Digital Cables
 

In article , Dave Plowman (News)
wrote:


However, most co-ax cable used for phono circuits will be centred around
75 ohms.

My recollection is that the values for 'audio' analog coaxs tend to be for
capacitances in the range from below 100pF/m to around 600 pF/m. This
implies a wide range of impedances - even if we ignore the effects of the
cable resistances, etc, which will change the values in a frequency
dependent manner at audio frequencies.

Fortunately, it doesn't matter much. :-)

Slainte,

Jim

--
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Audio Misc http://www.st-and.demon.co.uk/AudioMisc/index.html
Armstrong Audio http://www.st-and.demon.co.uk/Audio/armstrong.html
Barbirolli Soc. http://www.st-and.demon.co.uk/JBSoc/JBSoc.html

Digital Cables
 

In article , Serge Auckland
wrote:
Eiron wrote:


The characteristic impedance doesn't apply at audio frequencies, so
you can just consider the CLR values.

A minor correction in the interest of precision: Characteristic
impedance *does* apply at all frequencies,

As my own minor correction: I'd prefer to say that 'apply' here might be
better used to mean the decision of the person who wants to analyse or
assess the behaviour. On that basis, I'd say that it generally makes little
sense to try to apply characteristic impedance as your analysis model to
domestic analogue audio cables if only dealing with audible signals. There
are much simpler methods.

Slainte,

Jim



it's just that it's
irrelevant for analogue audio frequency signals on the sort of lengths
used domestically. If you were to be setting up analogue music-lines as
the Post Office had up to a few years ago when distances could be many
hundreds of kilometres, it was certainly relevant.

S.

--
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Audio Misc http://www.st-and.demon.co.uk/AudioMisc/index.html
Armstrong Audio http://www.st-and.demon.co.uk/Audio/armstrong.html
Barbirolli Soc. http://www.st-and.demon.co.uk/JBSoc/JBSoc.html

Digital Cables
 

In article , Serge Auckland
wrote:


Impedances as above, but as to what frequency they apply above, it
depends on the capacitance and inductance characteristics of the cable.
The formula is Fc=2/2Pi x root(LC) according to my reference, where L is
the inductance/unit length and C is the capacitance /unit length.
Characteristic impedance is root (L/C) above the cut-off frequency Fc.

I don't recall the formula, so the above may be correct. However its form
surprises me as I'd expect the value to depend upon the resistance (R')
and/or shunt conductance (G') per unit length as well as the capacitance
(C') and inductance (L') values...

My recollection is that, if we neglect shunt conductance and dielectric
losses, then the characteristic impedance turn over would be at the
frequency where jwL' is comparable with R'.

Slainte,

Jim

--
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Audio Misc http://www.st-and.demon.co.uk/AudioMisc/index.html
Armstrong Audio http://www.st-and.demon.co.uk/Audio/armstrong.html
Barbirolli Soc. http://www.st-and.demon.co.uk/JBSoc/JBSoc.html

Digital Cables
 

On Fri, 24 Nov 2006 15:49:21 +0000 (GMT), Jim Lesurf
wrote:

In article , Serge Auckland
wrote:


Impedances as above, but as to what frequency they apply above, it
depends on the capacitance and inductance characteristics of the cable.
The formula is Fc=2/2Pi x root(LC) according to my reference, where L is
the inductance/unit length and C is the capacitance /unit length.
Characteristic impedance is root (L/C) above the cut-off frequency Fc.

I don't recall the formula, so the above may be correct. However its form
surprises me as I'd expect the value to depend upon the resistance (R')
and/or shunt conductance (G') per unit length as well as the capacitance
(C') and inductance (L') values...

My recollection is that, if we neglect shunt conductance and dielectric
losses, then the characteristic impedance turn over would be at the
frequency where jwL' is comparable with R'.

Slainte,

Jim

The formula is sqrt((R + jwL)/(G + jwC)), where G is the conductivity
of the dielectric, and R is the resistance of the wire - all for the
standard length that yields the L and C values.

