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Drivin’ That Train

 

Well, ya can't tell by looking but these pickups are out of magnetic phase. Gibson did this on purpose in all their stereo guitars. Did anybody ever play this one?

I’m not an engineer but as long as I’m driving this train, I’ll take a stab at some scientific stuff that is pretty well misunderstood. The issue is out of phase pickups-particularly on stereo guitars like 345s and stereo 355s. I’ll try to keep this simple which shouldn’t be hard because I really don’t totally understand the science anyway. There are two kinds of phase to consider-electronic and magnetic. When two sound producing elements feeding the same source (amp) are out of phase, the result is subtractive rather than additive. Simpler? Instead of hearing the sum of the signal, you hear the difference. That means the parts of the two signals that are alike will cancel each other out. That’s why when your pickups are out of phase, only the middle position is affected. The individual pickups, working alone, have no phase issue because there aren’t two sources. Simple, right? Same goes for speakers in an amp with more than one speaker. If they are out of phase, one speaker is pulsing outward while the other in pulsing inward. The result is less than the sum of the parts (because it isn’t). But it gets more complicated with pickups because there are two different types of phase to consider. Magnetic phase and electronic phase. As with speakers, if you solder one speaker correctly but you solder the ground wire to the “hot” terminal on the other (and the hot wire to the ground terminal), your speakers will be out of phase. With vintage pickups, it’s a little harder to do because the ground wire is the braid and the hot wire is the strand. I learned about electronic phase from my years in video. If an audio cable from one channel was out of phase with the wire from another and the same signal was present on both channels, the sound would be thin and reedy with pots channels open but full with only one open. But electronic phase isn’t really the usual problem with a stereo guitar. The problem here is the magnets. Gibson intentionally configured the magnets to be out of phase, although I’m not entirely certain why (help me out here, anybody). Inside a humbucker pickup, there are two coils wired in phase with each other sitting above a magnet. This means that the one coil sits on the magnets South pole and the other coil is sitting on its North Pole. Normally, the magnets of both pickups are going in the same direction-each has the “north” pole going in the same direction. In a 345 or stereo 355, one magnet is north pole over the slug coil  and the other is south pole over the slug coil. This is why simply turning the pickup around by 180 degrees doesn’t work. You would have to turn it upside down. With a stereo output the pickups would be going to separate channels so even if both pickups are active, the don’t “sum” because they aren’t being processed by the same amp (or channel). When you use a mixdown cable or simple swap out the jack for a mono one, you get the difference which is that thin reedy tone that some folks like (Peter Green was famous for this). You can’t fix this with the wires or the pickup positions, you have to physically remove one magnet and flip it over top to bottom, like a pancake and reinsert it. This requires removing a cover which is never advised. It doesn’t matter which pickup because phase is relative (both can be south pole up or north pole up). I read a post on a guitar forum that said that a player got around the phase issue using a Fender blackface amp using both channels. He stated that since the two channels are out of phase-which they are-that the out of phase pickup problem was rectified. UPDATED: I didn’t think that would work but I was told that it actually does but it doesn’t address the larger problem which is folks who want their 345 to be mono and in phase and feeding a single input.  I still suggest that a 345 is at its best when using its stereo circuit. Wanna take out the Varitone? Go ahead but there are lot of cool things you can do with a stereo guitar, especially if you’re into pedals.

Here are a couple of PAF magnets. The N pole has been marked. Here, the N poles are facing the same way, so if these were in the pickups, the pickups would be in phase. Also note that the magnets stick together because the S pole of one is adjacent to the N pole of the other. Opposites attract. I f your magnets aren't marked (and they won't be) that's how you tell if they are in phase. It doesn't matter which end is N or S only that they are pointing in the same direction to be in phase.

16 Responses to “Drivin’ That Train”

  1. Butch says:

    Hi Charlie, I don’t know what’s really happening scientifically here but I know that when I plug a stereo ES into the separate channels a blackface combo with reverb, the middle pu position reacts as two separate sources and sums out of the amp as what were used to with a mono ES (in phase). It even has a slight volume bump vs. the slight volume drop you usually get with both pickups on a mono ES, with both channels set the same. I go stereo into a non reverb BF and I get the out of phase drop. A tech described the reason to me as it was due to the fact the normal and reverb channels were out of phase on the rev. amp and in phase in a non reverb BF (I’m only talking real vintage here.) I also have two BF combos w/reverb that I modded to have rev/vib on both channels and discovered that the stereo ES’s were reacting like a non rev. combo (out of phase PU’s, in phase channels or whatever is really going on?) Again it was explained to me that the mod put the channels in phase? BTW I was told that this is the same reason that you can jump non-rev. amp channels for more gain but not the rev. versions. I haven’t tried this myself though. I enjoy your site very much, Butch. (a friend of Eric Parker.)

