Cables and wires

[CJ]

does capacitance matter that much?  can the coax be thought of as a wave guide, ie:  inductance and capacitance distributed along its length as to not cause as much loss  as your C meter reads for a 10 ft section?

like guitar cords or instance, the capacitance figures are all over the place, all the way up to 500 pf,  how bad will this swamp out pickup hi end?

 

[SIXTYNINER]

Sixtyniner, if I read you correctly, your making a general request for info from folks who know a lot about wire and its proper applications? 

I think CJ summarized it:
Mogami's website has a pdf that is pretty comprehensive:
http://www.mogamicable.com/pdf/Mogami_Tech_cat2014.pdf

I ordered some W2944 http://www.mogamicable.com/category/bulk/console/  for rack stuff and other audio projects, and have not looked back since. Yes it's a bit pricey, but damn if it isn't flexible and a pleasure to work with.

Thanks for post Boji
i posted mainly for type and size cables normally  used for  the inside box connections  ,
audio signal ,  and power supply in various common voltages type ,

secondary , as well , but not less important
for external connections between different type of devices and instruments,

about mogami type links  ,
do you use the same type of mogami cable for inside the box audio signal and power supply connections ?

does capacitance matter that much?  can the coax be thought of as a wave guide, ie:  inductance and capacitance distributed along its length as to not cause as much loss  as your C meter reads for a 10 ft section?

like guitar cords or instance, the capacitance figures are all over the place, all the way up to 500 pf,  how bad will this swamp out pickup hi end?

Electric Guitars are very sensibles to cables (...all the rest apart) ,
also because the pickups type and configurations change the sound  of the same guitar ,

Some year ago i was on a Musical Instruments store with some friends that play guitar ,
to attend a showcase dedicated to guitar amps , fxs and cables
it started with most used guitar models (Strato…. , Tele… , Les P…. , SG …. , Psr … , etc..)
played in combinations  with most used gtr amps (Fend…., Marsh… , Vox… , Mesa …., etc..)
after this first part of the showcase ,

5 minutes break for coffees , ears , and related (fortunately    )

the second part was dedicated to pedal boxes fxs , and the endless combinations
fortunately the gtr demonstrator guys limited themselves to show the most standard used combinations
and few  other specific (otherwise i suppose we still be there…..  )

and the third part , after another break ,
was dedicated for live test of various type of cables (and related prices) 
connecting different gtr models to different gtr amps and sound type like
clean, clean with long reverb , chorused , distorted , ….

also some different type of cable for guitar pedal box effects bridges was live tested

for what i personally could notice ,
the most evident sound differences between the various type of cables
was localized in the mid and hi frequencies range,

we can say that the cable can be an equalizer  ?

and only as well (for beginners)
as for the gtrs , the same thing is for microphones cables ,
overall tube and condenser studio microphones ,

a bit less but not less important
also for "Line" type connections,

reason why i posted that a dedicated thread also in the Meta section
that include informations , mainly as diy help ,
about good type and size of cables to use for most type of inside boxes connections
like:
-audio signal ,  between pcb , audio transformers , in-out connectors etc..
-power supply (3,5V , 5V , 12V , 15V , 17,5V , 24V)
-48V phantom power

would be a much valued help ,

and even more with included a section  with some info
about some good type and size of cables to use  for connect  :
studio and live microphones  to preamps ,
gtrs to amps (as above mentioned)
keyboards to mixer or AD converter input
multicore cables for :
AD-DA converters and analog mixing console to analog outboards as insert , summ unit , control room box , etc..
patch bays ,
Analog tape machine inputs and outputs ,

 

[Gold]

about mogami type links  ,
do you use the same type of mogami cable for inside the box audio signal and power supply connections ?

Mogami makes “console cable” which is shielded twisted pair that is a very small diameter and very flexible. It’s great for inside boxes. It now comes in the resistor colors.

I had a bunch of mogami 2pr I pulled from an old installation that I wasn’t using. I stripped off the outer jacket and am using it inside boxes. It’s larger diameter but as long as the box isn’t packed with wiring it’s fine.

