I bought a Laserdisc player in august 2001. It didn't have all the outputs I wanted, so I decided to build an interface for AC3 digital sound.
It is not complicated, just a matter on finding the right spot to tap the audio. The AC3 stream is modulated in the right sound channel, so the trick is to build a circuite that doesn't interfere with the audio path in the laserdisc player (= high impedance) and that has a low output resistance. This circuite is usually called an emitter follower, or an impedance converter.
Below is a couple of links I found during my research. I used a breadboard and a modified variant of ac3cir2.gif, from DIY Dolby Digital (AC-3) Modification Page, see links and pics below. Transistors BC546B and BC556B, or MPSA06 and MPSA56 (or equivalent) can be used instead of the UN2112 and 2SA1037K transistors. Since the circuite is a converter and not an amplifier it doesn't really matter which transistors to be used as long as you put the NPN and PNP's in the right place.
Pictures of my "upgrade"
