Extreme cable capacitance measured. Why?

Started by BDuguay, July 06, 2006, 10:00:39 AM

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BDuguay

I have a very short (4'') cable for use between 2 pedals that I suspected was causing severe tone loss. The cable is a 'standard' garden variety cable that 'functioned' properly in that there was continuity between the hots, and same for the sheild. I measured it's capacitance last night and got a wopping .33mf!
I have some 20' cables that max out 800pf. Does anyone know what would cause such a high reading for such a short cable?
Thanks,
B.

R.G.

Either an embedded cap in the cable, or, like any capacitor, lots of conductor surface close together.
R.G.

In response to the questions in the forum - PCB Layout for Musical Effects is available from The Book Patch. Search "PCB Layout" and it ought to appear.

BDuguay

Thanks R.G.
Yeah, I just picked the brains of a co-worker and fellow musician (that's suggesting that I too am a musician and clearly that's not the case but, you know what I mean) who's more knowledgeable about electronics than I am. He suggested that if the cable gets bent to extremely, or severely twisted, the braided sheild can 'balloon' and create all sorts of grief. Namely an increase in capacitance. I'm not afraid to ask questions and risk looking stupid that's for sure. I'm learning more and I like it that way.
B.

Paul Perry (Frostwave)

Try measuring the resistance between hot and ground as well!
I bet that you will find there is a high resistance, probably caused by conductive plastic shield being shorted to the signal wire.
The multimeter meausres capacitance by seeing how much AC test signal will run thtu a cap (or similar method), you can fool it if there is a resistance there.