P-Rails + triple shot + 5 way switch

[mrosebrock]

mrosebrock,

Thanks for supplying that helpful info.

From the pics, I don't see any obvious issues except that because the STK-4M's Red wire is taped off, that means that pup is always running in humbucking mode, and so when it is combined with a single coil from either the Bridge or Neck P-Rail, the result won't be hum-canceling.

But most worrisome is that you say you are hearing hum when either of the p-rails are active by themselves and in humbucking mode. That shouldn't be happening. My suspicions would be that there is either a loose ground or cold solder joint on one of the grounds, or the guitar needs shielding added. Maybe some of the other forum members here will have some more specific insight into what the issue is.

Additional info:

STK-4M Main coil polarity is South Up. Other SD Stack models have North Up polarity.


Ref:

Classic Stack Plus - how its wires should be routed:
https://forum.seymourduncan.com/foru...ups-on-a-strat

STK-4M vs Other Stacks magnetic polarity:
https://forum.seymourduncan.com/for...-stk4m-classic-stack-plus-strat-rwrp-polarity

Diagram attached of 3 Classic Stack pups wired up showing that White wire is hot, Brown & Black goto to Ground, and Red is an optional series-link wire that can be used for coilsplitting or taped off.

Just some additional info. The humbucker modes are pretty quiet overall but still can have some noise at high gain levels. The single coil setting on the p-rails has more hum than that and the P90 hum is about twice that of the single coil. I carried the guitar around the room last night and I definitely found a few positions where the hum went mostly away. I turned off the lights and tried to pinpoint a common cause but could not find it. I also tried this with another guitar with the same results but the other guitar was much quieter overall (it is just a HSH with no fancy stuff). I opened up the cavity and messed around with a guitar cable connected and the hum increased by a ton when I put my fingers on the common red wire or touched on the circuit board on the 2 dots on the upper left corner of the circuit board. Moving the cables around or away from each other didn't do anything.

 

[Jack_TriPpEr]

Just some additional info. The humbucker modes are pretty quiet overall but still can have some noise at high gain levels. The single coil setting on the p-rails has more hum than that and the P90 hum is about twice that of the single coil. I carried the guitar around the room last night and I definitely found a few positions where the hum went mostly away. I turned off the lights and tried to pinpoint a common cause but could not find it. I also tried this with another guitar with the same results but the other guitar was much quieter overall (it is just a HSH with no fancy stuff). I opened up the cavity and messed around with a guitar cable connected and the hum increased by a ton when I put my fingers on the common red wire or touched on the circuit board on the 2 dots on the upper left corner of the circuit board. Moving the cables around or away from each other didn't do anything.

If either p-rail in humbucking mode is exhibiting hum only when high level of gain is applied, then that sounds normal and not unusual.

Also, just in case you were not already aware, when either of the individual coils of the P-rail are used all by themself, they should be expected to exhibit hum. They are singlecoils after all, so they will have 60 cycle hum. And the hum will sound louder on the P90 coil vs the Rail coil because the Prail coil is a louder/hotter coil.

If you sre noticing changes in hum that are dependent on whether lights are on or off, or whwre you are located in the room, then that is hum due to EMI/RFI interference, which is separate from 60 cycle hum and the solution for that is adding more/better shielding to the wiring in the guitar.

 

[mrosebrock]

If either p-rail in humbucking mode is exhibiting hum only when high level of gain is applied, then that sounds normal and not unusual.

Also, just in case you were not already aware, when either of the individual coils of the P-rail are used all by themself, they should be expected to exhibit hum. They are singlecoils after all, so they will have 60 cycle hum. And the hum will sound louder on the P90 coil vs the Rail coil because the Prail coil is a louder/hotter coil.

If you are noticing changes in hum that are dependent on whether lights are on or off, or whwre you are located in the room, then that is hum due to EMI/RFI interference, which is separate from 60 cycle hum and the solution for that is adding more/better shielding to the wiring in the guitar.

Yes I do expect some hum on higher-level gain but this guitar seems very extreme compared to my other one and any other guitar I have had. I'm in Australia so I'll get 50 cycle hum. I did take the guitar around the room the other day and found a few small places where the hum went away or at least down to normal levels. Nothing I turned off or on had any effect. I used a multimeter today and all of the grounding seems ok. Even all the pole pieces on the single coil are grounded all the way to the output jacks. On both p-rails, only 1-2 of the pole pieces per pickup are registering a beep. I'm not sure if this is normal or not as I haven't done it before. I thought all 6 would register. On the rail side, one of them registers and the other pickup doesn't.

In terms of shielding, I have some aluminium tape and have seen some videos but I'm not quite sure how to ground the shielding in the cavity or in the pickup slots. I'm not against it though. I did buy a new expensive power strip today with RF reduction so I'll try that too. The luthier has also agreed to have another look and properly check all the grounding (which he didn't do before). I'm also wondering if some of the wires were left too long and the silver wire of the p-rail is exposed in some places in the cavity.

 

[mrosebrock]

If either p-rail in humbucking mode is exhibiting hum only when high level of gain is applied, then that sounds normal and not unusual.

Also, just in case you were not already aware, when either of the individual coils of the P-rail are used all by themself, they should be expected to exhibit hum. They are singlecoils after all, so they will have 60 cycle hum. And the hum will sound louder on the P90 coil vs the Rail coil because the Prail coil is a louder/hotter coil.

If you sre noticing changes in hum that are dependent on whether lights are on or off, or whwre you are located in the room, then that is hum due to EMI/RFI interference, which is separate from 60 cycle hum and the solution for that is adding more/better shielding to the wiring in the guitar.

Hmm, so tonight I hooked my guitar up to a portable audio device and virtual amp on my phone and used the same exact amp and tone. I went into another room and everything was completely within tolerance on all pickup modes. This made me think maybe the wiring or audio interface in my guitar room was causing this. However, when I came back to my room with the portable amp solution and turned off the noise gate, I got exactly the same ridiculously loud hum. Despite this, I still unplugged absolutely everything in the room and the noise persisted. I took a walk outside carrying my mobile rig and look what I found precisely behind the wall of my guitar setup...60+ years old substandard wiring with ceramic fuses and on top of that, the main power line to the house also comes there too at the corner of my room. I guess it has always been there but something about this guitar and the p-rail setup amplifies it.