If this doesn't bother you, or you have an external DAC, great. I like to see a circuit perform as well as it can be made to; for me the problem is that this noise limits the s/n ratio of the whole system, at it's worst it is 27dB above the thermal noise floor. The fact that it only affects one channel led me to believe that the issue was one of board layout, and close inspection seems to confirm this:
As you can see, the inverting input node, which is usually the node most sensitive to interference (dotted yellow) of the left channel is much smaller than the Rch one. Further, the right channel trace is directly behind the end of the neon display, where much energy is radiated. It also changes layers in this area (between the pink dots), possibly increasing susceptibility. It is genrally good design practice to minimise the length of the inverting input node to minimise stray capacitances, and to reduce the scope for parasitic oscillation and instability. In this case the noise is probably being coupled through the RCH inverting node, and to a lesser extent through the trace from the DAC. To try and reduce this I made a quick and dirty shield from aluminium foil, insulated with mylar tape. I fitted this between the back of the neon display and the PCB, then soldered a wire to the incoming power ground. Here is a noise floor measurement done after the mod, of the worst case situation (brighteness max -1) encountered before the mod: as you you can see, the noise is virtually gone. This mod may cause problems with the wifi reception though (because there is now a shield over most of the front). Also don't do this unless you're happy voiding the warranty, maybe destroying your SB, and also probably violating some FCC rules ;) Anyway, something can and should be done to fix this problem in the next hardware revision. +-------------------------------------------------------------------+ |Filename: modded-brightness-max--1.jpg | |Download: http://forums.slimdevices.com/attachment.php?attachmentid=3317| +-------------------------------------------------------------------+ -- *Isaac* ------------------------------------------------------------------------ *Isaac*'s Profile: http://forums.slimdevices.com/member.php?userid=13183 View this thread: http://forums.slimdevices.com/showthread.php?t=32045 _______________________________________________ audiophiles mailing list [email protected] http://lists.slimdevices.com/lists/listinfo/audiophiles
