Dummy coil for Danelectro

Hi,

this is yet another Danelectro upgrade that I did recently. This guitar was always kind of noisy and hissy, but I did not really mind, but then we were playing at a gig where the lighting and other electronics created a lot of bad stuff that got picked up by the lipstick pickups, fortunately I was standing far away from my amp otherwise it would be a disaster, not only it would hum but also squeal. After that I was recording some guitar parts and again, it was in a place that has a lot of fluorescent lights, computers, fans etc. When the guitar was positioned so that the noise was the worst, it was half as loud as the actual playing! That was really insane. So I did some research and I found a pretty nice solution produced by Suhr company for Stratocaster guitars and similar thing made by Ernie Ball that is used in their guitars - a dummy coil.

I won't go into the actual guitar pickup functionality, it is explained in many other places around the internet. But basically, every pickup picks up a noise/hum. If you want to cancel the hum, then you need to pick it up again, but out of phase, so it cancels itself out, like if the noise was a sine wave, one coil would pick up a top peak and another coil the bottom peak, which would leave zero signal. This is how the humbucker pickup works, you have (usually) two more or less identical single coil pickups that are wound in opposite direction (magnet polarity is also reversed so the actual audio signal from strings does not cancel out also). If you for example remove the pole pieces from one coil of a humbucker, you would get a "single" coil that is cancelling out hum. But since the signal goes through both of these coils, the resistance and inductance of the other coil also affects the sound. So what I'm trying to say is, that you need to find some balance between hum cancelling effect and a tone changing effect, ideally, you want 100% of the first and 0% of the second effect, but that is just impossible. But you can get pretty close.

Ok, so I told the theory anyway, might as well continue. There is a patent here, that explains one very basic physics principle regarding coils, particularly guitar coils and them picking up noise.

http://www.google.com/patents/US7259318

It says, that you can create a coil, with much less resistance and inductance, thus a coil that would not affect the tone (it does, but you can't tell the difference). All you need to change is the coil area, the area inside the coil. This area for a guitar pickup could be, let's say 10 cm2. The pickup has 5000 turns of wire and for example 5k ohms. If we were to create a coil, big coil that would fit inside the guitar, under the pickguard or backplate (the Suhr way) with area let's say 100 cm2, then the dummy coil would need only 500 turns. And here comes the best part - the wire gauge doesn't matter, so you can wire it with much thicker wire than the pickup, so you end up with a dummy coil that has a resistance like 50 ohms and also negligible inductance, so your tone gets changed very, very little.

Back to the Danelectro. Calculations: bridge pickup is 4,02k ohms, I estimated 43 AWG wire gauge, 9,75 cm2 area of the coil, 16 cm perimeter of one turn. In some tables you can find electrical resistance of copper wire, for 43 AWG and my pickup, it results in 512 m of wire. That divided by 16 cm leaves 3200 turns. Multiplied with the area it leaves 31200 cm2*turns - this is the hum picking value of the pickup. Save this value for later. (All of this is questimating, because the effectiveness of a coil comes into effect too, pickup coil is not very effective because it is far from round, these calculations are done for two coils with the same shape).

Now where to put the dummy coil, how should it look like? How big? This was actually, for the Danelectro very challenging, there is no backplate to use the Suhr design, I can't just remove a magnet from some other lipstick pickup because there is no plastic bobbin inside of these, in order to remove the magnet, you destroy the coil. Danelectro is hollow, but you can't really reach inside that well. 

Article about installing dummy coil inside a Stratocaster (there is also another article about Telecaster on that site) https://sites.google.com/site/stringsandfrets/Home/noise-reduction-for-sc-pickups

I decided to put the pickup inside, using a plexiglass bobbin that I made for this. After careful measuring, it was clear that I could fit a round coil with 5 cm in diameter max. Back to the calculations, I have the 31200 cm2*turns, this divided by area of a circle that has 5 cm in diameter (20,43 cm2 area) leaves aprox. 1530 turns. That's a lot, but this is the biggest coil I can fit inside, so decided to go for it.

