75-ohm Cables For DVD-A?

[David Meek]

Is it best to go with a true 75-ohm cable when carrying the 5.1 channel signals from a DVD-A player to your receiver/pre-pro?




David - HTGuide flunky
Our "Theater"
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[Andrew Pratt]

No 75 ohm cables are for video not audio. Audio tends to be much higher ohm ratings (110 etc)

[Lex]

Actually, your close Andrew, audio is 50 ohms. That's why a 75 ohm video cable will carry audio but not vice versa, but in my opinion, coax for audio, is never the ideal solution. why? Shielding, dielectric (insulation) are different. Less shielding is better for audio applications, unless heavy heavy RFI, EMI interference is present.

regards,
Catman

[David Meek]

Thanks gentlemen (loosely applied ), that helps.

Okay Lex, you've just named your own poison. Today's my birthday and I suspect that a Panasonic RP-91 is hiding somewhere in the house. If that's the case, I'm obviously going to need cables for the DVD-A output. What do you recommend? I KNOW you have SOMETHING to recommend. . . . :B




David - HTGuide flunky
Our "Theater"
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[Chip]

Thanks gentlemen (loosely applied ), that helps.

Okay Lex, you've just named your own poison. Today's my birthday and I suspect that a Panasonic RP-91 is hiding somewhere in the house. If that's the case, I'm obviously going to need cables for the DVD-A output. What do you recommend? I KNOW you have SOMETHING to recommend. . . . :B

David,

I use Blue Tigers for my 555ES.. Great cables



Lexman,

Since i have a Ref50-Ref200.5 on order, i'm going to need cables too. What do you recommend ?




Chip Engle


"Concrete ain't a spectator sport"


<a href="http://www.htguide.com/bilder/index.cfm?fuseaction=arkivbilder&userid=0&selected userid=336" target="_blank">My HT

[Kevin P]

I use Silvercats as analog interconnects for my SACD player. As Billy Crystal would say, they sound Mah-velous! :B




Official Computer Geek and Techno-Wiz Guru of HTGuide - Visit Tower of Power
My HT Site

[brucek]

David,

Let me give you my take on your question. It's just my opinion, and others may certainly disagree.

I have to say that the fixation that some audiophiles seem to have with regard to the 'impedance' of cables for audio interconnects is unfounded. It's a very common engineering practice to ignore characteristic impedance and consider only the DC resistance of a cable (transmission line) when the line is short in comparison with the wavelength of the electrical energy that it conducts. Now, I would consider a one or two meter cable short in comparison to a 10 kilometer wavelength (and that's at 20Khz audio frequency).

In fact, in very short cables, in relation to the wavelength of the signal, the resistance of the line is considered completely insignificant and the energy transferred is considered lossless. This would definitely be the case for an audio interconnect with regard to impedance matching.

Characteristic impedance is a culmination of the 4 standard distributed electrical constants that a transmission line will possess of (capacitance between conductors) and (inductance along its length) and (resistance of the wire) and (low level leakage conductance between the conductors). Actually the L and C are so dominant in an infinite line used to calculate the impedance value, that the formula for characteristic impedance derives down to the square root of L over C......
When a coaxial cable, for example, is specified as 75 ohms, this is not a DC resistance, but an AC impedance that states if I terminate this cable in its characteristic impedance with a 75 ohm load, then that impedance will be reflected at its input. The line will theoretically then appear as infinite, and will exhibit no standing waves or reflections from the load, with its ratio of voltage to current being constant over the entire length of the line.
Well, so much for the technical stuff. Kinda boring.

The interface between a audio preamp and power amp (or in your question of DVD-A player and preamp input) is considered a line level, high impedance connection where the input impedance of the power amp will usually be in the order of 10Kohms-100Kohms with the output impedance of the preamp being in the order of 100 ohms. This is a voltage bridge type, high impedance connection, where the preamp acts as a voltage source with a very low source impedance and almost no current is drawn. We are not interested in power transfer in this interface and we sure don't care much about the characteristic impedance of the cable used. Certainly, since this is a high impedance connection where we are considering an input impedance of usually greater than 10Kohms, you have to be aware of the small shunt effect that capacitive reactance of a long interconnect can have on higher audio frequencies. This reactance will create a small low pass filter effect. Low capacitance per foot is far more important in audio interconnects than impedance. This is especially important when using a passive preamp. With active preamps, when using short interconnects though, it's statistically insignificant. I'll give you an example of the significance of capacitive reactance. A good typical audio interconnect might realize about 25picofarads of capacitance per foot. For a three foot cable that would be about 75 picofarads. The shunt impedance at 20Khz worst case would be about 106Kohms. Not much of a low pass filter is it?

