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Hi,
I want to make a pair of Cat5e speaker cables. I hear that this type of cable has capacitance issues and that some amps don't work well with them. Can anyone advise me how to tell if they would be compatible with my amp / speakers?
Thanks,
Ken
Follow Ups:
Call the manufacturer and ask, or make a Zobel network as a default. What amp are you using?
Sir Chris,How about NAD C320bee
any experience?Many Thanks
Audionuts
After doing a bit of google searching, it appears that this is an amp that doesn't perform well with high capacitance cables. You'll need to look elsewhere for cable with lower capacitiance, or build a zobel network, IMHO.
Hi Chris,
It sounds like maybe a better question is....How do I determine the capacitance of one of these cables? I guess part of the answer is that the manufacturer can advise after I know how the cable specs out on I'm guessing a multimeter with the ability to measure capacitance?? I appreciate the answer by the way.
Ken
I would like to revise the question yet again. Not knowing squat about amp design. What in the amp design causes the amp to be effected by a high capacitance cable?But to anwer KWillis's question better (I think)
CAT 5e has a nominal capacitance or 15 pF/ft for each twisted pair, so a ten foot cable is 150 pF for each twisted pair.
All those braided twisted pairs are actually parallel capacitors. Parallel capacitance is added normally. So for Chris's braided cable which consists of 27 braided pairs:
C T =C 1 +C 2 +C 3 ....+C 27
or
C T =27 x 150 pF = 4050 pF = 4.05 μF
or 405 pF/ft
nt
DammI seem to be having a problem lately with orders of magnitude, don't I.
The cable is 4.05 nano farads not micro farads.
nt
You can not just add up the individual cable capacitance of twisted pairs when they are bundled OR braided.The close proximity of other twisted pairs contributes to the overall capacitance of the total cable aggregate, increasing the total sum capacitance over that of the individual pairs.
Just as a star quad wired cable has more than twice the capacitance of two pairs of wires (actually very close to about 3 times the C), so do the multiple wire pairs interact with each other.
Unfortunately, there is no ready multiplier that can be used, as it depends on if they are merely bundled together (as in still in the jacket) or braided, and how tightly they were braided.
On average, for an adequate guesstimate, I would say that the multiplier would be somewhere between 1.25 and 1.5 over the capacitance of the number of pairs just added together.
BTW, 10 pairs is an odd number if you are working from sets of 4 pairs in a jacket, so most folks would end up with some multiple of 4 pairs for a single run, as this is the most convenient number to work with.
If braiding, then it becomes easier to deal with multiples of 3 and or 2, allowing one to 'three-braid' or double up via twisting, or some combination of both.ChrisVH recommends a full 27 pairs for full range use, and 9 pairs for HF bi-wire, while I have recommended no more than 16 or 18 pairs for a full range, or for each of a bi-wire. Either way, that's a lot more capacitance than you have been talking about, thus the practical limitations of about 10-12-15 feet of braided/bundled CAT5 (depending on how it is configured precisely), due to the sheer capacitance it represents.
Unfortunately, a large number of power amps are NOT unconditionally stable, and will become marginally stable, and prone to oscillation with SOME value of capacitance hung off the output, it is just a matter of how much it takes. Some NAIM amps will be prone to problems with ordinary zip cords, while other amps can have 1 F hung off the output.
Jon Risch
I have measured my 10feet of bi-wired cat5 (Belden 1871A which is a 25 pair cable) to be 7,000pf. I am testing it on a Quad 606 amplifier - no problems, the Quad is supposed to be unconditionally stable (from Quad manual). Some have said it will take much higher capacitance load. Some commercial cable is is higher than this, ie some Kimber models bi-wired. Anyone measured the inductance of Belden 1871A - I do not have an inductance meter?
JR: ""Unfortunately, there is no ready multiplier that can be used, as it depends on if they are merely bundled together (as in still in the jacket) or braided, and how tightly they were braided.""To determine the minimum possible capacitance that will result, adding is just fine. But yep, proximity to the others will certainly do as you say.
JR: ""On average, for an adequate guesstimate, I would say that the multiplier would be somewhere between 1.25 and 1.5 over the capacitance of the number of pairs just added together.""
Why guess? doesn't anyone have reasonable measurements that could be used for a form fitting equation? It'd be nice if Mudcat correlated all the variations he made, with capacitance overall. Same with CVH.
Cheers, John
"Why guess? doesn't anyone have reasonable measurements that could be used for a form fitting equation? It'd be nice if Mudcat correlated all the variations he made, with capacitance overall. Same with CVH."I can do that, but There is a problem with the assumptions. My tight braid may not be someone else's tight braid. But if Chris can just measure his, then we'll have a relative factor. I won't disagree with JR yet, but that 25 - 50% seems be a bit high to me.
My numbers ARE from measurements, from various configurations of CAT5 cables.I saw that range as a result of just bundling the cables together while still in the jacket (3 sets of 4 pairs=12 twisted pairs) versus a very tight braid of 27 pairs sent to me to measure by a friend.
Jon Risch
On average, for an adequate guesstimate, I would say that the multiplier would be somewhere between 1.25 and 1.5 over the capacitance of the number of pairs just added together.
So, you didn't guess. Could you please (if you remember the data and of course have the time) provide the measurements and the type of braid. Then we can make the necessary comparisons instead of guessing.BTW, have you tried different braids? I finishing a pair of cables based on a four strand braid that looks like a double helix (interlocking chains). when complete I'll measure them. It would be nice to be able to compare the capacitance of the various braid styles. And maybe useful too.
You'd need an LCR meter to measure the capacitance, as most multimeters won't do this. You could send to me when you're done and I could measure, or you could use a ballpark figure of about 500 pF per foot, if you want to ask the manufacturer.
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