For power supply connections in a box I use wire not jacketed cable.

 

[CJ]

this is interesting>

https://forums.prsguitars.com/threads/how-a-sweet-switch-really-works.839/

"Now, anyone without a background in electronics or physics is probably wondering why the designer of this circuit chose a 135 nanosecond delay line as the filter for the sweet switch circuit. Well, the answer is quite simple after one performs a few calculations. An electromagnetic wave travels at the speed of light through a vacuum, which is 300,000,000 meters per second; therefore, an electromagnetic wave can travel 300,000,000 / 1,000,000,000 x 135 = 40.5 meters in 135 nanoseconds through a vacuum. However, an electrical wave does not travel at the speed of light through a coaxial cable because all coaxial cables have what is known as a velocity factor. A velocity factor is a fraction of the speed of light, which means that a coaxial cable has different electrical and physical lengths. The velocity factor of a guitar cable is roughly around 78%, which means that an electrical signal can travel 300,000,000 / 1,000,000,000 x 135 x 0.78 = 31.59 meters in 135 nanoseconds. That number is important because it roughly translates to 31.59 x 39.37 / 12 ~= 104 feet of guitar cable. In effect, the delay line simulates the frequency attenuation and the phase shift imposed on a guitar signal by a 100-foot-long guitar cable (cables of this length were popular before the guitar world went wireless).

If one researches the history of the sweet switch circuit, one discovers that it was created for Carlos Santana. Carlos was known for using long guitar cables before he switched to using a wireless system. The sweet switch was PRS Guitars’ answer to the increase in brightness that a guitarist experienced when the capacitive loading effects of a long cable were removed from the signal path. There is little doubt in my mind that Eric Pritchard was behind this circuit."

a good read here>

https://www.st-andrews.ac.uk/~www_pa/Scots_Guide/audio/part7/page1.html

 

[PRR]

> can the coax be thought of as a wave guide, ie:  inductance and capacitance distributed along its length as to not cause as much loss  as your C meter reads for a 10 ft section?

Keep going on that thought and you will re-derive the Telegrapher's Equation, about 130 years too late for fame.

But for a start: put numbers on that thing! How much inductance does an audio cable have?? While not quite Guitar Cable, 8451 will be close-enough to know if we need more exact numbers from a specific cable.

Belden 8451 cable
Conductor DCR  14.1 Ohm/1000ft
Capacitance  Conductor to Conductor 34 pF/ft
Capacitance  Conductor to Other Conductor to Shield 67 pF/ft
Inductance  0.17 µH/ft

One foot at 0.17 µH/ft at 20KHz is 0.17uH*20KHz*6.28 which is 0.021 Ohms. Ten feet (3m) is 0.2 Ohms. 100 feet (30m) is 2 Ohms.

Compare with the C. 67pFd at 20KHz is about 120K. Ten feet makes 12K, 100' makes 1.2K.

An ignorant approach would lump all this together. For 100 feet we have 2 Ohms inductive series reactance and 1,200 Ohms shunt capacitive reactance.

Clearly for most likely line impedances, the 2 Ohms of L "does not matter", the 1,200 Ohms of C might.

However driving a 4 Ohm speaker, 2r inductance hurts the top significantly.

This points to the idea of "Characteristic Impedance". The line has both series and shunt losses. The split-difference between them is the best impedance to work the line. You can't measure this directly, it is the value which gives best results. The characteristic impedance of about any practical line will be 50 to 200 Ohms. For short good lines you can go way off this without much added loss. Go high, and you are looking into significant Capacitance. Go low, and you fight both Inductance and the cost of low Copper resistance.

The values of L and C are set by conductor dimensions and adjacent materials. We could raise L by adding iron; this usually "bad" so is rarely done. We can raise C by using solid materials to support the line conductors, or lower C with only vacuum (or gas) dielectric. Because the conductors do need support we are usually sticking solid stuff in there. Minimum C might be the old open-line telephone wires. Mostly we value a tough cable so PE plastic is common. For lower C we can use foam plastic, or spaced ceramic disks.

In fact we should solve for an infinite number of infinitely small L and C. But if you try this, you generally find that it is "no real difference" as long as the line is "short" compared to the wavelength. Audio in a wire travels a little slower than the speed of light. It takes 8250 feet (2500m) to make even a quarter-wave at 20KHz. In "studio audio" we never go to such lengths. Lump-sum approximations are close-enough.

OH!! A full derivation includes plain Resistance, both series and shunt. 1,000' of 8451 is R=14r and L=20r @ 20KHz. This makes a small difference, negligible on line impedance though significant on speakers. The shunt resistance of modern plastics is super-high for DC and well into the audio range. Typical may be G @ 10KHz 0.16µS/1000 ft which is 6 MegaOhms.

 

[PRR]

And for guitar specifically: there's like 5 Henries in a guitar pup. Another 29,411,765 feet (5000+ miles!!) of that 0.17µH/ft Belden cable would matter some; less, hardly at all.

 

[CJ]

^^^^^^^ Nice! Thanks!

Wow Oliver Heaviside was a heavy dude, all kinds of stuff going on, skip waves, Cherenkov radiation,

Sowter ended up using mu metal around the under the sea cable to improve transmission,

 

[CJ]

so what would, say, a 15 ft guitar cord do to these resonant pickup peaks?

how much current can a pickup put out?

Thanks!

 

[abbey road d enfer]

I don't know where this graph comes from, but it's the type of data that's almost useless and confusing, for two reasons:
A) the linear scale on both axis doesn't reflect the perception of these characters; in fact theres only about 8 dB between the most resonant and the less resonant, and the range of resonant frequencies is just about half an octave.
B) the parasitic capacitance of pick-ups is about 100-200pF; any piece of cable is going to change that significantly, and the volume and tone pots' load will considerably damp the resonance.
What I mean is that, although  this info is exact, it is however incomplete and does not relate much to what happens in reality; most people interested in that (musicians, luthiers) are not savvy enough to understand better.

 

[Speedskater]

We should note that the short form Radio Frequency Characteristic Impedance formula doesn't kick in until somewhere between 100 kHz and 1 MHz.  At lower frequencies you need to use the long form formula and the impedance will be different at each frequency.

 

[PRR]

That graph is for pickup alone in a test jig.

On most stages the pup has a volume pot and 3-30 feet of cable after it. For a wide range of likely cases, the impedance at the amp end of the cable is nearer 50K than the 5K-800K on that graph. 50K source driving 300pFd is about 11KHz roll-off. Guitarists are not very troubled by not-long cables, the cap in the guitar's Tone knob may have significant effect on the peak.

 

[CJ]

here is the article with the graphs>

https://courses.physics.illinois.edu/phys406/sp2017/Lab_Handouts/Electric_Guitar_Pickup_Measurements.pdf

so if a guitar pickup had a Z of 75 ohms, you could drive a mile of coax. But since the Z of the pickup is higher than 75 ohms, there will be loss in the audio zone?

 

[CJ]

pic from >

https://en.wikipedia.org/wiki/Coaxial_cable

wow, Heaviside invented coax, why do some people get all this stuff? look at Issac Newton, got all the stuff,

what about a 8K to 75 Ohm transformer inside the guitar? never mind, to much voltage drop,  ???

 

[PRR]

> what about a 8K to 75 Ohm transformer inside the guitar?

Why not skip the snarly skinny wire and wind directly to 75 Ohms? Would not take 15+ minutes to wind a pup as it does for usual windings.

Les Paul wound to ~~200r for his studio model (looked like a dynamic mike to the console). Probably wound it in a quarter the time of a hi-Z job.

The thing is: guitarists do not want 20KHz through a mile of cable, they want high S/N at the grid of a nearby 12AX7 withOUT a costly transformer.

 

[CJ]

Had the chance to play an LP recording, worked great for Les but was a little lacking in the rock and roll dept. ie clean as a whistle.  very quiet, different frequency response,