Twisted pair wiring

[wanders]

I'm confused as to the correct wiring for shielded, twisted pair turntable connectors. I have some nice cabling containing a single twisted pair plus a ground wire, all wrapped with a braided copper shield, then wrapped in a rubberized outer skin.

Obviously, each wire of the pair connects to either the positive or negative post; but what about the ground wire and the shield. I'm hearing that the shield is to be connected (grounded) to the negative post at the downstream end. Then I'm hearing that a second ground connection must be established to create a true shield.

Then, what about ic's hard wired to the turntable vs. detachable, double ended patch cords.

Appreciate any advice.

 

[AndrewT]

Identify the signal carrying wires.
These MUST be connected to the Signal Terminals. Remember that Signal Hot and Signal Return are both SIGNAL carrying wires.

Any other wires in your cable are likely to be for screening, or Earth interconnections, NOT for Signal.

 

[gootee]

Andrew is right. I will add that "usually" the signal and signal "ground" wires (the twisted pair) are BOTH kept isolated from chassis ground. The drain wire that is connected to the shield is usually connected to chassis ground.

If the cable is used as an interconnect, the drain wire would ideally be connected to the chassis ground on both ends, unless that causes a ground loop.

If the cable is used internally, from input connector to the input resistor for the first active device, then the drain wire is usually only connected (to chassis ground) at the connector end and to nothing at the other end. The signal ground wire is usually kept isolated from the chassis, at the connector, and only connects to the ground end of the input resistor.

 

[wanders]

Thanks to both for taking the time. Let me see if I understand this:

- The drain wire is in contact with the braided shielding, therefore, the drain wire and braided shielding are the same thing; so the messy braid can be trimmed away and just the drain wire used.

- In this case, I'm interconnecting a turntable to a pre-amp using two single twisted pair cables. The turntable has a tonearm wire terminal block to which the interconnect cables connect directly - no rca jack on the turntable end. The terminal block has separate connecting posts for all four signal wires, plus a fifth post for head-shell ground (two black wires), chassis ground, and pre-amp output ground wire. For each cable, the two signal wires connect to the appropriate posts on the terminal block, the drain wire from each cable connects to the grounding post discussed above. This means that, when fully wired, the grounding post would contain the two black head-shell wires, the chassis ground, and the two drain wires (one from each cable).

- The preamp end of each interconnect cable ends in a male rca jack. The jack wiring contains only the + and - wires from the cables (no drain or ground). The output ends of the two drain wires should be tested to the preamp ground lug (maybe they form a ground loop, maybe not).

If my understanding on this is correct, then,assuming that the turntable had fixed, female rca panel jacks installed, how would rca to rca patch cords be wired?

Thanks again for looking at this.

 

[AndrewT]

RCA or phono plugs only have two connections. They are both Signal connections. Both connections must go to signal terminals at both ends.

These interconnects are usually coaxial cable. The core wire is Signal Hot. The screen wire is Signal Return or called Signal Ground. I don't like the term Signal Ground, because of the ambiguity that ensues. Signal Hot and Signal Return never connect direct to Chassis.
But you will often find that Signal Return connects to the Main Audio Ground and that Main Audio Ground is then directly connected to Chassis.
In this situation (and all situations) it is VERY important that every Signal Hot is kept paired with it's Signal Return over the whole route from Source to Receiver.

 

[wanders]

RCA or phono plugs only have two connections. They are both Signal connections. Both connections must go to signal terminals at both ends.

These interconnects are usually coaxial cable. The core wire is Signal Hot. The screen wire is Signal Return or called Signal Ground. I don't like the term Signal Ground, because of the ambiguity that ensues. Signal Hot and Signal Return never connect direct to Chassis.
But you will often find that Signal Return connects to the Main Audio Ground and that Main Audio Ground is then directly connected to Chassis.
In this situation (and all situations) it is VERY important that every Signal Hot is kept paired with it's Signal Return over the whole route from Source to Receiver.

Thanks, Andrew, In this case I'm not using coax, I'm using shielded twisted pair cabling - one twisted pair per cable, one cable per channel. The chassis ground, and turntable headshell ground, are routed out of the turntable directly to preamp ground without coming into contact with any of the four signal wires. I've been advised, however, that, for the shielding to work as a shield, it too must be grounded.

I wonder if you agree that the shield must be grounded? If so, the logical ground point would seem to be chassis ground, which is what I think GooTee advised.

 

[AndrewT]

Yes, ground the shield.
Yes, ground the shield to Chassis.
That then connects all the TT metal parts and the pre-amp Chassis and the shield to the same point.

 

[wanders]

Thanks.