Help: Parallel port - FTL sound adapter [SOLVED!]

[jpx72]

Hello DM fans!
I was wondering if anyone here can help me figure out how to make a homebrew connector for the parallel port of my old computer to reproduce the original FTL interface/"sound adapter":

I was searching on the web for some connection schematics but without luck. Anyone can help me with that? Maybe someone with the original adapter can retrace the connections on that thing.
I am playing DM on an original 286 machine and the internal speaker has too low volume...
Thanks for any answers!

[Gambit37]

Wow, that's super oldschool! Welcome to the forums

I do have one of these adapters but to be honest I don't really want to take it apart. I'd like to help you but don't really want to potentially mess up the adapter. If I can get a second one of these then I'll certainly take a look for you.

[jpx72]

Yeah oldschool power! ;D


Thanks for the answer, I really have no idea if there are any components inisde of that adapter or the audio output is simply connected directly to one of the pins of the parallel port. So it needs to be opened to find out. But don't worry and don't open your adapter, I believe the schematic is out there...

[Gambit37]

Wayne Holder (Dungeon Master producer) designed the adapter and his background was originally electronics, so I wouldn't be surprised if there's some custom gubbins inside it. (He also worked out how to play digitized sound on the original Atari ST, something it couldn't easily do.) Smart chap, Wayne.

[jpx72]

If I understood this right, I need to build a "digital-to-analog converter" (DAC) on parallel port.
I have found one schematic which looks interesting, but I am totally unsure if this is the thing I was searching for:

I guess I'll try to build it and see.

[Paul Stevens]

You seem to have it right.

The adapter comes apart easily....no screws, just
snaps together.

Pictures are at:
http://dianneandpaul.net/CSBwin/Adapter-Back.JPG
and also 'Adapter-Front'

It is a 2-sided board so you can see all the traces
if you are careful. Pin 1 simply passes through.
Pin 2 goes to the resistor ladder. etc.

[jpx72]

Wow! Those are amazing photos! Thank you very much for taking your adapter apart!
I will try to build it and post my results here. Thanks again, I knew somebody on this awesome forum will be able to help me!

[jpx72]

Hi again! Took me a while (been too busy) but I have made me an adapter according to your photos. But I have trouble detecting it by the game. During the startup where you have to choose the audio hardware, the option [*]FTL ADAPTER is not available for selection. There must be some pin(s) in the parallel port which triggers this option but I don't know which. Would you be so kind to trace/measure with any multimeter a couple of pins, that are hidden behind the female audio jack?
I need to check all these pins: 10,11,12,13,16,17,25 - all from the parallel port.
Here are your pictures side by side with numbered pins:
http://img521.imageshack.us/img521/5416/adapterp.jpg
Also, is there something written on the resistor-ladder? I would like to know to identify this component exactly.
Thank you.

[Phoenix]

Interesting device. It's hard to see where all the traces are going when they go under the resister network. and the 3.5mm jack. I came across this Discover the hidden 8 bit Sound card in your PC a while back, I'm not sure how relevent it will be in this case though.

[jpx72]

Ok I sat on the pictures once again and I think I have it:
http://img585.imageshack.us/img585/6353/scheb.png
I will try to build it (only the audio part) and see if it works. (BTW pin 25 should be GND so connect audio jack accordingly, I don't know which of the pins on the schematical representation of a Jack is ground )

[jpx72]

Ok so I built it according to the scheme above and....SUCCESS!!!
Go on, try it yourself!!!

[Gambit37]

Very nice, well done. That's got to be the epitome of retro-gaming dedication!

[jpx72]

Ok so thanks to Paul Stevens I was able to exactly recreate the schematics for the FTL Adapter!

Here is the updated redrawn schematic with exact components:
http://img27.imageshack.us/img27/6043/sche2.png

So the resistor ladder is different than I have built, I have used 1K/2K resistors, but the original is using 100K/200K => R/2R ladder type:

Higher value resistor ladder will probably eliminate the background sound distortion I keep hearing from my adapter.

[terkio]

Nice work. I am impressed, you sure know how to use a soldering iron.

Using a 1K/2K ladder versus the original 100K/200K looks wrong to me. This is too much load on the DB25 outputs, the D/A convertion will be not so good.
Presumably, the DB25 outputs are TTL, a too high impedance for driving a 1K/2K ladder.

[jpx72]

Thank you for the technical explanation on the disadvantage of using small resistors on the output!

The schematic is now a part of the Dungeon Master Encyclopaedia at http://dmweb.free.fr/?q=node/1514 !