GFS Pickups

Again this was inspired by watching YouTube. So how did I get the idea of looking into pickups from Guitar Fetish? First of all, I was watching a video by a prominent YouTuber from whom I have watched quite a few videos and these videos were in general sticking to facts and the truth which you know by now is the main purpose of this website. Anyway, he had purchased a guitar from Guitar Fetish that he was checking out and this guitar was equipped with GFS pickups (I am not sure which), but since I have purchased stuff from GF before and I was familiar with the GFS pickups, I decided to check them out, as in measuring every parameter that I thought would have interest for this site. Second reason was very simple, I liked what I saw when I read the information about the pickups, the technical information, not the hoopla buzz words, which I typically ignore because they are meaningless. I had also seen a video with a guy instructing how to adjust screw height in humbuckers equipped with such. Now, I have expressed elsewhere my dislike for the humbuckers with screws elsewhere, but I could not really avoid them if I wanted to do something with screw height, now could I?

So I got on the GF website and started to look for the right pickup, I wanted a slug/screw pickup and I found a type with AlNiCo magnets. Perfect! To be precise, they are PRO AlNiCo 5 BKPRO109 and 110 for bridge and neck position, respectively.

I was also interested in their trademarked Kwikplug system so I got a few of the female side Solder Blocks, but I could not get any male plugs to match them, so they got shelved for now! I will be clear later, I went back some time later and got some pickups that were already Kwikplug and they came with mating plug and cable. These were the so called KP – GFS Crunchy Rails type, KPH93 and KPH94. As you may know, I am very fond of rails pickups, especially the “full size” ones.

The first thing to be tested was the pickup response to a vibrating string, the voltage output from the pickup when subjected to my pickup tester that I have used on several occasions on this website. The video I had watched, the guy had adjusted screws half a turn up from flush for the B and A, one full turn up for the D and G strings and the two E strings remained flush with the top of the pickup. What I wanted to see was the difference between flush and 1 full turn up, for the same string. In other words, the only thing that changed was the screw height, everything else remained the same.

The result can be seen in Fig 1 and I will let you judge if the difference is significant or not, I do not think the difference is big enough to bother! The blue waveform is with 1 turn out, the orange one is flush. I was slightly puzzled by how wiggly the waveform turned out because I had done what I could by adding a fully shielded cable to the “pig tail” out of the pickup, so how did noise (which causes the wiggly lines) get in there? I found out later the the cable out of the pickup is NOT a properly shielded cable, what appears to be a shield is just a bare wire that runs along the insulated ones in the cable, a so-called “drain wire”. You typically see drain wires with foil shielded cables (that I do not promote). The cable and the drain wire are connected correctly just as I describe in the Guitar Shielding page, the drain wire is connected to the base plate of the pickup and there is no connection to the pickup coil wires at all. Bravo GFS! All four wires are brought out, two per coil. One from each coil are soldered together for a real humbucker. I measured with the wires like that and with the coils individually, I might add, for measurement only. I really hate that coil split shit!

The result of the humbucker measurement can be seen in Table 1. The Resonance Frequency fo is measured and the equivalent PU capacitance calculated as described in “Resonance Measurement”. I could not stay away from measuring each PU coil separately, the results are in Table 2.

The nomenclature in the table is according to wire color, g = green, r = red, b = black and w = white. R is coil resistance, L is coil inductance, fo is resonance frequency and Co is the calculated coil capacitance. In the true humbucker configuration the red and white wires are soldered together, in Table 2 these two are un-soldered. This was done mostly for intellectual curiosity, elsewhere, I have talked about equivalent diagrams for pickups and set certain conditions for parameter values. The conditions do not fit 100%, especially for the inductance. The capacitance is pretty close. This finding is just something to take notice of, it does not make the equivalent diagrams or any explanations in connections with these wrong in any way. As an example, we can look at inductances. In Fig 1 the total inductance, Lt, for PRO 109 is 6.47 H whereas in Fig 2, the partial inductances are 2.68 H and 2.8 H. Adding the two yields 5.48 H which is about 1 H less than for the total Lt. This in itself is something that must be looked into further since both R and L are measured with a reliable, good quality LCR meter. It looks like I have to look into the way inductance is measured and a what frequency and so on. As I have hammered home in many other places, capacitance in pickups, C, CANNOT be measured with a LCR meter!

As mentioned before, the pickups are named KPH 93 and KPH 94 and they pretty much went through the same measurements, except there are no screws (thank goodness) on these, they are my favorite type, full size rail pickups. So the measurement in my simulator is comparing the two types of pickups and you would be expecting a difference, if nothing else by the indicated data. What is depicted in Fig 2 is not so much for comparison but for studying the waveforms.

Notice how much smoother these waveforms are, the noise has been rejected and here is the reason. The cable is truly shielded, meaning that the shield is made up of individual strands of wire surrounding the insulated cables, an arrangement which works really good. Since this is a real humbucker, there are only 3 wires out, the coil center “tap” is combined at the input to the Kwikplug (terminal marked “2”).

A Problem: I mentioned the “great shield” earlier, but when I first measured out the pickup, basically just Ohmed it out, I discovered that the shield which was only supposed to be connected to the base plate, nothing else, was also connected to one of the output signals (black wire). That was very disappointing indeed, so far everything looked so good! This was on KPH 93 so I quickly grabbed the other one, KPH 94, that did not show this behavior, it was all perfect. Starting to look at the pickup, to be more exact, the Kwikplug arrangement and found a solder bridge between terminal 3 copper pad on the PCB and the rivet that was holding the Kwikplug to the baseplate of the pickup. The rivet was not supposed to be connected to anything, but a solder mistake connected this rivet to terminal 3 thereby shorting this terminal to the baseplate which was correctly connected to the cable shield. It must be mentioned that the terminal 3 pad and the rivet are too close and that an accident like this could be all too common, so if you have one of the Kwikplug type pickups, please check them out because it is possible, depending on your connection in the guitar, that the pickup in not working correctly.

Individual measurements for the pickups in Table 3, and based on the values measured, it is obvious that the 93 is for the neck position and 94 is for the bridge, as advertised by Guitar Fetish. So far so good!

Without taking the pickup apart, we are maintaining the three wire system with the white wire connected to the “mid-point” of the pickup coils a more detailed measurement was performed. Table 4 shows the results of this. In this case it would be expected that things were a bit more even, base on the symmetry of the pickup design.

If we take the easy part first, comparing the calculated capacitances, we see that for KPH 94 it is dead nuts on, (59.4 + 61.3)/2 is 60.35 pF which is just about equal to 60.1 pF in Table 3. For the KPH 93, the numbers are a few pF away from the value in Fig 3, but they are, for all practical purposes, equal. The inductance values still do not add up, no pun intended. This is something I need to work on next, as mentioned before, it is not a significant issue in a practical sense, but my scientific mind needs to know. I can think of a few reasons that it would be different, but I have to work on it a bit to find the exact reason.

Also, I started measuring the B flux density of the pickups, I will put it up when I have a result. So, as they say on TV, please stay tuned!