As audio technology progresses and older technology becomes more undesirable, the Alesis ADAT Black-Face can be found for below $100. With 8 channels of 16-bit, 48kHz audio, this unit has the capability of playing back and recording laser shows with sychronized audio effortlessly and without a computer.
There has been at least one good ground-breaking guide published (see modification manual) that steps you through opening the unit and performing DC modification on the circuits to allow the ILDA signals to pass. However, as built, the ADAT is incapable of recording and playing back the full 10V differential of the X and Y channels - clipping at approximately 9.7V. Many laserists in the past have simply 'lived with' this shortcoming, but it can be removed easily by adding a few resistors.
First, the input and output circuits. Only one channel is shown in the following schematics, but due to the nice PCB layout mirroring of the other channels, it is sufficient to allow modification of all channels.
Input:
Output:
Ilda Connectors:
Modification on the input board: Beyond the DC coupling modification described in the link above, the R5 resistor of channels 1 and 2 (X and Y) can be changed to 47k. (In my case 46k was the resistors measured value)
Modification on the output board: This board comes DC coupled, but you need to compensate for the gain change performed in the last step. For channels 1 and 2, place 267k parallel with R1 and 98k parallel with R20. Now, For this project I decided to make the RGBI channels single ended instead of differential to be compatible with both differential projectors and single ended projectors that expect 0-5V modulation input. This should make it more universally compatible with existing projectors with and without differential inputs. For this mod, place 7.74k parallel with R20 on channels 3,4,5 and 6. I reached 7.74k using specially selected 1k and 6.7k resistors in series. For safety, I recommend adding a voltage clamping circuit to this output so that your modulation voltages will not exceed 5V.
Finally, when wiring up the output, if you did the single ended modification, ground the RGBI- outputs, or if you did not, connect these to the 3,4,5,6- differential outputs.
Result:
Input Board:
Output Board:
ILDA Connectors:
Now She's a true laser ADAT!
The interlock passthrough switch can be closed in order to close the interlock loop when only the ADAT is connected to the DAC, otherwise it should be open. X and Y polarity switches are optional, but nice to have.