The "D'tar input jack test"...

Discussion in 'Shock Brother's DIY Amps' started by King Fan, Sep 19, 2020.

  1. King Fan

    King Fan Poster Extraordinaire

    Posts:
    5,591
    Joined:
    Jan 1, 2013
    Location:
    Salt Lake City
    Ever since @D'tar posted it in a help thread about the all-too-common "SAS" (silent amp syndrome) I've been impressed with the simplicity and usefulness of his test for input jack wiring on Fender amps.

    As we all know, the clever design, wire and resistor topology, possible variations in jack rotation, and especially the complexity of the 4-input (5E3 etc) version make for a lot of possible ways your signal doesn't actually make it intact from guitar to V1.

    I always try to look up and quote his original post when I see Fender-build SAS, but finally decided it'd be easier to steal the darn idea and stick it in a little Excel table I could post when needed. As usual, his way is complete, simple, correct; any mistakes here are mine.

    upload_2020-9-19_14-55-13.jpeg

    I post this here not only for general consideration but also to make sure he gets all the credit. Then I can stick this in SAS threads and let him use his infallible eagle eyes to spot the one tiny wire among hundreds that got lost on its way home.
     
    Last edited: Sep 19, 2020
    jsnwhite619, robrob, Paul-T and 11 others like this.
  2. D'tar

    D'tar Friend of Leo's

    Posts:
    3,006
    Joined:
    Jan 11, 2013
    Location:
    WNY

    Ha! Thanks @King Fan ,

    I'm not worthy! I'm sure I learned that long ago, in a galaxy....right here! I've searched for that post several times myself. As much as I love to help.... I prefer to copy/paste whenever possible. Lol

    So, thanks for wrapping it up in a nice little package for us. Downloaded image!
     
    James Knox, King Fan and Kevin Wolfe like this.
  3. Junior Little

    Junior Little Tele-Meister

    Posts:
    246
    Joined:
    Jul 26, 2018
    Location:
    Rural Illinois
    Just want to affirm the utility of this test. While assembling the input jacks in a BFDR build and running the resistance checks I kept getting the wrong answers. Removed the resistors, checked values and reassembled - twice! Still no go. So, I broke out the magnifying glass for a closer look and found that the switch on the #1 input wasn't making contact with the tip! Replaced defective input jack and viola! All's good.
    Thanks @King Fan and @D'tar for posting this very useful bit of info!
     
    D'tar and King Fan like this.
  4. King Fan

    King Fan Poster Extraordinaire

    Posts:
    5,591
    Joined:
    Jan 1, 2013
    Location:
    Salt Lake City
    You nailed it. I love Switchcraft jacks but switch / tip separation is prone to misalignment. My buddy got a new amp from a boutique builder but found it would cut in and out when he wiggled the cable. I had the same thing but it only occurred with George L plugs, which seemed to be a micrometer skinnier than Switchcraft plugs.

    Same thing can happen on output jacks of course. In addition to the resistance tests here, I wiggle the plugs, try different cables, and, like you did, pull out some magnification to confirm good contact when unplugged and good separation when plugged in.

    FWIW if this happens you can usually give either the tip or the switch prong a tweak with your needle nose -- they tend to hold position nicely once you get the separation right.
     
  5. Junior Little

    Junior Little Tele-Meister

    Posts:
    246
    Joined:
    Jul 26, 2018
    Location:
    Rural Illinois
    Unfortunately the original jacks weren't Switchcraft brand, just cheapies that came with the kit. I tried to bend it back into shape and only buggered it up more. So, I replaced it with a Switchcraft.
    I always assemble my jacks outside the chassis using an old brass grounding plate to make things a bit easier to see and to solder. Also, I build and test at every step - power supply, jacks, etc. Makes for less headaches and removes a bit of troubleshooting down the line.
    Anyway, one less problem using this simple test!
     
    King Fan likes this.
  6. D'tar

    D'tar Friend of Leo's

    Posts:
    3,006
    Joined:
    Jan 11, 2013
    Location:
    WNY
    Well.... I, for one, am a bit disappointed here. No one got to copy and paste the image into your troubleshooting thread! Oh well, theres always a next time! Lol

    Glad you were able to find your issue. Yes, some of the switchcraft clones are less than desirable to say the least
     
    Last edited: Sep 24, 2020
    Junior Little likes this.
  7. Collin D Plonker

    Collin D Plonker Tele-Afflicted

    Posts:
    1,095
    Joined:
    Jun 2, 2020
    Location:
    Delaware
    Cool
     
  8. Junior Little

    Junior Little Tele-Meister

    Posts:
    246
    Joined:
    Jul 26, 2018
    Location:
    Rural Illinois
    You know better than most here that somebody, somewhere is going to have an issue with their input jacks. And it will be because they didn't read your test procedure, and the @King Fan graphic illustration thereof, prior to firing it up!

    It's these kinds of things that need to be embraced by beginning amp building enthusiasts. And I, for one, appreciate everything I've learned from this site along the way. This site is gold thanks to folks like you two.
     
  9. JamesAM

    JamesAM Tele-Meister

    Age:
    35
    Posts:
    172
    Joined:
    May 13, 2020
    Location:
    Virginia, USA
    Add one more here whose bacon this method has saved. I thought for sure I’d already identified the bad input jacks when I was rebuilding my 5e3 this summer, but this method helped me prove otherwise and change out the last one that was causing some noise. Thanks to both of you.
     
    Junior Little likes this.
IMPORTANT: Treat everyone here with respect, no matter how difficult!
No sex, drug, political, religion or hate discussion permitted here.