Cable Capacitance

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zentropa
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Cable Capacitance

Post by zentropa » Tue Feb 20, 2024 8:28 pm

Last week I found myself trying to disprove a friend of mine that believes that more expensive guitar cables are always better, making this the 4th conversation with local people I know in the past couple of months. I'm pretty sure these are the types of people that would buy $100 monster HDMI cables because the employee at the store told them they were better.

In trying to get actual numerical data I ended up doing a bit of a deep dive into cable capacitance and learned more than I probably needed to. I have often been able to hear noticeable differences in guitar cables, but mostly in cases where it was a particularly good or particularly bad cable. I'm sure most of the engineer-types here already know this, but for those who don't, the higher the total capacitance, the more treble and upper mids will be lost to cable length when using passive pickups.

Basically:
-A lower capacitance cable will sound brighter than a higher capacitance cable when the cables are of equal length.
-A coiled cable will have higher capacitance than a straight cable that is laying flat.
-Doubling the length of the cable will approximately double the total capacitance.
-Plugs add capacitance.

I did find that short length patch cables, ~6" and under have very little difference in capacitance unless they are particularly terrible quality.

The multimeter I used to measure the cables wasn't accurate beyond 10pf, so very short cable lengths probably weren't very accurate.

All measurements were performed with the cables laying as flat and straight as possible given my space restrictions.

I don't have any commercial Mogami cables, but I have a number of cables I made using Mogami 2524 cable, the cable they use in Mogami Gold (which is supposed to be rated at 39.6pf per foot). Each had different types of plugs.
15' = ~620pf = ~41.3 pf/ft = ~135.6 pf/m
7.83' = ~350pf = ~44.7 pf/ft = ~146.6 pf/m
1.33' = ~80pf = ~60 pf/ft = ~196.8 pf/m

I also tested a bunch of Monoprice Cloth Series cables, which I got new for: 20' for $10, 15' for $9, 10' for $6, 6' for $3
6' = ~270pf = ~45 pf/ft = ~147.6 pf/m
10' = ~420pf = ~42 pf/ft = ~137.8 pf/m
15' = ~750pf = ~50 pf/ft = ~164 pf/m (seems this batch of cabling for the 15' was quite a bit worse)
20' = ~850pf = ~42.5 pf/ft = 139.4 pf/m

Back in the 1990s I bought some SpectraFlex cables, which cost about 4-6x as much as most cables back then, but I remember feeling like they livened up my sound a ton. I still have two FatsoFlex versions from back then.
14' = ~390pf = ~27.9 pf/ft = ~91.4 pf/m

Audioblast HQ-1 (which is supposed to be rated at 38.2pf/ft).
4' = ~240pf = ~60 pf/ft = ~196.8 pf/m
1.5' = ~100pf = ~66.7 pf/ft = ~218.7 pf/m

For the hell of it I tested a 20-year old Fender cable that was ~$10 new:
10' = ~400pf = ~40 pf/ft = ~131.2 pf/m

As for short cables total capacitance (measured length plug to plug), values are +/- 5.
Boss BCB-6 stock 6.5 inch: ~40pf
Boss BCB-3 stock 6 inch: ~40pf
Boss BCB-60 stock 7 inch: ~50pf
DOD PRC-6 stock 4.5 inch: ~60pf
Gorge L's .155 3.5 inch: ~20-30pf (it kept flipping between the two and never stabilized)
Mogami 2319 6 inch: ~40pf
Canare GS-6 4.5 inch: ~30pf
Audioblast HQ-1 4.5 inch: ~30pf

I sold my 20' George L's .225 cable to a friend before I could test it, but I was curious since those are supposed to be ultra low capacitance.

This chart might be helpful if you are curious about more:
https://www.shootoutguitarcables.com/gu ... chart.html

I will add that a major motivating factor for doing this was reading someone claiming that Monoprice guitar cables were over 90 pf/ft (~295 pf/m), but that is very false, as I believe what they were testing wasn't a guitar cable.
However, that same person tested a coiled up Roland Black series 10' and got a measurement of 318pf = 31.8 pf/ft = 103.35 pf/m, which would probably have been slightly lower if they had measured it laying flat.

I did find it interesting that the SpectraFlex cables, which I always thought sounded way better than every other cable brand I tried going back to my teen years, are in fact much lower capacitance than most cables.

I'm returning the multimeter to Amazon since it wasn't accurate enough for me, so I can't do any more testing, but this was a mildly amusing way to kill some time on a Saturday.

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laurie
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Re: Cable Capacitance

Post by laurie » Tue Feb 20, 2024 9:33 pm

A great overview, thanks!

