Audio click generated by Power Saver mode
Recently designed an audio system I call a DTI or Dual Transceiver Interface. The device mixes audio outputs from two back mounted transceivers and delivers it to the user via a shoulder mounted speaker mic and ear piece. Push button volume and transmitter selection is via a remotely mounted control module slightly larger than a 9V battery. Works great except for an annoying click that is generated by some Cobra radios when they enter power saver mode. Normally very faint it becomes a nuisance when amped by the DTI
An oscilloscope trace indicates it's generated by some sort of diode/capacitor arrangement in the radios circuit. It occurs right in the optimum audio range and intensive attempts at filtering proved untenable until I used a single 27uH inductor to ground. This completely eliminated the effect with minimal if any degradation of the audio signal. Works great on a bread board with leaded inductors. Put it together on an SMD platform and it won't work. The SMD inductor will not do the job the leaded inductor does.
To prove it, I actually installed the same leaded inductor inside the radios on the audio output. One end on the audio jack pin out the other to ground (electrically the identical place in the circuit just in the radio not the DTI). Click eliminated. Replace the same inductor with a 27uH SMD inductor and it wont work.
The only thing I can think of is the core material. Could the ferrite core of the SMD device be the culprit here? I know this is generalizing but isn't a 27uH inductor a 27uH inductor regardless of it being a wire wound leaded unit or a multi layered SMD? Shouldn't I get the same result from the both inductors?
Last edited by Copper Dog; 5th April 2013 at 10:32 PM.