ILDA ADAT Blackface Modification Guide - Expanded

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:
http://hacylon.case.edu/laser/ADAT/Input.png


Output:
http://hacylon.case.edu/laser/ADAT/Output.png

Ilda Connectors:
http://hacylon.case.edu/laser/ADAT/Connectors.png


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:
http://hacylon.case.edu/laser/ADAT/ADAT_Input.jpg

Output Board:
http://hacylon.case.edu/laser/ADAT/ADAT_Output.jpg

ILDA Connectors:
http://hacylon.case.edu/laser/ADAT/ADAT_Back.jpg

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.

Hey, why not use just simple divider inside XY input jacks, as Pango suggests ?

On the output side - balanced output featuring low output resistance of 600 Ohm led me to use 2kOhm pots for analog size/phase control for X and Y separately.

Piotr.K

It seemed that a modification of the existing differential circuit was more elegant and could be standardized. With the given solution, 10V in = 10V out. Not so with the voltage divider. Also, by not using 2k output pots, the 510 ohm output impedance is maintained, so distortion will be minimized over cable runs. Not so with an output pot.

I highly recommend this modification esp for the RGB pallet. I had issues with dim modulation and not getting full brightness out of ADAT's. This was due to driver boards for lasers that couldn't use diff modulation since the - is often tied to PS -. Once I completed this mod, the tires on cars appeared brighter and also peoples hair. ANything that was showing to dim or barely now is visible!

So excited, now just hope to address some of the pallet issues with a CC board from DZ.

Thanks Drlava!

john

Dave Here,
Old Lasermedia guy.
I'm setting up a show here in NC , will be purchasing your flexmods ( Nice piece ) and am using Alesis Adat's for editing, recording and playback.
Just now putting the pieces together.
I have done the DC mods according to Pangolin on the ADAT, but am confused and like to understand what I am doing and why.
They reccomend the Elco plug pins for output to provide the proper voltages for driving things and being a "what you put in you get out" type of recorder device: Why do they not use the same plug pins for signals in? Instead use the phone jacks.??
They do not explain it, I thought you might shed some light on this.
Do the Elco inputs not provide sustained DC throughput?
Thanks
David Cross

Once you do the DC blocking cap removal mods both the 1/4" jacks and the ELCOs provide DC coupled outputs. The caps were there to prevent loud popping from the application of DC to sensitive audio inputs. If you do not have the desired DC coupling in laser, your images will swim around the center and not be stable.

Steve

Quote:

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Originally Posted by nitestix

Dave Here,
Old Lasermedia guy.
I'm setting up a show here in NC , will be purchasing your flexmods ( Nice piece ) and am using Alesis Adat's for editing, recording and playback.

---

Hi Dave, nice to (forum) meet you. It's great to have vets here.

Quote:

---

They reccomend the Elco plug pins for output to provide the proper voltages for driving things and being a "what you put in you get out" type of recorder device: Why do they not use the same plug pins for signals in? Instead use the phone jacks.??

---

It doesn't matter very much whether you use the Elco plug or the single ended jacks for input, as long as you scale your signals down to prevent clipping. With the phone jacks, there is one less connection to worry about, since they are single ended so that's my guess as to why they suggested those. However you have to be very aware of clipping in the signals if you use the jacks, where my mod detailed above will not clip with any proper ILDA input signal.

All of this is post DC modification of the two ADAT boards as per Pangolin.
I understand removing the " floating to zero" audio concept and creating a pure DAC input/output recording system.

Question:
The ADAT will record what you put into it " voltage " , Record it and play it out to you.
input should match output, record to playback ( Using the same input/output banks )

The Phone jacks are specked +/- 2.5 V for mikes and low level inputs and outputs.

The Elco plug is specked +/- 10V for higher levels and lowered noise.

The standard scanners are +/- 10V and colors ( LD Drivers ) are 0-5V

So , if the Elco plug has the voltage span to match all the desired driver outputs and the input range to match the generated signal inputs and needed output voltages:

WHY does pangolin want you to use the phone plugs for input with resistors in line to reduce the input voltage instead of simply using the ELCO for input and output.??
What goes in , comes out !

Hope that helps.

David

That's a question that probably only they can answer. But the balanced inputs are actually +/- 9.67V max, not 10V so there will be some clipping on them if you don't do the above mod, or turn the gain down a bit.

Pangos 1K is a CYA move to lower the voltage by making a crude voltage divider, and or to limit current into a sensitive load. Older Galvo amps or a pcaom usually had a low input impedance as on most of them the first thing the signal sees is a 2K potentiometer or smaller. ILDA spec is 600 ohm impedance, just like audio.

Steve