Buzz generated by the PSU

[Tazio]

Firstly, switchmode power supplies are noisy by nature as they operate by using a transistor to "chop" the mains frequency in such a way that the resultant square wave can have a mark/space ratio that allows the waveform to be filtered and rectified to a DC output that is a lower voltage than the input. The first thing that I would check is that the auxiliary DC output shares a ground with the main output. If this is not the case and they are separate, this might account for the buzz. I see the supply also has an "independent" 12V supply which might be preferable to use. Alternatively, run the LED's off the main supply with appropriate current limiting resistors.

Thank you mate.

Firstly, switchmode power supplies are noisy by nature as they operate by using a transistor to "chop" the mains frequency in such a way that the resultant square wave can have a mark/space ratio that allows the waveform to be filtered and rectified to a DC output that is a lower voltage than the input. The first thing that I would check is that the auxiliary DC output shares a ground with the main output. If this is not the case and they are separate, this might account for the buzz. I see the supply also has an "independent" 12V supply which might be preferable to use. Alternatively, run the LED's off the main supply with appropriate current limiting resistors.

I've tried the indipendent output obtaining the same buzz ... and was also thinking about using the main output as you said. I'll give it a try at soonest.
On the other hand, there is a recommendation from the supplier that I don't understand:
"- Attention: Since the switching power supply only stabilizes the main voltage, the current of the independent and auxiliary output must be less than the current of the main voltage output; for example, the current of the main voltage at the time is 10mA, and the auxiliary and independent cannot carry loads above 10MA." Anyhow I think this is related to the stability of the voltage output and not with my problem, right?

 

[Punter]

That's an interesting wrinkle Honestly, in any amplifier, the most they might do for a secondary supply would be to add a regulator which is powered off the main PSU. As we don't have a circuit for this unit, I think the idea would be to calculate the right dropping resistor for the lighting and run it like that. It's odd that they have this caveat on the aux and independent supplies but *meh* it is what it is!