ATM Filter SMPS

We have designed a passive filter circuit to remove much of the high frequency noise from the SMPS source. The circuit consists of two LC filtering stages, built with SMD (coils and resistors) and through-hole (capacitors) components. Depending on the type of power supply, noise attenuations between 8 dB (2.5x) and 23 dB (14x) can be achieved. The DC resistance (DCR) is approximately 100 mΩ.

The filter circuit is arranged on a small 35mm by 40mm board on which the wires are directly soldered with the I / O connectors. The unit mounts inside an insulated miniature plastic box where hot glue is applied to hold the cables securely in place.

The maximum input voltage of the filter is 35V, supporting a maximum current of 3A. With these voltages and current value ​​we are within the limits of most portable audio products on the market, from those that use the 5V 1A USB power supplies, to the 24V that Naim uses, through the 12V 2A of Pro-ject, Rega or Topping. The customer will only have to determine the type of connector of the power supply. Originally, it has the standard 5.5mm diameter connector with a 2.1mm internal pin (male/female), the internal pin being the positive. In case our audio equipment has another type of connector, we will need to add a suitable adapter.