  2. chuckNC says:

    I can add that I did some experimenting with a Gibson Faded Flying V that I rewired for stereo operation. Some of my amps have 2 channels in phase and some out-of-phase. The ones that were out-of-phase were returned to in phase when the neck pup’s magnet was flipped. The in-phase amps responded the same way with the magnet flipped back the other way. Running a pickup into each channel pushes the amp harder, much the same way as jumpering channels does. That’s Why Freddie King was able to get so much drive out of his Twins and Super Six amps. You can’t see it easily in most 70’s-era youtube clips but in a couple you can see his stereo cord plugged into both channels. It’s a different, more powerful sound than he gets when he’s running mono. (You will hear the squawky out-of-phase sound on some of his 70’s recordings. I think he liked the option of getting that sound sometimes too, but it IS very different.)

    I used to have a Dano git that had the 2 pups wired in series. The middle poition was guttier than either individual pup. Sort of how I experienced my stereo guitar run into 2 channels. A very useful option IMHO.

  3. Kerry Leeds says:

    Hi Charlie,

    I too find that my stereo guitars have full signal strength (no phase cancellation) when using a stereo Y-cable through both channels of my 18W EL-84 amps. But don’t tell- let’s encourage everyone to buy 335s and leave those pesky 345s and 355s to us!

    Cheers,

    Kerry Leeds

  4. Chris W. says:

    Hey Charlie,

    I’ll just add some technical comments:

    Technically we are talking about polarity and not phase here. Phase is a common term that is used by almost everyone, so it’s not something I’ll harp on too much. I’ll usually call it phase myself if it is brought up in a conversation as “phase”. And for a sin wave, a 180 deg phase shift is equal to a polarity inversion. It’s ingrained in our lingo like the tremolo/vibrato thing.

    Electronic polarity inversion and magnetic polarity inversion are two different ways to achieve the same effect. If a given pickup responds to to a string moving into the pickup with a positive voltage, flipping its magnet will flip that voltage to negative. Flipping the coil leads will then put it back to positive again. So:

    Magnet coil polarity
    normal normal +
    normal reversed –
    reversed normal –
    reversed reversed +

    At the pickup’s output, there is no distinction between magnetic and electronic phase. We could in fact switch the leads on a 345 neck put to put it back in phase with the other, but then the cover goes hot and picks up Mexican radio. It also hums when you touch it.

    Regarding why Gibson did this, I think it’s to avoid the sound increasing in volume when both pickups are used together with a stereo amp (or two amps). It also tends to add a bit of spaciousness by tricking our ears with unexpected spacial cues, with the polarity difference simulating true phase changes (resulting from longer arrival times) that would be present if one of the amps was farther away from the listener.

    Also, the guys above are right about the second channel of many amps putting the pickups back in phase. This is different than a stereo amp though, since a stereo amp usually has the same polarity on each channel. It sounds more normal because we have different speakers for each signal, with different path lengths to our ear in most cases. For a GA-79, they are also throwing the sound in different directions, adding to the spacial effect.

  5. Chris W. says:

    Formatting problem in my chart above. I’ll try again:

    magnet____coil_____polarity
    normal____normal_____+__
    normal____reverse_____-__
    reverse___normal______-__
    reverse___reverse_____+__

  6. OK Guitars says:

    Thanks Chris. I think we had this discussion once but I knew that if I started talking about polarity, nobody will know that I’m addressing what is commonly referred to as phase. I didn’t think you could correct a polarity problem by reversing the electronic phase but I stand corrected and yield the to the true engineer-not just the guy driving the train. If I had a blackface Fender, I probably would have known this because I would have tried it. But all my Fenders are tweeds and I don’t believe the channels are out of phase on them.

  7. chuckNC says:

    Chris W’s post above contains the principle behind the hum-cancelling wiring of single coil pickups. This is sometimes called RWRP wiring, standing for Reverse Winding/Reverse Polarity. When you run a normal/normal and a reverse/reverse pickup the “middle position” (both pups on) the sound will be “in-phase” (aka matched polarity) but with the hum magically zapped. I gig with a P90 guitar that has this feature. The middle position sounds just like a normal/normal+normal/normal guitar would except dead quiet–a real plus.

