When using the JBL Flip 3 (or JBL Flip 2 or JBL Flip 4) as a permanent speaker for music or Text-to-speech announcements, connected through the AUX input and powered consantly it still goes into an automatic standby after some time of silence and it's a major problem in this use case. Depending on how long the silence was and how loud the new input audio is, it may take between 3 to 30 seconds in my experience before it resumes playing. For lack of a better place I'm posting here the information I have on solving this.
- Obviously emitting the audio signal at maximum volume from the computer and lowering the volume at the speaker reduces the time for it to wake up. Downsides: less volume control for the computer (especially problematic if it's remotely controlled), still won't work if the audio played is relatively quiet or short (such as a home-automation announcement) so not a definitive solution.
- Mixing unaudible waveforms into the audio output, either low frequency (< 20Hz) or high (> 15kHz). Downsides: ugly as a solution but works. Extra power use.
- Possibly the best solution is the Bluetooth + Volume Down long press key combination that seems to switch the audio processing mode on or off in the speaker. There are some other combinations for reset functions that are posted on different forums but don't seem to do much. Bluetooth + Volume Down long press doesn't reset the speaker, just toggles some mode and this seems to actually work. No downsides. The only mention of this was found in https://www.ifixit.com/Answers/View/405479/Why+playing+via+AUX+cut%27s+on+quiet+passages+in+the+songs-movies in an answer by radu_cloud.
- Hacking the speaker's PCB. The schematics are available and very clear in the Service Manuals (https://elektrotanya.com/jbl_flip_3_sm.pdf/download.html for Flip 3) and it seems that simply grounding the gate/base of the Q12 MOSFET may be the solution and may also improve audio quality. This is based on answer by Victor Titov @deepsoic in https://www.ifixit.com/Answers/View/405479/Why+playing+via+AUX+cut%27s+on+quiet+passages+in+the+songs-movies which is for JBL Flip 4, but based on the Flip 3 schematics this part of the PCB is very similar and Q12 (and Q10/Q11) are directly on the AUX IN path close to the input. In fact the piece of schematic in that ifixit answer is either from the Flip 3 schematics or is identical between Flip 3 and 4 down to the component identifiers. Downsides: may affect some of the hardcoded sounds.