In cable making, the term "ground" refers to the physical ending of the shield, which for some cable types, is connected on both ends, for others it is connected only on one end, and for a few other types of cables the shield is grounded directly to external points. In all cases, the grounding configuration is a determinant factor for the effectiveness of the shield and thus for the overall performance of the cable. The grounding of cables is called to play two key roles. Firstly, to create a path between the shield and the connected device in order to help discharging all unwanted signals and noises that have been intercepted by the shield, and secondly, to create directional conducting paths between the grounds of all connected devices, so as to guide ground currents to earth. Before we proceed to the description of the grounding solutions we follow and apply to our cable designs, it would be very helpful to examine some of the problems that may appear and affect the performance of a system due to improper grounding.
One of the most difficult problems to diagnose and resolve in a system of audio and video components is called ground loop. Ground loop occurs when two or more electronic devices are using more than one connection path to reach common ground, creating this way a closed "loop" circuit through which, ground currents of different potential may flow. In such a case, the electrical level of the shields, which is normally varies form very low to zero volts, starts to fluctuate above and below zero with a significant difference in voltage, causing interference on the transferred signals.
A very common example of ground loop in an audio system is when, ground currents of two or more connected units "meet" on multiple paths that are created by the ground wires of power cables and the negative signal conductors of the single-ended interconnect cables that are operating also as ground paths between the connected units. The ground currents that flow through this closed loop circuit are usually generated by voltage differences, inductions from cables and devices, poor cable shielding, other wiring errors, ground faults, and normal leakage. In practice, various problems may appear as a result of ground loop, starting from simple noises, up to major component damage. In all cases, the role of cables is very important since they are integral parts of a system, and thus will also be parts of any ground loop that may be created, either as "causes" of the problem or as "victims" of it. The most frequent problems caused by ground loops are:
- In a ground loop circuit, the connected devices are usually producing currents of different potential. These currents may induce voltages in the audio circuitry of electronics and in the signal conductors of cables, causing hum noises at 60Hz or 50Hz (depending on each country’s AC frequency), and some other times electrical noises at higher frequencies.
- A ground loop can also be one of the main causes of common-mode noise. Common mode noise is the electrical interference which is induced on all signal or all power line conductors of a cable in the same direction. In a case of ground loop circuit, where currents are flowing continuously in one direction across the shields and ground wires of cables, a common mode noise could be developed.
The specific resistance of ground wires and shields will cause voltages that inevitably are induced to the internal conductors, affecting the signal. The higher the shield or ground wire resistance is, the greater the voltage will be. Another example is when ground currents flow continuously on the direction through the ground wire of a power cable, affecting this way the line and neutral carrying conductors. In both cases, this noise is injected into the audio circuitry (through interconnect cables) and even worse into the power supplies (through the power cables), affecting the performance of devices.
- Another problem that may be created in a ground loop circuit is when some switching or inrush currents inside electronic devices are producing transients of high energy. These transients usually prefer to travel on their way to earth through the grounded shields of interconnect cables instead of the ground wires of power cables, a fact that may affect audio signals and in some cases where the surge is high enough it may cause serious equipment damage.
A very frequent problem that may affect unbalanced and poorly shielded interconnect cables, is the antenna action. This action usually occurs on cables which are grounded on one end and their grounding configuration is proved improper and unable to discharge effectively the noise currents from the shield. In such a case, the RF signals are using the cable as an antenna, by increasing voltage along the shield. This voltage takes the form of common mode component, with the unwanted result of affecting conductors that carry audio signals.
The grounding techniques of Signal Projects
By aiming at the most effective discharge of noise currents from the shields of our cables, we have designed specific grounding configurations according to the requirements of each cable type.
The traditional unbalanced interconnects are structured with one conductor and shield. In this configuration, the conductor is the carrier of positive signals and the shield is acting both as the negative path and the grounding path between the source device and the receiver device. Due to this structural characteristic, all traditional unbalanced interconnects are more vulnerable to ground loops that can be created when there is an increased potential in one of the two connected chassis.
The most effective solution to this problem can be provided by the use of balanced cable designs that can even be applied to unbalanced type connections. In this case, one conductor is used for the positive voltage, the other conductor is used for the negative voltage and the shield is usually grounded either on the input termination, or the output termination. In Signal Projects, our unbalanced interconnect cables are based on exactly the same internal geometry and cable design with our balanced interconnect cables.
