New homemade electric clavichord - need electro-magnetic pickup expertise

[gotkovsky]

Hello everyone,

I've been working for a while on a new electric clavichord design. Here are a few pictures of the build:






I'm currently working on the pickups and would love a little help from forum experts, as electronics is not exactly my forte.

I want to design a first humbucking bridge pickup which for now, looks like the following:

1 — The 3D printed plastic bobbin.


2 — 10 cylindrical magnets inside each bobbin.


3 - Copper coil.


4 - 4 bobbins in a row, bobbin 1 and 3 contains north facing magnets (in blue), bobbins 2 and 4 contains south facing magnets (in red).


5 - A single and long pole piece of steel joins all the bobbins.


6 - Schematic view of the wiring that I came-up with. "S" means start of the coils, "E" end of the coils.


I've read articles about pick-up design and understood that in order for two coils to be in a humbucker configuration, one the coils had to be reverse-wound and one of the magnets had to have its polarity reversed. I based my design on this, but I don't know if the fact that my pickup design contains only one long pole-piece which contacts all the magnets will make the whole thing not work. I can always make 4 pole pieces but one long piece would be easier.

I'd be glad to discuss this design with folks here. I kind of need to know if this could work before I spent time building this  . As it's probably pretty simple for some of you here, I thought I should ask.

Thanks in advance, and don't hesitate if you wanna know more about this project.

Cheers,

Kevin

[Jenzz]

Hi :-)

Interresting project !

There are two things that came to my mind: I think all magnets should be facing the same magnetic (sounth) pole. Otherwise, the magnetic fields cancel out at the turnover points, resulting in loss of fundamental tone for these strings.

A humbucking effect can only be achieved when both coils 'see' the same amount hum /magnetic field, so the inverting coil configuration can cancel out the hum and leave the signal intact. Due to this, both coils should be as close to one another as possible (hence the configuration on humbucking guitar pickups).

Jenzz

[gotkovsky]

Hi Jenzz, thanks for the reply, you are absolutely right, the two coils have to "see" at least the same strings, not necessarily at exactly the same spot, but it should be somewhat close (like on a classic electric guitar humbucker which have two stacked or side-by-side coils). Not sure how I completely missed this in the first place 

After a few iterations I finally came up with this design:



It's basically a single coil pickup divided in 4 sections for ease of production. Each bobin has its coil, winding is clockwise. All the magnets (40 in total) are facing the same magnetic pole and linked via a single pole piece (4 mm steel rod). The bobbins have been slightly enlarged to accomodate 2000 turns of 0,1 mm copper wire. I'm planning on wiring the 4 coils on a DPDT switch to test various configurations (parallel vs series, etc.).

I'll also make a wooden cover shield, with its inside faces coated with copper tape connected to ground:



And it will probably be fit like this on the harp:



 
Cheers,

Kevin

[Jenzz]

Hi :-)

If you wind the pickups yourself, you might could incorporate a sort of extra winding in each of the bobbins only for the hum canceling.

This came to my mind as i remember the Bartolini Bass pickups for Music Man Stingray basses. These feature a 3-coil concept were the middle coil has no magnets, only to pick up the hum and do the canceling by the way was it is connected to the other two coils.

Jenzz