Voltage Control - WTPA1

edited May 2012 in WTPA1 Mods
Just wanted to share with you a mod I just successfully completed:

Each of the 6 WTPA buttons now has a front panel input to allow a gate signal or similar to trigger the buttons, thus a VC sequencer can be used to record, play, apply effects and generally make the thing schitz out.

Once I've found a picture host I'm happy with, I'll post the schematic.

Essentially it is based on a 40106 hex inverter, with inputs protected by bridging diodes and current limiting resistors, output of inverter performs a 'pull up' for the push buttons, and takes the chip inputs low as required.



  • Great work! Sounds like you covered your bases really well.
    Please do post that schematic when you get a chance -- you can always email it to me and I'll post it.
  • edited May 2012
    Awesome-o - fro sho! Sounds almost like you used a
    Sympleseq from Stacy @ Hex inverter. I've got a
    kit for a 1x8 here with gate/reset and
  • Sure thing TB, in your inbox.
  • From /tilted/:


    For simplicity, I've just shown 1/6. In my WTPA I used all 6 inverters, one for each pushbutton.
    With an open connection to the input, the inverter is pulled low by R1.
    in this case, or with a low signal input, the inverter output goes high and simply acts as a pull-up (via R4) for the pushbutton.
    With a high signal input, the inverter output goes low and pulls down the pushbutton line.
    If the input signal goes beyond the 0v-5v supply rails, D1 and D2 reigns it back in to protect the inverter chip, which in turn should protect the PIC in the WTPA.
    R2 and R3 prevent excessive loading of the input signal, particularly during excursions beyond the power rails, and keep the 220k resistor manufacturers in business.


    Thanks! You could get away with R2 and R3 being lower (47k is probably fine) and it's an AVR not a PIC, but those are nitpicks.
    This is a textbook-quality example of this kind of circuit and I would have designed it the same way.
    Nice work and thanks again!
  • Ace I'm doing this ASAP.

    All about the euro these days.

    Just need to get my firmware upgraded...
  • guys what diodes should i use for this?
  • 1N4148 or 1N914 should do, there's no current involved.
  • edited December 2012
    got nearly everything here for that circuit... only thing missing is the 220k or 47k resistors for R2, R3. i do have left 33k, 330k, 470k, 487k, 510k. can i take some of those, too? which one would be best? for the diodes i have 1N4148 or 1N4936... which should i prefer? is it right to connect the +5V to the RegVcc point on the WTPA mainboard?
  • 33k is fine
    1n4148 should do OK
    And yep, RegVcc is a 5v supply.

    Good luck!
  • edited January 2013


    i finally bought the recommended resistors and tried them all... 220k and 47k are both working fine. i chose 47k in the end. i took the 1N4148 diodes. plus i also added a hold switch for S05 (FX HOLD), so you don't have to feed two GATEs, if you just want to play with the FX.

    works brilliant! everyone with a modular system do it! it's really a totally new WTPA play experience, cause your fingers can't be as fast as a LFO... at least they shouldn't. ;D

    i also found a nice bend... i tried more and there are a lot of open solder points, but my WTPA case is already quite full and the build in effects are enough for me right now, but one spot is really cool. it let's the sample kind of stutter and repeat every second twice (kind of... don't know how to describe it better), which is also great combined with the CV option! here it is (just connect those two points with each other):


    hadn't found that before: http://www.narrat1ve.com/forum/comments.php?DiscussionID=19&page=1#Comment_891
    ... so after all still more i need to try

  • Great work! You've clearly put in a lot of hours modding that WTPA; thanks for documenting it for everybody.
  • edited January 2013
    thanx. :O)

    (another thing... the metal plate on the left is not connected yet. i was planning to make a body contact bend, but it doesn't work directly. at least the screws are holding the GATE-input-PCB now. :D ... but in another project i'm working on a square wave LFO of which the speed can be controlled by a body contact. just have to get that into higher frequencies and connect it to the WTPA sync in and it might be a nice feature. i'll post an update, when/if i got it working.)
  • That's a good idea. You could try using that plate as the capacitor in a relaxation oscillator (using an op amp or your favorite gate) and a big resistor (2.2M, say) and you'd get something in the range of WTPA sample frequencies. You could use a smaller resistor too (you'd probably have better ckt behavior) and divide down the output of the oscillator with a flip flop.
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