I noticed noise coming from the speakers, when no audio signal was present. Changing USB-port did not help. I seemed like my USB ports were noise polluted! When I connected a power-bank (lithium-ion battery) to the speakers, the noise disappeared, but during pauses in the audio, the power-bank shut itself down!
I decided to build a noisefree 5 V DC PSU using a transformer with iron core and a 7805 which has 68 dB ripple rejection and low output noise. The 7805 is thermal overload protected and short-circuit protected. I had all parts laying around, so the building cost was nil.
|Figur 1. The noisefree PSU.|
|Figure 2. Noisefree PSU with open lid.|
|Figure 3. AC Adaptor.|
|Figure 4. Circuit diagram.|
|Figure 5. The circuit board seen from the bottom.|
Now I can enjoy music and speech without background noise - and a good feeling of having improved something!
73 from OZ1BXM
My homepage: http://oz1bxm.dk