How do I install a headphone jack with volume control into a DIY system that is going from raw audio source to 5 watt amp to speakers? Is it safe to put it in after the amp or will that damage the headphones? If it isn't and it needs to be wired in before the amp, what part/s do I need to have headphone volume control that'll also control the speakers' volume (I want one knob for both)?
Why wouldn't you split the line level signal going into the 5W speaker amp into a separate headphone amp? Then you have independent control. If you wanted to, you could use the insertion of a headphone into the jack to mute the speakers.
I don't want independent control though. I want only 1 volume pot to control both headphone jack and speakers. Yes, I plan on using the headphone to cancel the speakers but I don't want to damage headphones (or my eardrums) by wiring the jack in after the amp. Very simply put, I want to take raw sound from an HDMI to RCA adapter and amplify it for speakers but with a volume controlled headphone jack and I want that volume control to control the speakers too like a regular stereo does.
The line level input won't drive headphones so the headphone jack has to wire to the output of the amp. It might be more power than you need depending on the impedance of the headphones. Some headphone jacks will automatically cut off the speakers when you plug in the phones.
If the amp doesn't have a built in volume control then you would usually wire the volume control in between the input signal and the amp input. You want a stereo potentiometer with the same value as the input impedance of the amp.
Ok. To prevent overpowering the headphones in that scenario, what if I used a 5 post normally closed headphone jack with L/R + speaker wires connected then a resistor of some sort (sorry, my terminology is limited in this dept) on the headphone ground with the speakers' ground bypassing said resistor? Would that work?