Hardware connections to headphone jack

[w9ran]

I have a question about using external devices connected to the 3.5mm headphone jack that I haven't found answered elsewhere.

Initially I used a powered speaker (which has it's own battery) plugged into the headphone jack. Worked just fine.

Since I want to have speaker audio in my project, I next went to one of the cheap little PAM8403 stereo amplifier boards mounted in the same enclosure and powered from the same +5V power supply that provides power to the Teensy and Audio Shield. This means there is a common ground connection between the 5V return and the Teensy GND pin, but per the caution silkscreened on the board, I did not connect the headphone ground (HPVGND) to the Teensy GND. I'm pleased that feeding the audio from the L or R pins on the headphone jack to this audio amplifier seems to work just fine (i.e. with only the signal pin(s) connected and no connection the the headphone jack ground).

Since it works I can't see anything wrong with this approach but would appreciate any comments. I could provide AC coupling between the two grounds (i.e. with a capacitor between HPVGND to GND) but I don't think it will make any difference. The fact that this works as it does is a plus for my project.

Bob

 

[PaulStoffregen]

Yes, common ground and not using the DC offset "virtual ground" of the headphone jack is perfectly fine, if you're happy with the sound quality.

For others who may find this thread later by searching, sometimes using the common ground works great, other times it results in strange noises. It really depends on the details of what other non-audio stuff you're powering, and especially any external connections to grounded equipment (like your PC through the USB cable).

This sort of connection is probably also relying on AC blocking capacitors in that amp board. Again, if it works, no worries. Just know this advice isn't 100% universal to all amp boards. Amps that are DC coupled would need capacitors to block the DC offset of the headphone signals.