Partial Coil Split with HPF - or is it?

andyg_prs

Firstly, I may have misunderstood the basics, so let's start with a Plain Coil Split

Imagine I have a Dimarzio humbucker and I have Green hot, White ground for one coil and Black hot Red ground for the other. I can see that taking the white and black to ground leaves the Green to White coil unaffected, but the Black to Red coil is shorted out as the Black (hot) is shorted to ground to the Black to Red Coil is inactivated.

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Now take a partial coil split where the white and black wires go to ground via say a 6k resistor. The idea is that the Black to Red coil isn't fully shorted out. Somehow the resistor mean that the Black to Red coil isn't totally shorted out.....as the resistor, well, resists the direct path to ground....so some current still makes it through the Black to Red coil.

Now that kind of made sense to me originally, and I've done it before. Next, I got a Dimarzio DP188, side by side single coil sized humbucker.

I had the guitar routed for it and it wired in with a push push pot....and as I expected the single coil was way too low output.

So, I tried a partial coil split. I could get the volume I liked but the single coil like sound was way too bassy.

I googled and found this set up.



Different wire codes to the Dimarzio, but the idea is that the full coil goes via a capacitor to bleed through the treble frequencies, and the coil that is shunting to earth goes via a resistor to ground...to partially shunt it out.

With some experimentation I found 2nF capacitor to give me the sound I liked.

But here is where my brain starts to get twisted. The wiring job was bad with dull joints etc as my soldering iron tip broke part way through the job etc.....and I had a duff push push pot, so I got fresh stuff and decided to wire it all up again with a "test rig" - extended wires allowing me to easily clip in different value components while the guitar was still plugged into my amp.

Taking the wiring apart, I realised that I had mistakenly reversed the split wires.....so I was actually pushing the shunted coil over the capacitor not the full coil.

So in my tests, I did it 'properly'. I quickly arrived at my 6k resistor being the value that worked for me. Any capacitors in circuit not only made the guitar sound weedy but also I got lots of hum.

Another effect was that the tone control stopped functioning like a tone control and acted more like a volume.

Having checked I had indeed wired everything as planned, I went back to my original mistaken wiring.

So, with the partially shunted coil going over the capacitor. No hum, tone control worked fine, got a much nicer more chimey single coil like sound.

So, here are my questions.

1. In either partial coil split, or partial coil split with capacitor (HPF), I started to wonder, why does the resistor not also drop the volume of the active coil? A volume pot is essentially a variable resistor right? So why does the resistor not also reduce the volume of the coil that is in circuit, the one that isn't being shorted out?

2. Why would putting the capacitor in series with the resistor, and acting upon the full coil (as per the diagram) have the effects it did - sounding weak, lots of hum, tone control changing function?

3. Why would putting the capacitor in series with the resistor acting on the partially shunted coil work beautifully? - of course what works works, and I'm happy with the results!

A few pics that hopefully might help.

The original design, based on green ground, red hot, white ground, black hot
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What I ended up with (the wording is incorrect now):

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And my test rig




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Thanks,
Andy

PS - with thanks to @Kittyfrisk for sending me a bunch of wires / clips and those useful spring loaded blocks you can see in picture.​

Kittyfrisk

Bloody hell, if I knew you were going to bugger about with a Vigier I never would have tried to help 
Hope you find your happy place tone 

andyg_prs

it's my number one guitar too....but I know my limits, I played with the wiring but I had a professional route the body for the taller neck pickup.

ICBM

That will work as you've wired it because the resistor is acting as a partial coil split for one coil and the cap is cutting bass from the other, so there is less cancellation of volume and low frequencies (including hum, so that is still reduced). As it was with the first scheme, the same coil is being used for both, so the signal will be thin and weak, and the tone control will roll most of it away.

However, that's not a good way to wire it - you're relying on both switch poles to pass the signal, so if one goes iffy you will lose the sound completely. A better scheme is to connect the red wire to both lower terminals (in place of the blue wire), the white wire to both middle (green) terminals, and the cap between the two, and the resistor connected to both top terminals (where the cap is now). That will achieve the same switching but with parallel switch poles for maximum reliability.

andyg_prs

I've confused things by showing the original scheme for a different pickup.  Also, the idea from the old forum is that the capacitor is dumping the bass to ground.  I must admit.....I'm not clear if whatever goes to ground is being dumped....or ultimately if the ground is part of the hot/ground circuit....but the impact is to brighten the sound.

So I'm confused how the capacitor is working.  Regardless, adapted for my pickup, the suggested wiring was this:

The red / black coil is getting dumped, as the black is hot but is getting shorted to earth...but partially beacuse of the resistor.

