How to determine capacitance with the info I have

Jelco does not have the capacitance of it's headshell and arm wiring for the 750.

They can provide the capacitance of thier tonearm cable, at 15pF/ft conductor and 37pF/ft for the shield. it is 1.2 meter.

How does this figure into a capacitance for the cable ? Do you add the conductor pF and shield pF together, times the total number of feet right and left cable ?

Also, does anybody have a guess of the tonearm capacitance of the 750D tonearm wire and head shell wiring ?
Wayne in Northern Ohio, USA
If you have access to a capacitance meter it is simple enough to measure.
A conductor and a shield don't have significant capacitance by themselves. The capacitance exists BETWEEN conductors or BETWEEN a conductor and a shield.

I don't know exactly what the cable configuration is, but I'll hazard a guess that it provides two conductors for each channel, within a shield, and the cable terminates in rca connectors at the destination end, and both the shield and one of the two conductors for each channel are grounded to the rca ground sleeve. And that the 15pf/ft represents the capacitance between conductors, and the 37pf/ft represents the capacitance from the ungrounded conductor to the shield.

If that is correct, then the capacitance seen by the cartridge would correspond to the sum of the two capacitance figures you cited.

I would say that a very rough guess as to headshell and tonearm wiring capacitance, given that the total distance involved is probably a little more than a foot, would be 40pf.

So the total capacitance, based on those assumptions, is 40 + ((15 + 37) x (the number of feet in 1.2 meters)), which works out to 245 pf for each channel.
... times the total number of feet right and left cable ?
The capacitance on one channel has essentially no effect on the other channel, so the two cable lengths are not added together.

-- Al
Al, thanks for the info, that is what I was looking for. It also seems to be an extremely high capaitance cable for use with a MM cartridge ?
Hi, you don't mention type of cartridge you will be using. If it is MC you don't have to worry about capacitance. If you will be playing with a MM/MI it may be worthy to have a capable meter for the tool box.

Here is a cheap example which I don't have any experience with but looks like it would do the job.

This is the one I use which also allows measurements of resistance and inductance (LCR meter). Nice meter that will last for years to come.

As noted in post above you measure between ground and hot with the cables disconnected from everything but the capacitance meter.

Brad yes it will be a MM, which is what started this quest for the total, which seems to high for MM. I will check the meters out.

Al, thanks for the info, that is what I was looking for. It also seems to be an extremely high capacitance cable for use with a MM cartridge ?
Hi Wayne,

Yes that does seem somewhat high, and the phono stage or preamp input will add a little bit more, whether it does not have adjustable input capacitance, or does have it and the adjustment is set to its minimum position.

But in your post in the current thread that was started by T_bone you indicated that your Ortofon wants to see 400pf, so you should be fine with that cartridge (and many others). And capacitance generally isn't all that critical anyway. The effects of a mismatch would be in the upper treble, as discussed in that thread.

It's also certainly possible that I'm guessing wrong as to how the cable is designed. But given the two numbers that were specified, 37pf/ft and 15pf/ft, I can't readily envision a configuration that would result in a capacitance substantially lower than what I calculated.

Obtaining a meter, though, as suggested by the others, would certainly be the best way of obtaining an accurate answer.

Best regards,
-- Al
Thanks Al, That Ortofon and many in the same series are looking for 400pf. The cartridge I am looking at now is rated at 100pf, big difference. That is what started this hunt for information. We are a distributor and sell meters. My digital does not have capacitance. I should be able to grab one with capacitance to check.
I also am finding after reading and emailing several cable people, that the lower conductor to conductor(thier words), is what most of the cables are spec'd at. So in the Jelco it would be 15pf/ft. Some of the others web sites and emails spec thiers at 15 to 20pf/ft. Nobody uses the sheild as part of thier spec, right or wrong it seems.