Fix for background noise as printed in Blitz 7 by Edwin Blink:
I and probably everybody else is annoyed be the background noise the SAM has. Especially when you listened to a nice piece of music at a volume when the music ends instead of silence noises follows.
After a while I got used to it (well... accepted it) and didn't bother anymore until I decided to replace my speaker with a headphone to stop my enviroment getting annoyed and to enjoy stereo sounds more. You ever tried it ? Glorious noise orchestra isn't it (Ahem!). Then I decided to do something about it.
The main cause is generated by the ASIC inside the SAM this one does a lot of electronic switching at a high speed which causes small power drops on the 5 volt power line. The SAMs power supply can't handle this problem and even has problems with larger power drops also.
Due to its design the SAMs power supply uses two 5 Volt voltage regulators of 1 Amp. Each output has a resistor and then are connected together. The resistors are used to prevent short circuiting the outputs. This method causes slow reaction to voltage drops.
To reduce noise in a easy and cheap way, all you have have to do is cut the component L3 from the PCB board and solder an 1N4148 diode at its place.
L3 is located below the SAA1099 sound chipand just above the disk drive connector. L3 has a cyan-ish collor also on the left side you can see a crystal component (small metal case) and at the right a resistor.
When soldering the diode make sure the cathode marked by a coloured ring, is upwards (pointing to the SAA sound chip) if you soldered it in the wrong direction no harm is done but you won't here any SAA sound.
The diode gives the SAA soundchips output filter its own little power supply. Which is not drained by the SAMs other hardware as the diode blocks it.
I also use a different power supply and this reduces noise also.
The combination of both reduces the noise a lot. There's still some noise left. However I only hear it at a loud volumes.
I now use a headphone on my SAM, and enjoy the SAMs sounds even more than before.