I had a small spool of 0,22 mm (32 AWG) enameled wire that I used, after some 1500 turns it was clear that the spool could give me around a hundred more turns, so I used it all. I then used a very simple setup to test the hum cancelling qualities using a breadboard, PC soundcard oscilloscope and a guitar amp. First I measured (this oscilloscope is very crappy but just for comparing hum levels it is fine) the response of a bridge pickup, amp was set to very high gain distortion channel so the hum is amplified a lot and therefore visible in the scope. I got around 120mV p-p. Then with the bridge and neck pickup in series (which formes a humbucker) it gave me 55mV p-p. So I was aiming for this value with the dummy coil and a bridge pickup in series. First, it was around 65mV p-p, that's not bad. Then I removed 50 turns from the dummy coil and measured again, now it was 55-60mV p-p, another 50 down, now I had that 1500 turns which was calculated, it gave me 50mV p-p, which is even better hum cancelling effect than the humbucker setup! This is probably due to the fact that Danelectro pickups are not identical like the two single coils in a humbucker. I was customizing it for the bridge because I use it for gainy sounds and the neck for clean. Resistance of the dummy coil is 140 ohms.

Although the mains cycle hum got cancelled completely, I must have some weird source of EM interference at home because from time to time there is some weird noise coming from the single coil (tested with my Les Paul tapped humbucker to test if it was really some interference and not the guitar). This noise is not present in our rehearsal room. Interesting fact remains though, that this noise gets cancelled with the bridge and neck pickups in series, even though the mains hum is cancelled less. This is probably because of the different shape, wire, and other things of the dummy coil.

Sound is awesome, everything works fine. Position of the dummy coil in the circuitry required no difficult changes, as you can see from the schematic, when you select the bridge pickup, the dummy  coil is in series, when you select the middle position (humbucker - neck and pickup) one end of it is not connected and when selecting the neck pickup, the current flow reverses so the dummy coil changes polarity and works for the neck pickup too, which is awesome. The switch in the schematic is ON-OFF-ON type, sorry I could not find the correct schematic symbol for it.

Also I changed the potentiometers, because I just don't think that the volume and tone for each pickup is practical. The first schematic is the original, the second is the upgraded. Potentiometers in the second schematic are done in the 50's style, so that I won't loose highs when rolling down volume. And also the tone control became actually usable, it now has much better control and range, I might learn to use it after all!

Pictures:

Dummy coil core cut from plexiglass and glued together

Wound dummy coil, wax potted

Dummy coil shielded

Mounting plexiglass piece, hole in it is for a screw that holds the bridge pickup in place

Testing the hum cancellation

The dummy coil is positioned between the pickups under the pickguard

Schematic

Danelectro shielding and stuff

Hello,

in my first article on this page, I shielded my Danelectro DC59 using an aluminum foil. It was better than nothing, but it had its flaws. One of that flaw was the bad contact between a pickguard shielding and shielding in the control cavity. Then there was the issue of shielding the cavity itself, since this guitar is hollow, and you just can't reach with the tape everywhere on the insides, because in order to do that, you would need to take the body apart. And of course, the aluminum foil looks kind of cheap and not pretty. 

But then my friend wanted me to shield two if his bass guitars, and at that time I found a good deal for a copper tape on Ebay, so I bought a lot of it and shielded these bass guitars with it. It worked great so I decided to give my Danelectro the same treatment. But this would just solve the material, but not the actual flaws I mentioned earlier. Then I found an article, where the author described his original production Danelectro from the 50's, and how he wanted to make it playable again. Anyway, there was a picture that he took of the controls shielding, which was really cool looking.

