NEOS PC AOM to QM2000 Optimumized

Discussion in 'QM2000 series of products' started by Andy_Faulkner, Aug 19, 2005.

  1. Andy_Faulkner

    Andy_Faulkner Member

    We just got some more equipment and included in this is a

    NEOS PC AOM marked as a 64040-75-.1-BCH-16M / 3162

    Could you please advise what are the best connections to use for connection to a QM2000 for optimum performance and compatibility?

    We have at present:

    4,7,10,13,15,18,21,24, TTL's connected to Pangolin Pin 3 (blanking)
    1,3,6,9,12,14,17,20, 23 -V connected to ground & also ground to Pangolin Pin 25

    2,5,16 connected to Pangolin Pin 7
    8,11,22 connected to Pangolin Pin 6
    19 connected to Pangolin Pin 8
    25 connected to Pangolin Pin 5

    Using this configuration I feel we are not using the full benefits of the Neos and would welcome your advice.

    I am thinking we should connect 6 of the 8 Neos channels directly to the 6 colour signals of pangolin + / - pins (Balanced line) for best results and if we do what should we do with channels 7,8.

    Hope you can clarify.
     
  2. Pangolin

    Pangolin Staff Member

    Hi Andy,

    I am not familiar with the NEOS model you have presented, but generally you always do the same thing with PCAOM. Generally you "strap" channels that are similar, to the same QM2000 color output.

    Normally you may have two or three reds (671nm and 647nm and 641nm). Visually, there is no difference between these, so it does not make sense to use a separate QM2000 output channel on each of these, so you tie the signal inputs of these together and drive them from a single QM2000 output.

    Normally you may also have several greens that look the same, such as 530nm and 520nm and maybe even 514nm. You might consider strapping all of these together.

    The real gain is on the blue, since there is a tremendous visible difference between 488nm, and 476nm and 457nm. For these colors, you generally use separate QM2000 output channels.

    So in other words you might do something like this:

    * 671, 647 and 641nm Inputs on a PCAOM all tied together at the PCAOM driver, and connected to a single QM2000 output.

    * 530, 520 and 514nm Inputs on a PCAOM all tied together at the PCAOM driver, and connected to a single QM20000 output.

    * 501 may be tied to an individual QM2000 output if desired. Alternatively, if your laser has a YELLOW line, this might be a better use of a QM2000 output channel.

    * 488nm tied to an individual QM2000 output.

    * 476nm tied to an individual QM2000 output.

    * 457nm tied to an individual QM2000 output.

    One thing to note is that while the NEOS and QM2000 both have balanced signals for color, we still recommend that you tie the negative color outputs to ground.

    If memory serves, all of this is covered in the help file. Have you looked there to see? I believe we cover different connection scenarios along with different number of channels, and the benefits of each technique...

    Bill
     
  3. Laser Dude

    Laser Dude Member

    Bill, I have a question here.

    You just mentioned to ground the negative side on the color outputs even though they are balanced. Why do you recommend forcing it to an unbalanced system?

    Will this improve the output level?

    Thanks,
    Eric
     
  4. Pangolin

    Pangolin Staff Member

    Hi Eric,

    It is a good question. The sad fact is that most people in the industry simply can not *properly* "handle" differential signals.

    We have done our best to work with suppliers in the industry, including NEOS and Cambridge Technology. For those with whom we have worked, their products are perfectly suited to the industry. Unfortunately, these are not the only suppliers who are selling into this industry and, despite the fact that we openly say that we will help anyone from any company to improve their products for our industry, essentially at no cost to them, not everyone has sought our help.

    As a result, you have some companies who's PCAOM driver will flat-out malfunction if you feed a negative voltage (of any kind, from any leg for any reason) into them. And you have others who are just not all that bright... The result is that equipment gets damaged -- either our QM2000 (as a result of putting voltages "back into" the QM2000), or other's equipment that can not handle negative voltages.

    There is another factor which is that the output of our QM2000 represents what is called a Gyrator. This is a special circuit which behaves like a transformer. If you only hook up one leg (like unfortunately many not-too-bright people do), all of the voltage will go out the other leg. This leads to "phone calls" with people complaining that they aren't getting the right color signals. They aren't measuring it correctly either... but they aren't getting the right signals.

    As a result, two things have happened. First, around 2 years ago, we changed the design of the QM2000 such that the negative COLOR outputs are already grounded for you. In the past, people clearly demonstrated that they could not handle it, and now there is simply no choice. We did it for them because... they just can't handle it. As a result, guess what. No more phone calls, no more emails, no more equipment being damaged. Second, for those with older QM2000s, we recommend that they ground the negative outputs so that nothing will be damaged. Since it is hard to tell if people have an older or newer QM2000, we simply tell everyone to ground the negative color outputs. Given the Gyrator output, what this does is force all signal out of the + color output. In other words, nominally (if the palette is trained to do so and all "brightness" related controls are set to 100%) you will get a 0 to +5V signal out of the color outputs. Now, even if people use a meter and connect only the + output, they will see what they expect.

    Also there is a common misconception about balanced and un-balanced signals. I have written about this before, but for completeness I will include it here as well.

    The reason you use a differential signal is so that any interference that is picked up along BOTH WIRES can be subtracted AT THE RECEIVING END, thereby restoring the original signal being transmitted. What this means is that the ENTIRE ONUS of balanced signal restoration is on the RECEIVER and NOT the transmitter. "Grounding" the negative output at the TRANSMIT side is a perfectly legitimate use of differential transmission because, interference will be picked up, along the line, equally on both wires, and removed by the receiver. The technical term for this technique is "pseudo differential" and it is used in most industrial systems. Note that this same technique is also used by many pro-sumer audio products that use a differential line.

    Basically, we decided that what's good enough for everyone else is certainly good enough for Pangolin. Again, after the mod and when people follow our recommendations -- no phone calls, no emails, no complaints. And no more damaged equipment.

    Internally we jokingly refer to this change as the "Jack Nicholson mod". I invite you to watch the movie "A few good men" staring Jack Nicholson, to discover why we call it that.

    Bill

    PS: Note that the entire discussion above relates only to color signals, and not to XY signals. The XY signals emanating from the QM2000 are still fully balanced differential signals. People don't seem to blow them up... On the other hand, scanner drivers require a + and - power supply, so there is never any problem with them receiving a signal that goes below ground. Plus, there are far fewer scanner and driver manufacturers out there when compared to diode driver suppliers and PCAOM suppliers.
     

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