[Jeff A]

I'm planning to install a PS Engineering PMA4000 Audio Selector Panel in my RV-8. The wiring diagram shows the shield of each set of shielded wire connected to the 'Lo' line of its respective component. Almost every other audio system I've ever dealt with (that I can remember) has the shields connected to a common point (daisy-chained) like the audio panel case or the power ground.....this includes a number of PSE's other audio panels. Any idea why PSE has you connect each shield individually on this particular panel?

 

[TCONROY]

Jeff,
PS Engineering makes the best intercoms out there. They are the most quiet and provide the best shielding against noise, especially in fiberglass aircraft. The PMA-4000 install diagram does indicate to tie the shield with the Lo. This prevents a ground loop from occuring, which causes excessive noise from strobes/inverters..etc. This is absolutely the correct way to do it as it leaves the shield 'floating' on the opposite end. Sheilds are always connected at only one end to prevent such ground loops from occuring.

I was/am an avionics installer and can tell you many stories of ground loop problems. Follow PS Engineering wiring diagram (current revision is 5) to a T and you will be fine.

Trevor

 

[Jeff A]

Thanks for the first post Trevor. Welcome.

I figured there is no way to go wrong if I follow the PS wiring diagram. Just not sure why they do it both ways on their systems and diagrams. Most of the certified / installed systems I've worked with (as my tiny mind remembers) have a common ground for the shields. To be sure, I will definitely follow their install instructions.

 

[newsum]

Connecting the shield to the low of the signal seemed a little odd to me also and a little clunky to connect. I think one reason this is done is that audio panels have a lot of inputs and their just aren't enough pins on the connector to dedicate to shield ground connections. This technique must work for audio signals or PS Engineering would not recommend it as they are experts with audio panels.

All the low side input pins are common (connected together via the internal ground plane). For example on the top connector (female pins), pins -1, -2, -3, -6, -7, -9, -10, -11, -12, & -25 are connected internally via the GND plane. If you are not using all of the inputs, you could use the low side of one of the unused inputs for a shield ground connection.

 

[Jeff A]

That's what I was thinking.

That's what I was wondering about the more I read the install instructions. I realized every single pin was used up on both connectors and figured that was their solution to terminating/connecting the shields. Since this is a 4-place audio panel, but only a 2-place airplane, I will have the passenger Lo inputs left open on both connectors. I may try the shield to Lo connection first, but if it proves too cumbersome, I will connect all the shields to an open Lo contact. Thanks for the verification, newsum.