Here is the article

As you can see, there is no need to shield the body itself. This pocket or enclosure that completely covers the controls is fixed to the pickguard, so everything has solid connections and it also cuts the material used and so on ... it is simply a perfect solution. Of course, this is only usable if you have the jack mounted right next to the potentiometers, if you have a reissue Danelectro with jack on the side of the body (or if you put it there), then you need to come up with a different solution.

As you can see, I removed the aluminum foil completely and put the copper tape just near the controls because there is no need to shield the entire pickguard. Next, I needed something that would form the actual enclosure around the controls, because the tape itself is very thin and would not hold shape. I decided to use cardboard (from pizza box). The pictures are quite self-explanatory here, I really documented the whole process thoroughly so you can see the steps. No rocket science there, just making a box from a piece of cardboard which I covered in the copper tape after it was finished.

Done :)

I also reworked the wires coming from the neck pickup, as you can see, I used two shielded wires (one of them has its shield connected only on the pickup side to not cause ground loops) instead of the fat stereo one, which was really inflexible and hard to work with inside the cavity (yes I accidentally switched the green and black wire, because I'm used to the standard "black is ground" coloring).

So that covers the shielding. But there was another quite important thing I did to this guitar. As you can see in the pictures, I added a new selector switch. On the next picture, there is an original switch (the chrome one), which was very noisy, there was cracking sound when selecting and overall it wasn't very comfortable to use. I bought a similar one (the black one), but it was way worse.

The idea for this particular switch also came from my friend's bass guitar, which had this one and it was super comfortable to switch and also it is very simple and easy to work with. The bass is a Jolana D-bass, a Czechoslovakian made bass guitar that strongly resembles the Rickenbacker bass guitar. It is basically a Les Paul switch which has its bowels bent 90°. After some research, I found that this is a standard switch on the Jazzmaster guitars, so I was ready to buy it. Of course, there is always a catch, and with this switch, it's a big one.

The standard Danelectro switch is an ON/OFF/ON configuration, meaning that the pins are connected to nothing when in middle position and then in the outer position the middle pin and one of the outer pins are connected. The standard Les Paul switch is ON/ON/ON configuration, the outer positions function the same, but in the middle position all the pins are connected to each other. And this type of configuration is impossible to use when you want your middle position to be both pickups in series and one pickup alone in the outer positions. The Les Paul configuration (which is just me saying it is a "parallel in middle" configuration) is shown in the next pictures. As you can see, the switch is mechanically very simple, the plastic thing connected to the knob just moves the outer steel sheets away from the inner ones and breaking contact.

When I was searching for this Jazzmaster switch, I looked if they have it on StewMac, and they did (I bought it on Ebay eventually, this was just me looking for more information). And also, someone in the comments section for this product said, that it is possible to modify it for series pickup configuration by just taking it apart and change the place of the sheets. It is kind of not easy to explain in words, so I'll just post more pictures.

Switch dismantled

As you can see, the switch is very simple. In order to make it work like I wanted to, I needed to use longer screws, because I will be adding new layers (steel washers) to make space for the new configuration. But there is some plastic insulating cover on the screws that also hold the layers properly. The screws are M3, the holes are something over 4mm in diameter (it fits M4 screws, but they are somewhat loose).

So I took longer M3 screws, and tried to make them thick enough to tightly fit the layers. At first, I just used an electrical tape as shown in the picture above (the new ones are on the left, steel washers that will be used as another layers also shown). But the tape was impossible to fit, because when it was tight, it tended to curl up, and when I removed some of it, it was loose. So I used heatshrink tubing on the screws, two layers which made exactly the right diameter. Unfortunately I don't have a picture of that. Here is the modified switch finished, as you can see, it makes connection in the outer positions instead of breaking it.

Oh and I got rid of the piezo pickup, which I didn't like anyway, it picks everything you do with the guitar, every touch, every scratch since it's hollow. And the sound was rather meh.

And here is the Danelectro in its full glory :) Very nice guitar. When I bought it, there was a sticker on the head which said "totally shielded". Well it was far from it, but now it finally is. With a new smooth and comfortable switch.