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  • Balanced Guitar Pickups

    I've been playing with some Focusrite computer audio I/O boxes lately and have found, a bit to my surprise, that the DI input jacks (line inputs switched to DI mode, not independent jacks) are not only high impedance as expected, but they're differential (balanced).

    So this got me thinking. Since a lot of pickups these days are constructed with the two ends of the winding coming out through two conductors of a shielded cable, and one side only gets grounded to the shield at the guitar's output jack. If you replaced that jack with a TRS jack, connected the two ends of the pickup winding to the tip and ring of the jack, and the shield of the pickup cable to the sleeve, you'd have a balanced connection if you connected it to a balanced input with a TRS cable. You'd also have an unbalanced (conventional) input if you connected it with a standard TS guitar cable.

    I suspect that most noise is picked up by the pickup rather than the cable, but if that cable does tend to act as an antenna, the balanced output and differential input would improve the common mode noise rejection.

    Now, this isn't a construction project yet, but food for thought for those of you who customize the wiring in your guitars. There are obvious considerations about how to deal with pickup switching and controls that need to be dealt with. As a thought exercise, though - a single pickup wired straight to the jack - it seems like a pretty good idea.

    I remember back when dinosaurs roamed the earth reading an article about Chet Atkins in which he said he made low impedance pickups for his guitar to get lower noise and less high end loss, but he didn't say specifically that they were balanced or what he was connecting it to. Gibson made a Les Paul Recording model which indeed had low impedance balanced-wired pickups with an XLR connector at the output, and a special amplifier to go along with it. So the idea isn't new, it just, I guess, never really caught on.
    --
    "Today's production equipment is IT-based and cannot be operated without a passing knowledge of computing, although it seems that it can be operated without a passing knowledge of audio." - John Watkinson, Resolution Magazine, October 2006
    Drop by http://mikeriversaudio.wordpress.com now and then

  • #2
    I'd think you would know that low impediance is 600 ohms.
    This boost the voltage and lowers the current for long transmission distances. (like they do with AC transmission lines)
    This preserves the frequency responce and signal quality.
    Its converted back to high impediance at amp.

    You would NOT get low impediance just sticking a TRS jack in the guitar with any wiring combination.
    Nor will it reduce any noise associated with guitar pickups other than the cable might be better quality.
    Guitar pickups are high impediance. Even the weakest coils are above 3K ohms.

    If you want a low impediance guitar install high to low impediance transformers in the guitar like thay do with the Les Paul Recording guitar.
    It will be good for clean tones recording direct. http://www.flatearthguitars.com/files/LP_Recording_71_77-Sig_Guitar_Bass.jpg

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    • #3
      What you can do thats really cool is use a TRS jack and run stereo pickups like a rickenbacker.
      Record each pickup to a separate track and blend the two pickups after they are recorded.
      You can even have different effects on each plus sone actual stereo separation due to the string vibrating
      differently over each pickup. Its like putting your ears between the two pickups.

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      • #4
        I've heard about that but never done it, but it sounds like it could be really cool.
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        • coyote-1
          coyote-1 commented
          Editing a comment

          UstadKhanAli wrote:
          I've heard about that but never done it, but it sounds like it could be really cool.

          Blackmore tried something like this in the mid-late 70s, as the EMI generated by the computerized rainbow stage prop was extreme and interfered with lots of shows. I remember him not being happy with that result either, and eventually the rainbow itself was ditched because of it.


      • #5
        There's less difference between balanced and unbalanced than we often tend to think. For either balanced or unbalanced, the signal is the difference between two pins. For unbalanced, one just happens to be grounded. The coils on the guitar will "pull" on the ground lead as it "pushes" on the hot lead.

        When connecting two pieces of AC-powered gear, the difference is more significant due to the signal ground being connected to the power ground; neither end expects the other end to be jerking power ground around at audio frequency rates. (To the extent one does, we get ground loop hum.) But a guitar is passive and it's floating. (The floating part is more important than the passive part.)

