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Parallel wiring - a manifesto

Discussion in 'Pickups & Electronics [BG]' started by micguy, Jul 10, 2012.


  1. micguy

    micguy

    May 17, 2011
    Hi Folks!

    Sorry in advance for the length of this, but this is something that I don't see much discussion about, and I want to share what I know on the topic - partly so others can use what I know, but also to see if there are other folks that have done what I'm doing.

    About 60 years ago, Leo Fender invented the electric bass. When he did that, a lot of things made sense in the context of that era. One of those things was the impedance of the pickups he made. With vacuum tube amps of that era, more signal was a good thing. Hence when he made pickups, he wound them pretty hot - more signal was good. When you look at different string instruments - acoustical and electric, you find that they have impedance peaks (where the system resonates) in the vicinity of 3 KHz - where are ears are most sensitive. Stradivarius did this (though he didn't probably understand frequencies like we do today) in the top plates of his violins. Leo did this via the number of turns on his pickups (and the capacitance of the cable from the guitar or bass to the amp)

    OK, it's 60 years later, and it worked fine at the beginning - so what's wrong with this?

    Today, we have better circuits. Were not fighting for signal to noise as much as back when Leo started. We can afford to think of lowering the impedance of our pickups some, if we gain something for it. And there are things to gain.

    The resonance (a large part of the sound of a passive electric bass) is the result of a poorly controlled system. The inductance of your pickups is part of it. The capacitance of the cable you use is part of it. The input impedance of your amp, DI box, preamp - whatever you plug into, is part of it. Vary one thing, and the sound changes. Maybe a lot, maybe a little. This results in all sorts of things - guys changing pickups to change their sound, hoping the next pickup will have that "magic". I'm an engineer/scientist by background, and like being able to predict and control things. The sound of my basses is no different to me.

    If you wire humbucking pickups (say, a P bass pickup) in parallel, rather than in series, the impedance goes down - by a factor of 4. Many of us are familiar with the change in sound - it sounds "thin". But, it doesn't have to. What happens when you wire a pickup in parallel, and don't change anything else, is you move the resonance frequency of your bass/cable combo up in frequency. You don't have enough inductance to have the resonance where your ears like it. This can be fixed, however. All it takes is a capacitor.

    When you wire the pickup in parallel, its impedance goes down by a factor of 4. If we lower the capacitive loading impedance by a factor of 4 (quadruple the capacitance), the system will behave like before - same resonance frequency. So, we add a capacitor in the bass - before the volume control.

    What have we gained?

    1) By lowering the impedance of our bass, we have made it less sensitive (by a lot) to cable variations - as we have 4 times as much capacitance, a little more or less doesn't change things as fast as before.

    2) We have made it less sensitive to resistive loading variations - adding a DI box won't change the sound that much. In fact, the change from resistive loading variations can be compensated with the tone control.

    3) The volume control won't affect the tone as much. When
    you turn down the volume on a normal bass, you put resistance between your pickup and the cable capacitance, and the resonance goes away. The capacitor we add to the bass is before the tone control, so that resonance (while it shifts some) stays when you turn the volume down.

    4) We have control over the sound of the bass - by changing the capacitor in the bass, we can change the sound of the bass. It's like changing pickups, but at a small fraction of the price, and we can move the resonance up or down at will.

    5) The tone control will work over a wider range - it will go "up" and "down". A lot of bassists use their bass with the tone control full up a lot of the time. By lowering the impedance of the pickup, the tone circuit loading is less, and at the top of the control, it'll be brighter sounding. The sound they used to have at the top will be more in the middle of the range.

    Drawbacks:

    1) You have to turn the volume up on your amp a little, as you have less voltage at the output of your bass. If the circuit you're using is a decent one, you'll actually get less noise, as the impedance of the source (your bass) is much lower.

    2) Doing this is more work than just changing pickups, and involves a little more understanding of what's going on. I measure the impedance of my pickups, and do circuit modelling so I can nail the sound I want in fewer tries.

    OK, so I've talked/typed your ear off. What practical use is this to other folks?

    As a first step, if you have humbucking pickups your don't like the sound of, don't throw them out. Try this instead:

    1) Wire them in parallel. Yes, they'll sound thin. We can fix that.

    2) Get a couple of capacitors - start with 1000pF and 2000pF. Solder the 1000pF across the volume control on your bass. that should change the sound towards "less thin". If you want to go further, try the 2000 pF cap. If that's still not enough, use both capacitors in parallel (3000pF).

