1. Win a Broadcaster or one of 3 Teles! The annual Supporting Member Giveaway is on. To enter Click Here. To see all the prizes and full details Click Here. To view the thread about the giveaway Click Here.

Adding blinking indicator light to tremolo footswitch

Discussion in 'Shock Brother's DIY Amps' started by mattmayhem, Oct 11, 2020.

  1. mattmayhem

    mattmayhem TDPRI Member

    Age:
    33
    Posts:
    42
    Joined:
    Jan 14, 2017
    Location:
    Portland, OR
    TLDR: Given a standard vintage fender tremolo footswitch, what circuitry would be needed to add an LED that blinks with the tempo of the tremolo? Anyone willing to help me out or draw something up?

    Full Story: I use a super compact pedal board with all mini pedals so about a year ago I built a reverb/trem footswitch. It has LED indicators for on/off and works with all my amps that have the traditional vintage fender footswitch set up. Recently however, I read that my new magnatone's footswitch would flash the tremolo indicator light in time with the trem tempo, and sure enough, the footswitch blinks the trem tempo with all my amps! So I opened it up to see if i could understand what's going on in there, but the PCB with surface mount components is totally opaque to me... Looks like there are a couple footswitches out there that do this (magnatone and swart at least). Anyone have any idea how they achieve this? Any info, links, drawings, etc would be super helpful. Thanks!
     
  2. sds1

    sds1 Tele-Afflicted

    Age:
    44
    Posts:
    1,621
    Joined:
    May 4, 2017
    Location:
    Orlando, FL, USA
  3. Phrygian77

    Phrygian77 Friend of Leo's Gold Supporter

    Posts:
    2,469
    Joined:
    Apr 30, 2016
    Location:
    Crawfordville, FL

    I was thinking in the direction of an LED biased LFO, but that makes much more sense. Coincidentally, I just started looking into LND150s, specifically for tremolo circuits.
     
  4. sds1

    sds1 Tele-Afflicted

    Age:
    44
    Posts:
    1,621
    Joined:
    May 4, 2017
    Location:
    Orlando, FL, USA
    Cool, yeah I used LND150 there and also in a subsequent harmonic tremolo circuit project (using 6X LND150). Worked well in either case. I'm not sure if the Rd/Rs in that oscillator circuit above are good or not. That Rs at 100R looks a little fishy. Maybe ignore what I did and work the load lines for yourself. :)
     
    tubegeek likes this.
  5. mattmayhem

    mattmayhem TDPRI Member

    Age:
    33
    Posts:
    42
    Joined:
    Jan 14, 2017
    Location:
    Portland, OR

    Thanks so much! Super helpful! So now that I having done a little more research, I think I have an idea of where to start breadboarding at least. So, it seem that I can use the voltage on the tip of the footswitch cable as Vin. My one question is, what's the purpose of R29 to ground?
     

    Attached Files:

    sds1 likes this.
  6. sds1

    sds1 Tele-Afflicted

    Age:
    44
    Posts:
    1,621
    Joined:
    May 4, 2017
    Location:
    Orlando, FL, USA
    Hmm does the magnatone switch have an external power source like a battery or wall wart? For my circuit, you have the AC signal on the oscillator and then you have a constant voltage source for the LED. For a typical Fender type pedal you'll not have the power supply for the LED (indicated +5V in my schematic). Not sure how this can work...

    R28 and R29 form a voltage divider. You have to divide down the oscillator signal so that the transistor sees around 0.7VDC at the base (pin 2) and switches on. Once the voltage is in the ballpark you'll be able to tweak the final values as they will affect the blinking behavior a bit (basically longer or shorter LED off time between cycles).
     
  7. mattmayhem

    mattmayhem TDPRI Member

    Age:
    33
    Posts:
    42
    Joined:
    Jan 14, 2017
    Location:
    Portland, OR
    Gotcha, that's kinda what i figured from the little reading I've done. The magnatone switch has a 9v battery and a 9v plug option. I personally plug my home made switch into a 9v power supply. I have a 2N2222 transistor that I can use, but any tips on how to determine the appropriate values for R28 and R29 to get my voltage down?
     
