Hi. Most modern audio amplifier ICs utilise a floating system for the audio output. eg TDA8944. ie there is no common return. Blew one up trying to connect a 3 wire headphone. Does anyone know if there is a way (other than a couple of 1:1 audio transformers) to connect a common grounded output device? ie earphones or headphones. TIA

 

One way would be to remove the common connection between each of the headphone speakers, and connect each separately to the outputs.

 

Presumably you are using a series resistor to limit the power to the headphones?
Try putting the series resistors in the common return: one from the sleeve of the jack to the -ve of each amplifier. That produces a -(L+R) signal on the sleeve terminal, and you should still get the stereo.

 

The output could have a DC voltage on it with respect to ground, if the amplifier is powered from a single supply. In that case, use a coupling capacitor; there will be a big turn-on thump, but the attenuator resistors should reduce that.
https://diyaudioheaven.wordpress.com/headphones/headphone-attenuation-adapter/
It might be easier to just provide a dedicated headphone amplifier. Example:
http://diyaudioprojects.blogspot.com/2007/08/grado-ra1-headphone-amplifier.html

 

Further thoughts on post #3. . .
If your series resistors are the same as the headphone impedance, the junction of headphone and series resistor is at 0V, and the two 0V points could therefore be joined to make the common ground terminal with no loss of stereo separation.
Obviously, the headphones are not entirely resistive, so there would possibly be some slight loss of stereo separation at high frequency, unless you neutralise the headphone inductance with a parallel RC circuit, but headphones aren't usually very inductive, so it might not matter.

Alternatively, to make it perfectly balanced, you could connect two pairs of headphones .. . . . his and hers perhaps?
Then all you need is a headset with attached microphone so you could talk to each other.. . . .

 

Or, use 2 separate Amplifiers with a much higher Power-Supply-Voltage.
.
.
.

 

The simple approach will work but it will be less efficient. Presuming the amplifier uses a single supply, possibly 12 volts. So connect the common line that is tied to both earphones to the amplifier supply common, NOT the amplifier output. Then use a suitable capacitor to couple the "+" output of each channel to the appropriate earphone. Leave the other amplifier output connection open. It will not be as loud, but how much power do earphones need?? The added advantage is that the "sleeve" terminal of the stereo output jack can be at ground with no problem.
A bonus is that the "-" outputs of each amplifier can be used to feed a second stereo headphone jack, also with the sleeve grounded. But it will also need the two capacitors.

 

You could use one half of the amplifier. You will need to add capacitors.

 

Thanks guys. I'll give the capacitive isolation a whirl. Regards

 

Before you do - your headphones will probably be 32Ω and rated at about 0.1W. Think how much power will be dissipated during that switch-on thump. Maybe as much as 2.5W for a TDA8944. I know it's only brief but will it damage the drivers? either thermally or due to excusrion limits?