What is the purpose of Capacitor 3 in this schematic?

Discussion in 'Luthier's Corner: Guitar & Bass Technical Discussi' started by NoahL, May 7, 2010.

  1. NoahL

    NoahL Member

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  2. Jef Bardsley

    Jef Bardsley Member

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    C3 is a "treble bleed". A real one, not the kind you use on a volume control (which would be C2, and properly called a "treble bypass"). It tweaks the resonant frequency of the pickups. Sort of a permanent tone control.
     
  3. NoahL

    NoahL Member

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    I see, thanks. Do you see this on many Strat-style guitars, or single-coil guitars? Or is it something that G&L uses specifically for the hot MFD pickups in the S-500? Reason is that I want to use this scheme for a Warmoth Strat with Sheptone ABs, and so I'm not sure if C3 is necessary. I guess I should just experiment. Anyhow, generally speaking, why would this axe have C3 and others not?
     
  4. Keyser Soze

    Keyser Soze Member

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    My guess would be that the MFD pickups tend to be very wide range and he wanted to tame some ice-pick stuff. It really only functions when the treble knob is full up.

    If your 'full up' tone is too shrill something like that might prove useful. But it is going to be very pickup, and overall set-up specific.
     
  5. Tone_Terrific

    Tone_Terrific Member

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    I've never seen that, before.
    I recently installed an s500 pup into the neck posn of a Tele. Loud and kind of toppy. Now I wonder if the pup was designed to run into that circuit, rather than the controls being an afterthought as they are on Fenders.
    I would not use that circuit on other pups without experimenting first.....don't solder or make holes.
     
  6. Jef Bardsley

    Jef Bardsley Member

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    Leo put a lot of work into the G&L wiring schemes and they are designed for specific pickups. MFD pickups are ceramic, and do tend to sound brittle. All G&Ls that use them have something going on in the circuit that will tame the treble. ASATs for instance, have the tone pot wired so even when 'on 10' the resistor is still in the circuit, effectively halving the value of the 250K volume pot.
     
  7. Scooter Burbank

    Scooter Burbank Member

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    Thread revival.

    I picked up a somewhat modded 1985 S-500, and I'm trying to make sure the capacitor values are correct. The treble and bass caps are correct; however, I can't make out what the value on the volume cap should be in this schematic:

    http://www.glguitars.com/schematics/S-500_EarlyStyle-schematic_drawing.pdf

    My guitar has a cap on the volume that reads: 101 1kv.

    Is this correct? Looks like the cap in that schematic starts with a 2.
     
  8. Rockledge

    Rockledge Member

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    I wonder if it is a typical 102 cap that appears wrong side up in the drawing?
    If so, if I remember my cap reading right that makes it a .oo1mf
     
  9. bagpipe

    bagpipe Member

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    Capacitor 3 is not a lateral flux-capacitor but a lateral-flux capacitor; that is, lateral modifies flux, and lateral flux is attributive, rather than flux capacitor compound and lateral modifying capacitor. Flux is commonly used in electronics and electromagnetic theory and application, but rarely in the context of a capacitor. In general terms, flux simply means the rate at which some quantity (such as electric charge or magnetic field) changes through a conductor (e.g. charge flux).

    While they are not generally called flux capacitors, the common inductor is an electrical component whose function in many contexts could be thought of as a flux capacitor - it consists of a coil of wire that converts and stores electrical energy as a magnetic field where it can be retrieved when the magnetic lines of flux collapse.

    Clear?
     
  10. Scooter Burbank

    Scooter Burbank Member

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    Thanks, Rockledge. Does it make any sense for the cap on mine to read "101," and then below that "1kv"? Trying to figure out if this is the original cap.
     
  11. walterw

    walterw Gold Supporting Member

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    as mud ;)
     
  12. walterw

    walterw Gold Supporting Member

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    anyway, yeah, a .001 cap between hot and ground will trim off some treble. how much depends on the rest of the circuit.

    the S-500s are pretty strong pickups, but IIRC have relatively few windings and low DC resistance, getting their output from the steel-pole + ceramic magnet construction (which most cheap import pickups use too, oddly enough).

    they thus have lots of highs to go with the strong output, which i guess G&L wanted to slightly tame out of the gate.
     
