Hi,

I bought this £400 Spdif coaxial cable for my audio system. While checking for any shorts in the cable I picked up a 10K Ohm resistance in the cable. Curious to find out I took the blue putty off the connect to find a 10K resistor connected between the ground and signal conductor. This is the first coax cable I have come across with a resistor inside. I am wondering what could be the technical reason for this, and could it cause damage to the equipment? I have attached a picture for everyone to look at.

 

It will not damage any equipment. I believe that SPDIF uses a differential driver and receiver. In some equipment this is actually an RS-485 device. If there is no driving source you want the potential levels on the two inputs to be equal and discharge the distributed capacitance of the cable. Normally this 10kΩ impedance would be in parallel with a smaller termination resistance at the receiver. Does this cable only have one resistor or does it have one at each end?

http://cds.linear.com/docs/en/datasheet/485fk.pdf

PS: I know for a fact that the Wadia 121 DAC uses RS-485 transceivers for the SPDIF inputs.

PPS: I'm even more impressed that you paid that much for a cable and then hacked it!

 

Hi,

I bought this £400 Spdif coaxial cable for my audio system.

You paid what?

 

I'm double impressed that someone would pay £400 for a digital audio cable where a standard £10 cable would give the same results.
Ranks right up there with £500 power cords.

 

Thanks for answering my question. So to answer your question the 10K resistor is on the receiver end, and I don't see any on the source end.

So after looking around I came upon a video link below. Where it explains why you would terminate a Coax cable with resistance. Apparently it has something to do with not allowing reflections to get back into the cable from the receiver end. And the termination resistance matching the characteristic impedance of the cable.

As being discussed in this video:
https://www.youtube.com/watch?time_continue=4&v=zrDxSM91Jcg

 

But 10k is way too high to be a termination resistance.
Such a resistance is usually in the neighborhood of 50 to 75 ohms for coaxial cable (the characteristic impedance of the cable).

 

Just return it and buy a $10 one..
You got massively ripped off..

 

Just return it and buy a $10 one..
You got massively ripped off..

EEVblog #29

But, but, but its special, per their site.

Here is a simple and non-technical way to view a digital signal in a wire and while not what happens it is a more accurate model than a one or zero. A single electron is not enough to trigger a response from audio equipment. So we need to think about the signal as a “swarm” of electrons almost with a shape. To turn a signal on or off requires a small amount of time and a magnitude of the “swarm” is necessary, the shape of which is affected by many factors and which in turn affects leading and trailing edges as they are read. However as we said, while a little closer to the truth this is still not what actually happens.
...
A review
“I have just put Tellurium black interconnects into my system and have found even prior to 'burning in' they are stunningly coherent. There is a balanced presentation which exudes detail but does not render any part of the sound overblown, no part of the presentation audibly overshadows another part. This coherence is critically important. "

 

Sounds like the "Monster" kind of stuff to me too.

BTW, you might ask whether the cables contain any tellurium. That is, before you return them. Most tellurium is radioactive:

Naturally occurring tellurium has eight isotopes. Five of those isotopes, 122Te, 123Te, 124Te, 125Te and 126Te, are stable. The other three, 120Te,128Te and 130Te, have been observed to be radioactive.[9][10][11] The stable isotopes make up only 33.2% of the naturally occurring tellurium; this is possibly due to the long half-lives of the unstable isotopes. They are in the range from 1013 to 2.2 × 1024 years (for 128Te). This makes 128Te the isotope with the longest half life among all radionuclides,[12] which is approximately 160 trillion (1012) times the age of the known universe.

There are 38 known nuclear isomers of tellurium with atomic masses that range from 105 to 142. Tellurium is among the lightest elements known to undergo alpha decay, with isotopes 106Te to 110Te being able to undergo this mode of decay.[9] The atomic mass of tellurium (127.60 g·mol−1) exceeds that of the following element iodine (126.90 g·mol−1).[13]

The main use of tellurium with which I am familiar is an alloy of copper to make it more machinable.

John

 

Just return it and buy a $10 one..
You got massively ripped off..

Heck, he got off easy! These folks will sock you £400 just for a USB cable. Or £2292 for a set of XLR cables. And they don't even appear to pre-condition their cables like these people do.

Their explanation of why they don't publish any technical specs for their cables is... illuminating.

 

But 10k is way too high to be a termination resistance.
Such a resistance is usually in the neighborhood of 50 to 75 ohms for coaxial cable (the characteristic impedance of the cable).

You do have a point, 10K resistor is too high. The cable seems to be working fine but yesterday after about 6 hours of use my DAC/Amp had a slight burning smell coming off it .

 

Even respected component manufacturers need to cater to the 'audio' clients. It's just good business and 'it has to be done' to sell.

 

By "cater" to the clients do you mean "pander" to their ignorance?

John

 

Ok let me explain the cable retail price is around £400. I bought it off Ebay for about £150. So as it came off Ebay I tested the cable for continuity and short with my basic multimeter. While measuring for shorts I picked up a 10K resistance. Puzzled by it I unscrewed the plugs, took the blue putty off and there in front of me was a sight of 10K resistor.

 

Even respected component manufacturers need to cater to the 'audio' clients. It's just good business and 'it has to be done' to sell.

The Panasonic article is "ENLIGHTENING" Oh dear

 

By "cater" to the clients do you mean "pander" to their ignorance?

John

Hypothetically, if someone requests a 'product' with those types of specifications you can't pander to them with technical brilliance.

 

By "cater" to the clients do you mean "pander" to their ignorance?

John

More like "taking advantage of their ignorance"

 

More like "taking advantage of their ignorance"

Snake Oil is expensive to make and purify to SEMI grade Alpha-Omega purity.

 

It will not damage any equipment. I believe that SPDIF uses a differential driver and receiver. In some equipment this is actually an RS-485 device. If there is no driving source you want the potential levels on the two inputs to be equal and discharge the distributed capacitance of the cable. Normally this 10kΩ impedance would be in parallel with a smaller termination resistance at the receiver. Does this cable only have one resistor or does it have one at each end?

http://cds.linear.com/docs/en/datasheet/485fk.pdf

PS: I know for a fact that the Wadia 121 DAC uses RS-485 transceivers for the SPDIF inputs.

PPS: I'm even more impressed that you paid that much for a cable and then hacked it!

Papabravo my other coax cable from Chord does not have any resistor between the ground and signal and has been working fine. I understand your point about keeping the potential the same at both ends then why don't we see this as a common design feature in all coax cables? The only difference between the Chord and Tellurium is that one has a plastic outer plug and the other has metallic ones.

 

Papabravo my other coax cable from Chord does not have any resistor between the ground and signal and has been working fine. I understand your point about keeping the potential the same at both ends then why don't we see this as a common design feature in all coax cables? The only difference between the Chord and Tellurium is that one has a plastic outer plug and the other has metallic ones.

Try with the old cable to see if smell comes - if not, try the new cable to see if smell returns. If it does, feel the length if the cable looking for hot spots (unlikely with a 10k resistor). Confirm smell is coming from specific component.