On Wednesday, November 14, 2018 at 10:23:52 AM UTC-5, wrote:
I have two Tascam DR-05 recorders and they both exhibit the same
phenomenon: when they are recording complete silence, there are faint
irregular ticking noises on the left channel.

This occurs when using an external circuit which disconnects the
internal mics, but the circuit only needs to be plugged in, not
connected to anything, for it to happen. If there is any sound on the
channel, the noise immediately stops, but re-starts about one second
after complete silence returns.


try connecting an audio signal generator do create say a 1 kHz sine tone.

slowly drop the level.
at some level the clicks will start.

observe the tone during the clicks for clues. Does the tone change in anyway due to the clicks?

Also with the external input connected to nothing, do the clicks change depending on if the external input is open vs shorted or terminated?

These recorders often apply a few volts of DC power to the input to power mics.

Put a scope on the input line and see if the spikes are actually present on the input line. Or connect the input to another audio input that you can listen to , do the spikes come OUT the audio input?

If you apply a small DC signal to the input through a current limiting resistor , will that stop the spikes? Try both polarities?

Is there a schematic available?

mark

also, the wave file posted shows clicks in both L and R, is it bot or just L?

Also the clicks in the wav file are alternating polarity, up then down then up etc. might mean something to you

mark