Little Dot MK III - noisy / oscillation?

[audio_tony]

I recently purchased a 2nd hand Little Dot MK III headphone amp, with the intention of using it both as a pre amp and heaphone amp.

However, when I connect it to my power amp, my wife (and my son) say they can hear a high pitched tone (oscillation?) yet putting my scope on the output doesn't seem to show much of interest (IMHO anyway!).

Here is a pic taken off the scope (apologies for the poor quality).

Timebase is: 5mS

Input sensitivity is set to: 5mV per division

This is a feed straight from the output of the preamp sockets (no connection to power amp here) straight into the scope via RCA leads.

Is this just noise in the trace, or some very low level oscillation perhaps?

 

[audio_tony]

That trace is a bit misleading.

With all power to the Little Dot switched off (but still plugged in) the trace remains!

Therefore it seems to be some kind of earth loop.

However this doesn't explain the oscillation my wife and son say they can hear.