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View Full Version : TC-7520 - what kind of cable for S/PDIF via electrical coax?



Quietschbox
05-05-2009, 15:49
Connection:
Squeezebox s/pdif electrical out to TC-7520.
Need a proper cable for this, not too shabby, but don't know were sensible starts, ends, and when hype begins.

The 7520 should be shipped soon, so should i order
http://www.beresford.me/UK/DIGITAL_COAX_CABLE_.html
before Stan sends? It's not a cheap one, for my standards, though surely you always can spend 100.000 for some super duper 50cm, if you want to, and in that light 20 quid might be fine. I don't know.

Also, besides question 1., "which type of cable", question 2. "what length should it be"?
Stans product has 1m. While I read somewhere cables should be 1,5 metres at least, because otherwise signalreflections do occur. Your comments on length, would that be a no for Stans 1m?

chrism
05-05-2009, 15:55
Hi,

1.5m appears to be the recommended min length. I bought a Mark Grant Coaxial cable (1694A) and it cost about £18.00 or so delivered. It has cannare connectors which are supposed to be true 75 ohm connectors. See markgrantcables.co.uk.

It is a bit "stiff" so you need to make sure you don't need to go round tight bends or the SB will be pushed over.

Regards

Chris

NRG
05-05-2009, 16:07
.... It has cannare connectors which are supposed to be true 75 ohm connectors. See markgrantcables.co.uk.....

Which appears to be a bit of waste of time as the RCA socket they plug into are not 75 ohm. You'll only get an impedance match if using BNC plug and socket.

Gazjam
05-05-2009, 16:36
These cables do make a difference.
I went through a stage of trying a lot of different ones and found differences in presentation - Stans one being a good one..

I tried NVA, Gotham, Belden, standard interconnect and others.

Best one I found is the NVA Super Sound Pipe (by far), the best of the rest being the Belden 1649a, which I thought was a fair bit better than all the rest.

This was in my system, your milage may differ though.

I only needed a short length to connect DAC to my Squeezebox, so I could get away with a short length of NVA Sound Pipe.

I go the cable as a trade for my squeezebox linear power supply - probably would have stuck with the Belden if I hadn't.

Ali Tait
05-05-2009, 17:11
From what I've read,0.75m is supposed to be the ideal length for this kind of i/c.

chrism
05-05-2009, 17:28
From what I've read,0.75m is supposed to be the ideal length for this kind of i/c.

Hi Ali,

Can I ask where you read that recomendation as it does appear to be at odds with what has been discussed on PFM.

Regards

Chris

kalozois100
05-05-2009, 17:57
I can also recommend markgrant belden one as it is value for money and better than stans one in my set up . I too have read top reviews of the super sound pipe but it was out of my price budget :(

http://cgi.ebay.com.my/NVA-70cm-set-SSP-Super-Sound-Pipe-Interconnect_W0QQcmdZViewItemQQitemZ220357911350

Quietschbox
05-05-2009, 18:05
These cables do make a difference.
I went through a stage of trying a lot of different ones and found differences in presentation - Stans one being a good one..

I tried NVA, Gotham, Belden, standard interconnect and others.

Best one I found is the NVA Super Sound Pipe (by far), the best of the rest being the Belden 1649a, which I thought was a fair bit better than all the rest.

This was in my system, your milage may differ though.

I only needed a short length to connect DAC to my Squeezebox, so I could get away with a short length of NVA Sound Pipe.

I go the cable as a trade for my squeezebox linear power supply - probably would have stuck with the Belden if I hadn't.


Oh no, this question seems to be a direct hit into the Hifi-Vodoo pot? :scratch:

What about "impedance"? Is that important? I never looked into that.
Also, how can a cable type have a specific impedance value, in spite of
varying length?

Should I make it easy and stick to Gazjams opinion and choose Stans, even though it's no special length?
Stan should know what he does, but how should I know how he ticks. :confused: He didn't reply when i asked him about the cables.

And while this came up, the standard question, "how can a digital signal be affected by sufficiently good cables still"?
No need to open a book for that, I just always wonder...:scratch:

I have to add, i am living in germany, so while suggestions may be useful if they also have technical data,
these products aren't neccessarily on sale here.

"APOGEE WYDE EYE WE-RR-2,0 S/PDIF", 58 Euros...
Belden 1649a without plugs is available, 3,40 Euro/m. Should i solder one myself, but where to get proper plugs?

NRG
05-05-2009, 20:24
The reason the cables apparently sound different is due to reflections because of the none optimum termination. Terminate SPDIF correctly and these differences magically disappear.

Thorsten, when he used to post a lot on the various forums demonstrated that 1.5m was a good cable length choice with RCA connectors or use an very short cable IE ~15cm

Ali Tait
05-05-2009, 20:41
Chris,
Sorry been trying to find where I read it but I can't! Memory like a sieve...
Probably a load of guff anyway.

NRG
05-05-2009, 20:50
BTW some old threads on DIYAudio question the validity of the Canare 75Ohm claim as the dimensions of the RCA mean the impedance can't be met...

Ali Tait
05-05-2009, 21:09
One way would be to solder a 75ohm resistor on the signal wire between the coax and rca.Might be worth trying and see if there's a difference.

chrism
06-05-2009, 08:02
BTW some old threads on DIYAudio question the validity of the Canare 75Ohm claim as the dimensions of the RCA mean the impedance can't be met...

Hi Neal,

I have compared the Canare connector solution with soldering the cable straight through to the board and could not detect any difference to the sound.

Have you come across something better that you would like to share?

Regards

Chris

Quietschbox
06-05-2009, 09:22
The reason the cables apparently sound different is due to reflections because of the none optimum termination. Terminate SPDIF correctly and these differences magically disappear.

