Stacked Single-Coil Pickup - Charlie Christian Style

[archtopguy]

I'm building a Charlie Christian type pickup for an archtop I have and I'm experimenting with some different designs. Some of the features are: 1) 3-hole mounting and rout which fits inside a typical humbucker ring footprint. Therefore, if I can't get the p/u to sound right, I can just go down the humbucker route. 2) The pickup blade is removeable so I can try different blades for string balance and re-use blades to speed up prototyping. 3) On the latest designs, a single A5 magnet lies vertically inside the bobbin, south up, with the blade attached to it directly. 4) The last one I built has two coils stacked in an attempt to create a hum-cancelling pickup.

With regard to the last point, the attempt was a disaster as the pickup is even noisier than the single coils. - and this is what brings me here
Both coils had approx 7500 winds of 38awg, wound in opposite directions and wired in series. The tot output was just over 5kOhm and the signal is strong, even with the single A5.

Does anyone out there see some obvious flaw with this design?

Thanks in advance,

John

[big_teee]

Moved to this thread.
Hi John:
Welcome to the forum.
That is an interesting pickup you made.
This thread is fine!
I did a strat stacked prototype project back in the spring of 2013.
So I am pretty rusty on what I did, but I just went over it again.
In my project, here were some observations of the characteristics of a Stacked design pickup.
The top coil is nearest the strings, and seems to pick up the most signal.
The bottom coil acts more like a dummy hum canceling coil.
The signal has to go one direction in one coil, and the opposite in the other coil to hum cancel.
Once the coils are wound, care has to be given to which way the coils are turned.
Just flipping one coil over changes the direction the signal is going.
In your pickup configuration?
So if you apply the + output signal to the start lead of the top coil?
The finish lead of the top coil would connect to the start lead of the bottom coil.
The finish lead of the bottom coil would be grounded.
For this reason I always wound both coils the same direction.
In my layout, I applied the + output to the top coil start lead.
Tied the finish lead of the top coil to the finish lead of the bottom coil.
Then grounded the start lead of the bottom coil.
Other characteristics of a stack, is that they are extremely bright.
To offset the brightness, I used a lot of wire.
So I ended up with two 44awg coils wound to over 10k, for each coil.
So lets see if that makes any sense?
Terry

[archtopguy]

Hi Terry.
I basically treated this like a humbucker, as if the slug coil was turned upside-down and placed underneath the adjustable coil. So the + is connected to start of top coil; start of lower coil is grounded and finishes are connected. The two coils are wound in opposite directions. I didn't pot the pickup as I wanted to hear some hum-cancelling effect first.

[big_teee]

Hi Terry.
I basically treated this like a humbucker, as if the slug coil was turned upside-down and placed underneath the adjustable coil. So the + is connected to start of top coil; start of lower coil is grounded and finishes are connected. The two coils are wound in opposite directions. I didn't pot the pickup as I wanted to hear some hum-cancelling effect first.

I think Your pickup is wired wrong.
It should be like one bobbin is sitting on top of the other.
Is your pickup using 2 bobbins wound separately, or is it built all in one piece?
T

[archtopguy]

It's a large bobbin with a divider - sort of like two bobbins stuck together. I wound one clockwise, then switched direction and wound the other counter-clockwise. If they were both wound clockwise, for example, then they would both have south-up polarity and same winding direction. This would be different to a normal humbucker where one bobbin is south-up, the other north-up, and both wound in the same direction. One noticeable difference I can think of is that the lower coil must be in a more dense magnetic flux because it is right on the bar magnet. I'd be interested in understanding the reason why it doesn't work. Judging by the signal (when clipping on a jack and tapping with a screw driver), and by comparing to other successful builds, I think the sound will be decent. Except the whole idea was to get rid of the hum.

[big_teee]

Try wiring the finish to the start of the other.
I did rod magnets.
Though one continuous magnet, one bobbin is treated north and one south.
I still contend you have them wired wrong.
You still have the signal running the same direction.
That won't cancel hum, and may be out of phase.
T

[big_teee]

Here's a diagram of the two coils.
This is looking down from the top on both coils.
The switching directions from one coil to the other coil, is how hum canceling works.
T

[LtKojak]

Does anyone out there see some obvious flaw with this design?
[ATTACH=CONFIG]36379[/ATTACH]
[ATTACH=CONFIG]36380[/ATTACH]
[ATTACH=CONFIG]36381[/ATTACH]

Good job! It looks great, but at least from where I see it, it looks HUGE.

Does it fit in a p'up cavity?

[archtopguy]

It's big alright! If you look at the diagram I posted, there is an eliptical shadow over the side profile of the pickup which indicates the rout. It is 80mmx30mm, so the pickup is put in on its side, then lifted into place to meet the mounting screws. I use rubber piping instead of springs and it's easy enough to instal. The metal blade and pickup cover are attached after the pickup is mounted. The decorative cover will probably be attached with double sided tape while the blade just clicks onto the magnet. I'll attach a pic of the first prototype which is currently installed.

[big_teee]

That is a nice set up!
Did you try rewiring it?

[John_H]

Hi Terry.
I basically treated this like a humbucker, as if the slug coil was turned upside-down and placed underneath the adjustable coil. So the + is connected to start of top coil; start of lower coil is grounded and finishes are connected. The two coils are wound in opposite directions. I didn't pot the pickup as I wanted to hear some hum-cancelling effect first.

Nice work. That's a beautiful guitar. The magnet polarity won't affect the hum cancelling. I agree with Terry. If the wind direction is reversed on your bobbins, the finish of the top coil should be connected to the start of bottom. I think two bar magnets stacked edge to edge with a shorter blade on top, might give better coupling.

[archtopguy]

I just did some testing and re-wiring. I made a chart with findings. The last try was with the wiring proposed by big-teee and interestingly it was quieter than my original wiring but only about the same as the single coil on its own.
wiring variations stacked humbucker.pdf

[big_teee]

Stacks IME are very inefficient, and you see lots of trials, but for the most part no one uses them.
I use & make 3 types of pickups.
1. Single Coils
2. Side by side Humbuckers
3. Sidewinders.
Though I've experimented and tested them, I leave Stacks and tapped SCs to others.
Side by side humbuckers are the most efficient, because you have two sensing coils.
GL,
T

[mr fab]

correct me if I am wrong...
the principal of a humbucker is to have two coils in phase but one is RWRP to the other.

as I see it you have the bottom coil reverse wound, however you also need the flux through this coil in the opposite direction.

this could be achieved by making another bobbin with a space in the middle to insert magnets laterally

I hope this makes sense... its like a sidewinder pickup on its end

[big_teee]

correct me if I am wrong...
the principal of a humbucker is to have two coils in phase but one is RWRP to the other.

as I see it you have the bottom coil reverse wound, however you also need the flux through this coil in the opposite direction.

this could be achieved by making another bobbin with a space in the middle to insert magnets laterally

I hope this makes sense... its like a sidewinder pickup on its end

RW is the humcanceling factor.
You don't even need a magnet in the coils.
You can use a steel blade, and put the magnet on the bottom.
There are stacks made that way and they work fine, as fine as stacks work.
T