Jump to content

Prosink?


hungrych
 Share

Recommended Posts

There have been some studies that seem to say that 1 meter is the ideal length for a coaxial spdif digital cable... though I'm not sure of the science behind it. Generally I would assume that for analog cables shorter is better as long as there is a constant impedence down the length of the cable.
Just correcting myself here. The theory is from Steve Nugent at Empiracle audio and the optimum length is actually 1.5 meters. There is a review in the most recent issue of UHF where they listen to two cables, each at 1m and 1.5m... they alll liked the 1.5m ones better.
Link to comment
Share on other sites

The easy way:

a) Pick some decent coax. The Risch stuff will work fine. It will probably be 50 or 75 ohm, because it's hard to find anything else.

B) Put a resistor (of value 50 or 75 ohms, cable dependent) from the center pin to ground at the sink (amplifier or whatever) end of the cable.

The KG approved way:

c) Figure out what the output impedance of your source is. If it's less than 50 or 75 ohms, put a resistor in series (with the center pin) to make it 50 or 75 ohms.[1]

Before a): Use a TDR to measure the precise impedance of the cable and make sure that impedance is constant to within the precision of your choice, then pick out 0.1% resistors of the appropriate values for steps B) and c).

[1] If your source has an output impedance >75 ohms, use 300 ohm TV antenna-cable twinline or 450 ohm ham radio nutjob twinline. Decent quality 300 ohm stuff is almost impossible to find, but the beauty of this trick is that you won't hear a difference.

Now go out and buy the most expensive connectors you can find, because they do still affect the sound.

I'm not sure I follow you on the [1] comment. Why won't you be able to hear a difference? ???

My source (an AQVOX USB 2 D/A) has an output impedance of 120 ohm @ 1 kHz (XLR output voltage is +14 dBu).

So, to make a correct termination for this particular source I should:

a) get a 300 ohm cable

B) measure its characteristic impedance

c) solder a resistor in series on the source termination to raise the termination impedance to whatever the cable measures

d) solder a resistor from the center pin to ground on the destination termination with a total resistance equal to the characteristic impedance of the cable

e) use quality connectors

Please correct me if I got anything wrong, this is really not my strong side... :-[

Link to comment
Share on other sites

You can't measure the characteristic impedance without a TDR.

You don't really need to, either. Since you're DIYing, you can either:

a) Use 300 ohms for wire that has 300 ohms on the box;

or,

B) Be anal and make the cable with 270, 300, 330 ohms, pick the best-sounding one, then bracket +/- 30 ohms to be sure, then bracket +/- 10 ohms, repeat centered on the new value, bracket +/-5 ohms, repeat, bracket +/- 1 ohm, repeat. But you'd have to make 24 cables, or modify the original pair 23 times -- so I'd at least suggest stopping when you can't hear a difference! In all fairness, though, you might not hear a difference at even the first step. The advantage of the bracketing procedure is that you'll find the best value compromise between the termination of your cable and the load on your system, which could be many many ohms off the actual impedance of the cable. You might therefore end up with a cable that sounds even more mindblowingly-awesome than a "proper" ProSink-ed cable, but that sounds awful when you put it on a different rig and/or change your source and/or amp.

The idea of bracketing and the idea of the best value for the termination resistor being different than the impedance of the cable have not been tested (by me, anyway). Use at your own risk (of sanity, in any case).

Link to comment
Share on other sites

I wouldn't call it "truly" ProSink-ed, since it's getting quite far from the idea. A "truly" ProSink-ed cable has a resistor from signal to ground at the sink end of the cable, equal in value to the impedance of the cable, nothing more or less. The in-line source-impedance resistor that Kevin describes may (and probably will) improve performance, but also customizes the cable to that system -- just like my crazy "bracketing" idea. Call it 'ProSink Custom' if you really want a shiny Genuine Marketing Term for it, I guess :)

Regarding connectors--

I'm a big fan of the Cardas SLVR/GSMO and especially the SRCA.

The WBT Nextgen have more detail & top end, but the Cardas are more musical & natural.

Since the connectors in my experience are the only thing that affects the sound of a ProSink-ed cable, you can really go to town tweaking and comparing here.

Link to comment
Share on other sites

  • 2 weeks later...

How do you ensure the security of the connection of the resistor from signal to ground? I am a bit concerned with my soldering skills and maintaining that connection through repetitive plugging in and out. Do i just need to heatshrink the shit out of it to ensure the connection doesnt get jolted and broken off?