Thorsten, when he used to post a lot on the various forums demonstrated that 1.5m was a good cable length choice with RCA connectors or use an very short cable IE ~15cm

Hi NRG, thanks for explanation. Looks like a potential Vodookiller.
I'll dig that and do a search.

NRG
06-05-2009, 10:03
Hi Neal,

I have compared the Canare connector solution with soldering the cable straight through to the board and could not detect any difference to the sound.

Have you come across something better that you would like to share?

Regards

Chris


Yes, BNC plug and socket.

chrism
06-05-2009, 11:06
Yes, BNC plug and socket.

Hi Neal,

Not certain how this would improve on soldering straight to the board but it is a solution. Hacker did the BNC soln to his Squeezebox on PFM.

I think I will stick with the Mark Grant cable with the Canare connectors as it does the job well in my opinion and is a cheap solution.

Regards

Chris

Quietschbox
06-05-2009, 18:43
http://www.positive-feedback.com/Issue14/spdif.htm
http://www.epanorama.net/documents/audio/spdif.html

Two articles i found. Didn't finish them yet.

I am confused on wave impedance=75 Ohm and termination resistor 75 Ohm.
So far i assume that any (video/TV) cable with wave impedance 75 Ohm will be fine and do, but what about termination with 75 Ohm resistor? Isn't that a confusion with the cable impedance and thus unneccessary?

And talking 75 Ohm resistor termination, does the TC-7520 have these built?

StanleyB
06-05-2009, 19:08
Many people confuse resistance and impedance.

Quietschbox
09-05-2009, 09:18
http://www.positive-feedback.com/Issue14/spdif.htm
http://www.epanorama.net/documents/audio/spdif.html

Two articles i found. Didn't finish them yet.

I am confused on wave impedance=75 Ohm and termination resistor 75 Ohm.
So far i assume that any (video/TV) cable with wave impedance 75 Ohm will be fine and do, but what about termination with 75 Ohm resistor? Isn't that a confusion with the cable impedance and thus unneccessary?

And talking 75 Ohm resistor termination, does the TC-7520 have these built?

Quote:
S/PDIF (or Sony/Philips Digital Interface) is a digital signaling standard specified at 75 ohms characteristic impedance and terminated on both ends. This means that the source driver (in the Transport) must have an output impedance of 75 ohms and the receiver (in the DAC) must have a parallel resistive termination of 75 ohms. If these terminations are both set to 75 ohms, then ideally the signal will propagate from the Transport to the DAC and no reflections will occur on the transmission-line that connects the Transport to the DAC, assuming that all components of the transmission-line are also 75 ohms.

Summary:
Terminator1(75 Ohm)--------cable(75 impedance)----------Terminator2(75 Ohm)

leo
10-05-2009, 16:05
I've just made a 1m S/pdif cable using 1694A terminated with 75R BNC's.

Tried with two different dacs AYA and Sabre the results was quite interesting, the sound was a little warmer with the 1694A, it gave the impression of slightly less dynamics

Cable I normally use is 1505A terminated with 75R BNC's
, I may have to try other alternatives too

scrufftyguy
27-06-2009, 10:33
I'm planning on getting some Mark Grant coax, as I've had quite a bit of stuff from him before and I've always been very happy! Is there really a big benefit in using 1.5m lengths as the squeezebox is going to be right next to the DAC, so 1.5m seems a bit excessive. Might I be better getting an optical cable for a short distance? :)

Ade

Marco
27-06-2009, 11:23
Hi Ade,

Why not send Mark a PM and ask him what he thinks? He's a member here :)

As he makes his own cables he could make one up to a custom length for you, providing he feels that performance is not unduly compromised.

I use his 1694A digital coaxial cable, from Belden, between my modified Sony transport and DAC and I must say that it's the best example of its breed I've heard, outperforming cables at many times its price.

However, I also know that other swear by high quality optical leads. I think you need to try both in your system to decide which is best for you. Most cable companies provide a trial period with a full money back guarantee, so the means to conduct a meaningful comparison is there :smoking:

Marco.

scrufftyguy
27-06-2009, 11:32
Thanks for the reply Marco.

Is your coax longer than the recommended 1.5m?

Ade

Marco
27-06-2009, 11:56
Nope, just standard :)

I'd PM Mark (you'll find him on the members list) and ask him for his advice. He's very knowledgeable and helpful.

Marco.

scrufftyguy
27-06-2009, 12:36
Just sent him a message...I'll see what he recommends.

Thanks again.

Ade

Marco
27-06-2009, 13:03
No worries, matey. Let us know how you get on :)

Marco.

scrufftyguy
27-06-2009, 20:31
Hi again Marco.

He doesn't seem too concerned at the length of cable and more or less says get whatever length I want, and I can try a few cables out first! I think i'll take him up on the offer once I've bought the DAC!

Ade

Marco
27-06-2009, 20:42
Sounds like typical Mark, Ade - very helpful. I'd definitely take him up on his kind offer as his cables are top-notch :)

Marco.

scrufftyguy
27-06-2009, 20:51
Certainly will, It'd be good to hear for myself if there's any difference (to my ears) between the coax and the optical too!

Ade:)

Marco
27-06-2009, 21:33
There will be differences, providing that your system has the required resolution to highlight them.

Generally, I find that the best coaxial cables give music slightly more weight and 'texture', whereas good optical cables often sound 'airier' and offer marginally better fine detail retrieval.

However, it's definitely one to 'suck and see' for yourself :)

Marco.

Gazjam
25-07-2009, 19:44
Many people confuse resistance and impedance.

Usually caused by Reluctance.... :)