Phase reverse switch and humbucking

[Jeremiah]

After wiring up my project guitar with 2 mini humbuckers, and, among other things, a phase reverse switch on the bridge pickup, I find that when I use this switch I seem to lose the hum-cancellation and the guitar gets pretty noisy.

I'm assuming this is not an expected effect of putting one pickup out of phase with another, and somewhere along the line I've done something wrong with the wiring (like maybe having something connected to hot that shouldn't be, like the shield or pickup cover.)

Any clues about what I should be looking for to correct this? (I actually quite like the out-of-phase sound but the hum is quite annoying.)

 

[line6man]

That sounds normal to me.

Humcancelling works when you have two sources of hum that are 180 degrees out of phase, such that the destructive interference reduces the amplitude of the hum, or even cancels it altogether.
When you put the pickups out of phase, the signals may be 180 degrees out of phase, but since the hum was out 180 degrees to begin with, that buts it back in phase, while the regular signal is out of phase.

 

[Steve_Karl]

That sounds normal to me.

Humcancelling works when you have two sources of hum that are 180 degrees out of phase, such that the destructive interference reduces the amplitude of the hum, or even cancels it altogether.
When you put the pickups out of phase, the signals may be 180 degrees out of phase, but since the hum was out 180 degrees to begin with, that buts it back in phase, while the regular signal is out of phase.

You're statement seems to imply that it takes 2 pickups to achieve humbucking quiet, but we know that it's possible to have just 1 pup installed that is HB and be quiet?

I've done reverse phase switches before in Les Pauls with mini hb pups and never had any hum problems, but I'm not a wiring expert by any means.
Maybe I just got lucky.

 

[GoDrex]

I never noticed any extra noise when I had my guitar wired up for OOP sounds - either parallel or series.

 

[Jeremiah]

That sounds normal to me.

Humcancelling works when you have two sources of hum that are 180 degrees out of phase, such that the destructive interference reduces the amplitude of the hum, or even cancels it altogether.
When you put the pickups out of phase, the signals may be 180 degrees out of phase, but since the hum was out 180 degrees to begin with, that buts it back in phase, while the regular signal is out of phase.

I see how this would be the case if both pickups were single coils; normally one is RWRP, so they cancel hum when connected together, but if one was out of phase, the hum may be back in phase as you say.

But where both pickups are humbuckers, each should be individually hum-cancelling, so I wouldn't have thought that putting them out of phase with each other would put the hum back.

But I might be wrong...  :icon_scratch:

 

[drewfx]

If PU1 doesn't hum on its own, and PU2 doesn't hum on its own, PU1 + PU2 shouldn't hum either. So, I'm guessing something is miswired.

Are these 2 or 4 conducter HB's? How exactly did you wire the OOP switch?

 

[dbw]

Pics would help, or at least a sketch of your wiring.

A single humbucker works because it contains two pickup coils that cancel each other.  1 - 1 = 0

Two humbuckers should still work, in phase or out, because each cancels its own hum.  0 + 0 = 0 - 0 = 0

If you switch the phase WITHIN a humbucker (using a 4-conductor pickup) you will get lots of hum because the coils reinforce each other's hum rather than canceling.  1 + 1 = 2

 

[dbw]

You're statement seems to imply that it takes 2 pickups to achieve humbucking quiet, but we know that it's possible to have just 1 pup installed that is HB and be quiet?

A humbucker IS two pickups.  That's the whole idea  :icon_thumright:

 

[Steve_Karl]

You're statement seems to imply that it takes 2 pickups to achieve humbucking quiet, but we know that it's possible to have just 1 pup installed that is HB and be quiet?

A humbucker IS two pickups.  That's the whole idea  :icon_thumright:

Yes. Now I remember - and thanks for the light bulb !

 

[Dan025]

You're statement seems to imply that it takes 2 pickups to achieve humbucking quiet, but we know that it's possible to have just 1 pup installed that is HB and be quiet?

A humbucker IS two pickups.  That's the whole idea  :icon_thumright:

Yes. Now I remember - and thanks for the light bulb !

it all depends on the phase switch, is (A) one coil on the pickup out of phase with the other or (B) is the phase on the whole pickup reversed to be out of phase with the neck? depends on how he wired it. if he used option a some noise is normal. if it is option b then something is wrong, cold solder joint or burnt switch or something. pic's and diagrams would help

 

[Funky Phil]

I am guessing that the pickups have metal covers?
The hum is caused by the cover on the reversed pickup becoming "hot" (signal)

If this is the case, then you need to rewire one of the pickups (the one you are reversing) so that the cover is seperately earthed.
This is easy to do if you have 4 conductor wiring...not so easy if you have "old style" two conductor wiring.
If you have 2 conductor wiring, then you may have to open the pickup up and make a seperate cover earth wire.
(So you will have three wires from this pickup - signal hot and cold, and cover earth.

 

[dbw]

:sign13: Yes, good point Phil... if you have a 4-conductor pickup, make sure the bare wire is ALWAYS grounded.

 

[Steve_Karl]

I am guessing that the pickups have metal covers?
The hum is caused by the cover on the reversed pickup becoming "hot" (signal)

If this is the case, then you need to rewire one of the pickups (the one you are reversing) so that the cover is seperately earthed.
This is easy to do if you have 4 conductor wiring...not so easy if you have "old style" two conductor wiring.
If you have 2 conductor wiring, then you may have to open the pickup up and make a seperate cover earth wire.
(So you will have three wires from this pickup - signal hot and cold, and cover earth.