        Yeah, I know I'm oversimplifying.
        learjeff.net

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        • #6
          I'd think you would know that low impediance is 600 ohms.


          Uh . . . why so arbitrary. Yes, I'd consider 600 ohms to be "low impedance."


          This boost the voltage and lowers the current for long transmission distances. (like they do with AC transmission lines)
          This preserves the frequency responce and signal quality.
          Its converted back to high impediance at amp.


          Um . . relevance? AC transmission lines don't care about impedance, they do, however, run long lines at high voltage to reduce the current so they can use smaller wire (but bigger insulators). This really has nothing to do with small signal transmission (like from a guitar to an amplifier) because there's virtually no power involved.


          You would NOT get low impediance just sticking a TRS jack in the guitar with any wiring combination.


          Of course not. You'd get the pickup's impedance. But you could get it on a balanced line. Are thinking that low impedance is balanced and high impedance is not? That's absolutely incorrect.


          Nor will it reduce any noise associated with guitar pickups other than the cable might be better quality.


          No, it won't reduce noise picked up by the pickups themselves. But it could reduce noise picked up by the cable. That was my point.


          If you want a low impediance guitar install high to low impediance transformers in the guitar like thay do with the Les Paul Recording guitar.


          Yes, you're definitely confused about the non-relationship between impedance and balanced connections. Get thee to my web site and start reading the technical articles.
          --
          "Today's production equipment is IT-based and cannot be operated without a passing knowledge of computing, although it seems that it can be operated without a passing knowledge of audio." - John Watkinson, Resolution Magazine, October 2006
          Drop by http://mikeriversaudio.wordpress.com now and then

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          • #7
            What you can do thats really cool is use a TRS jack and run stereo pickups like a rickenbacker.
            Record each pickup to a separate track and blend the two pickups after they are recorded.


            Isn't that how stereo wired guitars are usually arranged? Sure, it uses a TRS jack, but not for the purpose that I proposed.
            --
            "Today's production equipment is IT-based and cannot be operated without a passing knowledge of computing, although it seems that it can be operated without a passing knowledge of audio." - John Watkinson, Resolution Magazine, October 2006
            Drop by http://mikeriversaudio.wordpress.com now and then

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            • #8
              There's less difference between balanced and unbalanced than we often tend to think. For either balanced or unbalanced, the signal is the difference between two pins. For unbalanced, one just happens to be grounded. The coils on the guitar will "pull" on the ground lead as it "pushes" on the hot lead.


              That's the general case, and almost always the case if you're talking about guitar amplifiers, but I was talking about the instrument input on a specific models of computer audio interface from a particular manufacturer. These is a differential input. The output of the preamp stage is the difference between the tip and ring signal, just like a mic preamp is the output of the difference between pins 2 and 3.

              If the pickup is wired so that the two pickup leads go to the two inputs of the differential amplifier, you'll get the pickup output amplified just as you expect. One side goes positive with respect to ground, the other side simultaneously goes negative. But suppose you have some noise that's picked up by the cable. Both conductors, since they're close together, will pick up the same noise, at the same amplitude, and the polarity of the noise on both cables will be the same. Let's say you have 1 volt of noise on each cable. Those go into the differential input (along with the desired pickup signal). It does it's thing, 1v - 1v = 0v. Goodbye, noise.

              Now that's only half the job, though. We refer to inputs like mic preamps as "balanced" but really, outputs are balanced (or not). Inputs are differential (or not). Balanced means only that the source impedance of both legs is identical. It says nothing about the number of ohms except that it has to be the same on both legs. It says nothing about the voltage. One can be zero volts. This is what's called "impedance balanced" or more accurately, "single ended balanced."

              Equal source impedances as well as equal load impedances will insure that a current induced in both cables will have the same voltage at the inputs of the differential amplifier,


              When connecting two pieces of AC-powered gear, the difference is more significant due to the signal ground being connected to the power ground; neither end expects the other end to be jerking power ground around at audio frequency rates. (To the extent one does, we get ground loop hum.)


