference node and shield in your head. You first have to correct that in order to think correctly about where various conductors connect together.
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In our world of audio equipment you will always be connecting different equipment together, so you want to minimize the potential difference between the shield and the conductors travelling inside the shield to reduce capacitive coupling of shield noise, and you need a way to keep the common mode voltage between different pieces of equipment within reasonable limits, so you connect the circuit 0V reference node to the shielding enclosure at one point so that their voltage potentials are tied together.
By connecting only at one point you do not create a path for current to flow through the audio circuit due to voltage differences at different points on the shielding enclosure.
I sincerely appreciate your explanation
I'm an old amateur builder of pedals and tube amps and I try my best to learn as much as I can.
I've always looked at the concept of shielding comparing it to a noise drain. If the connections are correct, the noise will be drained down to a common drain that will be connected to GND and the system will be quiet as a mouse. That's why sometimes you connect only one end of a cable for instance. When I build a pedal the aluminium enclosure is the shield and to it I connect input and output connectors and the board's ground plane through one spot alone. The GND plane in turn is connected to GND (negative terminal on the PSU). The PSU connector is isolated from the enclosure. Maybe I'm doing something wrong but I've had no noise problems so far.
What do you mean by stating "they are the same?" The circuit reference is for audio signal return currents and being the "0" reference for the audio signal, the shield is for forming a conductive surface around the circuit so that external EM fields generate currents in the conductive enclosure and not in the audio circuitry.
Those are different things, so I would say that no, they are not the same. Thinking that they are the same and that they can be connected together at any random point without regard for where currents flow and where those currents generate voltages across the conductor resistance has been a perpetual source of noise problems in otherwise decent gear.
Sorry, but I didn't state exactly that, or at least I didn't mean it like that.
"I agree that Chassis/case connects to GND at one place only" is not "Thinking that [...] they can be connected together at any random point".
When I stated "Since Chassis/Case connects to GND I understand that they are the same
only their purpose changes." I meant that the shield ends up connected to GND. Sorry for the ambiguity. I guess I look at things sort of like plumbing!
Note that having a switch in the shield path makes it mostly ineffective at radio frequencies. My preference is to correctly connect the shields with as low inductance a connection as possible, and if you find that you need to break the shield path either use a cable with shield connected at the transmit end only, or use a female-to-male XLR adapter with pin 1 disconnected internally at the receiving equipment end.
That's a good idea! Thanks for the tip
Thanks a lot for your help
Cheers
Sono
