Understanding capacitance specs for audio interconnects

PeterCapo · « **on:** 23 Feb 2006, 02:47 pm »

Hi folks:

My first post in this forum!

My question follows reading Mr. Van Alstine’s interesting article on the AVA website regarding audio interconnects. Among other things I derived from the article is that I should select interconnects that are relatively low in capacitance for use with a vacuum tube preamp, such as my Dynakit PAS preamplifier.

My question is about how to understand and compare capacitance specs. Here are two specific examples from relatively lower cost interconnects:

1. A 1M set of Kimber Tonik interconnects with RCA connectors is specified as having a parallel capacitance of 52.0 pF @ 20 kHz

2. www.avcable.com sells a “Precision Low Capacitance Audio Patch Cable,” with RCA connectors, meeting Belden 1800F specifications. The stated capacitance is as follows:
a. Nom. Capacitance Conductor to Conductor @ 1KHz = 12pf/ft, and
b. Nom. Cap. Cond. to Other Cond. & Shield @ 1KHz = 26pf/ft

Other than allowing for the differences in the unit of measurement for length, it’s not clear to me how to compare the two cables given the way the specifications are presented.

Which of the two specs for the avcable interconnect more closely compare with the Kimber spec – or do they compare at all?

Given that capacitance specs appear to be stated differently, what guideline would you use to recognize an interconnect with low enough capacitance that it will not unreasonably roll off the high frequency response of a vacuum tube preamp, such as the PAS?

Any assistance appreciated.

Thank you.
Peter

avahifi · « **Reply #1 on:** 23 Feb 2006, 03:59 pm »

Well at the worst case the Belden cable has half the capacitance per foot (26 pf vs. 52 pf) although I am not sure what Nom. Cap. Cond. to Other Cond. & Shield represents --- perhaps the rating between the two wires molded together to form a stereo set --- I have never considered that issue before --- probably I should have. I think a direct comparison would be between the single cable 12 pF per foot for the Belden to the 52 pF per foot of the Kimber cable --- or the Belden is likely four times lower capacitance per foot --- a much better choice.

12 pF per foot is about as low a capacitance per foot I have seen for interconnect cables so likely no point to search further.

Frank Van Alstine

gitarretyp · « **Reply #2 on:** 23 Feb 2006, 04:20 pm »

The two capacitances for the belden are conductor to conductor and conductor to shield/drain wire. It's a shielded twisted pair cable.

I think the kimber spec is 52 pF per meter, which is ~ 16pF per foot.

Kevin Haskins · « **Reply #3 on:** 23 Feb 2006, 04:24 pm »

I hope Frank doesn't mind me jumping in here. If so feel free to delete me Frank.

Most twisted pair designs are relatively low capacitance. If you have four stranded construction you double your capacitance per foot. Some of the exotic "designer" cables have MUCH higher capacitance with the long foil ones being hidiously high.

Also understand that the connectors have a capacitance so they throw off your calculations for a short 1M cable quite a bit. On a longer 50-100ft run you see in pro audio they are not as much of a factor.

I personally wouldn't worry if one cable is listed as 20pF/ft vs. 30pF/ft. Both are low enough that it will be a non-factor in the lengths we use in home audio. Any good twisted pair design with a shield will be low capcitance.

My choice is the Canare twisted pair because I like their jackets. They are flexible and come in different colors. The percieved quality of the Canare is much higher than the Belden cables and I like having equipment that not only performs good but feels good. You know... it's like a mechanic with his tools. There are a lot of tools that do the same job but some of them just feel better in your hand than others.

Canare L-2T2S 22pF/ft Less than $0.50/ft

Buy it at Markertek

http://www.markertek.com/Marketing.asp?target=CANARE

avahifi · « **Reply #4 on:** 23 Feb 2006, 07:38 pm »

No problem with your post. Good information.

Frank

Listens2tubes · « **Reply #5 on:** 26 Feb 2006, 05:36 pm »

I have used Canare Star Quad L4E6S four conductor microphone cable that is rated 44ohm, 57pF . Is this concidered high capacitance?

avahifi · « **Reply #6 on:** 26 Feb 2006, 06:28 pm »

Using the Canare cables for speaker wires or interconnect cables?

If interconnect cables, then its about four times as high a capacitive load as the Belden cable mentioned above.

You tell me if that is good after everything I have said about it (capacitive loads) in detail.

Frank Van Alstine

Listens2tubes · « **Reply #7 on:** 26 Feb 2006, 08:54 pm »

I used the Star quad for short custon length (30") interconnects. The high capacitance is the tradeoff for the excellent EMI/RFI rejection of this cable. I had read that this would not affect things if the cables were kept under 2 meters. As mine were to be much shorter and I was interested in the rejection qualities this made sense to me. Now I read about 12pF cables and start second guessing. I built these interconnects back in 1997 and have been happy with them until now. It's just midlife crisis and audio nervosa showing their ugly heads. Either way I have vowed to not change anything until I have had an extended listening session with my new T8...when it arrives.