              Congratulations! You've just recognized The Pin 1 Problem.


              But a guitar is passive and it's floating. (The floating part is more important than the passive part.)


              But ground problems aren't the only source of hum.
              --
              "Today's production equipment is IT-based and cannot be operated without a passing knowledge of computing, although it seems that it can be operated without a passing knowledge of audio." - John Watkinson, Resolution Magazine, October 2006
              Drop by http://mikeriversaudio.wordpress.com now and then

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              • #9
                Running a balanced hi-Z (or even guitar-Z ;-) ) line won't do a thing for inductive coupling (hum due to EM fields inducing a voltage in the coil(s) of the PU).

                However, if you had a shielded humbucker PU with excellent balance between the coils, a shield connection running back to the preamp, and a floating differential feed to a differential input... you just *might* notice a slight reduction in any noise that may otherwise have been picked up by a single-ended connection. Of course, a shielded cable with 100% shield coverage might give you the same benefit without all the "non-standard" circuitry.

                Honestly, the best thing you can do if hum pickup at the guitar is a problem would be to install shielded active pickups. A friend who plays a Tele used to have horrible problems playing at one particular bar. He replaced the PUs with a drop-in EMG set and his Tele had no more hum at that bar.
                "There is no best in music."
                -- Neil Young, 1987

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                • #10
                  I think the passive volume controls in a guitar are going to pose a problem for you.
                  They would cause an imbalance wired as is and you would have to shield the guitar cavity
                  independantly. The normal signal to ground method of using pots wornt work.

                  The other item is guitars pickup requires instrument level to sound right.
                  I have no idea what model the Focusrite, there are many. But it sounds to me like the input is either low impediance or line level balanced,
                  neither which is correct for a guitar pickups signal strength straight in.

                  I'm guessing its a balanced line level input designed to connect a balanced preamp output.
                  If thats the case, preamping the pickup signal for a line level input or converting the
                  signal to low impedance fro a mic level input is needed.

                  In any case, I record direct all the time and have no hum issues and I even still use an older CRT monitor in the studio.
                  All my single coil guitars either have the cavities grounded with copper foil or had the single conductors wires to the pickups
                  replaced with shielded wire. Having shielded/grounded covers helps too.

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                  • #11
                    I think the passive volume controls in a guitar are going to pose a problem for you.


                    I did stipulate that volume controls and switches (as originally wired) may be a problem. My suggestion as an experiment is to simply choose one pickup, wire it up as a balanced connection, and see what it does for you. It's possible to rebuild the whole inside of the guitar to be balanced if one wanted to do so.


                    you would have to shield the guitar cavity independantly.


                    Now this is exactly where the balanced wiring would help if it was done correctly. I've run microphones through zip cord and no shielding without hum problems.


                    The other item is guitars pickup requires instrument level to sound right.
                    I have no idea what model the Focusrite, there are many. But it sounds to me like the input is either low impediance or line level balanced,


                    Nope, this is a real DI input, suitable level for an instrument, 1 megohm between tip and ring, or 500K when connecting "unbalanced." It's a Focusrite Scarlett series, and the Saffire Liquid 56 which I recently reviewed has the same DI input setup. These guys aren't ignorant.


                    In any case, I record direct all the time and have no hum issues and I even still use an older CRT monitor in the studio.