  13. Rockledge

    Rockledge Member

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    On some caps, a three digit number is coded as : the first two numbers followed by the the number of "0"s named by the third number, then move the decimal point back 6 places ( I think).
    For example, with a 102, it would mean 100 followed by 2"0"s or 10000.... then move the decimal point back 6 places to get the microfarad value of .01.
    I could be mistaken about this, haven't used it in a long time.
    So, a "101" would be the same as 100, with the decimal point moved back 6 places making it a .1 microfarad..............
    I think................
    And I think this code is only used on the disc shaped caps.
     
  14. Rockledge

    Rockledge Member

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    Where would you start to begin counting down trying to find a cap just to bleed off the highest overtones, the high biting ones?
     
  15. fumbler

    fumbler Member

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    Wow, that's a heck of a circuit for a passive guitar. 3 different value pots to go with the 4 caps. I'll bet that "Leo" guy might have been pretty good at designing amps if he had ever tried. :)
     
  16. SteveO

    SteveO Member

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    He couldn't play the guitar to save his life, though. He should have spent more time practicing and less time tweaking amps. :D
     
  17. engiblogger

    engiblogger Member

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    could be used to ground unwanted harmonics as a switch debouncer

    EDIT:
    Strat pickups usually have a DC resistance of about 7k. a simple low pass RC filter with 7kOhms and .001uF has a -3dB rolloff of about 23kHz.
    This takes away harmonics that are well beyond the range of human hearing. This could serve to mitigate feedback problems common in single coil pickups and lower the noise floor of your signal. All good things in my books!
     
    Last edited: Mar 20, 2012
  18. Sensible Musician

    Sensible Musician Member

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    This is what a circuit looks like when you tune it to the guitar. You end up with little fixes that shift it to where you want it to sound. Most of us do this by endlessly swapping pickups while leaving untouched all the components it makes more sense to change.

    Some of my guitars have trimpots to level out relative volume between switch positions, or the relative effect of the tone control, or both. Some use the exact trick shown in this schemo. I like to tune literally each guitar this way; easiest way is to run my switch (or pickup) leads out and breadboard my controls in an outboard box - or at least as a web of test leads on my bench.

    Someday I will properly study electronics and learn every trick with passive filters. But until then I've learned a lot of the tricks from just looking at schemos like this and asking questions like the OP is doing. Over time I've built up a bag of tricks that can solve most problems.

    C3 in OP's schemo lowers the peak of the overall circuit. Similar value and effect of the resonance switch on Seymour Duncan Pickup Booster in position 1. Similar value and effect of a long cable.

    Cap codes: it's easier for me to think of two digits as the number of Picofarads and the number as the number of moves in decimal places. So 101 is one decimal place move (the last digit is 1) and 10 (first two digits) is the value. So it's ten with one decimal move, or 100pF. Every multiple of 3 is a new unit: 103 is 10nF, (nanofarads) and 106 is ten microfarads. BTW it is much easier to read schemos using the correct units. E.g. if you need a 30pF cap in a Rat, instead of wearing the point off a pencil writing all those zeros, just write, "30pF." The 1kV is the voltage that a cap is rated for. Common practice is to use a cap rated for 2x the voltage your circuit is designed for - not an issue inside guitars. There should be one more marking on most caps - the tolerance. These are coded C though (?) - they go in order from very precise to very inexpensive. E.g. J is 5% and K is 10%.
     
  19. engiblogger

    engiblogger Member

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    Speaking from an electronics technologist's POV, This circuit looks to be really nice.
    as I said before, C3 takes away frequencies greater than the ear can hear. (noise reduction)
    C1&4 are for low pass and hi pass filters for tone control
    C2 will help take away VR2's scratchiness

    If you are really not sure whether you want to populate them or not, drill a hole on your pick guard for a SPST switch (on off switch) and wire it in series with C3 . you can do the same for C2 if you want. now you can select whether you want that cap in the circuit or not while you are playing.

    EDIT:
    As a very simplified rule of thumb. Caps want AC to pass through them and they stop DC from passing through them. the bigger the cap, the lower the AC frequency they will allow. Its a little more complicated than that but in good audio circuits, you generally like to see a lot of filter caps. they take away noise. the reason why you don't see them that often is because they are expensive for guitar makers
     
  20. engiblogger

    engiblogger Member

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    to clarify, flux capacitors are only used in time travel
     

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