Many thanks for your comments again Nigel.
I built and tested the unit yesterday, circuit as in my prior post but without the base resistor on the 2N4126 (PNP). This works fantastically with my Sony Experia Neo -> Sony NEX-5. I’ve achieved >5m reliably so I’m really happy with that. However it doesn’t work with my HTC Desire HD, this needs investigation but I believe this is due to HTC hardware not reproducing the audio file as well as the Sony.
Back to your comment Nigel, you are of course totally correct. My single current limiting resistor should be replaced with two 13Ohm resistors, one in series with each LED.
If I understand correctly you are also saying that due to the LEDs being pulsed I can safely exceed the current limit of the LEDs? So maybe I could use less than 13Ohm current limiting resistor. However at the moment I’m very happy with the light intensity of this unit.
I’ll post photos of my build and latest circuit diagram later today.
EDIT - Just measured the output of my audio jack on the HTC Desire HD, i'm getting Vpeak-to-peak of 0.560V between the L & R channels. This isn't quite enough to turn my first stage transistors on and so is probbaly why this circuit isn't working. The Sony must have higher voltage output. Oh and before anyone says it, i've checked and the audio output is working normal. My headphones with the phone work fine.
Seems like a very low voltage for the audio output though can anyone shed any light on this? Can anyone recomend some small signal transistors or other pre-amp stage? Thanks