Cables and connectors also have other properties to be aware of. Capacitance (in "Farads") is part of the bigger picture of LCR:
  • L=inductance, in "Henrys"
  • C=capacitance in "Farads"
  • R=resistance in "Ohms"
Plus the percentage shield coverage is an important indicator of how resistant the cable is to inductive and capacitive coupling to the outside world, and to itself if coiled.

For very high frequencies (in the MHz) a co-axial cable (e.g. a guitar lead) acts as a transmission line, and a whole other set of equations (Maxwell's equations) start to apply.

So... buy good quality cable with low LCR and very good shielding, then make sure to not inject any RF ;)

See my notes on practical experience with different cable here:
viewtopic.php?f=6&t=568
Last edited by laurie on Thu Feb 22, 2024 12:13 am, edited 1 time in total.

zentropa
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Re: Cable Capacitance

Post by zentropa » Tue Feb 20, 2024 10:09 pm

laurie wrote:
Tue Feb 20, 2024 9:33 pm
A great overview, thanks!

Cables and connectors also have other properties to aware of. Capacitance (in "Farads") is part of the bigger picture of LCR:
  • L=inductance, in "Henrys"
  • C=capacitance in "Farads"
  • R=resistance in "Ohms"
I knew more went into it than just capacitance, but capacitance is the aspect most people on forums and such tend to obsess over.

I know back when I was gigging my #1 consideration was "will this cable break or not." My current playing space has gym mats on a concrete floor, forcing me to use braided cables as anything with a pvc/plastic outer generates way too much static electricity from rubbing on the mats. Seems like a lot of the budget cables now are being made with better cabling than they were back in the 90s, but I'm guessing that has a lot more to do with the shielding than the capacitance (e.g. the old ProCo Excellines that were super common back then are only 55% shielding).

Lately I have been making more local guitar friends, and I'm realizing that trying to convince someone they don't need to spend $90 on an 18' guitar cable or $30-40 per patch cable that goes between each of their pedals can be rather difficult, particularly when they believe that the factory built ones are somehow infinitely better than making them yourself out of identical plugs/cable.

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laurie
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Re: Cable Capacitance

Post by laurie » Tue Feb 20, 2024 11:22 pm

I make my patch cables from a pair of Mode 24-610-0 connectors (about USD$2.50 for the pair):
https://www.mode-elec.com/Products/audi ... 14-18).pdf

And a short length of Japanese high quality microphone cable:
https://www.be-electronics.com/product_p/l2e5.htm

They work superbly, have almost zero capacitance, are rock-solid, and cost about USD$3 to make.

The biggest benefit - the pancake form-factor means they take up the least amount of pedalboard width of any connecter I've found so far.
.
20240220_162650a.jpg
20240220_162650a.jpg (108.88 KiB) Viewed 255 times
.
When the pancake plugs don't fit in the pedal (e.g. DD-7 input side the jacks are too close together), I use more expensive Amphenol right-angle connectors (about $5 each, for the rare times they are needed, and usually only on one end of the patch cable).

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bigtone23
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Re: Cable Capacitance

Post by bigtone23 » Mon Mar 04, 2024 8:11 pm

I remember when the discussions and arguments started popping up a few decades ago. Pretty sure what put it on the map for me was George L's and Eric Johnson's use of them. He used single coils and fairly long runs of cable with his touring rig, so low cap was pretty necessary. However, he also talked about not using all steel or all brass 1/4" plugs, but a mix. All steel was too bright, all brass too middy. Golden ears!

Either way, this didn't register to me. I couldn't hear the difference between a 18" coiled Rapco vs a 15' Spectraflex vs a 21' Monster Studio Pro 1000. Oh right, I was using guitars and basses with active, low impedance output. The great equalizer. In the 90s, I ran a 12' Monster SP1000 from my EMG Strat to my massive pedalboard, and then two 21' Monster SP1000 stereo out to the amps. In the pedalboard was about 6' of SP1000 interconnects and many, many older pedals that had various buffers and true bypass circuits. If I bypassed the board and plugged straight into the amp, there was about as much difference in tone and volume as when you bypass 5 BOSS pedals with a PSM5 in a BCB6. If I used a passive guitar, it was a noticeable load.

Using passive instruments (especially single coils), I can now hear the difference when the cable run goes north of 25-30'. I have liked Livewire Elites, they sound pretty chimey. Found this chart and they aren't as low cap as I thought. This is where that LCR relationship may be at play...
http://www.ovnilab.com/articles/cablechoice.shtml

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