Home made cables

[DrNomis_44]

I seem to remember a set of plug wiring-conventions set-out in one of my Jaycar Electronics catalogues on one of the pages with data and some schematics, I need to get myself a new and up to date copy of the catalogue anyway, so once I do, I'll put together a set of hand-drawn diagrams showing the correct wiring up for the different conventions, something I think should prove to be useful.

[Derek82]

I seem to remember a set of plug wiring-conventions set-out in one of my Jaycar Electronics catalogues on one of the pages with data and some schematics, I need to get myself a new and up to date copy of the catalogue anyway, so once I do, I'll put together a set of hand-drawn diagrams showing the correct wiring up for the different conventions, something I think should prove to be useful.

Thanks so much for the replies guys. Interesting stuff that I knew (and probably still do) know squat about.

Sent from my Moto G (5S) Plus using Tapatalk

[Simon Barden]

No, the correct term in this instance is polarity. This is an issue that comes up time and again on the Sound on Sound forums. Phase is time related and unless it's a single frequency sound, within milliseconds, the phase relationships between different frequencies are all changed. But in terms of polarity, a swapped polarity signal will always look like the inverse of the original signal. It's slightly pedantic, but swapped/inverted/reversed polarity is the technically correct term here.

And it often does matter about the pin connections on XLRs. At some time in the past, some countries used pin 2-ve, pin 3 +ve, whilst other used Pin 2 +ve, pin 3-ve. Obviously this caused confusion, so it was standardised as Pin 1 shield, Pin 2 +ve, pin 3-ve. This can catch some people out with old equipment.

It's all driven by microphone outputs. It's standardised so that a positive pressure on the mic diapragm causes a positive signal on pin 2 and a negative one on pin 3. This convention is then followed through all other connected equipment so that a positive signal on pin 2 of the mic caused a positive signal on pin 2 on the output of a connected mixer which caused a positive signal on the 'positive' output of a connected amplifier, and then a positive pressure to be produced by the attached speaker.

But knowing what pin is +ve does make a difference when you need to connect balanced to unbalanced equipment (and vice-versa). Without doing it correctly and connecting pin 2 to the tip of a TS jack, you will reverse the polarity of the signal.

[Paul_H]

Rane Corporation did a great white paper on audio interconnects: http://www.rane.com/note110.html

And just a minor point regarding the Greek symbol for phase... I believe it is Phi (not Theta) ø

[DrNomis_44]

You can also measure phase on a device called an Oscilloscope, in this case the phase is measured in degrees and is called the "Phase Angle", if you have one signal which is your reference signal and an identical but opposite-in-phase version of the signal, the opposite-in-phase signal will be 180 degrees out-of-phase with your reference signal, sorry if this is sounding a bit technical, now, if you add your reference signal and the 180 degree out-of-phase together both will cancel each other out and you will be left with nothing, this is assuming that both signals are identical and opposite-in-phase to begin with, this is also essentially how the XLR cables (called "Balanced-Cables") work to suppress hum and noise pickup.

Basically the theory goes like this, if the two signal carrying wires in an XLR cable pick up any noise and,or, hum then that noise/hum is going to be in-phase whether it is on the in-phase signal wire, or the 180 degrees out-of-phase wire, where the two signals arrive at the input of a device that the XLR plug is plugged into is when the magic happens, inside the device is some extra circuitry connected to the 180 degrees out-of-phase signal input, this extra circuitry "flips" or inverts the signal so that it is back in-phase with the other circuitry, but it also at the same time inverts the phase of the noise signal, so when the in-phase noise signal is added to the out-of-phase noise signal they cancel each other out and you are left with the signals that you want to hear.

[DrNomis_44]

Rane Corporation did a great white paper on audio interconnects: http://www.rane.com/note110.html

And just a minor point regarding the Greek symbol for phase... I believe it is Phi (not Theta) ø

Definitely a very useful website, I'd recommend everyone bookmarking it for future reference, and also download the pdf as well, cheers Paul_H.

[Paul_H]

As Simon has mentioned previously, I think it is more correct to refer to polarity when considering differential signals. Phase differences also imply time differences in a signal, whereas in a differential pair one of the signals is inverted without a time difference.

Balanced lines, however, do not need to carry differential signal, since the "balanced" refers to each line having equal impedance to ground. One practical implication of this is that unbalanced gear may be modified to provide a balanced output with as little as a resistor, a capacitor and a suitable connector.

[Marcel]

Polarity is correct.
Phase is correct (but only under specific conditions defined elsewhere)(not limited to 'time' differences)

It's a bad habit of mine to use less specific words, and then sometimes have to go back and explain myself.... you can also read it as "but that was automatically implied by the context of the ..." which for me as a working audio/radio/guitar/stage lighting/microwave/TV/VCR/studio/computer/turntable repair tech the 'context' can change nearly every other job or paragraph, as does the usage of various pins on some multi pin connectors.

Quite often in my work it is a case of getting accustomed to one 'standard' (usage, implementation or meaning) and then discovering that a dozen or more other 'standards' can also apply.... For example there are also 'standards' for the humble 3 pin XLR that define for single and dual loud speaker use (as was often done on Aussie Rock-n-roll PA systems in the '80's) as well as for DC power use (12V/24V & the much better known 48V phantom power) and then there is the vintage '50's radiogram bits of gear that have their own uses and ways of doing things with those XLR pins that are rated to and can carry 15A each., so it can be quite easy (as it was in my case) to only remember the first of each type of 'standard' that you were first introduced to, or maybe simply the standard you used the most....


A conversation spanner I'd like to throw for the amp builders among us here is this ....
3 pin XLR pins are rated at 15A continuous, (21A peak <1mS)
4 pin XLR pins are rated at 10A continuous. (14A peak <1mS)
5 pin XLR pins are rated at 7.5A continuous (10A peak <1mS)
TS is rated at 5A continuous (7.5A peak <0.1mS)
TRS is rated at 3.5A continuous (5A peak <0.1mS)

So a TS jack so typical of most guitar amp speaker connections is a convenient connector but can be pretty stressed on a 100W amp at max volume... and PA systems of the '80's were not wrong back then in using XLR's for speaker connections on PA amplifiers rated 450W RMS per channel at 8 ohms.

With P=EI and E=IR etc... and the maximum continuous amp ratings of our connectors...
When using a TS plug gives us a max permitted power of 225W on a 4 ohm load, or a max of 112.5W when using a 2 ohm load.
When using a 3pin XLR we can have a max of 450W on our 2 ohm load, or a maximum power of 900W being passed through the XLR into our 4 ohm speaker load...
Obviously nobody has said anything to some pro mega bass amp/cab builders... or maybe it's they just don't care...

[Simon Barden]

I heartily agree on TS jacks being very limited for speaker connection usage and 100W being a reasonable upper limit. All my higher powered cabs have Speakons fitted.

[Marcel]

Yep, Speakons remove all the speaker lead confusion for roadies... but puts them at odds with the lighting guys with their very similar Poweron connectors ... lol