Building cables with Mogami 2549

[SIY]

What would be a short run? Anything below 3 meters?
I'm genuinely asking, no disrespect intended

There’s no hard and fast cutoff, but for most applications, 3 meters is indeed a short run.

 

[Sylvia]

Thank you for the quick responses

 

[dalbert02]

Unbalanced wiring with RCAs: always use a high quality coaxial cable. Don't use microphone type cables. These are for balanced/differential working.

I have several spools of Belden 1855A, would you suggest I go that route instead? Below are the specs compared to Belden 1505F commonly used. It has higher impedance but lower capacitance.

1855A

Nom. Conductor DCR	Nom. Outer Shield DCR	Nom. Capacitance Cond-to-Shield	Nom. Characteristic Impedance	Nom. Velocity of Prop.
20.1 Ohm/1000ft	3.7 Ohm/1000ft (12 Ohm/km)	16.3 pF/ft (53.5 pF/m)	75 Ohm	82%

1505F

Nom. Conductor DCR	Nom. Outer Shield DCR	Nom. Capacitance Cond-to-Shield	Nom. Characteristic Impedance	Nom. Velocity of Prop.
12.2 Ohm/1000ft	2.4 Ohm/1000ft (7.9 Ohm/km)	17.0 pF/ft (55.8 pF/m)	75 Ohm	80%

 

[SIY]

I have several spools of Belden 1855A, would you suggest I go that route instead?

Much better. The capacitance differences are negligible, and resistance is easily low enough. Coaxial is the very best choice for single-ended.

 

[MaxwellsEq]

I have several spools of Belden 1855A, would you suggest I go that route instead? Below are the specs compared to Belden 1505F commonly used. It has higher impedance but lower capacitance.

1855A

Nom. Conductor DCR	Nom. Outer Shield DCR	Nom. Capacitance Cond-to-Shield	Nom. Characteristic Impedance	Nom. Velocity of Prop.
20.1 Ohm/1000ft	3.7 Ohm/1000ft (12 Ohm/km)	16.3 pF/ft (53.5 pF/m)	75 Ohm	82%

1505F

Nom. Conductor DCR	Nom. Outer Shield DCR	Nom. Capacitance Cond-to-Shield	Nom. Characteristic Impedance	Nom. Velocity of Prop.
12.2 Ohm/1000ft	2.4 Ohm/1000ft (7.9 Ohm/km)	17.0 pF/ft (55.8 pF/m)	75 Ohm	80%

This is a good plan.

 

[Sylvia]

I have seen that many coax cables have a connector called BNC (see attached picture)
Would it be possible to use a BNC connector instead of the standard RCA?
If so, does it bring any advantage?

 

[SIY]

I have seen that many coax cables have a connector called BNC (see attached picture)
Would it be possible to use a BNC connector instead of the standard RCA?
If so, does it bring any advantage?

BNC is usually a more secure connection, so it would be nice if it weren't for the fact that most audio equipment doesn't use BNC. So...

 

[MaxwellsEq]

BNC is a superior coax connector in just about every regard compared to RCAs. It's originally for radio frequency usage (and, hence video), but that doesn't stop its use in audio. Although irrelevant at audio frequencies, it can accurately match cable impedance of 50 or 75 Ohms.

The screen connects before the central pin. RCA has the central pin connect before the screen, which is a terrible design feature. I wish all audio gear used BNC for coax and XLR for balanced/differential, but we're stuck with the terrible RCA connector, because that's what is the common "standard".

 

[Speedskater]

The frequency differences are orders of magnitude different between the Ku-band and the audio band. Nothing that happens there—from a time domain perspective—applies to our area of interest.

Admiral Hopper shows us one nanosecond:

We have one of her nanoseconds up in the attic. My wife went to one of her lectures.

 

[Ken Tajalli]

It will work fine but is more complicated than necessary. The ideal single ended cable is coaxial. The closest you can come to that with the constraints of that particular wire is to use the shield as return, and connect the two inner wires together at the Hot pin.

+1

 

[Speedskater]

Connecting the cable 'shield' to the RCA shells at both ends, is more important than how you connect the second central conductor.

To expand on my earlier post:
The two concerns with line level RCA unbalanced, single-ended cables in modern interconnect systems are.
1] (AC power related) Common Impedance Coupling Noise currents.
2] Interference.
* * * * * * * * * * * * * *
With high frequency interference, the cable shield should be attached to the metal chassis's at both ends. The longer the cable and/or the higher the interference frequency, the more important this is.
At lower interference frequencies, a heavy braided shield is best.
* * * * * * * * * * * * * * * *
Common Impedance Coupling Noise currents.
You want as low end-to-end resistance of the shield/return as practicable.
This is more important with very long cables or two AC power circuits.

Bill Whitlock sometimes writes about this concern.

Kurt Denke has a page at Blue Jeans Cable.

In about 2003, Bruno Putzeys wrote on a DIY RCA interconnect cable:
Take a coaxial cable and dress it in a number of extra layers of shield salvaged from other cables.

 

[restorer-john]

So you disagree with the way that is pictured? Would you have some theory as to why it would be bad (...or less good?)

That wiring would be the worst way IMO, you could configure an RCA to RCA lead with two core shielded microphone/instrument wire. It's unsuitable cable for the purpose. Coaxial (single core/full shield) is what you should use.

The inners on 2549 have 4.5 times the resistance of the shield, they have significant capacitance to one another and you'll end up with a cable with no proper shielding, potential HF loss (long runs/high source impedance situations) and potential hum issues from chassis's being at slightly different potentials. Exacerbated with double insulated, non earthed gear or devices with SMPS supplies (X caps to 0V).

The cable is designed for differential signalling. If you must use it, for RCA-RCA, because it's all you have, connect both inners in parallel for the hots and fully connect the shield.