Wiring up the grounds

[fiat79]

I'm in the process of assembling a mulitple chip amp based on the board kit from BrianGT. There are power grounds, chassis ground, output ground and input ground on each board - any chance I can jumper some of these or do I need to run a separate ground wire for each?

[David Davenport]

Do you think that if the grounds could be jumpered together, the board designer would have done that instead of providing separate grounds?

Wire is cheap - run a separate wire from each ground to a common point on the chassis where the safety ground is connected.

Dave

[fiat79]

Thanks for your reply David, my question was in regards to multiple boards, 4 to be exact and of course this will lead to a boatload of ground wires. I'm just wondering what is to be gained via this approach vs maybe jumpering the boards together and then a set of wires to ground.

[AndrewT]

Originally Posted by David Davenport

....from each ground to a common point on the chassis where the safety ground is connected.

No,
wire each audio ground to a central star ground that is isolated from the chassis.
Now connect the main star audio ground to chassis. This can be a direct wire connection capable of passing Fault Current without failing. Fault Current can exceed 1kA. Or you can use a Disconnecting Network but this too must be capable of passing Fault Current.
Ensure the chassis is permanently connected to the protective earth (PE) often referred to as Safety Earth.

[David Davenport]

That was the short answer. The long answer is that even short amounts of shared grounds will result in interactions by common impedance coupling. This is explained in my article at http://www.raleighaudio.com/Audio%20...connection.pdf

This will involve a lot of wires. One way to handle that is shown here
Power connector

Dave

[David Davenport]

Andrew's way is also acceptable.

Dave

[fiat79]

I have been following Andrews writings/recomendations for a while and have bonded the safety earth ground to my chassis. I am using a star ground for all of my power and and a thin wired signal ground that I have the option of floating via a resistor or not as needed.

However, as I said, each pcb has 5 ground eyelets on it and with 4 pcbs, that would be 20 more wires. This would seem to cause more issues than it could ever solve, especially since all 5 points on the pcbs are already tied together.

I will most likely run a single wire soldered to one of the eyelets on each of the pcbs and tie it to my star ground and go from there.

[AndrewT]

Originally Posted by fiat79

........ each pcb has 5 ground eyelets on it ...................... all 5 points on the pcbs are already tied together.

then you have to trace the route of each of the dirty and clean currents to your chosen eyelet and decide whether dirty signals can contaminate clean signals.
Then select each of the 5eyelets in turn and perform the same investigation, finding the eyelet that gives the best isolation of dirty and clean signals.

If none then you may have to modify the PCB by cutting a ground trace or two and making multiple ground connections to the central star ground.

[fiat79]

Thanks Andrew, I will trace the paths and see what I come up with; I would be reluctant to cut any of the traces though as I am sure Brian did a more than competent job of laying it out. His boards are exceptional and of very high quality.

Surely, I am not the only one building a multi-channel amp using his boards.

[Peter Daniel]

Originally Posted by fiat79

5 ground eyelets

There are 5 ground eylets, as star ground is actually on each board, with a common point at OG (output ground). If you are using separate supply for each board, no additional star ground is needed.

If a single transformer is being used to power multiple boards, run wires from OG pads to a common point and use that point for connecting grounds from power supply as well. Run another wire to chassis ground.

More info can be found here: Commercial Gainclone kit- building instructions