    Chris W, are you the guy resposible for the Varittone PDF? If so, thanks! Great stuff there.

  8. Chris W. says:

    Yep, I’m the Varitone guy. 🙂 Excellent point about RWRP. The RWRP works because only the coils pick up RF, not the magnets. The same effect is happening in a humbucker too. The first humbucker I ever made, I accidentally wired both coils to the same polarity. I never heard a worse sounding pickup!

  9. Butch says:

    I’ve tried reverse the leads on one of a pair of out of phase pu’s and it didn’t put them back in phase, got the cover hum but not the result we all want. Woe that it would be that easy. Thinking about the amps again, I wonder if you has a giutar wired stereo but with “in-phase” pu’s, if you would get the opposite result from what I get between the rev/non-rev amps, magnetic polarity having nothing to do with it, pickups working independently, strictly an electrical phase phenom? Could it be that Gibson’s stereo amp had its two sides out of phase to each other and that was the reason that they felt that reversing the mag polarity was the way to compensate for this? Hmmm…Also..I’ve only had the desired result using two separate amps of any brand phase etc.

  10. Gordon Walker says:

    Hi Charlie,
    Just to complicate maters : I have a ’59 345 with non-original PAF’s that are not out of phase ( middle position with Varitone 1 = full sound. But riddle me this: using a stereo to mono ” mix-down” cord sounded alright, but switching to a stereo to 2 mono cable into the 2 channels of a blackface reverb amp
    made that guitar come alive. Q: Why did this happen with in phase p/u’s ?
    I’m against Varitone-ectomies, BTW. Tone-suckers ? That must be why Freddie & BB ( circa Live at the Regal) have such poor tone !

  11. Chris W. says:

    Regarding using two amps/channels for a stereo guitar: The amps volume and tone controls are VERY important for altering how much out of phase the signal in the air seems. Remember that an OOP signal is the difference between the two signals. The more different the two signals are, the less is being cancelled. Theoretically, if one channel of the amp was giving only everything below 800Hz and the other was giving only everything above 800hz, then the summed signal would sound very much like an in phase signal. You can demonstrate this pretty easily by using a summing cable for a stock 345 and turning down the volume a bit for one pickup. All of a sudden the output seems back in phase.

    In the case of an in-phase stereo guitar, using two OOP amp channels can sound really cool. You are listening to the difference between the two pickups, but the tone knobs and volumes affect what signals are being cancelled in what proportions. You can have a case where you turn down the bass on one channel and the bass gets louder from the amp. It’s also likely sending a hotter signal to the power stage of the amp, which can be good too.

  12. OK Guitars says:

    Read the comment from Chris W. Maybe he’ll chime in with sole further comment. He’s an engineer in real life.

  13. OK Guitars says:

    Again-not an engineer but I’m pretty certain that the Gibson GA-79 is in phase. Read Chris W’s post.

  14. Litcrit says:

    Butch is absolutely correct re: stereo guitars and Fender blackface combos, but vintage snob that he is, he forgot to mention that ANY FENDER REVERB COMBO, even dreaded Silverface amps, of which there are approximately 10 trillion out there, will work just great. With the stereo cord, The pickups are IN -PHASE and That middle position, summing the signals in series just blows you out the door! Do you guys really not know this????

  15. Jonne says:

    Hi there,
    I always thought that Gibson guys were just clever noticing that most amps with 2 channels were usually out of phase: all 2-channel Fender black- and silverface amps feat. reverb because the reverb channel inverts phase 180 degree and also most Fender brown and white tolex amps which has that harmonic, leslie like vibrato does the same thing.

    I’ve also own Gibson GA-79RVT and it worked same way. BUT all these amps are built few years later than first stero Gibson guitars. But same time when Gibson announced first ES-345 and stereo ES-355, they also released 2 amps to go with them: twin-cabinet GA-88S and single cab but multi-speaker GA-83S. These amps are so rare that I’ve barely seen one recent pic of these. But if anyone has ever played them and if they happened to work same way like GA-79RVT or most Fenders, the mystic might be solved.

  16. OK Guitars says:

    Those are rare amps but you see them on Ebay every now and then. I’ve never owned or played through any but the GA 79.

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