Dual Pultec Build Ground Noise

[Janalex]

Same place the srpp boards are grounded.

 

[RoadrunnerOZ]

Yeah - that way any ground issues are dealt with directly by the mains cable and not travelling to that cable via a circuitous path.

 

[Janalex]

And extending the shield to that chassis ground location with a simple wire is not an issue hopefully as the chassis ground point is not directly near the origin or destination of the power rails.

 

[RoadrunnerOZ]

Just ground the end that is closest

 

[Janalex]

And I just need this dual core cable for the extension running between the 2 boards, correct? In terms of the 12v rails coming out of the terminal barrier to the boards and the 6v led/bypass wiring what to use there? Shielded?

 

[RoadrunnerOZ]

It’s only short from the transformer to the first board terminal post so I wouldn’t worry. The DC from your new rectifier board is not going to radiate anything as it’s regulated and smoothed.

 

[RoadrunnerOZ]

Just shield the two AC runs between the SRPP boards.

 

[Janalex]

Got it. I probably won’t be able to get away with the parallel wiring I had at the input of the first board as this cable will be too thick to jam in there with the secondaries off the transformer. I’m gonna go with both pairs of the secondaries to the barrier terminal and then run the shielded long AC runs from there to the second board and regular non shielded twisted pairs to the first board nearby. The barrier will be mounted near the transformer.

 

[RoadrunnerOZ]

All good

 

[Janalex]

Today I successfully made the rectifier board and there’s the terminal block mounted. Tomorrow my M2 screws arrive for the M2 standoffs that I have for mounting the little PCB there on the side and tomorrow the Belden cable arrives. Hoping to test on July 4th

 

[RoadrunnerOZ]

Looks good - have you tested the supply yet? Test before you connect to the bypass boards and LEDs.

 

[Janalex]

Yes a perfect 6v!

 

[RoadrunnerOZ]

 

[Janalex]

I was a bit disappointed today when I tested it. I have equal noise from both channels so it may be another ground issue. For ease the yellow cables are the shield grounds and the 2 srpp grounds going to AC ground. I moved around the belden cables but that didn’t change much. There is also a thin yellow wire grounding the rectifier board to AC ground. One channel was alligator clipped bypassing the bypass board and the other went through the bypass board and noise was the same. Bypass boards and leds work and are connected with the twisted red pair

 

[Janalex]

I just hooked up both bypass boards. The closer board has a small bit more noise. This may suggest that most of the noise is related to some ground loop and only the “extra” bit of noise on the closer board is related to the AC hum.

 

[Janalex]

I just removed the yellow wire from the rectifier board to AC ground and drastically reduced noise to almost nothing. So now the bypass boards don’t have a reference ground. Adding a little jumper from ground on the board to the chassis changes nothing

 

[RoadrunnerOZ]

Adding a little jumper from ground on the board to the chassis changes nothing

I’m not sure I understand what you mean here because just prior to the above quote you said

I just removed the yellow wire from the rectifier board to AC ground and drastically reduced noise to almost nothing

When you say “Adding a little jumper from ground on the board” which board do you mean? The bypass board?

 

[ccaudle]

Also is not clear what the term "ground" entails on the bypass boards. I don't think a schematic of those was ever provided.
From the pictures the "ground" node on the bypass board possibly includes the shield pin of the input and output connectors.

 

[Janalex]

Yes I’m referring to the bypass boards. We had a wire going from the ground node on each bypass board to chassis x 4 (2 per bypass board). You can see it in the first post. Now that same wire is connected each shield to chassis instead x 4

 

[RoadrunnerOZ]

So the ground on the bypass boards relay is isolated from chassis? Only getting ground from your new rectifier board?