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Old 14th June 2012, 05:32 PM   #1
Einric is offline Einric  United States
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Default Low Capacitance Interconnect

Hey everybody, here is the schematic equivalent of coaxial cable.
I'm trying to see if there really is a difference between interconnects with high capacitance and low capacitance.

Two capacitors in series will have total capacitance equal to less than the value of the smaller capacitor.
What would happen if a VERY low value capacitor was placed in series with the capacitance caused by the interconnect cable?
I'd be talking about something less than 1 pf very high quality capacitor.
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Last edited by Einric; 14th June 2012 at 05:37 PM.
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Old 14th June 2012, 05:34 PM   #2
Einric is offline Einric  United States
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Stupid question....LOL!
The capacitance is a virtual one.
If I placed another capacitor in there it would be in parallel with the virtual capacitance.
Now I just need a theoretical capacitor to physically place in series with the virtual capacitance HAHAHA!!!
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Old 14th June 2012, 05:50 PM   #3
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At audio frequencies the capacitance is almost immaterial. 50R RG58 is as good IMO as most Snake Oil cables. It is the connectors at the end that make an appreciable difference.
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Old 14th June 2012, 06:06 PM   #4
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The nominal impedance of a coax cable is the sqrt of his inductance per meter, divided the capacitance per meter. If you choose a high Zo coax, it naturally will have lower capacitance than lower impedance ones.
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Old 18th June 2012, 04:47 PM   #5
kevinkr is offline kevinkr  United States
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Quote:
Originally Posted by KatieandDad View Post
At audio frequencies the capacitance is almost immaterial. 50R RG58 is as good IMO as most Snake Oil cables. It is the connectors at the end that make an appreciable difference.
Actually there is one case where this is absolutely not true and that is between a MM phono cartridge or the secondary of an MC step up transformer and the input of a phono pre-amplifier. I've still not found what I consider the ideal cable for this application.
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Old 18th June 2012, 05:36 PM   #6
DF96 is offline DF96  England
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Cable capacitance is quite real, not "virtual". You can calculate it from theory, and measure it with a meter. How much difference it makes in a particular case depends mainly on the source impedance, which is why it can be a problem with pickup cartridges. Fortunately, some cartridges are designed to cope with capacitance.

If you put a small cap in series with the cable then you will get low capacitance and low signal too. Generally not what you want. The small cap and cable form a potential divider.
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Old 18th June 2012, 09:02 PM   #7
kevinkr is offline kevinkr  United States
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<snip>

If you put a small cap in series with the cable then you will get low capacitance and low signal too. Generally not what you want. The small cap and cable form a potential divider.


WRT to phono stages tube based designs usually have appreciable input capacitance due to miller capacitance if high mu triodes are used, and much less if a pentode or cascode connection are used. There may or may not be much input capacitance margin left by the time that is taken into account.
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Old 18th June 2012, 11:45 PM   #8
sandyK is offline sandyK  Australia
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Einric
If your requirements are for a cable longer than the typical 1Metre length, have a look at the Blue Jeans LC1. They are very well made, and far better value for money than most .
Alex

Stereo Cables at Blue Jeans Cable
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Old 19th June 2012, 11:28 AM   #9
DF96 is offline DF96  England
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Nice to see someone selling cables based on their electrical properties rather than 'creative prose'!
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