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Resistor in line with pickup to add mids and volume

limalexandro

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Joined
Jun 24, 2020
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I have just registered in the forum but I have been reading stuff here for years. I was reading a post from 2002 (I know it's old) in which a guy named john abraham was asking about adding a resistor in line to a pickup to make it hotter output. Everyone said he was nuts in a summary. However, there is a mod called DGT used in PRS guitars which allow for something like a partial split of humbuckers. It is used to split PAF style pickups which tend to be to week when split. It works great. I have a guitar with it. I simply love it.
Now, the fact is that this mod is exactely what john abraham mentioned in 2002, a resistor in line with the pickup, in this case, a resistor in line with the pickup when it is split, so you can have this partial split. It allows for a split with more mids, less highs and consenquently the feeling of more volume than a normal split.I will leave a link for the DGT mod here.
https://forum.seymourduncan.com/showthread.php?273173-Partial-coil-tap-split-experience

So my question is, why not adding a resistor in line with a pickup that is too bright or lacking mids instead of buying a new one. Am I crazy as people said john abraham was in 2002?

Thank you all for the hours of reading and learning I got from here.
 

PaulD

Active member
Joined
Jun 25, 2007
Messages
673
Adding a resistor in series with a pickup can not increase it's output or boost any frequencies in any way. It is a passive component in a passive circuit and it can only do the opposite (reduce output or cut frequencies). The exact effect of adding any series resistance to a guitar circuit would depend on where it was added (before or after the volume pot) and the value of the resistance.

The article you linked to does not show a resistor in series with the pickup, it puts a resistor between the centre tap of the two coils and ground instead of connecting the centre tap directly to ground when the coils are split. This means that the pickup is not "fully" split and the second coil will still be partially active when the coil tap switch is activated.
 

limalexandro

New member
Joined
Jun 24, 2020
Messages
4
Adding a resistor in series with a pickup can not increase it's output or boost any frequencies in any way. It is a passive component in a passive circuit and it can only do the opposite (reduce output or cut frequencies). The exact effect of adding any series resistance to a guitar circuit would depend on where it was added (before or after the volume pot) and the value of the resistance.

The article you linked to does not show a resistor in series with the pickup, it puts a resistor between the centre tap of the two coils and ground instead of connecting the centre tap directly to ground when the coils are split. This means that the pickup is not "fully" split and the second coil will still be partially active when the coil tap switch is activated.

You are absolutely right about the resistor only being able to cut frequencies. It makes total sense. I spent some time with one of my guitars experimenting. My conclusions is below in case someone wants to try to experiment with that.

Adding a resistor between the ground cable of the pickup and the ground of the system (back of the pot) does change the sound. It cuts frequencies and reduce output a little. It gets muddier and muddier as you increase the value of the resistor. I started with 1k2 and went all the way to 470k. Then if you have a very bright pickup and want to cut a little of it, a 1k2 or 2k2, 3k3 resistor can help. However, you can achieve almost the same result using a resistor in parallel with the pot. A very common and known mod.

Now, about the DGT mod I included the link in my previous post (which again I say is fantastic), maybe is my ignorance, but a resistor between the center tap and ground when the pickup is in split mode is a resistor in series with the pickup. It is between the hot and ground having the pickup in the middle, right? In a seymour duncan pickup for example, black to hot, green to ground, white/red connected to a resistor and then to ground.


Thank you for your answer.
 

PaulD

Active member
Joined
Jun 25, 2007
Messages
673
a resistor between the center tap and ground when the pickup is in split mode is a resistor in series with the pickup. It is between the hot and ground having the pickup in the middle, right?

Yes it is but that is not why it has the effect it does. The relatively small amount of series resistance between the active coil and ground will have a fairly negligible effect. The reason it has the effect it does is that when the coil tap is activated the resistor is in parallel with the non active coil and forms a voltage divider with the active coil, some of the voltage developed across the non active coil is now able to pass through the pickup instead of being shorted to ground so the pickup is not fully tapped and both coils are still contributing to the signal (albeit one significantly less than the other). When the coil tap switch is not activated the resistor is out of circuit and plays no part.
 

limalexandro

New member
Joined
Jun 24, 2020
Messages
4
Yes it is but that is not why it has the effect it does. The relatively small amount of series resistance between the active coil and ground will have a fairly negligible effect. The reason it has the effect it does is that when the coil tap is activated the resistor is in parallel with the non active coil and forms a voltage divider with the active coil, some of the voltage developed across the non active coil is now able to pass through the pickup instead of being shorted to ground so the pickup is not fully tapped and both coils are still contributing to the signal (albeit one significantly less than the other). When the coil tap switch is not activated the resistor is out of circuit and plays no part.

Thank you very much, Paul. That explains why the resistor makes so much more "beautiful" difference in tone when in split mode if compared to simply putting it in series with the whole humbucker. I tried to find a good explanation for that everywhere and found nothing. Your response mentioning the resistor in parallel with the non active coil generating the voltage divider explains that.
 
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