Multi chassis grounding scheme.

[G]

Hi All. I was told once upon a time that you needed to use a "buffer" between safety ground and signal earth to keep the mains noise out of your music. I have made a diagram below as a reference for this thread. Take a look and tell me what you think. I am going to be building a two box preamp and I wanted to get the parts list down so I can see how much the financial damage is going to be. I'm not sure that I need to connect signal earth to safety ground in the circuit chassis. What do you think?

 

[Sch3mat1c]

Mains noise, shmains noise. Y'all are paranoid. Ground loop, now there's an actual concern from that scraggly old wire.

Tim

 

[G]

Mains noise, shmains noise. Y'all are paranoid. Ground loop, now there's an actual concern from that scraggly old wire.

Tim

Thanks Tim. That was helpful.

 

[fdegrove]

Hi,

Don't know wheter this would work O.K. in the U.S. but this arrangement is one of the possibilities that seem to work fine this side of the pond:

Cheers,

 

[jlsem]

I have made a diagram below as a reference for this thread.

Is chassis one the power supply chassis and chassis two the amplifier chassis? (from Frank's diagram)

John

 

[fdegrove]

Hi,

Is chassis one the power supply chassis and chassis two the amplifier chassis?

I'm the one responsible for numbering them....
So, yes, to me at least they are.

Cheers,

 

[G]

Thanks Frank. Hopefully the electrons won't be geographically aware.

 

[Luke]

If I understand this correctly, the signal ground of chassis 2 is not connected to chassis ground at all?

 

[leadbelly]

If I understand this correctly, the signal ground of chassis 2 is not connected to chassis ground at all?

Wow, talking about digging up an old post! If you mean Frank's diagram then yes, he is recommending that in the audio circuit chassis, there is no connection from signal ground to chassis, and that this connection only be made in the power supply chassis.

 

[Luke]

Thanks Leadbelly,

yeah I know its an oldie but these issues allways crop up
Ive got something like this and I cant get rid of the hum, Im going to redo the grounding as per this schema and see what happens.
Im terrible with grounding, I allways use star grounds but I think I need to put a bit more thought into it before wiring.
thanks!

 

[audiobliss]

Frank,
I am going through this same problem now. I posted it on the AA.

http://www.audioasylum.com/forums/tubediy/messages/15/153638.html

I am going to try your method, I see Audio Note also does it that way. Could you explane for me the perpose of the 100r resister and the bypass cap between the signal and safty ground.

I am just tring to understand it better.

Thanks

 

[SY]

Just in case Frank doesn't see this (he doesn't drop in nearly enough), the 100R breaks up a potential ground loop, and the bypass cap holds the chassis and signal ground together at high frequencies, thus providing shielding.

 

[audiobliss]

Sy,
Thanks for that reply, now I see. So how is the cap value chosen?
I saw that Audio Note used a .001uf cap while Frank's schematic shows a .22uf, both using the same resistor.

AB.

 

[Luke]

I have Just tidyed up my wireing and used screened cable for all signal wiring. I have used a signal ground point on terminal strips and all signal grounds feed back to the start ground. From what I have read and made in the past this looks pretty textbook stuff. It hums worse than before, go figure.

Is it possible its oscillating? I may have to get a signal and scope across it soon.