How Do I Measure Capacitance?

[watchnerd]

I want to measure the capacitance of my tonearm cable so I can determine proper loading for my MI cartridge.

I bought a Fluke 107.

What the heck do I do next?

What do I plug into what?

 

[dc655321]

RTFM?

Black cable into "COM", red cable into "600V/CAT III" (right side). Switch turned to second-last from right symbol (clockwise).

Though I'm not sure how well that DMM is going to perform what you want it to do...

 

[DonH56]

https://dam-assets.fluke.com/s3fs-p...930.643912056.1535294189-768787281.1535294189

Table 1 on page 6 of the user manual provides the symbol for capacitance. Page 8 shows the input terminals to use for capacitance. Page 19 describes how to measure capacitance.

I would lay the test leads flat on a table or whatever and spaced apart with clips near the end of the cable and take a reading. Make sure the cartridge is disconnected. Then carefully clip the leads to the cable (plus to center pin, minus to shield) without moving the leads and measure again. The difference is the cable capacitance.

You cannot hold them with your fingers as that would add too much capacitance and be highly variable.

The issue with using an inexpensive multimeter for this is that the capacitance range and resolution are too high to be very accurate for measuring cables. On the lowest range, that meter has 50 nF max reading and 0.01 nF (10 pF) resolution, plus the error band. Typically cables run around 20~30 pF/foot (RG-6, commonly used for TV and audio interconnects, is around 21 pF/ft) so you are measuring in the very lowest part of the meter's range. These meters are mainly to check large power supply decoupling capacitors and larger interstage coupling capacitors.

Most tonearms provide the capacitance of the cable to the connectors. You can look up the capacitance of the interconnect if you know or can figure out the type of cable. But frankly I would estimate the length in feet from cartridge to preamp and multiply by 25 pF/ft for a rough idea (25 because the tonearm wiring itself tends to have higher capacitance than the interconnecting cable and phono interconnects are often smaller and more flexible with higher capacitance).

At one time I used some low-capacitance cable (RG-79, ~10 pF/ft) to connect my TT to my preamp but that tends to be big (~0.5" diameter) and harder to handle.

I use an RLC meter or VNA but those are expensive options I borrow from work. At home, long ago when I had a TT set up, I would play a test record and measure the frequency response after the preamp, adjusting the capacitance for a flat response. That measures after the RIAA compensation and all that jazz but was easier to do with tools at hand.

 

[amirm]

The long leads on that meter are going to have a lot of error in small capacitances.

You need an LCR meter for most accurate measurements. This is one that I have which despite the low price, does well: https://smile.amazon.com/gp/product/B00EBPOEAC/ref=oh_aui_search_detailpage?ie=UTF8&psc=1

As you see, you can either put the leads directly into those long sockets or sue the short alligator clips.

 

[DonH56]

Make sure you ground yourself before taking measurements. Static can kill LCR meters (among other things).

Hey Amir, what is the range and resolution of that meter?

 

[amirm]

Here is the spec page Don: https://www.deree.com.tw/de-5000-lcr-meter.html

My only use has been to measure small lengths of wire.

 

[watchnerd]

https://dam-assets.fluke.com/s3fs-p...930.643912056.1535294189-768787281.1535294189

Table 1 on page 6 of the user manual provides the symbol for capacitance. Page 8 shows the input terminals to use for capacitance. Page 19 describes how to measure capacitance.

I would lay the test leads flat on a table or whatever and spaced apart with clips near the end of the cable and take a reading. Make sure the cartridge is disconnected. Then carefully clip the leads to the cable (plus to center pin, minus to shield) without moving the leads and measure again. The difference is the cable capacitance.

You cannot hold them with your fingers as that would add too much capacitance and be highly variable.

The issue with using an inexpensive multimeter for this is that the capacitance range and resolution are too high to be very accurate for measuring cables. On the lowest range, that meter has 50 nF max reading and 0.01 nF (10 pF) resolution, plus the error band. Typically cables run around 20~30 pF/foot (RG-6, commonly used for TV and audio interconnects, is around 21 pF/ft) so you are measuring in the very lowest part of the meter's range. These meters are mainly to check large power supply decoupling capacitors and larger interstage coupling capacitors.

Most tonearms provide the capacitance of the cable to the connectors. You can look up the capacitance of the interconnect if you know or can figure out the type of cable. But frankly I would estimate the length in feet from cartridge to preamp and multiply by 25 pF/ft for a rough idea (25 because the tonearm wiring itself tends to have higher capacitance than the interconnecting cable and phono interconnects are often smaller and more flexible with higher capacitance).

At one time I used some low-capacitance cable (RG-79, ~10 pF/ft) to connect my TT to my preamp but that tends to be big (~0.5" diameter) and harder to handle.

I use an RLC meter or VNA but those are expensive options I borrow from work. At home, long ago when I had a TT set up, I would play a test record and measure the frequency response after the preamp, adjusting the capacitance for a flat response. That measures after the RIAA compensation and all that jazz but was easier to do with tools at hand.

The long leads on that meter are going to have a lot of error in small capacitances.
.

Before I unmounted my tonearm and detached the tonearm cable from the DIN socket, I tried to do some tests on some other RCA cables I had lying around, one of which also has a ground wire.

The results were inconsistent and not believable, ranging from 2.1 micro Farad to .57 micro Farad, which are impossibly high in pico Farad for the length of cable I'm measuring (<1 meter).

I'm not sure if, with better methodology, I could get it more accurate or if this tool just isn't the right one for the job and I should get @amirm 's more suitable LCR meter....

 

[amirm]

You are never going to get super accurate results especially with short length of wire. Using 1 meter length, i was able to measure the capacitance reasonably well. See my tests here: https://audiosciencereview.com/forum/index.php?threads/when-12-gauge-wire-is-not-12-gauge.3/

 

[Wombat]

The capacitance of well designed tone-arms is not particularly significant. The interconnect and preamp input capacitances are much more influential.

 

[watchnerd]

The capacitance of well designed tone-arms is not particularly significant. The interconnect and preamp input capacitances are much more influential.

Ah, a semantics problem:

I'm not trying to measure the wire in the tonearm itself. I'm trying to measure the cable that connects from the tonearm to my amp.

In this case, it's DIN (5 pin or 4 pin, I forget) on one end and 2 x RCA + ground wire on the other.

I got it used with some turntable parts I purchased a few years ago. The manufacturer is Straight Wire.

 

[Wombat]

This type of adapter could help: https://www.ebay.com/itm/From-OZ-Qu...116130?hash=item21360371a2:g:f6YAAOSw4PxaR17f It is available from all the usual online sellers.

This would be better: https://www.ebay.com/itm/Pomona-Bla...=1024597190&hash=item4b0cac6e20#shpCntId#shId The banana plug spacing should be 3/4 inch centre-to-centre. Check with seller.