    OK, rant off, except for one question: Is anybody else doing this?

    Micguy
     
  2. PlungerModerno

    PlungerModerno

    Apr 12, 2012
    Ireland
    I'm game.... I've a Fender modern player Telebass... two humbuckers, bridge and neck.... a really thick dark tone...

    I like it a lot, but would love to have a push/pull pot that sets up an alternate circuit...

    Would wiring one or both of the pickups in parallel require rewiring the pickup internally? AFAIK The pickups I have are similar to split P's (but in a chrome housing)...

    Would it be possible to have a pickup wired in series and parallel, switching between the two? how could one incorporate two such pickups? seems tricky.
    My exploration will be as follows...
    1. Asses the pickup, establishing the possibility of alternate wiring.
    2. try the pickup in both modes.
    3. Re-assess.

    An active preamp would be an option, but might require more modding than I'd like. (physical routing for the module, or the battery).

    It's an Idea. Subbed!
     
  3. SGD Lutherie

    SGD Lutherie Banned Commercial User

    Aug 21, 2008
    Bloomfield, NJ
    Owner, SGD Music Products
    A couple of things; Leo Fender did not invent the electric bass. Electro String (Rickenbacker), who had pretty much invented the first magnetic pickup (Patented by George Beauchamp in 1934), had an electric upright, and in the 1930s, Paul Tutmarc made the first solid body electric bass guitar, the Audiovox "Model 736 Bass Fiddle."

    The Rickenbacker (1936):

    Probably made from Bakelite.
    rickenbacker36.

    Another Rickenbacker:This one was an aluminum tube.
    6a00e008dca1f088340120a53e6ba0970b-800wi.

    Another Rickenbacker (1935):

    [​IMG]

    The Audiovox bass guitar (1935):

    387_736_1.

    Another Tutmarc bass (1933):

    web_pht_bass.


    George Fullerton and Leo Fender did design the most successful electric bass however. Another reason to buy G&L basses! ;)

    Most pickups that are wired in series were designed to be wired in series. If you really want a lower impedance pickup, wind it that way. That also lowers the inductance of the pickup.

    However, with both parallel wired and lower wind pickups you lose output. That might decrease your signal to noise ratio on a passive bass. The best way to fix this whole issue is with an onboard buffer. That will eliminate the affects of the cable loading the pickups.

    As far as who's doing this? Many Bartolini single coil pickups are lower impedance for less noise. They even show how to use caps to tune the resonance of the pickup.

    Musicman pickups are wired in parallel and use a preamp for a low impedance type tone.

    Alembic pickup are low impedance, and use a preamp. Their preamp uses low pass filters to tune the resonance of the pickup.

    Villex use low impedance coils and transformers to step the signal back up.

    Active EMG pickup have high impedance coils, but they are wired in parallel (sort of) to the preamp.

    And of source anytime you use a two pickup bass like a Jazz bass with both pickup on, you lower the impedance.
     
  4. micguy

    micguy

    May 17, 2011
    Your first challenge is to assess the wiring of the pickups. If they've got 4 wire wiring into the control cavity, then you're gold - you can change to parallel wiring easily.

    If they're wired like "normal" P pickups (2 wires from each), you may or may not be able to easily re-wire them. Standard P's you can re-wire, but you have to go back to eyelets on the coil bobbins to do it right. There's some risk in messing them up, but a qualified tech can do it easily (I've done it).

    Some pickups are potted to where you can't re-wire them.
     
  5. mrbell321

    mrbell321

    Mar 26, 2012
    N. Colorado
    That's only true if you wire them in parallel. It's certainly possible to wire them in series and increase the impedance. I think that was the point of the original post.
     
  6. SGD Lutherie

    SGD Lutherie Banned Commercial User

    Aug 21, 2008
    Bloomfield, NJ
    Owner, SGD Music Products
    Most basses come with the pickup wired in parallel, and have for the past 50 years. Having a series option is fairly recent on Fender basses.

    The point of the original post was for two coil pickups like a P bass.
     
  7. micguy

    micguy

    May 17, 2011
    Agreed - the point of my original post was that certain advantages exist in wiring two coil pickups in parallel (and subsequently loading them to the desired resonance frequency)

    And SGD, I agree that Leo didn't make the first electric bass - perhaps I should have used the word "practicalized" rather than invented, as his was the bass that survived for decades, not the absolute first. I sit corrected.
     
