Balanced interconnect with 2 x 75 ohm coax cables? - Page 2

judderod · 8th February 2012, 09:12 AM

Good to know it was done before, on consumer equipment. It can't be that bad then!

Rane's wiring notes - Sound System Interconnection

Very interesting and useful.

So refering to my diagram, A to B to GND, and GND's within each unit is both the chassis ground and the audio ground.

I guess one option would be to remove the polymer shield from each coax, then twist them together so each shield is touching throughout the length of the cable. Then heatshrink the lot and seal the ends. Probably pointless though if ground loops aren't an issue.

marce · 8th February 2012, 11:41 AM

Just a question, but would these signal still be trully balanced? as with this configeration both signals are referenced to the GND for thier return currents more than to each other, as they would in a twisted pair cable?

judderod · 8th February 2012, 03:45 PM

AFAIK a balanced signal is irrespective of ground. Only the differential between SIG+ and SIG- is referenced.

I've since found some affordable solid silver twisted pair shielded. However still no affordable solid silver XLR's. Maybe there's another solid silver 3 pin connector I could use. If I could I'd do away with them altogether - after all, for signal quality, the best connector is no connector at all.

marce · 8th February 2012, 04:35 PM

For digital LVDS the definition of a differential pair, is having the same impedance to ground, but are alwqays routed as a tightly coupled pair, or as twisted pair in cables such as ethernet.
With both your cables being shielded, the lack of twisted pair and common mode rejection wont be as critical. But I am curious about the return currents for the analogue signals. With LVDS the return currents are catered for by the close coupling of the signal traces or wires when going off board. My thought is would the seperated signals use the shield of the co-ax for the return currents.

judderod · 9th February 2012, 03:48 PM

Sounds like you know much more about this than I do, but yes I would assume so. Both chassis and signal grounds are connected in the same way normal XLR's, it's just in my case there are 2 parallel or twisted screens making the connection, rather than just one screen, just one core, or just one screen and core (depending how the XLR is wired).

marce · 9th February 2012, 05:13 PM

Only digital, and as I learned recently some assumptions about low frequency analogue over interconnects are not as straight forward, and things that are
I am interested as I use both single ended and balanced (Behringer cross over), with some Ob speakers. I want to go all balanced, but my midrange amps are mono block class A valve (with solid state for the bass a Audiolab 8000A).
I do think with the distances involved etc that it wont make a bit of difference. Also as I do PCb design as a job, I have an interest in how signals get from a to b, and even though I have learned quite a lot over the years, the more I look into the subject, the less I find I understand, and assumtions and basic theory that is taught dosn't cover the full story.
courious, wont silver contacts tarnish easily, or is it not a problem?

judderod · 9th February 2012, 08:07 PM

If any part of your system isn't balanced then going balanced won't make a difference, except for the fact you'll be using a different cable so that might sound different.

I think we're all learning about signal transfer, even those who know everything are finding out new things. There are just so many ways to transmit and recieve data it's incredible.

Funny you should ask about tarnished silver. Apparently even black-as-ink silver oxide is more conductive than copper!

Silver is 5-6% more conductive (less resistance) than pure OFC copper.

AndrewT · 10th February 2012, 03:41 PM

Quote:

Originally Posted by judderod

Apparently even black-as-ink silver oxide is more conductive than copper!

Silver is 5-6% more conductive (less resistance) than pure OFC copper.

can you reference the data to confirm your assertions?

judderod · 10th February 2012, 03:55 PM

Yup...

Silver - Wikipedia, the free encyclopedia

Electrical resistivity and conductivity - Wikipedia, the free encyclopedia

And a subjective reference... Read from 'About Audio Note™ Silver Wires & the use of Silver in Audio Products'

Audio Note

AndrewT · 10th February 2012, 04:38 PM

I have had a quick scan through the three references.
I can't see where silver oxide is given a relative electrical conductivity.

Can you point me to the paragraph?