                    Hey, if you don't want to play, you don't have to play. But don't rain on my parade. I think the idea has potential, but I'm an engineer, not an electric guitarist. My guitars usually hum when I plug them into DIs in the studio unless I face the right direction to null it out. This is hum picked up by the pickups, not the cables, so it's a different problem. But the cable is a potential problem and this, if they built guitars right, is a potential solution.
                    --
                    "Today's production equipment is IT-based and cannot be operated without a passing knowledge of computing, although it seems that it can be operated without a passing knowledge of audio." - John Watkinson, Resolution Magazine, October 2006
                    Drop by http://mikeriversaudio.wordpress.com now and then

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                    • #12
                      I have often wondered why guitars haven't gone low impedance so that direct boxes and separate instrument inputs would be unnecessary, and the ability to run longer cables added. The posts above show some of the challenges. What are the issues at the amp end? Can existing classic amp designs be easily modified for low Z without changing the characteristic sound? Would the guitar signal sound different if it has to go through two transformers or equivalent active circuits (one at each end)?
                      "In a time of universal deceit - telling the truth is a revolutionary act."- George Orwell

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                      • #13
                        I have often wondered why guitars haven't gone low impedance so that direct boxes and separate instrument inputs would be unnecessary, and the ability to run longer cables added. The posts above show some of the challenges.


                        Those aren't challenges, those are excuses for . . well, I don't know what other than not doing it. The best argument against the balanced pickup wiring is that there's so much more hum being picked up by the pickups than the by the cable that it might not be worth it.

                        Understand that wiring the pickups doesn't make them low impedance. They're still as high impedance as ever, and still need a high impedance input in order to sound like they're supposed to sound.

                        The way to make a low impedance pickup is to use less wire. This has a lot of advantages - lower inductance, lower capacitance, and lower resistance. But the disadvantage is that a smaller coil of wire makes a poorer generator and the output would be very low. Probably on the order of . . . well, a dynamic microphone.


                        What are the issues at the amp end? Can existing classic amp designs be easily modified for low Z without changing the characteristic sound?


                        I don't see why not. Any decent mic preamp design should work fine. That would boost the signal from the pickup to essentially "instrument" level, and then you could overdrive the first stage of the amplifier, or the output stage, or anything else in between just like you normally do.

                        It would take some work to design a low impedance pickup that sounds as good as those that they've been making for 75 years, but there are contemporary pickup designers who I'm sure would be up to the task as long as someone could create the market that would justify the development.

                        One of the things that a designer would need to accommodate is how the load affects the magnetic circuit which affects the string mechanics. There's also something to how the source impedance affects some guitar amplifiers. There's a Milennia Media box that can be a DI or re-amp box. John found that he needed to offer a couple of different selections of output impedance (simulating the output of a guitar) when re-amping with it since this made a difference in how the amplifier sounded. I can't explain that one, but I won't argue with John's ears. He's a guitar player.

                        The reason, I suspect, why they make guitars and amplifiers the way they do is because they've always done it that way. If you had a low impedance guitar, you might find yourself in a place where you didn't have an amplifier to plug it into if you didn't have your own.


                        Would the guitar signal sound different if it has to go through two transformers or equivalent active circuits (one at each end)?


                        The low impedance design doesn't need transformers, unless you wanted to use a transformer at the input of the (pre)amplifier for the coloration. If you had a low impedance guitar and wanted to plug it into a conventional amplifier, then you'd need a transformer or an outboard preamp, and that would most likely change the sound.
                        --
                        "Today's production equipment is IT-based and cannot be operated without a passing knowledge of computing, although it seems that it can be operated without a passing knowledge of audio." - John Watkinson, Resolution Magazine, October 2006
                        Drop by http://mikeriversaudio.wordpress.com now and then

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                        • #14
                          Mike you dont have to be a condecending ass. I have degrees in electronics too. I've also been employed by major
                          manufacturers hald a lifetime, woop de do. Main thing is I do have a good 40 years practical experience in
                          music electronics. I'd be surprised if there isnt anything I havent tried or experemented first hand "but" I do keep an open mind.

                          I cant say for sure weather your idea would work because I dont have the schematics to analize.
                          All I could find is the specs like this. They seem to be the same for those models
                          Analogue Channel Inputs (Inputs 1-8)

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                          • #15
                            I'm reading this thread leaning some cool stuff, but
                            Mike you dont have to be a condecending ass.
                            How does a monkey eat an elephant?

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