The FTL Sound Adapter was supplied with some PC versions of Dungeon Master.
jpx72 has analyzed the adapter in order to build his own. This page contains the technical information you need if you want to build your own adapter.
[Supplied by Paul Stevens]
[Supplied by jpx72]
C1: Capacitor 4.7nF +/- 10% (Marking: 472K)
R1: Resistor 25,5 KOhms, tolerance 1%
RN1: Resistor Network 4610X-R2R-104. 104 means Resistance R = 10 x 10^4 = 100000 Omhs. Schematic: