The Story of a Vintage Pickup and Q - (also, we introduce some new models)
/This all starts with a vintage pickup pulled from an old Fender lap steel. It’s kind of a long story, so if you don’t want to read the whole thing, here’s the carrot-
We fingerprinted a vintage Fender pickup and then developed the most vintage correct Strat pickups we have ever made - the Z-Series™ Tru-Gauge™ ZV55 and ZV63.
Here’s how-
I was shopping for a lap steel towards the end of last year, and vintage lap steels are still a pretty good deal (I think, if you’re into that sort of thing). Certainly, some of the least expensive vintage wood you can buy. I homed in on Fender Champs, and I found a nice one, reasonably priced, from 1963. People generally complain about the pickups in the Champs (at the time an inexpensive, “student” model) as being “weak”, and I already had the plan to take the pickup out and replace it with a Convertible. The Convertible (along with its cousin the Juicy Bucker) makes a fantastic lap steel pickup with the two modes. But I received a very nice surprise when the guitar arrived.
As soon as the guitar showed up, I took the pickup out to measure it. I suspected this might be the case, but I was pleasantly surprised to find what amounts to a flat pole, low wind Strat pickup. The ’63 Champ pickup has 3/16” diameter AlNiCo5 pole pieces, as well as the same pole piece spacing, flatwork dimensions and coil height as a standard Strat pickup. The poles are slightly shorter to accommodate the flat, solid cover, but otherwise this is effectively a ’63 Strat pickup wound to mid ‘50s specs. After getting it fully measured, I started comparing it to my closest analog, the stock Z-Core5 Underwound (ZVU5), and I was surprised by what I found.
But before we get into that let’s back up a bit and talk about one of the most important measures of pickup performance, the electrical parameter known simply as “Q”. Q is the Quality Factor and it’s a measure of the extent to which an entity will resonate. Take a pendulum, for example. A pendulum with a high Q will swing for a long time before it stops. A pendulum with a low Q will stop swinging rapidly after a push. In guitar pickups, Stratocaster style single coils tend to have higher Q and PAF style Humbuckers tend to have lower Q.
A good way to get a feel for what Q “sounds like” is to consider what happens with tone and volume pot loading as in Figure 2. Figure 2 shows the impedance response of the neck pickup from my Fender JV Strat. Unloaded, the Q is about 5.9. Loaded with only a single 250 kΩ volume pot, the Q drops to 2.5. With a 250k Volume and Tone pot, the Q drops to 1.6. As the volume knob is lowered, the Q would drop further as the resistance to ground drops, the “resistive loading” is thereby increased, and more and more high frequencies are bled to ground.
In a very real sense, the Quality Factor is a measure of the “efficiency” of an oscillator or electrical device. And it’s one of the things that define the sound of, in particular, Stratocaster pickups. One of the reasons that it’s hard to make an authentic sounding noiseless Strat pickup is that things that are done to cancel hum tend to make the design less efficient, leading to a loss of Q. So, I was surprised to see that my ZVU5 had a higher Q than the vintage pickup, as shown in Figure 3. Initially I suspected that there was something different about “vintage AlNiCo”, driving the Q down a bit. Maybe this was part of the secret to that “vintage tone”?! But no, I soon realized that I just hadn’t measured enough pickups.
That leads us to another aside. Among other things, over this pandemic I’ve done a lot of work to automate and improve my measurement capability. I now do all of my basic measurements on a Quadtech 9600 LCR meter, which I’ve been able to automate to do full frequency scans between 20 Hz and 1MHz. I spent quite a bit of time doing basic measurements on pole piece materials over the pandemic, and I’ve made a lot or progress on my fundamental model for eddy current effects, but I’ll talk more about that at a later date. What I hadn’t been doing was measuring a lot of full pickups with this new, more accurate, rig. So, I got to work doing that, and rebuilt my database of improved, more accurate pickup measurements.
