Balanced interconnect with 2 x 75 ohm coax cables?

[judderod]

Just wondering if this could work well.

Assuming I have a DIY DAC with a balanced output, and I wired it to send the output to 2 x RCA sockets. At the other end is a DIY amplifier with the same sockets and wiring.

GND to sleeve of both RCA's

+V to tip of one RCA

-V to tip of other RCA

[x2 - so there would be 4 RCA sockets for balanced stereo]

Any good?

[kevinkr]

Unconventional, but should not cause any particular issues, just make sure all RCA jacks are grounded to the same ground point.

[DF96]

Slight possibility of a ground loop because of the two parallel screens.

[judderod]

Originally Posted by DF96

Slight possibility of a ground loop because of the two parallel screens.

I was thinking of leaving the output end of the shield disconnected. Both devices would share the same mains ground.

If that would help, I'm just guessing here.

[DF96]

You would then need excellent CMRR. Why are you using RCA with balanced connections? And why a pair of coax instead of a twisted pair?

[judderod]

Originally Posted by DF96

Why are you using RCA with balanced connections? And why a pair of coax instead of a twisted pair?

Hopefully this won't go OT as I'm sure there are others with differing opinions on this but the main reasons are:

1. I cannot find any solid siver conductor XLR plugs or sockets for less than thousands of $'s. There are solid silver RCA plugs and sockets available for a lot less.

2. I cannot find a solid silver-cored shielded twisted pair available on the market for less than about $100/m. I am currently using a solid silver-cored coax for single ended audio that costs a lot less than that (and sounds great I might add).

Here's the idea:



I figure there might need to be some combination of resistors and/or capacitors between A, B and GND on the amplifier side? I'm no good at design, only theory and implementation so thanks for any help

[mjf]

perhaps you can try this out with two pairs of cheap rca - cables (equal lenght, sitting tightly together...... with short pieces of heatshrink or so ).

[avcllc]

FYI, James Bongiorno used the two RCA sockets in a balanced cable connection in his Sumo line of amplifiers (circa. 1980's), preamp to power amp. This was before consumer electronics has balanced XLR connectors and associated circuitry.

[Speedskater]

The shield or in this case the two shields are not audio ground. They should only be connected to the chassis's. Not being part of the audio circuit, ground loops are not a mater of concern.
As "mjf" symmetry is necessary for a good balanced analog interconnect. So both cables (equal lenght, sitting tightly together...).

[avcllc]

You are indeed correct the signal+, and signal - are the center conductors of each individual coax, and the shields are chassis ground. I tend to agree with Jan Didden, that the use of a shielded twisted pair with Cannon XLR connectors work best for balanced connections. I was just pointing out that the use of two coaxial cables with RCA connectors was used in a production amplifier back in the '70's.
A good reference for connector wiring can be found on Rane's pro-sound website under tech notes section. They also explain pin 1 grounding in a balanced interconnect.