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Thread: dj crossfader/mixer

  1. #1
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    Sep 2015
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    Default dj crossfader/mixer

    i use mostly analog oscillators and things like that going into an ILDA converter at end of chain and then into my laser projector.

    i end up with several XY pairs of different animations i like to transition between, i'm wondering if theres a particular DJ style crossfader/mixer thing that might be good to use with my setup.

    I'm wondering if this DJ mixer would need to be dc coupled or anything like that, or if any standard dj mixer would be cool to try.

    i use a modular synthesizer and im comparing whether i should get a handful of modules to do this functionality or if purchasing a ready made product might be less expensive and do the same thing.

    also wondering if a DB25 A/B switcher box could be modded into a crossfader?

  2. #2
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    I'd reach out to DZ; He'll have some valuable input as the Z-5 has an internal crossfader for fading between the console and an external signal.

    You *MIGHT* be able to get away with using a cheap 2-ch (stereo) DJ mixer for x/y signals if you are doing something like abstracts which center around your scan origin (cartesian 0,0). If your signals have a significant DC component to them (abstracts with offsets, point-based animations, straight lines, etc.), your mixer needs DC coupling.

    In theory, you could modify a DB25 A/B box to be a crossfader...but it's likely going to be much more work than its probably worth to turn it into a true crossfader.
    Last edited by CountFunkula; 11-21-2017 at 11:17.

  3. #3
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    what do you mean by "true" crossfader? i think if it gives me some kind of transition instead of a hard click, i could be into it if its not too expensive or time consuming. i have friends who could mod one for me.

    also, i would be adding the offsets after the dj mixer, the dj mixer i think would be used more at the beginning, choosing what gets sent into my synth, from there i offset and do other stuff and then go into a proper voltage to ilda converter.

    but you raise a good point. what if the animations i start with at the beginning happen to have an offset or slow lfo somewhere in them, that will not translate. can certain DJ mixers be modded i wonder, or if i should just build it all from scratch.

    ill hit up dz for sure

  4. #4
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    Quote Originally Posted by maxcady View Post
    what do you mean by "true" crossfader? i think if it gives me some kind of transition instead of a hard click
    Exactly that. It gives you a "fade" instead of a "cut". Those A/B boxes are only an enclosure, some db-25 connectors, and a big mechanical multi-pole rotary switch.
    To turn it into a crossfader, you'd have to gut it and either replace the rotary switch with active electronics (essentially a whole bunch of vcas) or multi-gang potentiometer(s) for a sort-of-hacky passive solution.
    Last edited by CountFunkula; 11-21-2017 at 11:19.

  5. #5
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    thanks. do you think the CLICK from the switcher box (un-modified) would be harmful to the galvos? shoudl i only switch it when its not being sent to the projector? or can i click around whenever? i guess each one might be different and ill have to find out myself.

  6. #6
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    I use one of these at home for switching various DACs between a single projector.
    Click image for larger version. 

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    I can't definitively say whether or not switching while scanning hurts the galvos, but I personally have not had any issues. That being said, I try to avoid doing it. You'll see some trash'n'crash action while the switch contacts are going through the break/make cycle if you switch while scanning.

  7. #7
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    Hey guys! On the Z5 I have a crossfade circuit that switches XY from an internal signal to an external signal. It's similar to morphing in software. I have a completely different circuit to handle crossfade for RGB. Both circuit designs are configured to only handle 2 separate sets of input signals.

    If you have more than 2 sets of input signals I would recommend using VCA's to handle this. For example, if you have four XY signal sources then you would just need four 2 channel VCA's and just mix the output of all four VCA outputs together. Only the XY pair with the appropriate CV will get thru to the scan head.

    In the Z5c the color crossfade is handled by six single channel VCA's. I went with single channel VCA's because I have some ideas for future color mod capabilities.

    The Z5 uses a couple op-amps and a custom designed slide potentiometer to get the job done for XY.

    If you have any issues finding something already available I don't mind building up a custom product. It just may be a while before I can get to it as I have a couple project in line at the moment.

    This video shows an example of XY crossfade as well as RGB crossfade:

    Last edited by DZ; 11-21-2017 at 13:26.

  8. #8
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    If you are into the eurorack format, there are more than a handful of modules that can cross fade, Intellijel has a few (Planar, uFade) and Doepfer has a few as well.

    -Sal

  9. #9
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    Quote Originally Posted by discothefunkyhippo View Post
    If you are into the eurorack format, there are more than a handful of modules that can cross fade, Intellijel has a few (Planar, uFade) and Doepfer has a few as well.

    -Sal
    thanks sal, but those arent in stereo, and they just do one.. i was into the dj mixers becasue a lot of them have several channels, and they are all stereo channels. so you grab one slider and you are controlling the XY immediately. i already do this with my eurorack system and all brands of crossfading etc, and its a big giant mess. i'm looking to build a streamlined performance system thats fun to travel with and play in the dark intuitively. i'd even be down to mod a dj mixer if possible, they look so awesome for this task.

    if i stick with euro, i may go with a synthwerks quad slider for all laser XY pairs in one quad module, or perhaps several synthwerks modules, one for each laser XY as well as RGB:

    https://www.modulargrid.net/e/synthwerks-sp-4dp

    Click image for larger version. 

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    i still feel like i'm missing a piece of the puzzle, does anyone see a clever idea somewhere in here?

  10. #10
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    If you take two dual 10k linear sliders, wire them backward to each other, take the wipers through voltage followers (to minimize noise from the sliders), take the output of the voltage followers to x&y summing amps - when the sliders are both up you'll get full output from the normally wired slider & zero from the reverse wired slider - as you move the sliders down the normal slider signal is reduced and the reverse signal is increased. Faders intended for audio aren't linear - laser fades should be linear.
    "There are painters who transform the sun into a yellow spot, but there are others who, with the help of their art and their intelligence, transform a yellow spot into the sun." Pablo Picasso

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