It's the job of an audio interconnect to degrade the signal as little as possible. In that regard, since you want to present a relatively low voltage to the amplifier input, with as low a noise floor as possible, a properly shielded cable is important. Coaxial cable certainly fits this bill. Wouldn't matter if it was 50 ohms or 100 ohms characteristic impedance. The characteristic impedance of an audio cable is of little concern here. In fact the characteristic impedance of a piece of coax is only valid at higher frequencies - audio doesn't qualify...

Look for a well constructed, low capacitance interconnect using quality coaxial cable and you can't go wrong. Lex has exactly what you want..

brucek

[Lex]

David, happy birthday!

Well, if instead of a lump of coal, you do get an RP-91, oops sorry, wrong holiday. lol. There are many options in the catman bag of tricks. Two, that aren't even on the website. Yes, I been a busy boy. I now have a wire that is very similar to the SuperNova and Catalina wire, but at a lower cost. This is accomplished by using the bare copper shield as the ground, vs a passive ground with two internal twisted wires as the signal and ground. This wire costs me less, so I can pass the savings on to my customers. I just built 6 of them today.

Chip, certainly, silvercats a nice way to go, if the price isn't to high. But if not, I have to recommend the Novas, Catalinas, or the new hybrid Supernova, retaining nist if the benefits of the Novas, but at a lower price.

I also have a new less than that level of OF copper, not introduced anywhere as yet either. For super budget situations. I do love options!


Bruce, while obviously I respect your technical expertise. I am staying with the benefits of unshielded audio cables over their shielded counterpart for silver applications, anyway. Sure, shielded can sound very good. But it's said by many that shielding can inhibit audio quality at this high level of quality. While I can't prove that it does, I can't prove that it doesn't either...

Lex

[David Meek]

Thanks Bruce! 8) Now I have a few questions (OUCH! my wittle head hurts):

a 10 kilometer wavelength (and that's at 20Khz audio frequency)

I've been under the impression that the wavelength of a high-pitched tone (in the audible range) such as a 15Khz one was a "short" one, ie. measured in inches, whereas a lower pitched tone, say 25Hz, is measured in 10's of feet - hence low freq output being "omnidirectional" in a normal sized room. Is this difference due to one being a transmission along a line vs. transmission via air from a speaker? Some confusion here. . . .

The line will theoretically then appear as infinite, and will exhibit no standing waves or reflections from the load, with its ratio of voltage to current being constant over the entire length of the line.

A "lossless" line?

Low capacitance per foot is far more important in audio interconnects than impedance.

Then why do we spend so muc time worrying about the proper impedance? Salesmen? Not enough education on the users' part?

Thanks again for the great info!




David - HTGuide flunky
Our "Theater"
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[Kevin P]

I've been under the impression that the wavelength of a high-pitched tone (in the audible range) such as a 15Khz one was a "short" one, ie. measured in inches, whereas a lower pitched tone, say 25Hz, is measured in 10's of feet - hence low freq output being "omnidirectional" in a normal sized room. Is this difference due to one being a transmission along a line vs. transmission via air from a speaker? Some confusion here. . . .

Bruce is referring to wavelength of the signal traveling through the wire, which occurs at close to the speed of light. You're thinking of sound waves traveling through the air, which will have a shorter wavelength at the same frequency than an electrical signal in a wire, since sound travels a lot slower than electricity.

A "lossless" line?

Well, not completely lossless but less loss than a cable that exhibits reflections due to impedance mismatches. There is some loss due to resistance and capacitance but it's insignificant unless you're running mile-long interconnects.

Then why do we spend so muc time worrying about the proper impedance? Salesmen? Not enough education on the users' part?

Impedance is more important at higher frequencies (e.g. video, digital or RF) than at audio frequencies. Therefore, you'll always hear to use "75 ohm coaxial" for your video and digital cables, but this is less important for audio cables.




Official Computer Geek and Techno-Wiz Guru of HTGuide - Visit Tower of Power
My HT Site

[brucek]

Hey David,

Whoops, I was just about to post this answer and Kevin beat me to it with his great answers......I'll post my answer anyway..

Sorry, I didn't mean to hurt your head, I was just trying to give a little background for my answer.
Your questions are very good - it shows you read my way too technical answer.

I've been under the impression that the wavelength of a high-pitched tone (in the audible range) such as a 15Khz one was a "short" one, ie. measured in inches, whereas a lower pitched tone, say 25Hz, is measured in 10's of feet - hence low freq output being "omnidirectional" in a normal sized room. Is this difference due to one being a transmission along a line vs. transmission via air from a speaker? Some confusion here. . . .