Wouldn't we then, also, have to isolate the cover from the frame, or any contact with any other metal?

 

[dbw]

I am guessing that the pickups have metal covers?
The hum is caused by the cover on the reversed pickup becoming "hot" (signal)

If this is the case, then you need to rewire one of the pickups (the one you are reversing) so that the cover is seperately earthed.
This is easy to do if you have 4 conductor wiring...not so easy if you have "old style" two conductor wiring.
If you have 2 conductor wiring, then you may have to open the pickup up and make a seperate cover earth wire.
(So you will have three wires from this pickup - signal hot and cold, and cover earth.

Wouldn't we then, also, have to isolate the cover from the frame, or any contact with any other metal?

Nope

 

[Dan025]

I am guessing that the pickups have metal covers?
The hum is caused by the cover on the reversed pickup becoming "hot" (signal)

If this is the case, then you need to rewire one of the pickups (the one you are reversing) so that the cover is seperately earthed.
This is easy to do if you have 4 conductor wiring...not so easy if you have "old style" two conductor wiring.
If you have 2 conductor wiring, then you may have to open the pickup up and make a seperate cover earth wire.
(So you will have three wires from this pickup - signal hot and cold, and cover earth.

Wouldn't we then, also, have to isolate the cover from the frame, or any contact with any other metal?

Nope

i was gonna come back and add this but phil beat me to it. if it's a 2 conductor cable a modification needs to be made. if it is 2 conductors and shielded as i assume it would be id replace the cable with 3 wires or a sheilded "stereo" cable like you would find on a set of headphones. the bare shielding conductor would get soldered to the back plate and the two sheathed conductors would get soldered to the pickup coil wires.

if you simply add an external cover shield wire remember to desolder the original ground wire from the cover.

 

[Jeremiah]

Hmm...

The pickups are 4-conductor, and I thought about the grounding when I was planning the wiring - so the bare (shield/cover) wires from both pickups are connected directly to ground, and not to any of the switches. So I haven't intentionally connected anything to hot that shouldn't be. I might have made a mistake and accidentally let something touch another wire where it shouldn't though.

I'm not sure how likely this is, however, as all the ground wires are connected together at a central ground point, and I would have thought that if any were unintentionally connected to hot, then all of them would be, and this would result in the signal being shorted to ground, and I would get no sound at all. I might be wrong though...  :icon_scratch:

I do have a picture of the wiring, but I don't think it would be very helpful because there are a lot of wires, some of which are longer than they need to be so are all wound around on top of each other, and it's almost impossible to tell what connects to what from the photo.

The setup is: 2 mini humbuckers, series/split/parallel switch for each (on/on/on mini toggles), push-pull pot to put bridge pickup out of phase with neck, master tone, push pull pot to put bridge in series with neck, master volume. I don't have a complete wiring diagram as I extrapolated from sections of a few different diagrams, but the diagram I used for the phase switch is this: http://www.seymourduncan.com/support/wiring-diagrams/schematics.php?schematic=series_spl_parallel-w-phase. However, as I said above, I connected the bare wire directly to ground rather than to the switch.

I guess my next step is to take the pickguard off and test continuity throughout the circuit to check that everything that should go to ground actually does, and nothing that shouldn't. However, I'm going to take a break from thinking about wiring and stuff before my head explodes.:icon_jokercolor:

 

[Dan025]

Hmm...

The pickups are 4-conductor, and I thought about the grounding when I was planning the wiring - so the bare (shield/cover) wires from both pickups are connected directly to ground, and not to any of the switches. So I haven't intentionally connected anything to hot that shouldn't be. I might have made a mistake and accidentally let something touch another wire where it shouldn't though.

I'm not sure how likely this is, however, as all the ground wires are connected together at a central ground point, and I would have thought that if any were unintentionally connected to hot, then all of them would be, and this would result in the signal being shorted to ground, and I would get no sound at all. I might be wrong though...  :icon_scratch:

I do have a picture of the wiring, but I don't think it would be very helpful because there are a lot of wires, some of which are longer than they need to be so are all wound around on top of each other, and it's almost impossible to tell what connects to what from the photo.

The setup is: 2 mini humbuckers, series/split/parallel switch for each (on/on/on mini toggles), push-pull pot to put bridge pickup out of phase with neck, master tone, push pull pot to put bridge in series with neck, master volume. I don't have a complete wiring diagram as I extrapolated from sections of a few different diagrams, but the diagram I used for the phase switch is this: http://www.seymourduncan.com/support/wiring-diagrams/schematics.php?schematic=series_spl_parallel-w-phase. However, as I said above, I connected the bare wire directly to ground rather than to the switch.

I guess my next step is to take the pickguard off and test continuity throughout the circuit to check that everything that should go to ground actually does, and nothing that shouldn't. However, I'm going to take a break from thinking about wiring and stuff before my head explodes.:icon_jokercolor:

wow the funny thing about that is seymour duncan shows it wrong, :laughing7: they have the bare wire and the green wire connected directly to each other, that is fine without the phase switch but not with it... i tend to ground the bare wire to the body of the switch in this situation to keep it neat. having conductors from the same cable routed to different components gets messy, keeping it neat avoids problems.

however, it sounds like you had the right idea, so im guessing a bad solder joint or broken wire.

 

[BigBeard]

Is the switch connected to ground? Meaning did you attach a wire to the case of the switch or to a soldering tab on one of the washers and connect it to the back of a pot?  You can have some interesting noise problems if you forget to ground something