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Electronics help please!

Discussion in 'Hardware, Setup & Repair [BG]' started by thrash_jazz, Sep 12, 2003.

  1. thrash_jazz


    Jan 11, 2002
    Ottawa, Ontario, Canada
    Artist: JAF Basses, Circle K Strings
    Hi folks,

    I'm currently rewiring my fretless P-Bass. The pots are old and crappy and I'm putting in new ones.

    Issue is, I want to change the tone circuit from your standard pot-and-cap to a rotary switch, wired to different capacitors. I hear that this can give more tonal variety. I'm pretty sure I can make it go but I have a few questions, just to make sure...

    - The switch is plastic, so you can't ground it on the base as you can with metal pots. Would it work to run a ground wire straight from the switch to the bridge?

    - The switch is a two-pole, but the function I'm thinking of is a one-pole. How can I tell which lugs to use, which to ignore?

    - There are two lugs in the centre of the switch that seem to be universally connected. Am I correct in assuming that one of these is the hot signal and one is for the ground?

    As you can probably tell, I have never dealt with assembling multipolar, multifunction switches before, outside of DPDT's.

    Thanks in advance :)
  2. Thor

    Thor Moderator Staff Member Gold Supporting Member

    I can answer only a portion of your question, but doing this will resolve most of your other questions.

    Go to Radio Shack or your local electronics supplier, the guy who is supplying your capacitors. Acquire a multi function tester,
    ie a voltmeter. The difference between the cheap one and the 20-30 buck one is usually the quality of the leads.

    Buy the decent one, as you are gonna use this forever, I have had 2 in my whole life, only because I dropped the first one.
    [This thing is just indispensible once you bond with it.]

    A very useful function it has is an ohmeter usually with ranges Rx1, Rx10, etc. There is normally a AA battery in it that allows you to put 1.5 volts of DC current through circuits and test to see how much is lost. If you touch the 2 test leads together, it go all the way over to the right to 0.

    Do this to the switch and map the switch function. This answers your question of what is connected to what.

    Also check to see if current passes from any of the poles to the metal shaft or retaining nut of the switch, this will answer your grounding question as well.

    Also, keep in mind you can design the capacitance circuit just like you would a resistance circuit [ like hooking speakers together ] to give you more options:

    In parallel 2 or more capacitors

    C{total} = c{1} + c{2] + c{nth}

    In series for 2

    C{tot} = c1 x c2
    . -------
    . c1 + c2

    In series for 3 or more

    cTot = 1
    . ---------------------
    . 1 1 1
    . - + - + -
    . c1 c2 cN

    so it basically the opposite of resistance.

    You may choose to design the circuit as a simple low-pass fliter, or you may try for a more complex band pass filter.

    It is fastest to test this with the bass on the bench and the components temporarily wired togeter with alligator clips, and the amp plugged in and on to hear the results before you solder or install the components permanently.

    A simple book on circuits from radio shack or the library will help. Electronics is a science as well as an art, so if you do the math, you should come close to the desired results.

    Having measurement tools is a big plus here.



    It sure is hard to get the formatting on formulas to come out right, the submit function totally changes the spacing, sorry.
  3. thrash_jazz


    Jan 11, 2002
    Ottawa, Ontario, Canada
    Artist: JAF Basses, Circle K Strings
    Thanks Thor! :)

    I already have a tester, and I am officially a fool for not thinking of using it here.

    I am ok on designing circuits already (physics major here) but I don't have a lot of experience putting the suckers together.

    What I'm going for here is actually a bandpass filter. The math is done, now comes the part where I have to develop the practical skills they didn't teach us in school ;)

    Thanks again!
  4. Thor

    Thor Moderator Staff Member Gold Supporting Member

    Since you are a physics major, and a music aficionado, let me reccomend a book I am currently

    'Music, Physics and Engineering, Harry Olson, Dover Press, NY, 1967.

    Great book, though a bit technical. I wish I had found it 20 years ago.

    The tester should be super glued onto your right arm at this point.

    You will require a soldering iron, and rosin core

    Practice soldering on junk pieces of copper wires. Or strip stuff out of an old appliance such as a TV or VCR and use that for target practice.

    A heat sink is a good idea when soldering transistors or small op-amps like the 741 amp.

    The band pass can be made 'tunable' with a variable resistor , you should be able to find basic designs with a quick literature search. No need to re-invent the wheel, n'est pas?

    Your 'official fooldom' is forgiven, sometimes one is to close to the trees to spot the forest.
    This is a great application for a multi-tester.

    I encourage every serious bassplayer to own one.

  5. thrash_jazz


    Jan 11, 2002
    Ottawa, Ontario, Canada
    Artist: JAF Basses, Circle K Strings
    That's funny - I also have the Olson book! My version is even older than '67, too.

    Seeing those old diagrams of electric guitars is just too funny, but it is indeed a great book.

    I've already done my "target practice" on some cheap old capacitors (some of which melted, heheh... use a heat sink next time, eh?) and an LED circuit that I cut into my fretless.

    All ready to go now - merci beaucoup once more, O Thrower of Hammers ;)
  6. Thor

    Thor Moderator Staff Member Gold Supporting Member

    Melted it?

    I have a regular soldering iron 'Weller'with a
    light on the front and a two power setting controlled by the trigger.

    I also have a smaller radio shack one that is like a stick for detail work.

    RS has the heat sink, it is basically a small clamp style thing that will take up a portion of the heat that would otherwise continue up the wire, and fry your component.

    Practice, practice.

    May as well sweat some 1/2" pipe fittings while you're at it, if you can solder, you can sweat. It's all about heat control. Getting the joint hot enough, but not too hot. Using the right solder and flux.

    Olson was published in 1952, he updated it for the third printing in 1967.

    Like Kepler or Newton, the laws of acoustics haven't changed, I just haven't studied them enough, or have forgotten what I learned. So back to the books for me. I guess you could call it self propelled lifelong education.

    See you, O Thrasher of Jazz!

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