Anyone familiar with old school audio stuff?

[TitanDiddly]

This receiver that I just bought today has a plethora of connectors on the back. It has right and left RCA connectors for aux, phono, tape decks, and more. The weird thing is, all the RCA connectors are single conductor- nothing on the inside of the barrel, just the outer ring. i.e. the tip of an RCA cable will not be connected to anything. However, there is a screw terminal marked 'ground' mixed in with all the RCA jacks, so I assumed that that's where the missing conductor is. I just spent half an hour soldering up a minijack to dual-RCA and ground cable. So I've the outside rings of the RCA jacks connected to left and right positive, and the negative coming through the ground screw. Apparently, this is incorrect. Anybody have an insight?

 

[PurdueRy]

maybe they are BNC connectors?

 

[Eli]

In an RCA connector, the center lead is positive and the outside ring is ground.

 

[PurdueRy]

take a pic and we can be more sure

But I really think you are describing BNC connectors

 

[vshah]

pic?

 

[TitanDiddly]

Nope, not a BNC, definately RCA. Assuming that you trust my knowledge of connector shapes, a pic won't show anything. I'll take another look, though.

 

[DaveSimmons]

That screw terminal is for the phono input only! Most older turntables didn't have built-in preamps and so needed a different level input (the phono is not the same as the others) and turntables were for some reason more susceptible to ground loops.

So an older turntable will have 3 cables: L,R which can only go to the "phono" input, and a ground wire.

 

[TitanDiddly]

Originally posted by: DaveSimmons
That screw terminal is for the phono input only! Most older turntables didn't have built-in preamps and so needed a different level input (the phono is not the same as the others) and turntables were for some reason more susceptible to ground loops.

So an older turntable will have 3 cables: L,R which can only go to the "phono" input, and a ground wire.

OK, cool, know I know what that is. But where does my missing conductor go for the other inputs?

 

[DaveSimmons]

RCA line-level input connectors haven't changed in 30+ years, so I'd guess the negative should go to the tip even though you think the tip won't contact anything.

 

[Colt45]

ive never seen a hollow rca before. pics.

 

[Eli]

I'd just open it up and see whats going on if you're really that stumped.

 

[Excelsior]

Model/Make of receiver?

 

[Ornery]

Sounds like this was their solution to ground loop hum. Ground the chassis of each component to the receiver and cross your fingers.

Edit: Man, I misread the OP! Eli is correct, the OUTSIDE is the ground, which is what I thought was missing for some reason. For the center conductor to be missing is impossible. You can't see it on any of these, but it's there, deeper inside.

 

[Pepsi90919]

how do you know there's no centre conductor in the jack? how did you see in all the jacks?

 

[Analog]

I'm certain there is a center conductor. Its probably just tarnished or real dark and you can't see it. The ground is not only for phono, but also AM radio.

 

[TitanDiddly]

OK, you all are probably right and I'm just missing it. I'll re-do the harness tomorrow.

Now, back to my exegesis.