More specifically, for the construction of our unbalanced interconnects we use a truly balanced configuration with two conductors of the same cross sectional area, of the same type, of the same metal and of the same purity for both the positive and negative paths. These conductors are protected by exactly the same shielding materials that we use on our balanced cables, with the only difference being on the grounding, which in this case is connected on the "output unit" termination.
The reason why we follow this specific grounding configuration is because a) in most cases the noise currents will find better grounding circuits with lower impedances as they go downstream from the sources to pre-amplification units and from the pre-amplification units to power amplifiers, and b) we believe that it is more preferable to guide ground currents to the units with the lowest possible gain amplification.
Theoretically, the use of balanced cables would offer the best interconnecting solution for any audio and video device. Practically, this assumption would only be stable if the connected devices were based on entirely differential balanced circuits with proper grounding configurations.
Unfortunately, there are many audio and video devices which, even though offer the option of balanced input and output connections, they are based on pseudo-balanced circuits, which means that the truly balanced signal "before entering into" and "before exiting from" the processing circuitry, passes through transformers or additional amplifier stages in order to be converted from balanced to single-ended and from single-ended to balanced respectively.
This additional conversion path usually brings negative results in the overall performance of a system, since it is practically "canceling" the main role and the advantages of balanced cables and thus the advantages of a truly balanced topology. In most of these cases, the performance of balanced connections does not provide the expected results and the worst thing is that cable manufacturers cannot magically change the conflicting situation created by pseudo-balanced devices. On the other hand, the existence of some pseudo-balanced devices should never deflect cable makers from the original design characteristics of balanced cables.
In Signal Projects we are well aware of that and this is the reason why we strictly adhere to the basic design principles of balanced cable designs.
- One of these is the fundamental design characteristic of balanced cable structures, which is the use of one conductor for the positive, one identical conductor for the negative and a shield that is grounded on Pin 1 of both ends. This is the basic design configuration of balanced cables that, when connecting a system of truly balanced devices, has proved to be much less sensitive and vulnerable to ground loop problems because a) the shield is used as a dedicated path for the ground currents, and b) the differential transmission of signals is achieving a very effective noise rejections across the audible frequency range.
- Another characteristic of our balanced cables is the use of high quality braided copper shields that offer very low resistance to ground currents that will travel through the shield. The combination of aluminium foil with a properly grounded low resistance braided shield can offer excellent protection from the emitted interferences and a very effective noise current discharge.
- Even in balanced cables, a directional ground path would be very effective against the creation of ground loops. During the past years, many cable makers experimented with various techniques aiming to give a specific direction to the noise currents that move across the shields of balanced interconnect cables. One of these techniques was to solder between Pin 1 and the one end of the shield, a small resistor in parallel with a small capacitor.
This method offered satisfactory filtration for the interferences and also increased the resistance in one end of the grounded shield, guiding this way the noise currents to the other end with the lower resistance. In some cases, this technique proved effective. However, the existence of a capacitor on the ground path was always a risky venture, since in some cases it may even cause a shock hazard. Additionally, even that small increase in the resistance of "Pin 1 path" could influence the dumping factor of truly balanced amplifiers creating a number of negative results in their circuitry operation and consequently on their sounding performance.
Another technique that some cable makers applied in order to create directional ground paths through the shields of balanced interconnects was to connect the shield only on one end of the cable. On the one hand this method proved effective in the creation of directional ground paths, but on the other hand it was canceling the original structure of balanced cables and thus it was becoming inappropriate for all truly balanced devices. A further technique was based on a small circuit of diodes that was connected on one end of the shield. The configuration of this circuit was able to "open the doors" of the shield in both directions for all incoming ground currents (which means that it was not canceling the truly balanced topology) while at the same time, it managed to keep the "doors closed" on the one end for the currents that had already entered the shield.
The problem was that this technique was ideal mostly for custom applications, since the small circuit of diodes operated with specific currents and thus couldn’t be followed by any manufacturer who wanted to produce identical balanced cables for all balanced devices. Finally, we couldn’t end this section without referring to the most common technique that many DIY audio enthusiasts and even more professionals have followed and still follow in order to resolve ground problems. This technique is based on transformers which are usually placed on one end of balanced cables and they are connected both to signal conductors and to the shield, offering excellent results against ground problems.
