[sdiy] Signals leaking into the PSU?

[Mattias Rickardsson]

On Thu, 23 Feb 2023 at 00:38, Neil Johnson via Synth-diy <
synth-diy at synth-diy.org> wrote:

>
> In a bipolar system the only current that flows in the ground is the
> balance current, which is the difference between the currents in the
> positive and negative rails.  Ideally this balance current is 0.
>

Would it be worthwhile to completely avoid using the ground for anything
else than a signal ground reference, and power all current-drawing circuits
from the +/- supplies? If ground would be needed here, it would be a
buffered ground created by an op-amp buffer that draws its currents from
the +/- supplies, not from the ground it buffers. (Does anyone do it like
this?) :-)

As Roman suggested earlier IIRC, a much better way to drive LEDs is a
> constant current chain between the two supply rails, with switches
> (electronic or mechanical) across the LEDs to short them out when you
> want them off.  This has two distinct advantages:
> 1) it keeps the current draw constant, so no sharp edges of current on
> the power lines;
> 2) it keeps noise out of the common ground line.
>

Is there any recommended go-to circuit design for implementing a good
simple constant-current LED driver (preferably one with CV control of
brightness as well, for non-binary indication)? Feels like important
circuits like this would be great to have "standardised" in the community.
Oh, I'm then assuming a 25yr+ EE design that is guaranteed to be "better",
not the "bad" ones that other people rave about.  O;-)

The constant-current designs for LED-bar level meters found in mixing
console schematics are nice, perhaps the simpler circuits above are hiding
there as well?


> There is a veritable treasure trove of design knowledge in the form of
> analogue mixing desk schematics and service manuals.  Hundreds of
> them, from Mackie, AHB, Soundcraft, Neve, SSL, Studer, DDA, and so on.
> Many of them can be found with a little bit of googling.  And you'll
> see how to switch LEDs quietly, how to power opamps for low noise, and
> how to distribute power in a large bussed audio system.


Darn, need to switch (silently!) to googling instead... :-)

/mr
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