Separating Audio & Power GND, and GNDing b/t chassis

Question 1:
Is it generally "better" practice to keep signal and power grounds separated on the PCB, then bring those out to one ground point in the chassis/earth?

Question 2:
If I wanted to build several devices into several enclosures, and have one power supply (which is housed in a separate enclosure) power them all, what would be the optimal grounding scheme? Would I ground all of them to one point in the Power Supply Enclosure? Or have each device, and the power supply grounded to it's respective enclosure?

Thank you so very much!

The power supply does need to be connected to the signal ground at the reference point/star ground or whatever it is to be called. The point to be aware of is that it does introduce a fair amount of current, and therefore this current must not be allowed to flow through any of the audio ground paths, since it would then generate a voltage due to PCB trace resistances, which would become 'hum' or 'buzz' in adjacent circuitry.

Power amp design is where this becomes really important as you have a 'fragile' input stage and a high voltage/current stage for the output amp. The PSU for a power amp will usually have its own local ground (where the bridge rectifiers and the main caps connect to) and this will in turn connect to the signal ground.

With regard to the 'common supply for many devices' question, I'm not sure. You will need to have a chassis ground running from the PSU to the chassis of each device if you are using valves/high voltages. This should be kept entirely separate from the audio ground, and they should only connect (if at all) at the main PSU. It is probably best to run a separate ground line to each device for the audio supplies, with the star ground being in the main PSU. If you have any kind of 'daisy chaining' arrangement, you could have a very power hungry device at the end of the chain which would 'pollute' the ground for the devices that are inbetween it and the power supply.

Do keep in mind that the audio reference ground and the chassis/safety ground can, at least in theory, be completely separate. The chassis/safety ground is only there to stop a device from killing you. Any time you use a ground lift on a device, you are separating it from the audio ground, and you could wire up a studio with entirely separate audio and chassis grounds if every device you have allowed for this.

Anyway, I am no expert so.. :wink:

Bjorn

There is one AES paper in particular that comes to mind as an answer to this question. Neil Muncy's "Noise Susceptibility in Analog + Digital Processing Systems". AES should have it as a download for a reasonable price if you're a member, and not too brutal if you're not. It's a worthwhile read.