In many cases, power is supplied from an AC outlet for home audio, and the conductive noise in the power supply cable is regulated under EMC standards. Therefore, it is necessary to prevent noise from leaking into the power supply line during audio playback.
Methods of cutting the noise are generally introduced into the AC adapter or the ACDC power supply section, but it is easier to avoid the noise problem by applying suppression in the power supply section of the digital amplifier which is the source of the noise.
Figure 4 shows the results of measuring the noise leaking from the power supply line.
We can see that the higher harmonics of the digital amplifier switching frequencies are conducted as noise. Equipping the PLT10HH Large Current Common Mode Choke Coils and the BNX Series of Block Type EMIFIL® filters achieved an improvement of over 20 dB.
Figure 3 An example of countermeasures to deal with noise leakage from a Class D amplifier to the power supply circuit
Figure 4 Power supply noise measurement results before and after applying suppression products
Using the PLT10HH and the BNX products enables you to combine both suppression of noise interference from the power supply circuit to the audio equipment and suppression of the noise leaking from the audio equipment to the power supply.