Analog Audio Cables – VII

MAIN TYPES OF CONNECTION

Here we see some common types of connection, how to be links for the transport unbalanced signal to the balanced and mixed.

It’s represented the signal path from the output to the input of connections, the possible presence of the shield and the voltage values transported as generally used.

n.b. A signal that goes out to the voltage level example 1,223 V must be sent to a connection that accepts voltage levels 1,223 V, the same as for other voltage levels may be 0,775 V or 0.3 V, depending on the standard used, this not to undersize or oversize the circuit making the most of its performance.

The same applies also between balanced and unbalanced signals even with the same voltage level, balanced with balanced and unbalanced with unbalanced unless you have to be obliged to unbalance a balanced signal or vice versa, because the connection requires that all the problems and solutions seen in previous articles. The important thing is to keep the operating level between the input and output connections.

Unbalanced connection (ts)

1

Unbalanced connection (trs)

2

Insert Connection (trs – 2 x ts)

3

Balanced connection (xlr)

4

Balanced connection (xlr – trs)

5.png

Balanced connection (xlr) – unbalanced (ts)

6

Loss of 6 dB since the voltage is halved, the Return may also only be disconnected since it is not picked up from the pre-amplifier, but its signal it sends to ground so as to eliminate interference from it’s loaded.

Balanced connection (trs) – unbalanced (ts)

7

There are also alternative connections, not illustrated here, such as with the shield that acts as a conductor or always with the shield that is attached to the ground only at one end or even without a shield in the balanced and unbalanced connectors or with the mass that acts as a shield or from the conductor itself.

 

Ground Loop

The ground loop is the phenomenon by which you can hear the hum from the speakers (hum with fundamental 50 Hz for Europe and 60 Hz for the United States). This happens because the mass is subject to all the electrostatic and magnetic charges that there are during the signal path. When the disturbances are discharged to the ground by mass, if the ground rod is not correctly dimensioned so as to bring to the ground all the disturbances, or the mass itself is not adequate, it has a return of the disorder that will increase in value and will disturb the signal if shielded while creating exactly this effect. This perceive very well and especially when the audio is connected with the lights on a common electrical device or audio connectors places close to those currents, because in the cables circulates a high voltage current creating auto inductions around the cable itself that go to interfere with those near. You can solve this problem by removing the mass to the audio cable (if possible). This however can lead to problems in some cases, for example in microphones in which the mass is the only conductor, where they are unloaded all the spurious currents and noise. When I go to take away all these currents will be discharged on us that we touch the microphone and we have our feet on the ground, giving us a brief but annoying shock. It may also generate more noise along the connector, if it is the same mass that acts as a shield, or even cancellation of the signal if it acts as an audio signal conductor.

In devices such as mixers or sound systems, for example, even if take off the mass there is no problem, since it always has the ground conductor of the electrical cable, in fact in many devices there is the Ground Lift selector which serves precisely to eliminate the mass in the case hum. But it is not said that the problem is always resolved, and in many cases only attenuated beacause the only mass of the electrical conductor very often fatigue to transfer the full load interference in the audio conductor or from the disconnected mass. To eliminate noise in unbalanced cables is useful to use a Passive D.I. Box, as we shall see that having in its interior a transformer and thus does not pass direct current eliminates the trouble, since this noise is a kind of direct current. As an alternative to D.I. Box the most effective solution is always to interpose in the circuit a transformer with a transformation ratio of 1: 1, thus making all the noises generated by the current return will be deleted.

It should be recalled that, unlike the passive devices (transformers and cables as D.I. Box, audio signal processors with passive connections or even amplification devices with passive input), for example those active then servo balanced circuits, so in the presence of an amplifier, the mass must not be removed, as an integral part of the amplification process. In fact very often it can happen in the example of use Active D.I. Box that while removing the signal mass which is very often the one connected to the transformer, noise does not fade or weakens, this is because the disorder may be caused by the amplifier’s mass present in it’s internal (so in this case better to use a Passive D.I. Box ).

To obtain a correct wiring free or with minimum background noise and hum must be at least hold the conductors that carry low voltage values such as the microphone and line signal to 30 – 40 cm of distance respect to the power cables carrying tens of volts, and then that have especially if not properly dimensioned strong values of self-induction. And even more distant in the order of meters where possible the electric cables.

It’s fundamental that the electrical system to which you connect all the equipment is properly placed on the ground and that the load voltage is adequate to the need, for example if the audio system including any stage monitor and musical instrument has a total power 10.000 watts you will need for proper supply an electrical outlet in which to connect the whole load of 380 V at 32 A as P = V x I (power = voltage x current) = 12.160 watts which is well within the power used, by this simple formula you can calculate the values of voltage and current required.

