Tuesday, 15 January 2013

Negistrem/Negistron

Simple, but still seems like one of those super problematic circuits :) This one goes published as unverified for Madferret, who was after a unverified tremolo layout. So. Here you go. Let us know how it works out :)


22 comments:

  1. Thanks dude! After a bit of reading on DIY Stompboxes it seems like a J113 works well with it. I'm interested to see if I can get them s one going.

    ReplyDelete
  2. i really need to try this since i still havent got my frobnicator working correctly haha, thanks as always miro!

    ReplyDelete
    Replies
    1. So... Limiting the current didn't fix your frobnicator?
      +m

      Delete
    2. it helped, i do get signal through it but a turn of 0.00000001" of the trimmer for the current makes it go either bypass or a really sloppy signal with the effect, it has it's sweetspot but doesn't work as intended really. but it's not distorting like before.
      im out of ideas for it now. maybe i did something wrong, +9 > trimmer > board.
      tried with a battery to, same issue.
      i could record a demo vid to show you it's behaviour.

      Delete
    3. Well. Then you'll need a bigger trimmer :)
      +m

      Delete
    4. oh shit, might so be, you said you settled on 1.8k so i went with a 2k trimmer since i didnt have any 5k ones, maybe i should try a 10 instead then... after work!

      Delete
  3. No luck with this so far, I've got a signal but no tremolo. After reading a few other articles about this it looks like there's a problem with choosing the correct transistors. I'm using a metal can 2n2222a, which seems to be recommended, and a 2n5457 for the fet, I've also tried a 5458 and 5459 but nothing seems to get it going.

    One question that shouldn't really affect it though, did you mean leave sw3 unconnected as you've got sw6 marked down on the layout? Also did you number the lugs:

    1 - 4
    2 - 5
    3 - 6

    ReplyDelete
    Replies
    1. I even tried a J201, which everyone seems to think is the worst choice, just to see if it helps. I've also read that higher voltages help so I swapped out the battery for a fresh one which was reading 9.6v.

      Delete
    2. Numbering convention as you said, 2 and 5 are grounded - pin 6 unconnected. Compare to the schematic. Other position, 1µ and 10n to ground, and the other - 10n and 1µ lifted, 47n to ground.

      To tell the truth i'm not convinced if it was a good idea to made those switchable.. :)
      +m

      Delete
    3. Yeah, you're probably right about the switch. However, seeing as it's in I might as well make it work :)

      I think maybe a different JFETs may help, any suggestions? There's no where round here that sells a J113 in a TO-92 case so I may have to order one.

      Delete
    4. If you get the sound through from the FET, what voltage do you read at its gate? I mean - that should be getting a pulse that makes the tremolo effect - so if you have a pulsing voltage at the gate - then it's the JFET. If not - then the problem is around the BJT.

      Or so i figured :)
      +m

      Delete
    5. Good call, so here's the thing; I'm getting a reading of 3.74v - constant. So there's no oscillation. However, following the negistor circuit found here:

      http://www.diystompboxes.com/smfforum/index.php?topic=79654.0

      I've managed to successfully build an oscillating negistor, so the 2n2222a I've got is good and as far as I can tell the negistor part of the layout matches the negistor circuit I've used. I'm confused, this thing should be working. I've also socketed the limiting resistor so I can try a few different values but it's not made a difference.

      Delete
    6. Now try to attach the negistor to JFET gate and see what happens..
      +m

      Delete
    7. Gah, I'm getting a lot of freaky noises but nothing I'd consider to be a tremolo. I'm going to go at it after I've had some sleep, I still think this should be working as per your layout.

      Delete
    8. Haha. I knew this was going to be a tough one to crack!
      +m

      Delete
    9. One of the downsides of having the ability to work from home is that non working circuits can sit there staring at you mockingly, a constant reminder of your failure to MAKE THE DAMN THING F****ING WORK!!!! Having made a trip to RS Components to pickup some more 2n2222a's and having got plenty of oscillating tones but no tremolo I think the time is coming to introduce Mr Negistrem to my friend Mr Claw Hammer.

      Back to dirt pedals for a couple of days before I give this another go. Plus I've ordered some J113's and they should be here by then :)

      Delete
    10. Don't take it too personally. If that schematic is meant to work, i have all the faith that you are the one who can do it.
      +m

      Delete
  4. Wow, I've got the J113's and I still can't get this thing going. When I breadboard it all I'm getting is the oscillator sound but no guitar signal. I must be making some sort of basic error and it's probably staring me right in the face. So far I've learnt:

    2n2222a's are a definite - Metal Can's/TO-18 gave me the best results

    9v MINIMUM - Daisy chaining a couple of half dead PP3's gave me good oscillations so 12v is probably the ball park

    Trimpots aren't needed - They were just there to bump up the part count for a competition so feel free to either use 1M or 470k as Nordine suggests

    J201's are not recommended as they aren't designed to be used for fast switching like this

    I still have a lot to learn about debugging ;)

    ReplyDelete
    Replies
    1. On the positive side - you'll be learning a lot by debuggin' that bugger :)
      +m

      Delete