Why should a good powercord be shielded? The voltage and thus the current in a powercord is alternating its direction 50 or 60 times per second. Unfortunately this electromagnetic field does not only stay inside the cord, but also gets outside into its ambience. Yoe can prove this with a coil connected to a speaker: if you get close to an unshielded cord with the coil, you´ll hear a hum out of the speaker.

What does this mean for excellent music reproduction? As you now can imagine, especially the phono-input is endangered, since the signal voltages - which represents the musical information - are very low. For Moving Coil (MC) they are typically in the range of some microvolts
(1/1.000.000 Volt), and for Moving Magnet-systems (MM) at some hundred microvolts, resp. millivolts (1/1.000 Volt). The phono-cable between turntable and phono-preamplifier acts as an antenna and catches - similar to the coil in our thought experiment - the 50Hz-distortion and delivers it amplified as hum to the speakers. This unwanted influence is, at lower level, also present at all other HiFi-components. It decreases at larger distances from the cord, but crossing of audio-cable and powercord can be enough to cause hum. If whereas the powercord is shieded, the metal shielding avoids transferring the 50Hz-field into the ambience, because now it can flow to the ground via the protecting earth wire.

How should a good powercord be terminated? After taking off the insulation and shielding about 40 mm from one end of the cord, the insulation of each of the three single wires has to be removed at a length of 10mm. Then suitable core cable ends are pressed on with special plyers. On the other end, where the mains-plug will be connected later, alo 40mm of the insulation are taken off, but the shielding remains and must have the same length as the three wires. The insulation of the three wires are taken away and the shielding is thinned a litte and afterwards pressed into core cable ends together with the protecting earth wire. Also the two other wires are pressed into separate core cable ends. At this point it has to be mentioned, that only special suitable plyers should be used for this work. The blank Copper ends should not be soldered since a tinned contact will deteriorate under pressure.

Now mains plug and warm device plug has to be connected, make sure to connect all wires to the allocated pins! Tightly fasten bolts and strain relief!. Then close and fix covers and check correct assembly with an electrical measuring-instrument.

What is the difference between the two subtypes? A coaxial-cable consists of a - flexible, or better rigid - inside core conductor made from high purely Copper or Silver. This conductor itself is encirceled by an insolating layer of PVC, Teflon or another material. On the outer surface of this insulation is a - more or less flexible - layer of conducting material. This layer acts as a shielding as well. Then another insulating layer is brought onto the outside conductor.

A parallelsymmetrical cable consists of - as the name already indicates - two, or in rare cases more - parallel running inside conductors. These conductors are insulated and then encirceled by a shielding. Because the return wire is made from the same material as the other and also the cross section of both wires is identical, the music signal finds optimal conditions. Thus many experts think that this type is superior to the coaxial type.

The most important measuring value for audio-cables is the capacity, it is designatd in picofarad per meter (pF/m). Because the resistance is decreasing with higher capacity and cable-length, a low capacity per meter of the cable is important. Otherwise higher frequencies of the musical spectrum will be attenuated. At values of 100 pF/m you are on the safer side, even if longer distances have to be connected. The ohmic resistance does not play an important role, because the component which is connected at the receiving side has an input with high impedance.

What properties should a good audio cable have? In every case, a tight shielding is essential, especially if it is running close to other cables, in the worst case to powercords. The contact area should be coated with a noble metal, e.g. Gold or Iridium. Furthermore, a perfect and permanent contact to the socket is important and can for example achieved with a pressure mechanism, as AUDIO-TUNING-PITHAN offers.

How should a good audio-cable be terminated? The connection between cable and plugs is exclusively done by soldering. Because of its lower resistance, silver containing soldering material is preferrable.

Hum can have many different reasons, but most of all it is caused by different potential of the supplying voltages at the components. Furthermore, components with cheap and bad designed power supplies and phono preamplifier produce hum, if the signal-to-noise ratio is too low. In some cases the housing of the component is vibrating due too badly decoupled transformers. Then it may be helpful to use one of our resonance absorber RA85 on top of the case.

First some important presumptions to avoid hum from the beginning.

1.) All HiFi-components have to be feed out of one multiple socket outlet with low electrical losses! If possible, the powercord should be shielded. Our socket outlets with filter FNL6, FNL6s, FNL8 or FNL10 are fulfilling these conditions. You can use, according to the number of components to be connected, 6, 8 or 10 sockets.

2.) Do not place a component on top or close to another! The transformers, especially those of amplifiers, can interfere with the sensitive inputs of source components. Place all components separatly on a high quality rack.

3.) Do not use dimmers for ilumination, energy saving lamps, microwave ovens or mobile phones while listening music!

4.) Check - if possible - all contact positions of each powecord (soldering or contacts with bolts). A better solution: Exchange all low quality powercords which were packed together to shielded ones with higher cross section, e.g. to our model L125!

If the problem persists, please perform the following steps:

1.) Do not place audio cables (cinch or XLR) close to powercords. If the hum only occurs while listening LP´s, please check whether the thin ground wire from the turntable has proper contact to the ground screw of the preamplifier. Use only good shielded phono cables, for example our PSK2, which even has two layers of shielding against interferences. This is very important since the musical signal from the pick up is very small and thus sensitive.

2.) Exchange all other audio cables to shieded types. Do not forget the digital cables, they also can transfer hum!

3.) If the hum still persists, you should connect a high-quality line filter between the multiple socket outlet and the mains-socket. At this point our NFL50 was successful several times and could eleminate the hum-problem!

4.) If you own a radio-receiver (tuner), the hum can also come from the antenna. Then you should try a special current-filter, which is available in radio and TV-stores for little money. This filter is simply placed between antenna wall-outlet and antenna-cable.

5.) After all these actions there should be no more hum, if it is still present, things become a little more difficult. Disconnect all cables from the components and connect one after another e.g. CD-player - amplifier - speakers. Continue as long with source components, until the hum appears and try to locate the disturbing component.

6.) Now move with this part of your equipment into another room, or better, into another house and check, whether the hum is still present. If yes, you should ask for professional service, if not, there is a problem in your electrical house-installation and this should be checked by an expert.