In professional contexts, especially for the connection of the Sound System it is also useful to consider the peak values in order to connect the Sound Sytem to levels of voltage and current to enable the dynamic expression of the system. So if we have a Sound System from 3.500 watts rms and 10.000 watts peak is useful to plug it to an outlet at 380 V 32 A more than to a 230 V 16 A that would still enable to meet the system power requirements. In case the Sound System has high powers example 20.000 – 30.000 watts and beyond is useful to distribute the power of different lines so that for each power line falls within the system peak power.

It’s important to always have with you Passive D.I. Box to try to reduce any noise on the signal, balanced cables disconnected with ground (only to connect devices that have their own grounding) for the same reason, UPS and surge suppressors that help turn to eliminate noise on the power line.

 

Hum Noise Box

An alternative to D.I. Box Passive, especially for an economic matter being more simplified circuits, they generally provide a transformer with a 1: 1 transformation ratio (then not amplifying or attenuating and nether balancing signal, but a simple balanced or unbalanced input and output device). They are Hum Noise Box or De Hum or Hum Suppressor or Eliminator, they may have other names but the principle is the same, eliminate (not always possible for all the reasons previously seen) the noise generated by an unstable and correct power supply, the HUM. They can be single-channel (figure 1) or multichannel and / or mixed of balanced and unbalanced connections for input and output (figure 2).

Fig. 1 1 canale.jpg

Fig. 2 10085520_800.jpg

For a quality device, it is important that the noise on the line be correctly attenuated up to values > 100 dBs, that the distortion introduced on the signal is minimal, < 0,01% of THD % and a more linear frequency response possible in the wider possible bandwidth at least in 20 Hz – 20 kHz bandwidth, and in output ensure to be respected the dynamic of the input. As you can easily realize the introduction of a device like this always introduces even if minimal distortion values, so if it’s of quality better using cables with disconnected ground or quality Passive D.I. Boxes that generally offer superior performance even with the widest product choices.

 

Welding a cable

The end of the cable and that mean the connector (fig. 3 Jack TRS), (fig. 4 XLR), (fig. 5 Speakon), which sectioned is composed from the real connector in which the cores must be connected carrying signal and from the external hardware that will go then to it screwed for covering the part of cable connected. The external hardware it also acts from shielding against the interferences in how much when i go to weld the cable i must discover it so that to be able to tinned the part in copper to the same connector, so making the shielding of that piece of conductor jumps and as protection is well covered from the hardware of the connector. The hardware favors then the point of taking and insertion when the connector must be maneuvers and managed.

Fig. 3 8.png

Fig. 4 9.png

Fig. 5  10.jpg

When welding a cable then you should be careful, each copper strand must never touch in any way other filaments for not as seen in previous topics unbalance a balanced signal, introducing noise or just not work. Unless specially create for example an unbalanced connection to balanced cable.

The same applies for the connection of unbalanced line, so that the signal conductor touches the mass to avoid the loss of signal.

To connect the copper to the corresponding connection pin filament using the solid pond that at a temperature of about 200° becomes liquid, this liquid resting on the filament when it goes to release in a very short time, the pond in contact with the air it solidifies and the connection is made. However, be sure it’s a good connection and that does not break at the first pitch. Do not introduce too much tin as it may form bubbles which then prevent the hardware screwing of the connector or that they may touch other pins, in addition to having a lower outlet.

The pond as well as a conductor also acts as a protector against the oxidation of copper or silver generally used in audio conductors.

Before soldering the wires on its pin, it’s good to pass around the cable through the external hardware and the cable gland, to avoid, especially if the other end of the cable has been already connected to its connector, welding cables then no longer have the possibility to introduce it.

There is often also the cable gland (you can see in figure 5 in the image of the Speakon), very often retrievable in XLR and Speakon which is inserted inside the external hardware and serves as additional protection against interference and handlings of the conductor. The XLR Speakon as it often has a screw sleeve (below point 3 of the XLR and the blue color in the Speakon) that unlike the jack allows you to better dissect the connector for easy and convenient wiring not the allows the replacement of the specific component in case of damage without having to replace the entire connector. As shown in the XLR and Speakon image is screwed to the connector.

In Speakon given the strong circulating strains prefer to use a more sophisticated system of simple tin plating as to tighten the screw part of stripped cable.