Now this supposedly has the green / white coil going via the capacitor to let the bass get dumped.  However, my confusion here is....the resistor is in series after the capacitor, so shouldn't the resistor also be active on that coil reducing the volume? 


 Regardless, this hummed and sounded weak.



And then I changed it to this:  In theory the red / black coil is getting the bass dumped and most of the signal shorted, but that is resisted...by the resistor.

The green / white coil is left alone...but again, I'm confused as it still passes the resistor to go to ground.  So isn't that impacting it?

This set up has no hum and sounds great.



In summary, I'm confused that a standard coil tap via a resistor (black and white wires together to a resistor) doesn't impact both coils?

And then everything else above.

Sorry if this is unclear!! 

ICBM

andyg_prs said:

In summary, I'm confused that a standard coil tap via a resistor (black and white wires together to a resistor) doesn't impact both coils?

And then everything else above.

Sorry if this is unclear!! 

It only affects the coil which is then in parallel with the resistor. The cap doesn't send bass to ground, it blocks bass frequencies from the second coil so they don't cancel with the ones from the other coil, thus it remains hum (which is a bass frequency) cancelling.

On your new diagram, the best wiring is the black wire to the two bottom terminals, the white to both middle terminals, the resistor to both top terminals and the cap between black and white.

andyg_prs

I'm more confused

I have the best result from the bottom new diagram.

How do I determine which coil is in parallel with the resistor?  I can see that currently both coils have a series connection with the resistor.

With your wiring it seems as though with the resistor across the top two terminals, the white wire has a route through on the right hand to terminal to bypass the resistor completely.

Also it's surely the black wire that needs to hit ground to short out the coil......white goes to ground anyway.

And if you put a capacitor between black and white....then you have the capacitor between them permanently - when it's supposed to be a full humbucker, and not at all when the coil split is on....?

ICBM

andyg_prs said:

I have the best result from the bottom new diagram.

I know . It's just that there's a better way of wiring it to achieve the same thing.

andyg_prs said:

With your wiring it seems as though with the resistor across the top two terminals, the white wire has a route through on the right hand to terminal to bypass the resistor completely.

Also it's surely the black wire that needs to hit ground to short out the coil......white goes to ground anyway.

And if you put a capacitor between black and white....then you have the capacitor between them permanently - when it's supposed to be a full humbucker, and not at all when the coil split is on....?

No - what you have is that when the switch is down, the white wire is connected directly to the black wire and nothing else; when the switch is up, the black is connected to the white via the cap and the white is connected to ground via the resistor. Neither white or black goes directly to ground.

With my wiring, the same occurs - with the switch down, the white is connected to the black via the cap *and* directly via the switch so the cap is bypassed; when the switch is up, the black is connected to the white via the cap and the white to ground via the resistor... which is exactly the same.

It may be less intuitive, but it's much more reliable because now it would require a failure in *both* switch contacts simultaneously to stop it working, rather than a failure in *either* contact. And even if the switch fails completely, you'll be left with the signal being passed by the cap so it will still work reasonably well.

andyg_prs

Cool, right, your wiring, I now understand, sorry for being slow. 

First imagine a partial coil split with white and black going to ground via a resistor....Does the Green (Hot) White (Ground) going via the resistor to ground make any difference to that coil?

Second, in the second diagram, it looks to my eye like the black/red coil is both going across the capacitor and being partially shunted to ground.

However, maybe what I'm missing is what you said about the cap blocking the bass frequencies from the second coil.  But in both cases the black and white wires are joined by the capacitor...so I'm confused what is happening in each case?

ICBM

I think you're making it more complicated than it is .

Start by imagining it without the cap or the resistor - connecting the coil junction (white and black) to ground shuts off the 'lower' (red to black) coil completely, leaving a true single coil (green to white) which will sound brighter and much quieter than the humbucker, and hum because there's nothing to cancel the hum from it.

Now introduce the resistor - this means that the black/red coil isn't fully shut off, so the tone will be louder, fuller and not quite as bright. The green/white coil isn't affected. It will still hum a fair bit because there's only a small amount of cancellation between the two coils.

Finally, introduce the cap between the coils - this will stop most of the bass frequencies from the upper (green/white) coil passing through without affecting the majority of the sound, and if you've chosen the values of the cap and resistor correctly, the small amount that remains will balance the small amount that remains from the other coil due to the resistor, and cancel... hence no hum.

andyg_prs

That is great….but OCD here. Why doesn’t the resistor affect the green white coil?  A volume pot - a resistor does…

And why does it matter which side of the capacitor the black and white wires are?