Link to comment
Share on other sites

  • 3 weeks later...

Hell no you guys didn't start this thread after I dropped cash on a Cardas Neutral Reference .5 IC to go 'tween my Melos and my DAC-ah! I refuse to be paranoid about impedance and resistors and all those technical things - let me just throw money at the problem and sing "lalala" to myself! :-X

Link to comment
Share on other sites

Hell no you guys didn't start this thread after I dropped cash on a Cardas Neutral Reference .5 IC to go 'tween my Melos and my DAC-ah! I refuse to be paranoid about impedance and resistors and all those technical things - let me just throw money at the problem and sing "lalala" to myself! :-X

Actually your fine - I remember seeing that eric had measured the CNR on his TDR and it did not have any extraneous reflections, I believe according to his graph it was identical to his Nitrogens, so I believe you can assume the CNR has a very constant impedance down the entire length of the cable

Link to comment
Share on other sites

Actually your fine - I remember seeing that eric had measured the CNR on his TDR and it did not have any extraneous reflections, I believe according to his graph it was identical to his Nitrogens, so I believe you can assume the CNR has a very constant impedance down the entire length of the cable

No cable:

http://www.audiogeek.net/images/TDR-Cardas/TDR-Cardas%20Neutral%20Reference-Pages/Image1.html

Cardas Neutral Reference:

http://www.audiogeek.net/images/TDR-Cardas/TDR-Cardas%20Neutral%20Reference-Pages/Image2.html

Compare to Risch-type cable:

http://www.audiogeek.net/images/TDR-Risch/TDR-Risch-Pages/Image1.html

IMPORTANT NOTE ABOUT READING THE TDR DISPLAY ON THE CARDAS:

The Cardas Neutral Reference cables were *too short* for my TDR to resolve a discrete reflection (the second bump you see with the Risch cables). Therefore, the absence of that return reflection should not be considered as an indicator of cable quality. This is in fact a larger issue with my TDR and cable tests -- a more technologically sophisticated TDR would be able to show us impedance fluctuations down the line. (For example, a Tektronix 1503B that I had for a few days could resolve down to the difference between the connector and the cable itself.)

The ideal cable shows up on the TDR display as a peak that is absolutely identical to the original, but smaller in amplitude (due to the cable loading the TDR output). Any difference in the shape of the peak -- usually seen in the trailing edge -- represents points where the cable is distorting the signal.

Link to comment
Share on other sites

  • 6 years later...

It's really easy to implement on your own. You just need any cable that is 75 ohms and pretty consistent impedance across the whole cable, and each end of the cable is terminated with a 75 ohm resistor between the + and ground (don't quote me on that). Belden has lots of good wire options, their 1694 is rated at 75 +- 1.5 ohms across 1000 ft which is pretty darn consistent.

  • Like 1
Link to comment
Share on other sites

It's really easy to implement on your own. You just need any cable that is 75 ohms and pretty consistent impedance across the whole cable, and each end of the cable is terminated with a 75 ohm resistor between the + and ground (don't quote me on that). Belden has lots of good wire options, their 1694 is rated at 75 +- 1.5 ohms across 1000 ft which is pretty darn consistent.

 

Going from what KG said:

 

Pick a cable, any cable, there are only two ways to use it. The right way, and NOT the right way. The right way is to terminate

the source and destination ends in the characteristic impedance of the cable. Termination to ground at the destination end, and

a value at the source end that when added to the impedance of the preamp adds to the characteristic impedance.

 

You terminate the source with the characteristic impedance of the cable (75 ohm in your example) then terminate the destination end so that the source impedance + resistor = the characteristic impedance (preamp impedance + resistor value = 75 ohm in your example).

 

Of course I might be wrong too...

Edited by Nebby
Link to comment
Share on other sites

Is this the cable you refer to? Silver plated copper coax 50 Ohm http://www.gore.com/en_xx/products/cables/coaxial/precision_coaxial_cable.html

 

Have you tried Belden? http://www.mouser.com/Catalog/catalogusd/645/1282.pdf

 

Gore will happily make you anything you want. Minimum of 5000 feet.

You will not like the price.

 

I use 50 ohm cable.

Edited by complin
Link to comment
Share on other sites

  • 1 year later...

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

 Share

×
×
  • Create New...