How does a dummy coil work for N/S wound pups?

Pickups, wiring schemes, switch techniques and onboard active electronics for guitars

How does a dummy coil work for N/S wound pups?

Postby chicago_mike » 30 Jan 2019, 21:00

so in a jazz bass the single coils have one reversed wound for the hum cancel.

If you add in a dummy coil, would the dummy coil itself need to be like a hum bucker with 2 windings? so if either pickup is solo'd you select one of the dummy coils and then the other pickup gets the other dummy coil?

Or in such a situation, do you only need one dummy coil and it doesn't matter the way its wound?

Been thinking of making a dummy coil and testing it out.
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Re: How does a dummy coil work for N/S wound pups?

Postby phatt » 31 Jan 2019, 08:47

chicago_mike wrote:so in a jazz bass the single coils have one reversed wound for the hum cancel.

Note; the phrase "Reverse wound" is misleading.
To make two idential coils (wound in the same direction) out of phase you just flip the polarity on *one coil*. (Swap the two wires to one coil)
What is reversed is the magnets which returns the two signals back in phase but cancels the hum.
With a dummy coil there are no magnets so you only have to swap the wires.
Be aware that just using a PU bobbin with no magnets that has similar windings as the main PU will effect the outcome,, the Tone might be dulled.

chicago_mike wrote:If you add in a dummy coil, would the dummy coil itself need to be like a hum bucker with 2 windings? so if either pickup is solo'd you select one of the dummy coils and then the other pickup gets the other dummy coil?

Yes you can do that but not needed.
If you setup a switching system to flip the wires on one single dummy coil then each solo position has an out of phase dummy coil and no dummy when both main coils are active.

chicago_mike wrote:Or in such a situation, do you only need one dummy coil and it doesn't matter the way its wound?

Yes it matters which way they are phased see above.
Just wire it all up and if it hums,, swap the wires to the dummy coil,,
You have a 50/50 chance. :wink:
Which ever position gives the least hum will tell you if it's wired up right.

chicago_mike wrote:Been thinking of making a dummy coil and testing it out.

Google *Suhr back plate* for info on better ways to reduce hum than just a dummy PU bobbin.
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Re: How does a dummy coil work for N/S wound pups?

Postby bmxguitarsbmx » 31 Jan 2019, 20:38

You could make a single dummy coil work. Essentially wire all pickups in series, then use a switch to ground out either side of the dummy coil. Use a DPDT switch so you can switch the Hot lead as well. (Hope that makes sense)

Dummy coils will dull the sound, but if you keep in mind that Hum is roughly equel to Turns * Coil Area, you can decrease the number of turns needed by increasing the area the coil covers. Naking a large coil with low turns does work quite effectively at retaining the original tone. Essentially that is what the Suhr backplate is doing. (Magnetic permeability does play a role in hum induction, but if your jazz bass poles are Alnico, ignore trying to complicate the hum formula)
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Re: How does a dummy coil work for N/S wound pups?

Postby george giblet » 19 Feb 2019, 01:09

The thing to note is hum cancelling depends on the direction of the coil and polarity of the connections.
Phasing of the string signal depends on the magnets, coils and polarity of the connections.
For a given connection with hum cancelling, you can only change the magnet direction to make the final string phasing correct.
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