Telephone cable speaker wire

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Hello Harry, Jocko and All,
mrfeedback said:
Question - Given that DACs despite output filtering still emit RF junk, then DAC to AMP connections really ought to be via a transmission line (coax ?) correctly driven and correctly teminated?
Also for all other line level interconnections ?
Has any body tried this correctly ?
Why should balanced lines (do they) work any better ?
Harry's reply -
HarryHaller said:
Since Time Domain Reflectrometry deals with frequencies too high for even a cane toad to hear, why the the interest in TDR for a cable carrying audio frequencies. They invented something called a zobel network to adress this issue of stability driving capacitive cables.
H.H.
Harry, my interest/question is regarding behaviour of line driving stages and line recieving stages when conveying spurious RF on top of the audio with the condition of cable RF reflections due to mismatching.
Do we have a consensus on recomended Line Driver and Line Reciever stage topologies that can cope with long balanced or coax lines (e.g. - multicore snake) and reflections and spurious RF conveyed and picked up (e.g - stage dimmers)
My first thoughts are toward beefyish Class A non loop feedback and maybe SE.
Regarding balanced connections, I understand CMRR.
Question - No twin cable is perfectly balanced, so therefore reflections ought to be more (twice) an issue ? Yes/No ???

Regarding Zobel networks - Years ago I carefully impedence compensated the drivers in a high quality 8"/1" two way,
and further compensated the Canare star-quad cable/Box combination so that it measured around 6 ohms quite flat out to past 45 kHz, and slight drooping after that.
I didn't bother to compensate the bass driver sealed box resonance peak, though.
The amp remained stable and sounded rather better without the Zobel Stage - more Gaussian, more detailed but smoother, fantastic depth imaging (sounds from behind !), it went louder and the amp ran cooler !
My asian (pro) rack mounted souped up 120+120 amp driven to momentary clip went Real Loud, Real Big, and Real Clean !.

Hello, jgwinner
The TDR mentioned here is testing to determine the cable characteristic impedence, by experimentally fitting the optimum loading to the end of the line so as to minimise/eliminate reflected energy - i.e. - perfect power transmission.
For sinewave only, impedence sweep testing, a flat impedence characteristic implies zero returned energy anyway, but does not say anything about impedence discontinuities - only TDR can do this.

And as Jocko and Harry said, It's all about making your favourite records go louder = More Fun .... :)
And Jocko, thanks for answering.

Regards, Eric.
 
The TDR mentioned here is testing to determine the cable characteristic impedence, by experimentally fitting the optimum loading to the end of the line so as to minimise/eliminate reflected energy - i.e. - perfect power transmission.

Right, but I think what you are measuring is the 'edge' between the line and the load.

TDR's are used to check to see if a microwave waveguide is impedance matched, and similar work, as well as to check for an open or a short in a long cable. I've done both.

???

Think of a glass of water. When you see the 'bent spoon' it's because the electomagnetic impedance of the water is different of air, so you get a reflection. That's what the TDR measures.

== John ==
 
Pspice model

I just ran across a SPICE model I wrote that's pretty good for 24awg twisted pair from over ten years ago. It was extremely helpful at the time and quite accurate, at least for doing simulations on various telephone plant circuits (typically thousands of feet).

I designed this subcircuit to implement a generic balanced transmission line. You supply the R, L, G, and C parameters (per foot). The length of the line is set by a voltage source of 1V/ft.

Just in case you were interested...

jh
 

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Eric:

Hi jgwinner, yes the testing reveals mismatch between the line and the load.
Then remove this optimum load and measure it and you know the impedence of the line - yeah ?

Sort of - A TDR is a 'reflectometer' meaning it reveals the EDGE between the line and the load. Or any 'edge'. Not the characteristics of the cable itself necessarily.

Think of it this way, if you shine a flashlight at a mirror, you can't conclude that the air is reflective.

Hagtech:

VERY interesting. What are typical values per foot? Can you make a conclusion based on yor numbers?

== John ==
 
24awg values

The per/foot values of the transmission line are buried in the spice model. The values given are for 24awg twisted copper pair
solid core telephone cable (data from the ITT Reference Data for Radio Engineers).

R = 0.052 ohm/ft
L = 0.18 uH/ft
G = 4.3G ohm/ft (actually, 1 over this)
C = 15.9 pF/ft

I think the R and L values work out to be "there and back". That is, total circuit resistance of a 10 foot cable would be 0.5 ohm. CAT5 values will probably be similar.

To run several pairs in parallel, just multiply or divide the parameters appropriately. Interesting, the high frequency characteristic impedance works out to 106 ohms.

jh
 
Can one of us measure say, 10 feet of 10 pair and 20 pair and post the results of loop inductance, loop resistance, total capacitance and characteristic impedence ?
It should be easily obtainable from any electrical wholesaler for less than aus$3/meter .

My old HP cro is down and needs an EHT transformer - seems like getting a spare is a bit like getting some rocking horse s***.
Can any body help with old HP parts ?

My testing hands are cut off just now, so if someone can do these measurements, I'd be appreciative.

Thanks, Eric.
 
<i>"My old HP cro is down and needs an EHT transformer - seems like getting a spare is a bit like getting some rocking horse s***.
Can any body help with old HP parts ?'</i>

You could try <a href="http://www.oatleyelectronics.com/">Oatley Electronics</a>, they buy lots of RAAF surplus test and measurement equipment at auction, including HP scopes, they might have some parts as I think they refurbish before selling.


Regards
James
 
I too favour flat foil cable for speaker runs. I find that Allen Wright's method of two layers of foil insulated and joined at each end, better than anything else I have tried. I used copper foil instead of the suggested silver foil as for me cost is a factor. Different people bring their "special cable" for me to try resulting in me being very satisfied with what I have. My cables are 30mm wide and 1 meter long.
I would be interesed to know if one should reverse the cables from time to time or is there a good simple method of revitalising them?
Is the extra cost of sliver foil compared to copper foil worth doing?
 
Nasty:
 

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One of those cables (DNM Reson II) sounded harsh, thin, with tizzy white-noise treble. Bass was muddled and uncontrolled, mids were unpleasant/painful/fatiguing.

The other (4PR, 4VS) sounds more natural, with solid, deep bass, sweet, realistic treble, and less offensive midrange. Bigger soundstage and more natural detailing too.

If anyone is suffering with thin, spaced cable, give something like these or phone cable a try!!!


-Simon (expecting flames...)

edit: system is solid state amp, normal dynamic speakers, and similar interconnect. Also, to be fair the Reson sounded good on cheaper equipment... (ie. when I bought it several yrs ago!)
 
Cat 5 cables

I did some 50 diffrent combinations of construction and tried some 10-12 diffrent brands of the CAt 5 cables.They are good,but there is some level that you just can't go higher with them (I would say it is the level of 500-600$ for the pair of the shelf cables).
The copper foil and some other types of DIY cables I'm using have more to offer (better potential).Also best sounding CAT 5 based cables of mine had big capacity (500-600pF per meter),some amplifiers can't go with this.
Bartek
 
how are they braided?
Might not have pointed out, they are Kimber cables, sorry. Perhaps you thought they were DIY ones... There are 8 conductors: 4+/4-. Each 'conductor' is a bundle of cores, in 'VS', they are varying diameters. Not sure exactly how one would do a braid like that at home! 4PR and 4VS both sound nice, each use polyethylene (spelling?) insulation. This factor may also have a bearing on the SQ, being less harsh etc (the Reson cable uses teflon). Mr. Feedback will have something to say about it perhaps.

-Simon
 
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