GFS Nashville Vintage vs. Fender Fideli'tron

[antigua]

Vs.

Ken Willmott sent me some GFS Nashville Filter'tron style humbuckers, PAF clones that attempt to resemble Filter'trons with a metal cover than has that characteristic H hole in the top. I happen to have Fender Fideli'trons sitting loose, so I decided to you them as a point of contrast, since Fender Fideli'trons appear to be very good Filter'tron stand-ins. The GFS Nashville go for about $35, while the Fender Fideli's go for about $50 used apiece.

After taking a look, the GFS appear to be PAF clones with plastic spacers and ceramic magnets, so that leads one to think they will sound like a bright PAF, not a Filter'tron, but it turns out, that if the GFS is wire in parallel rather than series, it does get a resonant peak that is very close. GFS also loads the Nashvilles with a ceramic bar, which helps approximate the double tall AlNiCo bar of a Filter'tron.

Electrical Differences

Here is a plot that shows how the Fideli'trons compare to the GFS if the GFS are wired in series. The two higher peaks are the GFS bridge and neck in series, while the two lower peaks are the Fideli'tron, which is always in series. The GFS Nashvilles have a lower treble response, and much higher output than the Fender Fideli'trons.

In this configuration, the Fender Fideli'trons produce 2.3H and 1.8H inductance for the bridge and neck, while the GFS Nashvilles produce 6.6H and 4.3H inductance, very different levels of output.

But if the GFS are wired in parallel, they come very close together. In parallel, the GFS' now have inductances of 1.6H and 1.1H for the bridge and neck, which is lower than the Fideli'trons wired in series. The GFS' still have a lower peak despite the lower inductance, which indicates a higher degree of parasitic capacitance is at work, since the resonant peak becomes lower whenever either the inductance, or the capacitance, is increased.

Of course, this is unloaded, as though there were no volume or tone pots complicating matters, so here is the same plot above, but this time with the simulated effects of a guitar cable and volume and tone pots, by way of 200k ohms resistance and 470pF capacitance across the pickups:

Now, all of the sudden, the GFS Nashville's have a higher peak than the Fideli'trons interestingly, and this is because the GFS had a higher parasitic capacitance to begin with, and so the added 470pF capacitance didn't drag their peak frequencies down as far.

The GFS Nashville's still have a higher Q factor than the Fideli'trons, but that's nothing a little working of the tone knob on the guitar wouldn't correct for.

These plots are all made with the covers grounded, so the capacitive coupling between the coils and the covers and base plates, as well as the conductor cable, are all baked into the results.

Here are some raw numbers:

GFS Nashville Vintage Filtertron Style Bridge Humbucker R02

DC Resistance:

- series:     9.46K

- b/w coil:   4.71K

- r/g coil:   4.75K

Inductance:

- series:   6.598H

- parallel: 1.631H

- b/w coil: 2.940H

- r/g coil: 2.933H

GFS Nashville Vintage Filtertron Style Neck Humbucker R01

DC Resistance:

- series:     8.37K

- b/w coil:   4.13K

- r/g coil:   4.24K

Inductance:

- series:   4.323H

- parallel: 1.086H

- b/w coil: 1.801H

- r/g coil: 1.800H

Fender Fideli'tron Bridge

DC Resistance in Series: 5.13K

Inductance in Series: 2.325H

Fender Fideli'tron Neck

DC Resistance in Series: 4.46K

Inductance in Series: 1.7853H

Physical Differences

The other big aspect to consider is the magnets. Unlike PAFs, Filter'trons have a larger AlNiCo 5 magnet inside them, giving them a higher flux density than a PAF. I measure PAFs at around 230 Gauss at the screw/pole tops, while the Fender Fideli'trons measure closer to 300 gauss.

The GFS Nashville's meet this difference by using a ceramic bar magnet, and this causes the gauss at the GFS' screw tops shoot past the Fideli'tron to 320 to 350 gauss.

The higher flux density means more current, and more voltage for a given degree of string movement, as well as subtle tonal differences that are hard to pinpoint, owing to the exponential rate at which magnetic flux decreases with the distance between the strings and the charged pole pieces. But I'm glad to see that GFS didn't skimp out on this particular detail.

Here are some pics of the guts:

GFS Nashville

Fender Fideli'tron

Setup details:

Bode plots are made with a Velleman PCSGU250 and the supplied probes in 10x mode, with the function generator feeding a driver coil of 0.48mH, placed on top of the pickup and driven with 2Vpp. The pickup is connected to an integrator circuit, designed by Ken Willmottkenwillmott.com/blog/, with a Velleman 10x probe, and fed back into the Velleman PCSGU250. I measured the probes' capacitance at 20pF, so that amount is subtracted from the capacitance calculation. The "loaded" tests have exactly 470k ohms and 200pF capacitance across the pickup.

The inductance and Q measurements are made with an Extech 380193 in "SER" series mode, and the mean value between the 1kHz and 120Hz modes is recorded. The capacitance value is derived from the inductance and measured resonant peak.

Magnets are tested with a Spin Doctor ERgravitastech.weebly.com/spin-doctor-er.html

[newey]

This confirms my experience with the GFS Retrotron that I used in my Epiphone LP Jr. mod. Although I used the "Memphis" version rather than the "Nashville", and I'm unsure of how their construction may differ one from another. But the guitar has a series/parallel P/P switch, and I do like the parallel setting, it does (to my ears anyway) sound more like a Gretsch pickup.

I did not think much of the coil-cut option with this pickup, though- the output dropped off too much.

[antigua]

I forgot to mention it here, but the Epiphone Swingster model does exactly that; it has a PAF sized "Filter'trons" that are are wired in parallel, and when you pull up on the volume knobs, they switch to series. The guys at Epiphone had the right idea. 

That being said, I do prefer the sound of genuine Fitler'trons, and I think it comes down to the higher strengthed AlNiCo bars they contain. I think the PAF form fact works best for warm tones, and if you want more bite, you're better serves with more flux, as is seen with Strat / Tele pickups, Super Distortions and Filter'trons.