Bare Knuckle Pickups Irish Tours, Analysis and Reivew

[antigua]

bareknucklepickups.co.uk/main/pickups.php?cat=strats&sub=vintage_hot&pickup=irish_tour



I bought this set a couple years ago, looking for "better Texas Specials", and the two popular sets this set cross shops with are the Fender Texas Specials and the Lollar Blackfaces. The Irish Tour bridge, wound all the way up to 7.5k, with a loaded peak of 3.03kHz, is substantially hotter than the bridge of either of those sets, with are both a few hundred hertz higher. The Irish Tour neck and middle pickups are also hotter than the Texas Specials or the Blackfaces, with loaded peaks around 3.5kHz, where as the others are closer to 3.8kHz. Overall, it's on the hotter, darker side of the "blues" pickups on the market.

The pickups look very attractive. The set follows the gray bobbin aesthetic with enamel wire, and the metal base plate looks great.

The capacitance is freakishly high with the neck and middle pickups at over 200pF, and the bridge is rather high, measured at 153pF. Typically, capacitance is somewhere between 90pF and 140pF for a Strat pickup wound to 6k. This means that, through whatever means, the copper coil wire is more densely packed than usual. Could be thin enamel coat, could be tight wind tension. The extra 50pF-100pF is equivalent to about two to three feet of extra guitar cable. At 3.6kHz, his high capacitance causes the neck and bridge pickups to have a rather low resonant peak compared to other Strat pickups that feature a 2.6H inductance. The Blackface middle pickup has 2.6H inductance also, and has a loaded peak of 3.8kHz.

Since the bridge has a base plate, I got a chance to analyze Strat pickup base plates in general, the details are further down in the post.


Bare Knuckle Pickups Irish Tour Bridge
DC Resistance: 7.51K
Inductance: 3.905H
(3.665H without baseplate,
3.830H with Fralin baseplate,
3.931H both stacked)
Calculated C: 153pF (163-10) (coil only, no baseplate)
Coil width: 0.5745"

With Baseplate
Resonant Peak:         dV: 13.0dB f: 6.51kHz (black)
Loaded (200k & 470pF): dV: 5.0dB f: 3.03kHz (red)

Bare Knuckle Pickups Irish Tour Middle
DC Resistance: 6.36K
Inductance: 2.635H
Calculated C: 210pF (222-10)
Coil width: 0.5470"

Resonant Peak:         dV: 15.4dB f: 6.58kHz (green)
Loaded (200k & 470pF): dV: 6.9dB f: 3.59kHz (gray)

Bare Knuckle Pickups Irish Tour Neck
DC Resistance: 6.37K
Inductance: 2.642H
Calculated C: 206pF (216-10)
Coil width: 0.5240"

Resonant Peak:         dV: 14.6dB f: 6.66kHz (pink)
Loaded (200k & 470pF): dV: 6.9dB f: 3.59kHz (black)

Pole piece flux density: 900G w/ flat stagger, 1050G estimated normalized. AlNiCo 5
- Without base plate, Gauss drops 50 -100G

Fralin baseplate width: 0.0555"
BKP baseplate width: 0.0445


Bode plot:





Base plate analysis:

This is the first set I've analyzed with a bridge that featured a base plate. I popped the base plate off, and measured it again in order to get with and without electrical measures. I also have a Fralin base plate kit to contrast with.

All metals in and around the coil have two properties with are of importance: permeability and conductivity. When the magnetic field generated by the moving strings or the coil(s) intersects with conductive metal, eddy currents causes a resistance that increases with higher frequencies resulting in loss of treble. When the metal is permeable, the magnetic field is slightly amplified, increasing inductance, which makes the pickup hotter (louder, less treble).

The base plates are made of steel, which is has a high permeability and a moderate conductivity.

The inductance of the bridge pickup starts out at 3.905H @120hz with the base plate in place. With the base plate removed, the inductance drops to 3.665H, a drop of 240mH, or a 6% drop. Just for fun, I placed the Fralin base plate on the pickup (pictured below), the inductance read 3.830H, which tells us that the Fralin base plate is less permeable and/or conductive than the BKP base plate to some extent, and it so happens that the Fralin base plate is thicker than the BKP by about 1/100th of an inch. The grades of steel used must differ.

This bode plot below compares the bridge pickup with and without the base plate, loaded (short peaks) and unloaded (tall peaks).

With Baseplate
Resonant Peak:         dV: 13.0dB f: 6.51kHz (black)
Loaded (200k & 470pF): dV: 5.0dB f: 3.03kHz (red)

Without Baseplate
Resonant Peak:         dV: 15.0dB f: 6.66kHz (green)
Loaded (200k & 470pF): dV: 5.9dB f: 3.17kHz (gray)




When the base plate is removed, the unloaded peak moves north east by 2dB and 150Hz. That just confirms that the inductance has dropped, and eddy current losses are reduced marginally.

The loaded difference is more important, the load presented approximates a guitar cable and a guitar's pots, so it reflects a realistic scenario. In that case, the peak rose by just under 1dB and increases the peak by 140Hz, but more importantly, it appears that it broadened the Q of the peak, providing a little more output between 1kHz and 3kHz, or the upper mids. However, the boost is only about 1dB, which is at the edge of what is audible to human hearing.

In conclusion, physics says the base plate should make the pickup "hotter", but in practice, the base plate only makes it a tiny bit hotter. This whole base plate business started with Telecaster bridges, and my understanding is that it was never there to make the bridge hotter, it was considered good practice to have a steel keeper along side AlNiCo to help it retain its charge, and it provided a threading for the three screws, as opposed to using the flat work as threading. The Tele bridge is a hot pickup because it tends to be wound over 7k with 42 AWG, that's hot with or without a base plate. This Irish Tour bridge is wound to 7.5k, it's high output with or without a base plate.

The important thing to realize is that the base plate raises the inductance, but that's exactly what happens when you add more winds of wire to the coil. The baseplate isn't doing much a few hundred more winds of wire wouldn't do. There is the issue of added eddy current losses, but those are exceptionally minimal here, as are hysterisis losses. Adding a base plate to a Tele bridge makes sense from an authenticity standpoint, but the practice of adding them to Strat pickups is mostly just gimmick that exploits popular misconceptions about the efficacy of base plates.




Pics:








Fralin base plate over the bridge, Extech LCR meter: