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DIY studio cable capacitance/resistance
Old 13th May 2019
  #1
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rhythmcomposer's Avatar
 

DIY studio cable capacitance/resistance

I need a bunch of short (3m perhaps) audio cables (non-balanced, jacks at both ends) for my home studio and am considering soldering my own. They'll be used between various synths and a mixer, patchbay and audio interface.

There's a whole lot to choose from, pricewise, brands and specs, but what I've read is that capacitance is an important factor in choosing a cable. Impedance is also mentioned, but from my understanding this isn't as important as getting something with a low enough capacitance rating.

So what specs should I look for when choosing a cable for this kind of use?
Old 13th May 2019
  #2
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Richard Crowley's Avatar
 

The impedance of the CABLE is of zero importance down at audio frequencies. When you get up into MHz frequencies , if you are transmitting RF, or making cable for digital audio or video, then cable impedance is an important factor.

The impedance of the SOURCE is important in selection of cables. Because if you are making a cable that goes between an electric guitar (or bass) and an instrument amplifier, then you need a low capacitance cable to prevent high-frequency loss. There is a style called "Instrument Cable" which is designed specifically for this application. For example: https://www.redco.com/Bulk-Instrument-Cable/

Otherwise, for use "between various synths and a mixer, patchbay and audio interface", neither capacitance nor inductance if of any significant importance. If I were making cables like this, my criteria would be to select something flexible, and something easy to terminate. I would use something like: https://www.redco.com/Redco-TGS-01-S...ced-Cable.html I assume you can identify similar basic cable like this in Europe.

Good for you, making your own cables. I encourage everyone to learn this basic skill.
Old 16th May 2019
  #3
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rhythmcomposer's Avatar
 

Thanks for the encouragement
I've made quite a few cables in my day, but this time around I've invested in a proper cable-stripper tool, so I should get a more consistent result.

Quote:
Originally Posted by Richard Crowley View Post
The impedance of the SOURCE is important in selection of cables. Because if you are making a cable that goes between an electric guitar (or bass) and an instrument amplifier, then you need a low capacitance cable to prevent high-frequency loss.
Quote:
Otherwise, for use "between various synths and a mixer, patchbay and audio interface", neither capacitance nor inductance if of any significant importance.
So, with low-level signals (mic, guitar etc.) you need to look into impedance and capacitance specs, but for high-level (line-level) signals this is of no concern?

I totally agree on the part of finding something flexible as I've had several cables in the past which were quite the opposite and hard to handle. Not much fun, but tricky to figure out which cables are flexible or not when mail-ordering.
By "easy to terminate" I assume you mean "easy to strip, solder and attach a jack connector at each end"? Or something else?

The Redco cable you've linked to is definitely cheaper than anything I've found here (and I can't find anyone selling that brand), but several music stores here sell a cable brand named Klotz which I understand is a German quality brand.

These appear to be sold several places, starting with the lowest priced type:

Klotz P0122 (balanced single pair wiring cable).
Flexible and cost efficient: this balanced switch cable with only 3.4 mm overall diameter is perfect for rack wiring and studio cabeling in applications without mechanical stress. This version with a jacket from FRNC is flame-******ant and halogen-free.

cond. construction stranded tinned copper, 7 x 0.20 mm (AWG 24/7)
cond. cross section 0.22 mm2
insulation polyethylene (PE)
core arrangement 2 cores twisted to a pair
drain wire stranded tinned copper, 7 x 0.20 mm
shielding AL/PET foil
outer jacket FRNC
overall diameter 3.4 mm
mechanics
min. bending radius 20 mm
working temperature -30°C / +70°C
electric
conductor resistance < 85 Ω/km
capacitance
cond./cond. 85 pF/m
cond./shield 160 pF/m
insulation resistance > 10 GΩ x km

Klotz MY206 (professional microphone cable).
A special rubber-like PVC material ensures flexibility at extreme temperatures (out-door recordings), additional cotton padding keeps the capacitance constant and avoids handling noise. Finally a particularly dense spiral shield provides maximum shielding even under large mechanical loads.

cond. construction stranded bare copper, 28 x 0.10 mm
cond. cross section 0.22 mm2
insulation polyethylene (PE)
core arrangement 2 cores + twisted cotton tracers
shielding bare copper spiral shield
outer jacket PVC, matt
overall diameter 6.15 mm
mechanics
min. bending radius 30 mm
working temperature -20°C / +70°C
electric
conductor resistance < 85 Ω/km
capacitance
cond./cond. 60 pF/m
cond./shield 110 pF/m
insulation resistance > 0.1 GΩ x km


Klotz AC106SW (unbalanced prime audio/instrument cable).
The AC106 audio cable can be used to connect guitars, keyboards and other line level devices. An extra thick outer jacket, double screening by a dense copper spiral shield with a layer of conductive plastic underneath and a thick PP foam insulation result in low capacitance, immunity from noise and disturbance and high mechanical reliability.

cond. construction stranded bare copper, 7 x 0.20 mm
cond. cross section 0.22 mm2
insulation polypropylene (PP) foam
1. shield conductive plastic layer
2. shield bare copper spiral shield
outer jacket PVC, matt
overall diameter 6.5 mm
mechanics
min. bending radius 30 mm
working temperature -20°C / +70°C
electric
conductor resistance < 85 Ω/km
capacitance
cond. / shield 95 pF/m
insulation resistance > 1 GΩ x km

Which one (if any) of the above would you suggest? Will the first (and cheapest) one suffice, or will I benefit from buying the last (and most expensive) one?
I don't think any of my synths/drum machines have balanced outputs, so I don't see any point in making anything other than unbalanced cables.
I only see the need for a small handful balanced cables (powered speakers connected the mixer output, possibly through a passive volume control box).
Old 16th May 2019
  #4
Gear Addict
 

For all mic- and line-level cables, I've been using Belden 8412 for a long time. There are plenty of good offerings from other manufacturers, and when I run out of Belden, I'll probably try Redco. Of the products you mentioned, either the MY206 or the AC106SW should be fine (depending on whether you need to make a balanced or an unbalanced connection); I wouldn't personally use the P0122, since it's not designed to handle much mechanical stress. It would be ok for semi-permanent connections, like internal wiring in a patchbay, but I wouldn't use it for patch cables.
Old 16th May 2019
  #5
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Richard Crowley's Avatar
 

Quote:
Originally Posted by rhythmcomposer View Post
So, with low-level signals (mic, guitar etc.) you need to look into impedance and capacitance specs, but for high-level (line-level) signals this is of no concern?
Sorry, I should have been more clear. It is not the signal LEVEL (low vs line-level, etc.) that is the factor. It is the IMPEDANCE of the source that is the factor. If the source is high-impedance, then parallel capacitance in the cable will create an inadvertent (but natural) low-pass or high-cut filter. That will "dull" the sound of the source (typically an electric guitar with passive, high-impedance pickup coils). That is why there is special "instrument cable" which is specifically designed for low parallel capacitance. But for your application, it doesn't sound like you have any sources that are high-impedance.

Quote:
I totally agree on the part of finding something flexible as I've had several cables in the past which were quite the opposite and hard to handle. Not much fun, but tricky to figure out which cables are flexible or not when mail-ordering.
That is true, but there are SOME clues. For example "install grade" cable is typically rather stiff, somewhat by design. It is excellent for pulling through walls or conduits, or for fixed wiring inside an equipment rack or behind a patch-bay, etc. But it is a terrible choice for a patch cable or regular interconnect cable (or a portable mic cable). And more generally, anything with a foil shield will not be nearly as flexible as something with a braided shield. And cable with a spiral (or "served") shield will be even more flexible than a cable with a braided shield.

For reasonably long mic cables (I have scores of mic cables that are 50ft long), I really like Canare L-2E5 because it is thin, lightweight and quite flexible. Thin and light are important when packing gear in checked luggage on international flights. And flexible is important for laying flat on the floor even in cases where you aren't set up for long enough to tape everything down to the floor.

Quote:
By "easy to terminate" I assume you mean "easy to strip, solder and attach a jack connector at each end"?
Exactly.

Quote:
The Redco cable you've linked to is definitely cheaper than anything I've found here (and I can't find anyone selling that brand), but several music stores here sell a cable brand named Klotz which I understand is a German quality brand.
Yes, that Redco branded cable is their "house-brand". I am not familiar with European brands, but I have frequently heard of people mentioning Klotz cable. If you can go to the shop and actually fondle the cable, then you have a much better sense of how flexible it is.

Quote:
These appear to be sold several places, starting with the lowest priced type:
Klotz P0122 - foil shield makes it not very flexible
Klotz MY206 - spiral shield means more flexible. But it is rather large and heavy-duty. Better for longer runs and perhaps not for short patch cables? But only you can judge what you like.
Klotz AC106SW - is unbalanced. And maybe that is all you need for your application?

Quote:
Which one (if any) of the above would you suggest? Will the first (and cheapest) one suffice, or will I benefit from buying the last (and most expensive) one?
If I had to chose from those three, I would think the second one would be more suitable. Although all the extra padding, etc. doesn't seem well suited for your applicaiton.

Quote:
I don't think any of my synths/drum machines have balanced outputs, so I don't see any point in making anything other than unbalanced cables.
I only see the need for a small handful balanced cables (powered speakers connected the mixer output, possibly through a passive volume control box).
Many people prefer using balanced cable even for unbalanced applications because it allows more options for connectors, telescoping shields, hum mitigation, etc. etc.
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