Had a problem with the E30 summing noise with frequent short hums that drove me crazy at night when there was no other sounds overlapping it. Literally just 5minutes ago fixed it! How? By swapping the USB cable that came with the Topping E30 with a little longer one from a Canon printer I owned 15 years ago. Seriously, no summing, no hums anymore. It's quiet as a grave now. Mindbening, I never thought there are differences in USB cables.
Edit: Nope, not solved by the USB cable. It's the frequency setting in windows. 44.1/fine, 176/fine, 192/hums, 352/hums, 384/hums
About checking when hum noise occurs in A20a
Connect only the power cable and speakers to the A20a. Do not connect anything to the input. Turn off the power switch of other audio equipment around you.
In my case, I set the volume to -00 in this state and only hear a very small amount of white noise (sometimes called hiss noise).
If both input 1 and input 2 are in the same state as me, there is no problem with the A20a. There are other causes of noise.
If hum noise still appears in this state, the power supply line is extremely distorted, or the power supply unit of the A20a is suspected.
When home appliances with built-in inverters are operating in the house, the waveform distortion of the power supply line may increase and induce noise. In particular, if hum noise is generated intermittently, it is often caused by the inverter.
I have experienced this several times at the request of a noise survey. Recently, the impact has been reduced by using SMPS with good performance, but confirmation is necessary.
Turn off the power of the surrounding electric appliances one by one and check the change in noise.
If hum noise still appears even after doing this, there is a possibility that the power supply unit of the A20a has failed. It takes patience above all to clarify the cause of noise.
The mainstream power line in Japan where I live is 2P 100V, and there is no connection to the ground pole. So it may be different from the 3P 220V environment.