  8. Paul-T

    Paul-T Tele-Holic

    Posts:
    511
    Joined:
    Nov 23, 2018
    Location:
    London
    The LND harmonic trem sounds very interesting - I searched for a thread on it, did you post one, or do you have any info/schematics pleeeaaase??
     
    sds1 likes this.
  9. sds1

    sds1 Tele-Afflicted

    Age:
    44
    Posts:
    1,621
    Joined:
    May 4, 2017
    Location:
    Orlando, FL, USA
    I didn't do a thread on that one no. It was just a standalone PCB for a clone of the Fender 6G12A (5x triode) harmonic tremolo circuit. The board works with tubes or LND150 and so literally no deviations at all from the OG circuit. Oh lookie and I added the blinkie LED too. :)

    [​IMG]
     
    Paul-T likes this.
  10. tubegeek

    tubegeek Friend of Leo's

    Age:
    60
    Posts:
    3,882
    Joined:
    Jan 31, 2020
    Location:
    Brooklyn, NY
    I think - to pull the base of the transistor to ground.

    EDIT - Never mind, already answered.
     
  11. tubegeek

    tubegeek Friend of Leo's

    Age:
    60
    Posts:
    3,882
    Joined:
    Jan 31, 2020
    Location:
    Brooklyn, NY
    The LND150 version uses the exact same circuit as the Fender harmonic trem? What's the power supply requirement?

    Interesting!
     
  12. sds1

    sds1 Tele-Afflicted

    Age:
    44
    Posts:
    1,621
    Joined:
    May 4, 2017
    Location:
    Orlando, FL, USA
    Ahh OK a battery, so that's the route you would take here as well to power the LED. I think I would have used a scope to determine the peak voltage of the oscillation. If you don't have a scope, a DMM may or may not work since the value is oscillating. But you then just figure out the ratio of the voltage divider to get you in the ballpark and tweak from there. The ballpark I refer to is somewhere > 0.7V because you want the transistor to stay on for more than just a blip.

    If you're unsure about voltage dividers, you can learn+cheat here:
    https://ohmslawcalculator.com/voltage-divider-calculator
     
  13. mattmayhem

    mattmayhem TDPRI Member

    Age:
    33
    Posts:
    42
    Joined:
    Jan 14, 2017
    Location:
    Portland, OR

    Thanks again for the info. That voltage divider calculator is a great tool!

    So I used my DMM and got ~2V peak. Going to the breadboard I tried to use the voltage divider set up with a 1M and a ~700K (voltage divider calculator estimated ~0.8V at the base) and the LED blinks perfectly, but the speed of the tremolo increases.

    I went back and tried to trace continuity on the magnatone board now that I have an idea of what's going on and got the circuit below (values measured in circuit). Any idea what the cap and zener diode are doing?

    Just to try it out, I used the schematic below that I found when researching transistors as switches and used the magnatone values (1M + 960K = ~2M) for Rb, ignoring the cap and zener, and things seem to work well with accurate blinking and no speed change ¯\_(ツ)_/¯. Any obvious issues dropping the voltage with just the resistor instead of the voltage divider?
     

    Attached Files:

    sds1 likes this.
  14. mattmayhem

    mattmayhem TDPRI Member

    Age:
    33
    Posts:
    42
    Joined:
    Jan 14, 2017
    Location:
    Portland, OR
    Just in case anyone stumbles upon this later, here's what I did that seems to be working with all 8 of my amps from the Fender Custom Vibrolux and Vibro-Champ to the Magnatone Panoramic Stereo and Gretsch 6161 (all bias modulated trem). Feel free to critique, add comments or improvements, etc... Thanks for the help!
     

    Attached Files:

    Last edited: Oct 13, 2020
    sds1 likes this.
  15. sds1

    sds1 Tele-Afflicted

    Age:
    44
    Posts:
    1,621
    Joined:
    May 4, 2017
    Location:
    Orlando, FL, USA
    If it works it works. I guess I didn't need that voltage divider. Not sure why.

    Also regarding the zener and stuff, not sure on that either. But I think one enhancement to a circuit like this would be to turn the sine wave into a triangle wave, and so I wonder if those component have anything to do with that.
     
    mattmayhem likes this.
IMPORTANT: Treat everyone here with respect, no matter how difficult!
No sex, drug, political, religion or hate discussion permitted here.