Yep, there is a big difference between electro-magnetic energy and energy that's been transduced into sound pressure. The latter travels at the speed of sound (modified by temperature) which is approximately 344 meters per second. About a foot every millisecond. So a 100Hz tone would possess a fairly long wavelength of 3.4 meters or about 11.3 feet.
Electro-magnetic energy travels at about the speed of light in a vacuum and when transmitted on a wire or through free space its speed is modified by a spec'd velocity factor. In air the velocity factor is small and on a wire the velocity factor is larger. For example, a piece of coax may possess a velocity factor of 0.66, which when multiplied by the speed of light will reveal the speed or more important, the wavelength. The rough formula for wavelength of electro-magnetic energy being 300 divided by the frequency in megahertz, with the answer in meters. Specs on cable always include the velocity factor. At audio frequencies, it just doesn't matter......

A "lossless" line?

Ah, a standard engineering practice to make things easy, is to remove factors when they are considered to be 'insignificant'. This occurs when values in a formula are completely overwhelmed by others and so we ignore them. For example, if the input impedance of a circuit was 50,000 ohms, I would not consider it 'significant' if I added 0.024 ohms to this figure.
If you reread my original answer you'll see I said, "the resistance of the line is considered completely insignificant and the energy transferred is considered lossless.".........
Given the practice (as I said in my original answer) of ignoring characteristic impedance and consider only the DC resistance of a cable (transmission line) when the line is short in comparison with the wavelength of the electrical energy that it conducts, I was referring to the fact that the DC resistance of the audio interconnect renders the line basically lossless. This is because the DC resistance of this short piece of wire is completely insignificant in relation to the voltage source and the input impedance of the device it's feeding. If the input impedance of a circuit is 50K ohms driven from a voltage source, then the DC resistance of the interconnect wire, which may be 0.024 ohms (~20 gauge-3feet) would be considered insignificant and I could say the line was lossless.

Then why do we spend so much time worrying about the proper impedance? Salesmen? Not enough education on the users' part?

Well, impedance is certainly important in many applications in HT.
It would be considered important for video connections where we have a 75 ohm impedance matched source, cable and load.
Many power amps aren't designed to drive speakers that possess less than 8 ohms impedance
It would be considered important when using passive preamps since they have a rather high (and usually variable) output impedance. The input impedance of the load is then important, as is the length of interconnects because their capacitive reactance (frequency dependant resistance) can create a low pass filter.

Anyway, you can read both our answers and I think you'll get it..

brucek

[David Meek]

Oh, duh. ops: I've only known about electricity and the speed of light since I was in elementary school. I shall now go climb in a hole in embarrassment.




David - HTGuide flunky
Our "Theater"
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[efarstad]

David, you just sat on me...I found this hole first! Perhaps we'll find a bigger hole so we can share in our ops: !

E





The Norwegian A/V Nut!
E-Cinema

[Eduardo]

This is all new science to me. ops:
I slept a lot in school so I must have missed this lesson.


Thanks for the lesson. (although I might be dreaming)

http://home.nc.rr.com/ejimenez

[Chip]

Lex,

Is the new hybrid Super Nova a silver clad copper cable ? I didn't see any reference to it on quantum. I think an all silver solution would be too bright on my ears. Somewhere in between all copper and all silver might just be the ticket. I just don't see anything silver clad on the websites.




Chip Engle


"Concrete ain't a spectator sport"


<a href="http://www.htguide.com/bilder/index.cfm?fuseaction=arkivbilder&userid=0&selected userid=336" target="_blank">My HT

[Lex]

Chip, the only silver clad shielded cable I have, is the coax like used on your blackcat. This is an all copper. Honestly, i am so busy now, that not much will get on the website, but I do tell people in email, evidenced by selling 2 orders of it this week, lol.

I do have some silver coated that could be used for braided, unshielded cables.

FYI, with over 2K worth of business to build this week, not much time for web development.

[Chip]

Chip, the only silver clad shielded cable I have, is the coax like used on your blackcat. This is an all copper. Honestly, i am so busy now, that not much will get on the website, but I do tell people in email, evidenced by selling 2 orders of it this week, lol.

I do have some silver coated that could be used for braided, unshielded cables.

FYI, with over 2K worth of business to build this week, not much time for web development.

Okeedoke Lex..




Chip Engle


"Concrete ain't a spectator sport"


<a href="http://www.htguide.com/bilder/index.cfm?fuseaction=arkivbilder&userid=0&selected userid=336" target="_blank">My HT

[brucek]

FYI, with over 2K worth of business to build this week, not much time for web development.

Lex - I'm thinking that you're not maximizing your available time. Time management skills are a valuable tool. I'll bet you're wasting time sleeping every night. If you cut that sleep time down to about 4 hours every day, you could use the freed time to be more productive.

I'll bet the guys at HTG could come up with all sorts of smart tips to alleviate that time crunch you're under........

brucek