  8. PlungerModerno

    PlungerModerno

    Apr 12, 2012
    Ireland
    Cool stuff. Ideas for non-destructive reversible mods are pretty good in general.
     
  9. SGD Lutherie

    SGD Lutherie Banned Commercial User

    Aug 21, 2008
    Bloomfield, NJ
    Owner, SGD Music Products
    I've been putting series parallel switches on my basses since about 1976, so it's an easy way to get extra tones.

    I also think many modern pickups are wound too hot.

    Well without George and Leo we wouldn't have what we have today. Leo had a knack for taking an idea and finding a practical way to build it and make it work. Same can be said of his electric guitars. He wasn't the first, but they are very successful designs even to this day.
     
  10. topcat2069

    topcat2069

    Dec 2, 2007
    Palm Springs
    So.... how would one make the output of the MFD pickups on a G&L equal in output when switched between the parallel and series positions ?

    I don't like the change in volume but I dig the change in tone.....
     
  11. SGD Lutherie

    SGD Lutherie Banned Commercial User

    Aug 21, 2008
    Bloomfield, NJ
    Owner, SGD Music Products
    You either have to reduce the series volume with a resistor, or actively boost the parallel volume.
     
  12. micguy

    micguy

    May 17, 2011
    Actually, you don't have to switch between series and parallel to get the difference in tone, if that's what you're after. Wire the bass in parallel, and switch in a capacitor as a load if you want to get the "series" tone. No change in volume, just in tone. That's part of the point of my original post - you can get whatever tone you want by loading down a parallel wired pickup capacitively, and you get the other benefits I talked about there.
     
  13. topcat2069

    topcat2069

    Dec 2, 2007
    Palm Springs
    OK so how do I do either one ?? The out put of the G&L overdrives my amp when set to series, and when both pickups are on (via the 3 way selector) POW!!!!!

    Take it to a good guitar tech ???
     
  14. SGD Lutherie

    SGD Lutherie Banned Commercial User

    Aug 21, 2008
    Bloomfield, NJ
    Owner, SGD Music Products
    What kind of amp is it? Do you have an active input? Try that one.

    Or lower the pickups.
     
  15. colcifer

    colcifer Esteemed Nitpicker Supporting Member

    Feb 10, 2010
    A Galaxy Far, Far Away
    So: it's like having active electronics, if active electronics lowered the output. Or not?
     
  16. SGD Lutherie

    SGD Lutherie Banned Commercial User

    Aug 21, 2008
    Bloomfield, NJ
    Owner, SGD Music Products
    Not really. Active electronics are able to isolate the pickups from the cable and the rest of your signal path, and are a line driver, so you get a stronger signal up the cable.

    Les Paul was an advocate for using low impedance pickups and amps, so you would have no signal loss. But to use them with a high impedance amp, you either need a step up transformer or a preamp. But guitarist didn't like the tone these guitars produced, since they were used to high impedance pickups. The Les Paul recording guitar had a rotary switch to switch different caps into the circuit to taylor the high frequency response of the pickups. But it still didn't sound like a high impedance pickup, and the higher wound pickups drive the amps differently. They have a different feel.

    Any under wound pickup will be brighter and cleaner sounding, and suffer a little less from these tone robbing affects. But they still suffer from these things. Because we use high impedance amps, lower impedance pickups seem weak. People seem preoccupied with high output pickups these days.

    What I do advocate are lower wound pickups. They get a better tone. It's easy to turn the amp up a little louder or use a preamp. That was also the point of using them in parallel. But I'd rather under wind them and wire them in series.
     
  17. micguy

    micguy

    May 17, 2011
    Yes, that's pretty much it. Lowering the impedance of pickups, whether through less winds, or parallel wiring, while it lowers the output, it's not enough that you can't compensate with some addition gain in your amp. It does make the pickups less susceptible to loading of the cable and other external loading variations - you'll see very little change with the typical cables and Di's you're likely to use by lowering the impedance by a factor of 4 with parallel wiring.

    And no, it doesn't make the pickups sound "weak". If you add the capacitor to bring the tone back to the realm of the "series sound", they sound plenty "strong". By doing circuit simulation (helps me to nail the right capacitance in one iteration), I can replicate the series sound exactly in a parallel wound pickup. I've done a bunch of basses, and they all sound pretty darn good.
     
  18. topcat2069

    topcat2069

    Dec 2, 2007
    Palm Springs
    I will try this !:hyper:
     

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