Some of what I was able to clarify is illustrated in Figure 4. Figure 4 shows the Quality Factor as a function of pickup inductance for a range of conventional Strats as well as the best examples of competitive noiseless Strats, and Zexcoil Strat-style pickups. As the figure shows, the Quality Factor of Zexcoil Z-Core5 models goes up as the inductance goes down. Where I dialed in the Z-Core5 line, around the ZVH5/ZMD5 level, they match with conventional pickups extremely well. But below that level, the response of AlNiCo5-based Strat pickups levels off at a Q of around 2.5, while the response of Z-Core5s continues to go up. I didn’t notice this effect at the time; I guess I just assumed that the Z-Core5 pole piece material response would be similar to AlNiCo5 since it was already matched up where I dialed it in. I developed the ZVU5 and ZVN5 models by simply reducing the winds compared to the others, the same way you would a conventional platform. It’s also pretty clear that there is nothing particularly special about the vintage Fender Champ lap steel pickup. It sits on the same line shared by the JV Strat pickup, a Tokai E bottom pickup, a couple of pickups from a Mexican Fender Robert Cray Strat, a couple of Fender Texas Specials and a Seymour Duncan SSL1. You’ll also note that all of the competitive noiseless pickups have significantly lower Q values than the conventional Strats.
So, now I had a job to do, close the Q gap at the lower output level. And I’ve got a few ways to do it. The first one is easy. Historically, and this goes back to the perspective of electrical efficiency, I’ve used the biggest wire I can in any given situation. That starts paying some big efficiency benefits in the low output regime, to the point where the stock ZVU5 measures only about 4400 Ω compared to a conventional pickup of the same inductance at about 5750 Ω. In fact, the stock ZVU5 uses mostly 40.5 gauge wire. Simply by increasing the wire gauge (decreasing the wire diameter) at the same number of turns results in a resistance increase of about 1000 Ω, lowering the Q as shown in Figure 5 (note that this shift in Q is conceptually similar to what happens with pot loading as in Figure 2, but that in this case it’s the resistive load of the pickup itself, not the pot, driving the change). But that still results in a Q of about 2.7, higher than the conventional AlNiCo5s. I had to change the pole piece material in addition to the wire gauge to fully close the gap, at least at the ZVU5 output level. A pole piece with slightly more significant eddy current effects is utilized in the ZV55 to drive the Q down just a little bit more. With the understanding I have of these effects (the core of our Tone Tuning Technology), it’s actually pretty straightforward to do this in a very targeted fashion, I just need a target. At the ZVN5 output level a different pole piece was not required, simply changing the wire gauge was enough. So the ZV63 shares the same pole piece as the rest of the Z-Core 5 line, but it uses 42 gauge wire wherever possible.
So what? Well, we’ve got two new pickup models that close the gap between Zexcoil and conventional single coil performance in the low output regime. The ZV55, at a similar output level to the ZVU5, uses all 42 gauge wire (the same wire gauge as most conventional Strats) and has specs that are almost identical to the Fender Champ lap steel pickup it was modeled on. It also sports a unique pole piece material that we don’t use in any other design. The ZV63, at the ZVN5 output level, uses 42 gauge wire in 5 of 6 coil positions and also has specs that almost identically match conventional AlNiCo5 pickups.
The slight Q tweaks to these new designs are like smearing a slab of butter over the already luscious tone of the current designs. And while these new pickups work great on their own, they also work fantastically well when paired with the stock Z-Core5s. Here’s an example. Use a ZV55 in the neck with a ZVU5 or ZVN5 in the middle to enhance the quack. This is the approach I use in my Pink Floyd tribute band rig. I was already really happy with my tone with a ZVU5 in the neck (for stuff like Shine On You Crazy Diamond), but with the ZV55 in there I’m just ecstatic.
We’re extrapolating this “Tru-Gauge” approach to our upcoming line of ZCore Tele bridge models as well. Look for them in early 2022.