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BEginner question about "Adding bits" to mess with a digital instrument bank

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  • BEginner question about "Adding bits" to mess with a digital instrument bank

    I just got my hands on a really wierd bare bones cheap keyboard, but it has around 100 digital interface instruments, and around the same about on rhythm's.

    Ive seen other keyboards in the past the add a patch bay and some sircuitry to "add corrupting bits". It seems like most of the time it jsut causes the keyboard to eventually need to be powered down and back, but you can occasionally get some rather epic crunchy instrument noises.

    Is there a basic way to ad a single bit into a logic sequence at will, or several bits? it seems like it shouldnt be a complicated circuit, Im just new at this stuff, getting past the basic pots and resistors, and learning how to make VCOs and effects modules.

    I couldnt find anything on google so help would be appreciated.


  • #2

    Make and model please? Keyboards are not generic. It also sounds like a consumer home keyboard rather than a pro instrument. Pro stuff won't have all the accompaniment stuff. They don't al use the same synthesis methods. Those Yamaha PSR series or home Casio boards, and all similar, have their programming burned into ROM, or even into custom ICs. Darn hard to break into those.

    If you can find the DAC stage, you can alter a data line to distort the output.

    I assume you have a computer. How simple would it be to add a bit or several to any of the programs?

    VCOs, VCAs, envelope filters, etc etc are all from the old analog synth world. In the typical PSR model they are not separate circuits.
    Education is what you're left with after you have forgotten what you have learned.


    • #3
      yeah the things I Was intending to ad were modules like magnetic tape head delays, photoresistor/12v motor tremolos, spring reverb tanks, things like that . The keyboard is a COMPLETE mystery. Ill do my best to get some pictures up.. as a general description, its a wild mix of hokey and... just wierd elememts., Its 5 otaves (54 key compass)., the only information on it is a model name of SK-560/
      No prand name. Its 100% a toy. that being said, it has full polyphoniics. Im pretty sure you can press every single key on tthe thing and get a tone.

      When you open it up, it has one of those "cursed" potted microchip, like what you would see on a basic un moddable kids "8 sounds keyboard toy"
      BUT the chip is then placed into breakout socket, giving extremely easy access to every single leg of the microchip.

      I was thinkthink that I could add a bit by finding out what the actual "bit voltage " is ( I assume just a square wave) . I'm just not entrirely clear on how I could just add them on or two or ten at a tme; I'm not sure how to create the control I need to ad soemthing that fest.

      Ill most more infor as IK find it, get a camera, and post some pics! cheers!


      • #4
        am I thinking in the right direction? maybe take a 555 or something similar, make an oscillator circuit, time it waaay down, then patch onto various legs of the cintroller as I load up instruments from thje bank?

        The more I look at this, the crappier it seems. I Want to punish it badly, and get something cool out of it hehe

        BTW plz dont mind my typing issues, new glasses are in hte mail and in blind as a bat! cheers!


        • #5
          Well, scope it and see what you are up against.

          I think you don't have a handle on the scale of this thing. The legs of the processor are not one function each. Data lines are bi-directional, They send and retrieve data. It might be addressing memory or creating a digital audio signal, all at the same time. Anything you do with a 555 is going to be orders of magnitude slower than the internal systems.

          Square waves? Well sorta. But more like relatively long spaces at one polarity, then short spikes to the other. 5v used to be common for digital logic, but these days 3.3v is more normal for central processors. It is all a timed and choreographed dance, not just square waves dancing along. If you lift an address line, most likely the program will instantly just stop.
          Education is what you're left with after you have forgotten what you have learned.


          • #6
            I'd just buy a multi-effects processor and be done with it.
            "Yeah, well, you know, that's just, like, your opinion, man."


            • #7
              I think this is a really exciting world - the term is 'Circuit Bending' - making something do what it was never intended to. There are some really fine and interesting sounds to be had from cheap, mundane consumer-grade keyboards. as per this demo


              • #8
                Here's a good read for you
                When I die I want to go quietly in my sleep like my grandpa did. Not kicking and screaming like the passengers in his car.


                • #9
                  Originally posted by Mick Bailey View Post
                  I think this is a really exciting world - the term is 'Circuit Bending' - making something do what it was never intended to.
                  Duh! Of course its called circuit bending. That's why it's in the circuit bending forum, dummy.

                  Applying any waveform or voltage to the main processor could damage it. A lot of the people in this game can analyse data signals and work out what's going on, but without a real insight (or clear instructions from someone else who has worked on this specific device) you're down to random chance in the absence of specific knowledge. A safer option would be to initially work with what you've got and intercept the analogue audio, which could then be more easily processed. Some additional filtering with a VCF (and be able to trigger this from a 555 LFO) and a sub-octave divider to really fatten up the signal would be pretty effective. You can then add delays, trem, etc without risking damage to the keyboard.

                  Edit: The manufacturer is Shen Kong, but I can't find a schematic or circuit block diagram. Other than this, there's a satellite power amplifier/power supply PCB located next to the LH speaker with a TEA2025 amplifier IC, so it should be straightforward to intercept the analogue audio. If you could post some pictures of the main digital board it may give some further insight in what can be done with glitching the circuit
                  Mick Bailey
                  Supporting Member
                  Last edited by Mick Bailey; 12-04-2021, 12:05 PM.


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