Adding momentary control to a latching circuit

Discussion in 'The Projects Forum' started by Idle Mind, Jan 21, 2007.

  1. Idle Mind

    Thread Starter New Member

    Jan 21, 2007
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    Hi, I'm a bit of an electronics noob so I really appreciate any help I can get on this.

    I've got a guitar distortion pedal that uses a momentary footswitch to toggle a latching circuit in order to turn the distortion on/off.
    I need to be able to switch this pedal on and off via a mono jack socket that will be shorted when I want the distortion activated. I really need this switching to be momentary, preferably I'd still like the original pedals footswitch to work with the latching circuit if the momentary switching jack isn't in use, but this isn't essential.
    I don't completely understand the latching circuitry so hopefully someone can point me in the right direction.
    There is a schematic of the pedal located here:
    http://www.godiksennet.com/images/sch/DS1PG2.jpg

    Thank you :)
     
  2. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    Hi,

    Q4 & Q5 make a flip-flop that control the conduction of three FET's. When Q6 & Q7 are on, the signal path gores through the distortion circuitry. When the flip-flop is in the other state, Q8 is on and makes a conduction path around the distortion.

    The question is how comfortable are you in changing the circuitry? Have you got a soldering iron and access to parts in order to make alterations to the printed circuit board?
     
  3. Ron H

    AAC Fanatic!

    Apr 14, 2005
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    I don't see any reason you couldn't simply wire the new switch in parallel with the footswitch. Since both are momentary, they won't interfere with each other.
     
  4. Idle Mind

    Thread Starter New Member

    Jan 21, 2007
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    Putting the new switch in parallel still just activates the latching circuit to toggle the distortion on/off, whereas I need the actual circuit to be momentary.

    To beenthere:
    That seems to make sense, I have a soldering iron and am reasonably confident with replacing parts on a pcb etc. I'm just not that good at understanding the circuitry so need stuff explaining well haha. I don't have many parts lying around but could get hold of anything I would need.

    Thanks a lot for the replies
     
  5. beenthere

    Retired Moderator

    Apr 20, 2004
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    Hi,

    Lemme see if I can come up with a coherent set of directions to make your circuit momentary. Be a bit patient. pls.
     
  6. Idle Mind

    Thread Starter New Member

    Jan 21, 2007
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    Thanks, I appreciate the help :)
     
  7. fanie

    Active Member

    Jan 20, 2007
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    Hi all,

    Idle Mind, a normal light switch is a latching switch, ie if you switch it on it stays on (untill you switch it off), The doorbell button is a momentary switch, you have to press it to make contact. If you let go it disconnects.
    Electronic circuits can do the same. If a latching gets an input it switch on and stays on until it gets another input that would switch it off. The momentary would switch on if it gets an input but will switch off when the input goes off.

    If I understand you correctly, you want to use a jack plug to act as a tempory switch ?... just put a small switch on the back of the mono plug ? If I misundersood you have to explain again.
     
  8. Idle Mind

    Thread Starter New Member

    Jan 21, 2007
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    Thats right yeah, basically I have a big footcontroller that does all my other effect switching from one unit with MIDI etc and I want to use one of its mono switching jacks to control this distortion pedal in a momentary way, so the distortion will only be on while the footcontroller is shorting the tip and sleeve of that mono jack.
     
  9. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    Hi,

    This is kind of a no going back modification to the existing circuit. It changes the Q4 - Q5 circuit from a flip-flop to a pair of saturated switches. Normally, Q4 will be on (in saturation) and will have Q8 in conduction, so the signal will go out undistorted. Pressing the button will turn off Q4 and turn on Q5, enabling Q6 & 7 to pass the signal through the distortion circuit.

    I can't give good instructions on how to do this, though. I can't make out the foil pattern to tell you how to cut traces and where to put in the two new resistors. Removing R26 & 27 is a start. Also C18 & 19. Put a jumper in place of C18 to make the button control Q4's conduction. After that, you'll need to figure out where and how to botch in the 1K resistors. An Xacto knife and a meter can help.

    Unless you feel pretty confident, you might not want to commit to the change. With some solder wick, you should be able to get the components out with no damage. This will let you replace them if necessary, but it will get messy.
     
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