I'd like to measure the capacitance of a cable that is twisted pair with a shield, example: Mogami W2549
Should measure capacitance between the pair of conductors, what about the shield to conductor capacitance?
So here is what I tried. The standard coax type Technics SL1200 phono cable is about 66pF for 47" including RCA connector. I am taking the measurement between two conductors.
But if I try a twisted pair with a shield cable, such as Mogami W2549, I will use the connected shields from BOTH channels (L+R) as the ground wire. The shields will become my ground wire, connected on the pre amp end and also the turntable chassis, just like the regular ground wire gets connected.
How do I measure capacitance now? Do I add the capacitance between "positive" and "neg" conductors and ADD the capacitance between "pos" and the shield and also Neg and the shield?
thanks!
Should measure capacitance between the pair of conductors, what about the shield to conductor capacitance?
So here is what I tried. The standard coax type Technics SL1200 phono cable is about 66pF for 47" including RCA connector. I am taking the measurement between two conductors.
But if I try a twisted pair with a shield cable, such as Mogami W2549, I will use the connected shields from BOTH channels (L+R) as the ground wire. The shields will become my ground wire, connected on the pre amp end and also the turntable chassis, just like the regular ground wire gets connected.
How do I measure capacitance now? Do I add the capacitance between "positive" and "neg" conductors and ADD the capacitance between "pos" and the shield and also Neg and the shield?
thanks!
I sense that your question is not so much about how to measure it - it is what it is.
But more about how to interprete it. What is the caapcitive load to the cartridge.
The capacitance from each of the signal wires to the screen is the same (or almost so) thus is 'common mode' and that does not load the signal, which is between the two signal wires.
So for the capacitive load of the cartridge, it is the capacitance between the two signal wires.
Plus the input capacitance of the preamp of course.
Jan
But more about how to interprete it. What is the caapcitive load to the cartridge.
The capacitance from each of the signal wires to the screen is the same (or almost so) thus is 'common mode' and that does not load the signal, which is between the two signal wires.
So for the capacitive load of the cartridge, it is the capacitance between the two signal wires.
Plus the input capacitance of the preamp of course.
Jan
The capacitance to the cable is still present in a balanced configuration. To see its effect you would need to remove the shield and remeasure (or some instruments allow you to drive a node to remove it from the measurement). The effective cap through the shield would be 1/2 of each conductors cap to the shield assuming you are measuring conductor to conductor since the shield to conductor C would be in series.