LC Audio Mains Filter Kit

Mains Noise Filter Kit - NETfilter 2400VA

The purpose of the NETfilter is to remove noise that enters electronic devices via the 240V mains system. It is typically noise from industry, refrigerators, fluorescent lighting or other household devices, which results in clicks, pops and other similar noises to be heard through the loudspeakers or even on the television screen. Most hi-fi equipment only uses small amounts of mains filtering, if any at all. Actual size 18 cm x 6.5 cm diameter, wire clamps are not supplied as we recommend soldering via the holes on the PCB as per the instructions below.

Many manufacturers of noise filters try to convince their clients to purchase one filter per machine; in which case they could sell maybe half a dozen filters per customer, whereas in reality only one or two are needed, depending on the current draw of your equipment. We recommend that one be used for all your signal sources, best connected to a powerboard and another for the power amplifier. This then covers all devices you have in your audio set-up, thereby preventing noises from unprotected units interfering with the others, either through the mains cable or more particularly through the signal cables. If you really want, you can use one for each individual device.

LC Audio NETfilter circuit diagram - note we supply a 275V VDR for Australia.

NETfilter Attenuation Data - dB Reduction vs Frequency.
Measured using a 75 Ohm input and 75 Ohm output HF generator and AC millivolt meter.

Construction

The NETfilter is a partial kit, that is all components are already mounted onto the circuit board but the only part not included is the power cord or power board you will connect it to. This kit is not very difficult. The case is a clever yet simple design with clip together shells and a locking flange. Supplied capacitors are correctly rated, either X and / or Y rated as applicable.

Prepare the mains input cable (plug side) by removing the outer insulation approximately 70 mm (2.76"). Cut the active and neutral (active is brown and neutral is blue) wires to about 20 mm (0.8") long and strip a few mm off the end. Leave the earth wire (green / yellow striped) the full 70 mm and strip off a few mm at the end. Do likewise for the output side (socket / power board) but make the stripped length about 90 mm (3.55") long. If the cable does not have an earth, then shorten the stripped length to about 20 mm (0.8") in total for both sides of the cut cable.

First feed each individual wire through the holes in the appropriate location for strain relief. Solder the plug side of the power cable active and neutral wires to the "Input" points. (Active is brown and neutral is blue.) Attach the other side of the cable (leading into the unit or power board) to the "Output" in the same fashion as the input. Note that the arrow indicated on the circuit board indicates the brown active (or red) wire, while the blue neutral (or black) is connected on the side without the arrow. This way you will maintain the correct phasing.

Any earth connection in the power cord you are fitting to the NETfilter to should be maintained for safety. The earth wires you have prepared as described above are to be connected to the "True Earth Connection" on the circuit board. The earth wires themselves can be fed through the larger hole by the mains solder connection for strain relief. If there is no earth in the power cable, then a "Genuine Earth Connection" can be optionally attached at the point "True Earth Connection". In that case the best method is a decent earth spike directly outside in the soil. We strongly recommend that a qualified electrician is employed to carry this out!

   
Steps to opening the NETfilter housing - Hover over each image for more details.