However, even if this method proved to be very effective, we cannot imagine a cable maker who has invested large amounts of money researching into the optimum combination of metal purities, conductor types and thicknesses, aiming at the most pure signal transferring, to cancel the results of his research by interpolating transformers between signal conductors.
After conducting many tests on the above mentioned techniques and after a very careful evaluation of their positive and negative aspects, we decided to follow a simple but very effective method in order to create directional ground paths on the shields of balanced cables, without affecting the fundamental characteristics of a truly balanced structure.
This method is applied inside the termination modules of our cables and it is based on a specific configuration of conductive materials that are used primarily to connect the shield with Pin 1 of both plugs and secondly to maintain a relative difference in the resistance values of these two ground connections. Knowing that noise currents tend to follow directions that lead to connections of an even slightly lower resistance, in our balanced cables the ground connections of female plugs will always provide a higher resistance than those of male plugs, because - as we mentioned above in the section of Unbalanced Interconnections - we believe that it is preferable to guide ground currents to the units with the lowest possible gain amplification.
In most system setups, the reactive current that floats across the shield of digital audio connections is not high enough to harm the digital signal. However, in cases where a ground loop circuit is created and noise currents are sufficient enough to corrupt digital data by affecting their flow (increase of jitter levels), we may experience negative symptoms like hum noises between 50Hz and 60Hz, digital whistles at higher frequency ranges and even some irritating colorations in the mid-band.
In order to achieve maximum performance and at the same time to provide maximum protection against ground loops and externally induced interferences, we have built our digital cables according to the geometry and the grounding configuration of our analog interconnects. More specifically, both our balanced and unbalanced digital cables are based on balanced cable structures with one conductor for the positive, one for the negative and one shield. With regard to the balanced digital interconnects, the shield is grounded on both ends of the cable according to the AES/EBU standards and in order to create a directional ground path on the shield of the cable, we apply exactly the same method that we described above in the section of "Balanced Interconnections".
Concerning our unbalanced digital interconnects, we do not follow the common co-axial cable structure that uses one conductor for the positive signal and a shield for both negative signal and ground, since we gained much better results with the use of a balanced cable structure and by having the shield connected only on the output plug, creating a directional ground path that leads to the receiver unit. The reasons why we chose the specific cable geometry and grounding configuration are presented above in the section of "Unbalanced Interconnections".
There are two types of noises that are closely related to power cables which are usually induced on nearby interconnects and more frequently on the connected devices, negatively impacting the system’s performance.
The first type is called Differential Mode Noise and it occurs on the Line and the Ground in opposite directions to each other, and the second type is Common Mode Noise which is occurs on all lines in the same direction. These noises are usually produced inside a ground loop circuit either due to currents of a different potential and opposite direction, or due to very high potential currents that pass through the shields of poorly made cables, affecting both line and neutral conductors.
A number of solutions like the use of transformers or common-mode chokes have been tested in many applications, resulting in the reduction and even in the elimination of these noises, while a proper and accurate twisted pair design always helped opposing currents to be wounded uniformly and to produce equal and opposite polarized magnetic fields that would end up cancelling each other out. Undoubtedly, the above solutions proved to be the ideal ones for some applications.
On the other hand though, we prefer to avoid the use of transformers and chokes in cables that will be used to connect high fidelity reproduction devices, due to a number of reasons which are mostly related to signal distortion. After many tests on various system setups and while at the same time being focused on the elimination of common and differential mode noises, as well as any kind of electromagnetic interference, we developed a sophisticated design for all our power cables which is based on the use of three completely isolated conductors with a completely independent shielding and grounding configuration for each one of them.
The shield of each conductor is grounded only on the male plug and not on the IEC plug due to three main reasons. Primarily, because we want to create directional ground paths towards the earth in order to safely and rapidly guide all noises that are blocked by the shield. Secondly, because we want to completely eliminate the possibility of a ground loop creation in the shields of the cable and thirdly, because we prefer to use only the ground conductor as the main connection between the earth and the unit’s ground, avoiding all these unwanted situations where ground currents of the circuit use the shield of Line and Neutral conductor to travel to earth.
Finally, in combination with this highly effective geometry, the use of proper ferrites will provide additional protection against all types of noises, making our power cables the optimum solutions for any system application.