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  1. AFex54

    A means of closing a JFET switch with a postive voltage?

    right from the start I was deluded by the MFOS 1V per octave keyboard when I proposed using the sample and hold, something obviously wrong is that the noise toaster is only 18mV per octave! there no way in hell holding a stable CV with a basic analog sampling circuit, a few μV of drift will send...
  2. AFex54

    A means of closing a JFET switch with a postive voltage?

    damn it, I forgot about power... well I dont think It'll be possible to do this, there will be 10 14-pin packages for all those pots! they will need a PCB and I barely fit in that board for S&H above (I didnt mention that the space on the right side is taken up by the speaker) Also above when...
  3. AFex54

    A means of closing a JFET switch with a postive voltage?

    I think the only way this would fit is if I could get CMOS switches in single, transistor-type packages to mount on the pots themselves . Do these exist? the op amp for S&H im a bit worried about, there is good chance a suitable one isnt available. rail to rail, very high impedence, very low...
  4. AFex54

    A means of closing a JFET switch with a postive voltage?

    Ive finally got some pictures of the actual synth First things first: There are 2 Noise Toasters !!! :eek: The overview : the grey knobs are the keyboard frequency pots, 2 knobs for a black key, 1 for a white key, the black keys are 'polyphonic' i.e they output 2 seperate CV for either NT...
  5. AFex54

    A means of closing a JFET switch with a postive voltage?

    sorry but the main problem is Ive already built the keyboard, and there isnt enough room inside the synth enclosure for all them components, the sample and hold may have accuracy issues but it doesnt require any modification of the keyboard and its tiny. so the problems im having are: -I need a...
  6. AFex54

    A means of closing a JFET switch with a postive voltage?

    Im not sure what you mean by that but I havent consider any other method than a sample and hold circuit, I originally seen the sample and hold in the MFOS CV keyboard schematic so i assumed that was the only way, my keyboard is a lot different to MFOS keyboard so its very possible there is an...
  7. AFex54

    A means of closing a JFET switch with a postive voltage?

    yes, thats it. its monophonic. BTW the VCO either doesnt oscillate or produces infrasonic frequencies below about 1V so getting absolute zero isnt vital
  8. AFex54

    A means of closing a JFET switch with a postive voltage?

    and ive managed to buy the wrong op amp again, the input bias current of this LM6144 is charging the sampling cap like it did with LM324 except 10 times worse . I dont even understand the datasheets so whatever i think I may know about a given component is probably wrong...
  9. AFex54

    A means of closing a JFET switch with a postive voltage?

    it was designed to be a low cost, Lo-Fi noise maker that a beginner would build themselves. it is by no means a proper synth, and it can run off 9V battery for hours, like 10mA consumption. you probably wont find many answers in this thread ,as CDRIVE pointed out earlier Ive unneccesarily...
  10. AFex54

    A means of closing a JFET switch with a postive voltage?

    its not a modular synth, its a MFOS Noise Toaster, I didnt design it. Im just adding trying to add a keyboard so it can be pre-tuned.
  11. AFex54

    A means of closing a JFET switch with a postive voltage?

    sure, its function is to accomodate the 'release' of a note, a staple of musical synthesizers is the ability to fade out the volume of a note once you let go of a key.... a.k.a release. its produces a much more fluid and organic sound, which is very important. so I am seperately controlling 2...
  12. AFex54

    A means of closing a JFET switch with a postive voltage?

    the 'reversing the diodes' thing became moot when I added the edit at the end of post #30 PN on the gate now are 1N4148s, I will get Schottkys for the CV
  13. AFex54

    A means of closing a JFET switch with a postive voltage?

    I built the keyboard myself , the keys were taken from an old keyboard but they are just pieces of plastic that go over the switches (which are leaf switches made out of very thin sheet of metal) to vastly vastly improve the look and feel of the switches, the original diagram with all the pot...
  14. AFex54

    A means of closing a JFET switch with a postive voltage?

    so the simple answer is even more diodes: I really hope we can bury the hatchet on this keyboard now
  15. AFex54

    A means of closing a JFET switch with a postive voltage?

    haha the pots will not be wired like that, If you can ignore pots and focus on red in relation to switches you will extract all the info you need from that diagram, In hindsight I should have edited your correctly wired keyboard diagram, sorry about the confusion! ''I updated the diagram with...
  16. AFex54

    A means of closing a JFET switch with a postive voltage?

    there is also a diode on every keyboard switch before the potentiometer to give a separate 'gate' signal when you press the key(which is just 9V, its a special trigger for the synth) I updated the diagram with the 'gate' signal for extra clarity :): this would be perfect for controlling the...
  17. AFex54

    A means of closing a JFET switch with a postive voltage?

    yes they are wired in parallel, which is so obvious now :confused: im surprised I didnt notice this either, however I notice this statement: ''physically the keys are at the bottom, the pots are mounted above the keys and the noisetoaster circuit boards are squeezed in just above the pots.''...
  18. AFex54

    A means of closing a JFET switch with a postive voltage?

    Yup thats it, and unfortunately the keyboard is wired like this, however this wiring reflects the physical layout of the pots and key switches in the enclosure, wiring any differently would conflict with the synths compact design. physically the keys are at the bottom, the pots are mounted...
  19. AFex54

    A means of closing a JFET switch with a postive voltage?

    nothing will cause it to fall to zero, it would maintain the last voltage until the next input from the keyboard takes its place. all the keys are tuned to different voltages, but even pressing the same key twice would 'renew' the voltage on the cap that may have began to droop. to clarify for...
  20. AFex54

    Simple way for LED to indicate at 2 different brightness's

    very clever, the transistors for each LED are actually part of the gate system for the sequencer which has now made me realise illuminating the LEDs during the ''step active,gate off'' stage is not as simple as thought. I will just forget about this trivial feature , it doesnt effect the...
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