Separate references to circuit ground?

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brucew268

Member
Joined 2013
#1
wintermute said:
AndrewT offered me some advice on the layout (as I also did it on strip board and was unsure what was important) I had all of the -ve side connections just along a strip from load back to the diode bridge. This is not good as there is shared current seen. Ideally the adj cap and 1.12K resistors should connect direct to the load (ie the zero volts point for positive and the -ve output for the negative) and not back along the strip (as is most convenient).
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AndrewT said:
I read about that layout technique about twenty years ago.
Then someone posted a link to a paper and it turned out to be that same one I read such a long time ago.
It really is important that low level current circuits do not share traces/wires with high level current circuits.
It is a development of that thought that brought me to realise that LOOP AREA of individual TWO WIRE circuits is what we need to strive for. Forming the TWO WIRE circuits becomes the first priority.

Wintermute's post19 sch shows the important LAYOUT considerations that are usually omitted from generalised sch that only show GND symbols.
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Does this imply that all three of these should each have separate references to circuit ground: A) smoothing caps, B) the post-reg circuit, and C) the reg adjust cap and resistors ? A & B are explicitly recommended in the quotes above, but what about C?

A-being relatively high current, B-needing strong reference to load, and C-protected from higher current?
 
#3
brucew268 said:
Does this imply that all three of these should each have separate references to circuit ground: A) smoothing caps, B) the post-reg circuit, and C) the reg adjust cap and resistors ? A & B are explicitly recommended in the quotes above, but what about C?
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Those three A-B-C should go in this exact series after each other, keeping in mind the second quote "LOOP AREA of individual TWO WIRE circuits is what we need to strive for. Forming the TWO WIRE circuits becomes the first priority."
I mean the right order is: 1) transformer secondary, 2) bridge, 3) smoothing caps, 4) regulator and all its wires.
How to wire regulator wires (common ground, adj, "hot" wire) depends on an exact regulator. For example, for LM317 and its brothers and sisters, there is an exact recommendation in a datasheet.
 
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#4
rayma said:
Yes, think of it as sensing the load voltage common. Here's a good general write-up for amplifiers.
http://hifisonix.com/wordpress/wp-content/uploads/2019/02/Ground-Loops.pdf
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What I meant was each (A, B, &C) should connect to circuit ground at the load rather than be in series with each other. I think this is what you are referring to. Will have a read, this looks interesting.


If using a resistor right at the end of the PS to raise the quiescent load, I assume all these loops would perhaps star ground at that resistor rather than after it since it is part of the load.
 
#5
This is related to interference pickup (loop areas of the send and return connections), and conducted
galvanic noise (hum, etc. due to the resistance of the interconnections).

The supply input capacitors have the highest noise (voltage ripple and current pulses), so their common
connections are noisy and must be connected to the rest of the circuit commons in a way that does not
inject that noise into the audio. See the description of the stub.
 
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