ICBM

andyg_prs said:

That is great….but OCD here. Why doesn’t the resistor affect the green white coil?  A volume pot - a resistor does…

Because the resistor is only across the red/black coil. It's still nearly a ground connection to the green/white coil - only a few Kohms, as opposed to the pot's 500K.

andyg_prs said:

And why does it matter which side of the capacitor the black and white wires are?

If you reversed the black and white wires, the black/red coil would go (nearly) to ground via the resistor and so not have its volume cut, whereas the green/white coil would have the volume cut and the bass frequencies *doubly* cut by both the resistor and the cap, hence it will hum and also sound weaker/thinner.

If this is tough to understand, don't worry! I had to think it through carefully to make sure I could try to explain it . It's actually a very clever modification to the normal coil-split circuitry.

andyg_prs

Thanks - I’ve grasped that all apart from a seemingly inverse relationship I don’t get. 

The sound I like has the black going across the cap to ground - so seemingly doubly cutting the red/black coil. 

The sound I don’t like with the extra hum has the white wire going across the cap to ground, so seemingly the green/white call being cut by the cap and the red/black only by the resistor. 

What am I missing?

ICBM

Oops! Sorry. Yes, it’s the other way round - I told you it was confusing . The correct scheme is white to ground via the resistor and black to the coil junction (white) via the cap.

Reverse the labelling in the previous post and it’s what I meant to say! (I’ll edit it.) The green/white coil goes to ground via the resistor (nearly bypassing the red/black coil) and the red/black coil goes through the cap to the coil junction (retaining just enough bass to cancel the hum).

In my defence, you have the hot and ground reversed from the conventional wiring where red is hot and green is ground .

andyg_prs

Please don't hate me....but.....this is what works
The black is going across the capacitor to earth via the resistor.....so isn't the red (ground) /black (hot) coil getting hit twice - shunted to ground via the resistor and also hit by the capacitor?  If not, that's what I'm failing to understand....sorry!

PS - Dimarzio tech said to have green hot, red ground...I just trusted them as they made the pickup

ICBM

andyg_prs said:

The black is going across the capacitor to earth via the resistor.....so isn't the red (ground) /black (hot) coil getting hit twice - shunted to ground via the resistor and also hit by the capacitor?  If not, that's what I'm failing to understand....sorry!

The cap *stops* the bass frequencies from the red/black coil being cut - it’s because you need them to cancel out the remaining small amount from the green/white coil. Caps block low frequencies and pass high ones.

A humbucker works because the two coils are both electrically and magnetically out of phase, so the signal is summed but the hum (which is purely electrical) is cancelled out. So to retain hum cancellation with a single coil you need to allow just enough signal through from the other one, but only at low frequencies. In a sense it’s doing the opposite of what you expect.

Reversing red and green makes no difference to the sound, by the way - as long as you also reverse black and white. I’m not sure why Dimarzio would have changed their standard wiring advice, unless it’s to match one of their major customers (MusicMan or Ibanez maybe), but it doesn’t matter. I’ve been wiring them in for long enough that I don’t need the instructions!

andyg_prs

Without the capacitor we are dumping most of the red/black coil including bass frequencies.

The tone was too bassy.

With the capacitor we are dumping most of the red/black coil but keeping the bass frequencies.  This cancels hum with the full green/white coil, fair enough.  But then why does the overall tone become brighter?

Re-considering your wiring:In the up position, we do go from black, across the capacitor to white still.....but doesn't the resistor get bypassed completely as there is a direct route to ground on the top right?  Wouldn't we leave the resistor where it was?

ICBM

andyg_prs said:

Without the capacitor we are dumping most of the red/black coil including bass frequencies.

The tone was too bassy.

With the capacitor we are dumping most of the red/black coil but keeping the bass frequencies.  This cancels hum with the full green/white coil, fair enough.  But then why does the overall tone become brighter?

The cap is *blocking* most of the bass frequencies. It allows through just enough to cancel the small amount left from the green/white coil going via the resistor.

andyg_prs said:

In the up position, we do go from black, across the capacitor to white still.....but doesn't the resistor get bypassed completely as there is a direct route to ground on the top right?  Wouldn't we leave the resistor where it was?

The resistor does stay where it was, it's connected to both top terminals - just link across them, like the other two sets.

andyg_prs

So bass frequencies from one coil cancel bass frequencies from the other coil?

In that case, why do humbuckers - coils wired in series, not cancel out all frequencies?

I’ve well and truly fallen down the rabbit hole!

ICBM

andyg_prs said:

So bass frequencies from one coil cancel bass frequencies from the other coil?

In that case, why do humbuckers - coils wired in series, not cancel out all frequencies?

The *signal* frequencies are summed. The *hum* frequencies are cancelled. It's just that hum is a low frequency as well.

andyg_prs

So that leaves me confused as to why the capacitor is brightening up a muddy sound.