Anderson Pickup / Wiring questions

Discussion in 'Luthier's Guitar & Bass Technical Discussion' started by jgraham, Jan 5, 2005.


  1. jgraham

    jgraham Member

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    A few questions:

    1. I have two guitars with an Anderson H2+ pickup in the bridge position. One is a Cobra, and the pickup is exactly what I'm looking for sound wise.

    The other is an Explorer. The problem I'm having is almost too much output on the Explorer to where palm mutes are actually causing the speakers to 'flub' out. The variables I see (other than the guitars themselves) are the pots and wiring. Would my 'flub' problem be caused by the different values of electronics, guitar itself, or more likely a pickup height issue? As I'm writing, I've got it all torn apart, so I'm going to install everything now and lower the pickup to see what happens.

    2. My next question is - what is the value TAG uses for the resistor in the vintage voicing circuit? Does that simply go in parallel with the coil cut and ground?

    3. And finally, on my Cobra's volume pot, there is a resistor in parallel to the cap between the center and hot lugs. Does anyone know what the values of these components are? Are they there to attenuate the highs when rolling the volume off?

    Thanks!
     
  2. Jim Collins

    Jim Collins Member

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    I'm not quite sure what you mean by "flub out." It could be pickup height, but it could also be the guitar, itself. What wood combinations make up the two guitars? It is rare that I find a pickup -- especially a humbucker -- that I love in two completely different guitars.

    The capacitor and resistor between the two lugs on the volume pot are not there to attenuate highs, but to retain them, as you roll off the volume. Losing some amount of highs when rolling off the volume is a natural part of the passive wiring in guitars. The capacitor between those two lugs is a compensation for that. A capacitor allows more highs to pass through, and inhibits lows. The capacitor in the tone circuit passes highs to ground. The treble bypass capacitor passes highs directly through to the output lug of the volume pot.

    If the value of the bypass capacitor is too large, it will pass too much highs through, and the guitar will suffer an apparent treble increase as you back off on the volume. Take a look at a late 60s or early 70s Tele. These things had a 1Meg volume pot with a .001uF treble bypass capacitor. That is a HUGE value for this function. Roll the volume back, and it sounds like someone kicked in an annoying treble boost. (This wiring was a major contributor to the Tele's ice-pick-in-the-ear reputation.)

    There are two ways to solve that apparent treble boost. One is to fit it with a smaller bypass cap. PRS uses a 180pF cap. (.001uF = 1000pf, so you can see how small that is in relation to Fender's choice.) PRS's value works quite well for humbuckers.

    The other way is to add a resistor either in parallel with, or in series with, the bypass capacitor. This resistor serves to smooth out the apparent treble boost. The resistor is a compensation for the fact that the bypass cap is too large. The bypass cap is a compensation for the natural loss of highs that occurs when rolling off the volume. Thus, the resistor is a compensation for a compensation. This is not to say that the bypass resistor/cap does not work, but rather the resistor may not be needed if the cap is small enough.

    What are the markings on the bypass cap, and what are the stripe colors on the resistor?
     
  3. jgraham

    jgraham Member

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    Thanks Jim

    I'm sorry I'm not great at describing the 'flub'. I'm using a fair amount of distortion (think metallica rhythm) and I really only notice it during palm muting. Basically the sound looses its tight definition with the second guitar. Instead of 'chunk chunk chunk' its more 'flub flub flub'. Like something in the signal chain is oversaturated. And the only variable is changing the guitars... and the guitars have the same pickup installed. Thats why I'd like to get the wiring on the Gibson as close as possible to the Anderson.

    The two guitars are:

    1. Anderson Cobra, Mahogany neck, back, maple cap, Bolt on
    2. Gibson Explorer, Mahogany neck, body, set neck.

    On the Anderson,
    The pot resistor bands are: Gold Yellow Blue Brown
    The pot cap marking is: 681

    The other resistor which I believe is the vintage voicing is marked: Gold Yellow Orange Orange
     
  4. Jim Collins

    Jim Collins Member

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    The 681 capacitor is 680pF. This is still huge. That's why you need the resistor.

    The orange, orange, yellow, gold resistor is 330K ohms.
    The brown, blue, yellow, gold resistor is 160K ohms.
    One one end, the stripe is usually either gold or silver. This is the tolerance of the resistor. (Gold = 5%.) The code is read from the other end.

    I think the real culprit, here, is the guitar. The major difference is that the Explorer has an all mahogany body. The bolt-on vs. set-neck will also make some difference, but I think the bigger difference will be made by the body wood.

    The maple cap of the Anderson will contribute a significant amount of brightness and snap to the sound. Such a guitar body can easily accommodate a darker, higher output pickup. The brightness of the guitar will come through. I think that is what you are hearing in the "chunk chunk."

    An all mahogany body with a set neck is usually a mid-heavy guitar. A darker, higher output pickup is usually a mid-heavy pickup, to some extent. Combine these two, and you could have a serious midrange hump. Such a midrange hump can translate into a very compressed sound. You won't hear too many highs, and it may sound indistinct, as you pile on the distortion.

    I think you might look for a brighter sounding pickup for the Explorer. I don't believe fooling with the bypass resistor/cap is going to change anything. That really only comes into play when you back off on the volume.
     
  5. jgraham

    jgraham Member

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    Wow - that really isn't the answer I expected, but it does make sense. I have a second Explorer that I've installed my PRS HFS pickup into that sounds just fine...

    Guess I'll try something else in this one. Thanks Jim!
     

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