[sdiy] Signals leaking into the PSU?

[Neil Johnson]

Hi Mike,

Neil Johnson wrote:
> 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.

Mike Bryant wrote:
> True.  But one problem is over the years various techniques come and go.  The best solutions invariably involve a large lump of metal along the whole length of the mixer with each separate card connected to it with a very short and very beefy wire.  But that left the perennial "do we connect the front panel of the card to signal ground on the module or leave it floating and have it grounded by screwing it into the frame."    And how do you connect grounds on two part modules with a cable to a rear panel ?

Indeed, that's why it is important to read widely so you can see the
various techniques, their tradeoffs, the history of development, and
so on.  Not just mixer schematics, but also synth schematics and
service manuals, and books on the subject as well (Henry Ott is a name
to google).  As the old saying goes, if you don't read history you're
doomed to repeat it.

> Similarly on smaller mixers do you use the case as the 'lump of metal' or try to route some sort of star grounding on the PCB(s) ?  Or just ground plane the whole PCB and use that for signals as well as EMI shielding ?  And then digital mixers came along which muddied things even more :-)

Yup, fun times.  Although, again, a lot of problems encountered in
digital mixer design are not new to the world, but oftentimes they're
new to the engineers who need to make it work.  Heck, the IEEE EMC
Society has only been in existence since 1957...

> There are very differing views on all of this from some very famous names so I won't say what my preferences were.

Someone once said engineering isn't politics.  I would politely
disagree: engineering a product consists of all sorts of tradeoffs,
and decision trees, and changing knowledge: look at the history - and
the aftermath - of Neil Muncey's AES paper on the pin 1 issue as just
one example.  (Awesome name by the way ;) )

Neil