10th February 2012, 04:38 PM	#20
AndrewT diyAudio Member Join Date: Jul 2004 Location: Scottish Borders	I have had a quick scan through the three references. I can't see where silver oxide is given a relative electrical conductivity. Can you point me to the paragraph? __________________ regards Andrew T.

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8th February 2012, 09:12 AM	#11
judderod diyAudio Member Join Date: Mar 2011	Good to know it was done before, on consumer equipment. It can't be that bad then! Rane's wiring notes - Sound System Interconnection Very interesting and useful. So refering to my diagram, A to B to GND, and GND's within each unit is both the chassis ground and the audio ground. I guess one option would be to remove the polymer shield from each coax, then twist them together so each shield is touching throughout the length of the cable. Then heatshrink the lot and seal the ends. Probably pointless though if ground loops aren't an issue.

8th February 2012, 11:41 AM	#12
marce diyAudio Member Join Date: Jun 2007 Location: Blackburn, Lancs	Just a question, but would these signal still be trully balanced? as with this configeration both signals are referenced to the GND for thier return currents more than to each other, as they would in a twisted pair cable?

8th February 2012, 03:45 PM	#13
judderod diyAudio Member Join Date: Mar 2011	AFAIK a balanced signal is irrespective of ground. Only the differential between SIG+ and SIG- is referenced. I've since found some affordable solid silver twisted pair shielded. However still no affordable solid silver XLR's. Maybe there's another solid silver 3 pin connector I could use. If I could I'd do away with them altogether - after all, for signal quality, the best connector is no connector at all.

8th February 2012, 04:35 PM	#14
marce diyAudio Member Join Date: Jun 2007 Location: Blackburn, Lancs	For digital LVDS the definition of a differential pair, is having the same impedance to ground, but are alwqays routed as a tightly coupled pair, or as twisted pair in cables such as ethernet. With both your cables being shielded, the lack of twisted pair and common mode rejection wont be as critical. But I am curious about the return currents for the analogue signals. With LVDS the return currents are catered for by the close coupling of the signal traces or wires when going off board. My thought is would the seperated signals use the shield of the co-ax for the return currents.

9th February 2012, 03:48 PM	#15
judderod diyAudio Member Join Date: Mar 2011	Sounds like you know much more about this than I do, but yes I would assume so. Both chassis and signal grounds are connected in the same way normal XLR's, it's just in my case there are 2 parallel or twisted screens making the connection, rather than just one screen, just one core, or just one screen and core (depending how the XLR is wired).

9th February 2012, 05:13 PM	#16
marce diyAudio Member Join Date: Jun 2007 Location: Blackburn, Lancs	Only digital, and as I learned recently some assumptions about low frequency analogue over interconnects are not as straight forward, and things that are I am interested as I use both single ended and balanced (Behringer cross over), with some Ob speakers. I want to go all balanced, but my midrange amps are mono block class A valve (with solid state for the bass a Audiolab 8000A). I do think with the distances involved etc that it wont make a bit of difference. Also as I do PCb design as a job, I have an interest in how signals get from a to b, and even though I have learned quite a lot over the years, the more I look into the subject, the less I find I understand, and assumtions and basic theory that is taught dosn't cover the full story. courious, wont silver contacts tarnish easily, or is it not a problem?

9th February 2012, 08:07 PM	#17
judderod diyAudio Member Join Date: Mar 2011	If any part of your system isn't balanced then going balanced won't make a difference, except for the fact you'll be using a different cable so that might sound different. I think we're all learning about signal transfer, even those who know everything are finding out new things. There are just so many ways to transmit and recieve data it's incredible. Funny you should ask about tarnished silver. Apparently even black-as-ink silver oxide is more conductive than copper! Silver is 5-6% more conductive (less resistance) than pure OFC copper.

10th February 2012, 03:55 PM	#19
judderod diyAudio Member Join Date: Mar 2011	Yup... Silver - Wikipedia, the free encyclopedia Electrical resistivity and conductivity - Wikipedia, the free encyclopedia And a subjective reference... Read from 'About Audio Note™ Silver Wires & the use of Silver in Audio Products' Audio Note

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