GSSL Ground Loop (again)

Isn't this a good old fashioned ground loop. Should the crc board be given chassis gnd from the IEC? What else is wrong with the picture?

A missing transformer and maybe the psu?

Udo.

XLR pin1 should go direct to the chassis at the connector and nowhere else.

Check this out:

http://www.ianbell.ukfsn.org/EzTubeMixer/docs/EzTubeMixer/SimpleMixer/grounding101v2.pdf

Cheers

Ian

Thanks Ian, great read.

How about like this? It seems like it would be better to not have the GSSL main PCB running it's 0V thru the CRC GND path? hence the straight shot to chassis...

Does it matter? One could go crazy with "Star grounding" every little GND point...

Isn't there going to be noisy currents on the CRC Gnd? All the transformer stuff and Bridge rectifier junk? That's why it seems like you would want the Main PCB to not ground "thru" that... is that right thinking?

No, go back to the first drawing and just remove the connection from XLR 1 to main board.  Main board ground reference comes from the CRC, then, if that is your PSU, that could go to "star" ground. 

I don't know what CRC is. I can guess but I would rather you told me.

Cheers

Ian

CRC is an off board rectification smoothing board. Rectifiers to Caps to 10ohm resistors to caps and I think one more stage. Works great!

Because of the smoothing caps on the CRC board, your going to want to reference your power ground were those smoothing caps are, otherwise its sorta defeating the purpose to have them. We can think of that as your "clean" power ground.
Then all your pin one, dirty/shielded ground you want to dump in the star ground. First drawing looks good lit mitsos said.

Are you still experiencing problems? Are you sure they are ground loops? Just don't want to jump the gun...maybe with the CRC board your voltage regs aren't getting enough power to properly regulate? Sorry kinda shooting from the hip here..


edit: upon reading everything again, once you have your power transformer everything will be good. You don't need to reference the center tap to chassis ground

OK, if I understand correctly the CRC board  is effectively the power supply, in which case:

1. The 0V from the CRC board should go directly to the earth bolt which is a bolt through the chassis.

2.The mains earth from the mains input connector should go directly to this bolt.

3. Connect pin1 of each XLR directly to chassis at the XLR.

4. Run twin screened cables from the XLRs to to IN and OUTPUT. Connect the screens to pin 1 of the XL but do not connect them at the IN and OUTPUT end.

5. Connect supplies and signal 0V from CRC to MAIN

6. Connect signal 0V from MAIN to TURBO and VU.

Cheers

Ian

So, Keith's CRC doesn't get a chassis connection(?)

Does that mean I need to ground main 0V to chassis (star) someplace?

jwhmca said:

So, Keith's CRC doesn't get a chassis connection(?)

Does that mean I need to ground main 0V to chassis (star) someplace?

Click to expand...

Keith's CRC does get a chassis connection - see point 1. above

Main 0V gets its chassis connection via point 1. above.

Cheers

Ian

I thought the center pin on the CRC input goes to the center tap of the transformer?

jwhmca said:

I thought the center pin on the CRC input goes to the center tap of the transformer?

Click to expand...

Well, I have never actually seen the schematic of the CRC board, so I am guessing here, but if it uses a centre tapped transformer for the HT then yes, the 'centre pin' of the CRC may well go to the transformer centre tap and this is most likely also the HT 0V that comes out the other side of the PCB. It is that HT 0V that needs to be connected to the chassis. If you post a schematic of the CRC I can be more specific.

Cheers

Ian

LOL, there's me thinking tubes all the time and ranting on about HT when this turns out to be a sand based device. I checked out the gyraf site but I could not find a separate CRC board.

Cheers

Ian

Ian, should be on the expat audio site

As Ian said.

For your wires to chassis connection, don't miss to scrap off any insulating coating/paint/anodizing for a solid and conducting/zero ohms connection. For your safety ground connection between IEC and chassis use green/yellow wire with diameter capable of current flowing at fault condition.
Be aware for the GSSL you might build 3 additional ground loops when fixing the main pcb to your case by metal/conducting standoffs when you miss to put insulating washers in between...

Rochey said:

Ian, should be on the expat audio site

Click to expand...

OK, found that - thanks for the tip. The CRC board is just a bridge and some extra smoothing to go between the mains transformer and the GSSL main board. So, the best place to connect 0V to the chassis would be from where the 0V enters the main board. It is not ideal, but with the PCB layout as it is it is the best you can do.

Cheers

Ian