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Thread: CYGN-B

  1. #481
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    Quote Originally Posted by Greg View Post
    Right. I did a round of that when I built the color mod signal to ILDA board. I'm wondering if single-ended DAC output to differential for ILDA is a common enough thing that someone here has offered a module that would save me wiring a bunch more op amps for each ILDA channel.
    Yes, I know the hassle of having to convert from single-to-double-ended with my old single-ended circuits.

    But here is the circuit I commonly use. The input to the first op-amp's 5K resistor-to-Gnd is from another TL084 opamp. The + and - voltages of 9v is from a battery operated version of the circuit. I normally use + & - 12v or 15v. Also, I am not showing ALL of the related op-amp circuitry in this photo.

    The XY Master potentiometer is a dual log slide pot.

    Click image for larger version. 

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    I've not ever seen a simple, plug'n play ILDA converter but that means little since I only cared about or needed to implement differential output XY pairs on my legacy laser circuits in 2017 when I bought a cheap ILDA RGB projector.
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  2. #482
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    Have you noticed a difference between using single ended signals as-is or adding this differential stage?
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  3. #483
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    Default single vs double ended

    for over 12 or more years I only used single ended line level outputs to scan driver amp inputs that were singled ended outputs to the scanner coils with never a problem., using line level, single ended xy cables, using xlr connectors w/dual conductor, shield cables, 25ft, 50ft long to scan drive amps with NEVER a noise problem, in every venue situation imaginable.

    To be sure, differentially driven lines offer better noise immunity but are they a must....8 ball says....only if you are a purist.
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  4. #484
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    lasermaster1977: Yes, the two IC2 stages are exactly what I used, except the 10Ks are 22Ks, the rails are +-15, and I don't have the 5K. I don't see it's purpose. However, there's lots I don't know.

    Quote Originally Posted by TheHermit View Post
    So, each audio sample is either a music track, X/Y galvo signal, or RGB levels + the associated control signals like size, position, etc... which are being decoded on the fly and applied to the output, simultaneously across 16 samples?
    Sort of. Every audio sample is an audio sample. When the .wav file loads, the total number of samples is known so fixed length arrays can be created for all those other desired signals. Then, for every audio sample, you know exactly which data line sample goes with it.


    Yeah, the 0-3.2V p-p issue is the same on the BELA platform. I solved this problem when taking the DOGN signals from the DigiMAX DAC using the attached bit of literature. It didn't work until I used trimpots for all the resistors and nudged the window open. I'll attempt to solve the reverse problem using the other attached circuit.
    Attached Thumbnails Attached Thumbnails UnipolarToBipolarVoltageFromDAC.png  

    circuit.png  


  5. #485
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    Ah, it was the earlier mention of HankLoydRight's ILDA conversion amp PCB that got my attention.

  6. #486
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    Quote Originally Posted by TheHermit View Post
    Thank you for asking, James. Thought you had written me off as a waste of time.
    TBH, I haven't tried your single ended amps, James. I don't want to run my galvos with a single-ended offset.
    But, I'm using some of those components to prototype the breadboard for the PCB. I'm using the MD100 DC convertor to increase the power rails on the TL084 op amps from 0 & +5VDC to -/+9VDC to provide more gain and offset.
    But whenever I add the smoothing caps to the MD100, it's output collapses and both overheat while under no load. Is this behavior only due to exceeding the capacitance of the load, which the datasheet says is a no-no? Do I simply need to add the caps after connecting the rest of the circuit?
    The datasheet also recommends 5 uF across +5Vin & Gnd, instead of your 10uF. Was that additional capacitance just for good measure?

    Thank you for your interest and assistance.
    I don't typically write anyone off. It usually seems to work the other way.

    You can use single ended signals into a differential input simply by grounding either the inverting or non-inverting input that you are not applying the signal to.

    For short cable runs, you won't notice any difference. Keep in mind the signal still swings between negative and positive, so there is no offset.

    It's exactly the same difference as single ended RCA interconnects vs. differential XLR connectors in audio. The whole idea of differential audio is that any noise picked up in the cable is canceled at the amp end because that noise is equal but out of phase between the two signal wires. Using an op-amp circuit to convert from single ended to differential will certainly work, but it is not without any downside. It adds cost, complexity, a potential point of failure and noise and distortion of its own.

    As far as the DC/DC converter goes, it sounds like you have a DC path from output voltage to ground somewhere. With no load at all it should not be passing any current, certainly not enough to get hot.

    James.
    Last edited by james; 07-10-2022 at 09:54.
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  7. #487
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    The correction amp kits that you got from me do two things in one op-amp stage. There is a
    variable negative voltage regulator that makes a stable offset null voltage that gets summed at the input of each op-amp to eliminate the positive DC offset from the DAC chip and the same op-amp stage has variable gain to raise the voltage up to drive the scanners and color mod inputs.
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  8. #488
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    It's an adjustable regulator to compensate for a range of offset voltages for different kinds of sound devices.

    The DC/DC converter isolates the input ground from the output. But on my pcb I tie them together so there is one common ground from the usb power all the way through to the output ground on the ilda connector.

    The DC/DC converter turns usb ground and +5V into ground and +9V and -9V to provide differential voltage to the op-amps.
    Last edited by james; 07-11-2022 at 13:34.
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  9. #489
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    Have you considered building one of the kits you got from me and setting it up as it was designed to be used?

    I'm pretty reliable for tech support. If I don't answer a forum post right away, it's because I didn't see it. In which case, just email me. I'm easy to find.
    Creator of LaserBoy!
    LaserBoy is free and runs in Windows, MacOS and Linux (including Raspberry Pi!).
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    All software has a learning curve usually proportional to its capabilities and unique features. Pointing with a mouse is in no way easier than tapping a key.

  10. #490
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    Quote Originally Posted by TheHermit View Post
    Am I correct in concluding that the differential inputs on the scan amps are only the 1st stage to eliminate line noise, leaving a single clean bipolar signal that is passed on to the power amps, regardless of whether the incoming line signal is differential or single ended?
    Yes, exactly.

    Likewise, any decent ILDA splitter will have a differential receiver as the first stage. This yields a single-ended output, which is usually fed into a gain and offset adjust amp before going to the output stage, where the signal must be re-converted back to differential before being sent on to the projector. All in the name of noise reduction.

    In fairness, the output of a differential receiver can be bipolar (centered on zero) or biased to be entirely positive (and centered on some positive voltage based on the position offset). But yeah, bipolar is more typical.

    Adam

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