Talk me out of bypassing the PL-700B Input Attenuators

[Gepetto]

So the same effect is achieved because the inmput ground plane is no longer grounded so we don't have ground loops possible NOT leaving one end of the shield loose??

Both RCA jacks have their shells connected to each other at the input end by the isolated copper plate that they mount into. Thus whether you use shielded twisted pair or single conductor coax this isolated copper plate becomes connected to pin 2 of each PL14_20 channel by either one of the twisted pair conductors or the shield braid of the coax. You see how that is same-same?

The wiring schematic I posted some time ago shows the coax type connections.

 

[Gepetto]

Cause Nav sent SOME REALLY NICE one conductor shielded #20...

You should give it a try. I have some nice mil spec Teflon coax that I use, great stuff.

 

[laatsch55]

Well, that's what Nav sent, he also sent some nice 2 conductor also...

 

[NavLinear]

Sounds like the single conductor stuff is what you should use. Like Joe said - same principle for the shrink at the floating end.

 

[laatsch55]

But he's not floating any more...

 

[Gepetto]

But he's not floating any more...

Who is not floating anymore??

 

[laatsch55]

If the shields are tied to ground at each end that used to mean ground loops. Or at least the possibility of ground loops..

 

[laatsch55]

Who is not floating anymore??

You...

 

[Gepetto]

If the shields are tied to ground at each end that used to mean ground loops. Or at least the possibility of ground loops..

Hi LeeT
When you used shielded twisted pair they were tied together in exactly the same manner. The wiring ends up no different whether wired in as shielded twisted pair or single conductor coax wire.

The floating plate is still floating Lee. It is separated from single point ground by a paralleled set of 2.7 ohm resistors from that single point ground to the copper isolated plate. The series resistor in each leg eliminates any ground loop.

 

[jbeckva]

LOL

You know.. I too have had this conversation before, and I went round and round til I got dizzy and fell out of my chair. Til I remembered/discovered one detail..

Lee - remember that between the ground plate at the inputs and the chassis SHOULD be the RCA jack's inside / internal swedge (whatchacallit?) insulator. The ground plate is lifted up by both of 'em. Soo.. you have the shields twisted together and tied to the ground plate, which in itself is isolated because of the insulator washers between it and the metal - then on the other end towards the WO 14 PCB, shields to pin 2's, hot/center/whatever ya got the signal coming in at to pin 1. Ground originates on the 14 PCB, then up through the 2.7 ohm (to float it) and to the shield of the cable. Then on the other end attaches right to the ground plate, which in turn is conducting the "return" on out from the RCA jacks outer ring - but there is NO grounding to the metal wall there.

 

[laatsch55]

Got it..

 

[Gepetto]

Got it..

You are using the insulating washers for the copper plate correct Lee? Must be the case. The ground for the RCA jacks comes only from the WO control board, nothing else.

 

[laatsch55]

yes Sir...

 

[wattsabundant]

The original input wiring used Belden 8451 wire. 8451 is intended for mic/line level use for point to point use in pro installations. It is 100% shielded. I've installed 100 foot snakes for microphones using 8451 and never had any noise/hum/buzz issues. It's not teflon and can be finicky, but it's not junk.The proper way to use it is to use a short piece of heat shrink on each end for point to point wiring.

 

[orange]

You know, I could tell you...but then again if you don't do it yourself how will you ever see if perhaps you just messed it up?