I've worked and example with some typical values, and you can see that
the effect only comes into play at lowish frequencies. By the time you
get up towards the top of the band, where it might matter, the cable
has returned to its true impedance, and the lumped model is no longer
needed to describe it - the transmission line is just fine.

http://81.174.169.10/odds/cable.html

d

--
Pearce Consulting
http://www.pearce.uk.com

Digital Cables
 

Jim Lesurf wrote:
In article , Anton
Gijsen wrote:
Serge Auckland wrote:

I don't think that anybody that knows how digital audio is transmitted
would believe that *any* digital cable will make a difference.
AES-EBU and SP-DIF signals are incredibly rugged, and provided the
cable is of 75 ohms impedance, what it's made of and how constructed
will have *no* effect on the signal transmitted.

Can some kind soul please tell me what the impedance of a "normal"
analogue phono-phono cable is?

Not really, since it will vary from one example to another.

Holy **** on a stick, guys! I didn't mean to start a friggin' argument.
What are you lot like?

The reason I asked is that I'm currently using a "normal" analogue
phono-phono cable as a digital cable between my CD player and AV amp,
and was wondering whether or not it was worth getting a "proper" 75 Ohm
impedance digital coaxial cable. Maybe if I could get hold of some phono
connectors that B&Q satellite coax cable would be good. Your thoughts...?

Digital Cables
 

On Fri, 24 Nov 2006 16:29:56 +0000, Anton Gijsen
wrote:

Jim Lesurf wrote:
In article , Anton
Gijsen wrote:
Serge Auckland wrote:

I don't think that anybody that knows how digital audio is transmitted
would believe that *any* digital cable will make a difference.
AES-EBU and SP-DIF signals are incredibly rugged, and provided the
cable is of 75 ohms impedance, what it's made of and how constructed
will have *no* effect on the signal transmitted.

Can some kind soul please tell me what the impedance of a "normal"
analogue phono-phono cable is?

Not really, since it will vary from one example to another.

Holy **** on a stick, guys! I didn't mean to start a friggin' argument.
What are you lot like?

The reason I asked is that I'm currently using a "normal" analogue
phono-phono cable as a digital cable between my CD player and AV amp,
and was wondering whether or not it was worth getting a "proper" 75 Ohm
impedance digital coaxial cable. Maybe if I could get hold of some phono
connectors that B&Q satellite coax cable would be good. Your thoughts...?

If that is the question, the answer is really simple - no. You will
know if the impedance of a digital connection is a problem, because
you will get errors in the data stream that cause ticks and burps. If
you don't have any of these, you have a clean signal and the impedance
of the cable is not causing problems.

d

--
Pearce Consulting
http://www.pearce.uk.com

Digital Cables
 

Anton Gijsen wrote:
Jim Lesurf wrote:
In article , Anton
Gijsen wrote:
Serge Auckland wrote:

I don't think that anybody that knows how digital audio is transmitted
would believe that *any* digital cable will make a difference.
AES-EBU and SP-DIF signals are incredibly rugged, and provided the
cable is of 75 ohms impedance, what it's made of and how constructed
will have *no* effect on the signal transmitted.

Can some kind soul please tell me what the impedance of a "normal"
analogue phono-phono cable is?

Not really, since it will vary from one example to another.

Holy **** on a stick, guys! I didn't mean to start a friggin' argument.
What are you lot like?

The reason I asked is that I'm currently using a "normal" analogue
phono-phono cable as a digital cable between my CD player and AV amp,
and was wondering whether or not it was worth getting a "proper" 75 Ohm
impedance digital coaxial cable. Maybe if I could get hold of some phono
connectors that B&Q satellite coax cable would be good. Your thoughts...?

That would be perfect. Just check that the cable is 75 ohm, not 50 ohms
and you're away.

By the way, There's a good chance that the "normal" phono-phono cable is
around 75 ohms. Also, on short lengths, even a bit of wet string will
work- literally. I've done it, and a few years ago, Canford Audio
demonstrated this at a couple of Trade Shows.

As to what we're like, we probably have too much time on our hands........

S.