As regards the dissolution of the pond is necessary a special instrument called soldering (fig. 6), there are various powers and therefore costs. A good soldering must have a power of about 30/40 w. They all work with a 220 V of voltage. The pond then, can also be gouged out after it is solidified, for example, for an error in the tinning or for a renewal of that conductor wiring. For remove using the appropriate tools, for example a special pump that sucks. The pond then a flux component (the smoke that you see when you sealed), this component allows the cable to last longer by avoiding the oxidation of copper. When going to heat up again the pond already soldered on the conductor of the flux is lost and so the pond can not be used more than once but must be replaced.

Fig. 6 11.jpg

n.b. Some manufacturers in place of the pond they use other typologies of material as the same copper and/or silver used in conducting filaments to guarantee a minor error of phase and isolation, a problem that results to be there when the signal crosses materials with different chemical and magnetic properties.

 

What goes skinned a cable?

The core of copper or silver is to be out of its protective coating as little as possible because the interference is directly proportional to the length of the skinning.

A copper connector in sight peeled 3 cm would have an interference (low pass filter) from about 12 Khz, is good so always use the protective connectors, and that in turn help against interference.

 

Cable Tester (fig. 7)

There are also the instruments which allow in a simple, precise and rapid, to identify welding problems, the wrong connections made or find the problem in the case in which the cable is damaged.

Fig. 7 cable tester Ebtech Swizz Army Live On Stage

Composed of special input and output connections for various building standards, including the XLR, Jack, mini Jack, RCA (some even have Speakon). Inserting the output of the input terminal and that of our cable in the appropriate connections and by calibrating the instrument prior to the intended purpose is possible through light signals or acoustic tone recognize the type of connection made inside the cable.

Some cables tester also include connections for fiber optic testing (in its various formats) and ethernet (in its various formats).

 

Acoustic Pollution

One of the main aspects related to noise pollution issues still being studied as a rule of law is the so called pollution at 50 Hz for Europe and 60 Hz to the states (which also includes the Ground Loop). This sinusoidal frequency at 50 Hz or 60 Hz is nothing more than the power supply frequency to which we link all our electronic devices such as television, hi-fi system, fridge etc … even if by ear does not perceive any sound that you can define an annoying noise except in cases of gross interference, that “sound carpet” exists and continues to spread in any room in which we stand, and where there is equipment connected to the power supply. This voltage which reaches our devices and especially if it crosses the wrong conductors sized, creates a background noise given by the continuous transformation of the electric current changes in heat with similar changes to a sinusoid by 50 Hz, the heat which then spreads into the environment setting in motion the surrounding air particles so as to produce a sound.

This phenomenon is significantly perceived in the vicinity of conductors carrying medium and even higher voltages.

This then, going back to our everyday life and then with our grid connected to eletricity, we can define pollution that although of low intensity is always present in the long run even if not perceived can cause stress to the auditory system even permanent damage.

As for the noise and interference loaded along the audio signal line we then:

Hum (as defined before with fundamental 50 Hz EU – 60 Hz US) created by a ground loop, but also to open audio lines and bad ground connections. The first harmonic Hum is 100 Hz EU – 120 Hz US generally caused and audible when you are worn out capacitors and power supplies and non-optimal operation. The second harmonic Hum is 150 Hz EU – 180 Hz US generally caused by power transformer, active circuitry and chassis ground ring.

The Buzz is instead a Hum with the presence of multiple harmonics in the medium and high frequency, always generated by one of the Hum problems only to a greater extent.

Hiss is instead the Hum distortion caused by the presence of harmonics in high frequency. The Hum + Hiss = Buzz.

 

Some manufacturers of Analog Audio Cables and Professional Adapters:

Some Manufacturers of De-Hum Noise Box:

Some Manufacturers of Cable Tester:

 

Below is the link to a video explaining how to repair and make XLR links:

Below is the link to examples of comparisons between quality audio cable:

 

More About Analog Audio Cables:

Analog Audio Cables – I (Technical Features, Shielding, Operating Environments)

Analog Audio Cables – II (Types of Connectors and Connections, Unbalanced Connectors and Connections)

Analog Audio Cables – III (Balanced Connectors and Connections, Passive Balancing)

Analog Audio Cables – IV (Active balancing)

Analog Audio Cables – V (Differences between Jack and XLR, Bantam, Speakon, Powercon)

Analog Audio Cables – VI ( RCA, MiniJack, BNC, Midi, Starquad, Edac, D-Sub, Socapex, Euroblock, Tipologie di Adattatori )

 

Buy Analog Audio Cables from the Major Store

 

Adapters

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Accessories and Fairlead

 

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