-Just another example of why I love the folks at Slim Devices.- Agreed! I've said it before, but I'll say it again, the guys at Slim Devices are refreshingly open, it's great stuff.
For a techy aside to the problem, it's very common for electronics to demodulate RF signals. You cannot hear the RF (even as an 'audiophile' I wouldn't argue that!) but what you are hearing is the effect of the electronics turning into an RF detector (i.e. radio receiver). It only really happens in junction devices, so bipolar transistors are worse in this respect than FET's, which have no actual rectifying (i.e. diode) junctions. For that reason FET-input amps are much better in RF environments than bipolar parts. Heavily degenerated bipolar parts perform better (in this respect) too. With AM transmissions you can actually demodulate the audio content (or data content) quite readily, which is why AM CB radios, or amateur radio / PMR transmissions are more prone to obvious audio breakthrough. Because the method for decoding FM transmissions is different, you often just get the effect of the carrier affecting the item, since the data or audio content is harder to demodulate. Low level (low current) stages and high impedance areas of a circuit are most prone to this problem (e.g. phono stages, high impedance op-amp inputs etc.), and the problen can manifest itself as direct effects, or the effect of the stage being driven into non-linearity by the RF. What I suspect, based on experience (but haven't analysed in detail yet) was happening here is the headphone amp cable was acting as a reasonable antenna and the RF was getting back into the headphone amp chip, which then gives it a direct path back to the input stage (via the chip's feedback loop). Good to see it fixed though and I'm happy to be of assistance! Andy. References for those that fancy a bit of light reading: - http://tinyurl.com/9wte8 stage rfi rectification sensitivity&la=en Page 10.39 on of this one... http://tinyurl.com/dhjvc stage rfi rectification sensitivity&la=en -- Andrew L. Weekes _______________________________________________ Discuss mailing list [email protected] http://lists.slimdevices.com/lists/listinfo/discuss
