i´ve just build a prototype speaker from a TDA7293 (http://www.ebay.de/itm/TDA7293-85W-100W-Mono-Audio-AMP-Amplifier-Board-AC12-50V-Update-vision-TDA7294-/201478109342), the circuit is quite straightforward. To avoid the noise of a switching power supply, i bought a toroidal transformer. While the music sounds astonishing good, in the quiet parts, or when there is no music, the system is humming in a quiet way but it is loud enough to be heard. I think, it is the 50hz.
So, how to filter the hum, since it originates from the toroidal transformer? But the transformer is giving AC, so i can´t filter it away. Does someone know, if this is a drawback of there cheap china rectifier? Should i buy a better one? And if yes, which one?
Ok, can´t attach a photo to a comment, (a little confusing because it seems, if i rather should edit my question than to add another answer), so i attach a new photo, i´ve already answered a question to stephen, maybe it is now all upside down...)
Hmm, it seems, if my comment were not added, so i type it here again. I´ve changed the setup but i can´t attach more than 1 photo (under 10 points), so i attached only the screenshot. I rearranged the setup, soldered most of the connection, but the hum is still there if i connect something to the input. I´ve feed some frequencies with a signal generator, and it is a little curious, the input signal seems to have more noise than the output. The hum is still there, but the music is rather good, if i can judge it on 30 year old blaupunkt car speaker chassis...