My setup is as following:
I use a Y-Cable for splitting an audio signal to two devices (boxes and earphones). The headphones have quite big speakers so they act also like a microphone – feeding back the signal to the boxes which then amplify the crackling signal.
Initially it sounded pretty easy to me, but it got more complicated than I thought. Additionally, I'm still not sure if there is a problem with the linearity of components up to 20kHz.
The idea was to use a Schottky diode in between the two devices, so none of them could back-feed the other. Unluckily the signal is only 250mV, so even a germanium Schottky diode with voltage drop of 0.2V is not so optimal.
Are there other solutions which are ideally passive or semi-passive by using a small part of the signal for their independent power supply? (Multiplying voltage until its common 5V and using only a few nA)
Ideally kind of a low signal diode: If the same principle works for big signals, there should be a way making it work also for small signals.
Or maybe a second reverse diode which will lift the "signal voltage drop" back up? For this I thought a logic connection that has a diode attached, but the logic chips need their own power supply.
What could be a simple circuit?
Other searches:
What I found using electronics between audiojack, was pretty sparse: One was the use of Schottky diodes (for bigger signals), the other was this (but not so related): http://www.instructables.com/id/How-to-Harvest-Power-from-an-Audio-Jack/all/?lang=de
Best Answer
Two opamps as non-amplifing buffers. Basically a powered headphone splitter. Can be powered by a pair of AAA batteries or smaller. Once buffered the signal won't back feed.
Basically
Retail ones, apparently now have usb cables for power as well, so no more batteries dying at the wrong time.