Digital Cables
 

Serge Auckland wrote:
Anton Gijsen wrote:
Jim Lesurf wrote:
In article , Anton
Gijsen wrote:
Serge Auckland wrote:

I don't think that anybody that knows how digital audio is transmitted
would believe that *any* digital cable will make a difference.
AES-EBU and SP-DIF signals are incredibly rugged, and provided the
cable is of 75 ohms impedance, what it's made of and how constructed
will have *no* effect on the signal transmitted.

Can some kind soul please tell me what the impedance of a "normal"
analogue phono-phono cable is?

Not really, since it will vary from one example to another.

Holy **** on a stick, guys! I didn't mean to start a friggin'
argument. What are you lot like?

The reason I asked is that I'm currently using a "normal" analogue
phono-phono cable as a digital cable between my CD player and AV amp,
and was wondering whether or not it was worth getting a "proper" 75
Ohm impedance digital coaxial cable. Maybe if I could get hold of some
phono connectors that B&Q satellite coax cable would be good. Your
thoughts...?

That would be perfect. Just check that the cable is 75 ohm, not 50 ohms
and you're away.

It is. I'll go and raid my local electronics shop tomorrow.

By the way, There's a good chance that the "normal" phono-phono cable is
around 75 ohms. Also, on short lengths, even a bit of wet string will
work- literally. I've done it, and a few years ago, Canford Audio
demonstrated this at a couple of Trade Shows.

Incredible! Not sure why anyone would want to do it, but I like the idea
of it.

As to what we're like, we probably have too much time on our hands........

Well, I wish I knew as much about electronics as you lot.

Digital Cables
 

Don Pearce wrote:
On Fri, 24 Nov 2006 16:29:56 +0000, Anton Gijsen
wrote:

Jim Lesurf wrote:
In article , Anton
Gijsen wrote:
Serge Auckland wrote:
I don't think that anybody that knows how digital audio is transmitted
would believe that *any* digital cable will make a difference.
AES-EBU and SP-DIF signals are incredibly rugged, and provided the
cable is of 75 ohms impedance, what it's made of and how constructed
will have *no* effect on the signal transmitted.
Can some kind soul please tell me what the impedance of a "normal"
analogue phono-phono cable is?
Not really, since it will vary from one example to another.
Holy **** on a stick, guys! I didn't mean to start a friggin' argument.
What are you lot like?

The reason I asked is that I'm currently using a "normal" analogue
phono-phono cable as a digital cable between my CD player and AV amp,
and was wondering whether or not it was worth getting a "proper" 75 Ohm
impedance digital coaxial cable. Maybe if I could get hold of some phono
connectors that B&Q satellite coax cable would be good. Your thoughts...?

If that is the question, the answer is really simple - no. You will
know if the impedance of a digital connection is a problem, because
you will get errors in the data stream that cause ticks and burps. If
you don't have any of these, you have a clean signal and the impedance
of the cable is not causing problems.

Nope, no ticks/burps/clicking/artifacts whatsoever. It just doesn't
sound as good as using the analogue output of my CD player, but half of
the selling point of my CD player is the DAC, so that might explain it.

Thankyou very much for your help.

Digital Cables
 

In article ,
Anton Gijsen wrote:
Can some kind soul please tell me what the impedance of a "normal"
analogue phono-phono cable is?

Not really, since it will vary from one example to another.

Holy **** on a stick, guys! I didn't mean to start a friggin' argument.
What are you lot like?

The reason I asked is that I'm currently using a "normal" analogue
phono-phono cable as a digital cable between my CD player and AV amp,
and was wondering whether or not it was worth getting a "proper" 75 Ohm
impedance digital coaxial cable.

Does it work? Or produce crashing and banging noises? Because if a digital
connection like this sounds ok it is ok - there are no shades of grey.

Maybe if I could get hold of some phono
connectors that B&Q satellite coax cable would be good. Your thoughts...?

Pointless.

--
*Money isn‘t everything, but it sure keeps the kids in touch

Dave Plowman London SW
To e-mail, change noise into sound.