The One Weird Thing About Gold Foil Pickups

Okay, the funky gold foil pickups found in cheapo Japanese and American gutiars in the 1950s and ’60s are popular again. And trend slut that I am, I’m smitten with them. But they do this one really weird thing ….

It has to do with the capacitive relationship between the guitar volume knob, pickups, and downstream pedals and amps. If you don’t use your guitar’s volume knob as an expressive device, this behavior probably doesn’t matter. But if you do, this is potentially a big deal, one worth considering before purchasing a pair of gold foils.

I first realized this as I was preparing my Gore Pedals demo for the NAMM show. Many of my pedal designs depend on the ability to alter tones from the guitar — it’s how I get away with using relatively few knobs. It’s the quality you hear in the first minute of my Cult pedal demo:

You just can’t do that with gold foils. Apparently, the rubber magnets in gold foil have a different capacitive relationship with downstream gear, relative to conventional alnico- and ceramic-magnet pickups. Some of the peaky, high-resonance sound you get when rolling back the volume knob on a guitar with gold foils are pretty cool, and I can certainly imagine using them. But I definitely have to modify my technique when using gold foils.

I recently reviewed one of the bitchin’ new Supro guitars for Premier Guitar. Their pickups are based on a different historic gold foil model, but they exhibit the exact behavior demoed in my first video above. After writing that review I spoke with Ken Calvet of Roadhouse Pickups, who created the excellent-sounding Valco-style gold foils for Supro. He acknowledged the unusual volume knob behavior and attributed it to the rubber magnets used in historically accurate gold foils.

My first video above demonstrates this property using a capacitance-dependent vintage-style Fuzz Face. Not only do you encounter the same thing with many non-buffered (i.e., cool) fuzzes and boosters, but also when plugging directly into an overdriven amp. You can’t summon clean sounds from a dirty amp via the guitar volume knob the way you can with most conventional passive pickups.

But despite all of that, I’m still crazy for the Lollar Gold Foils in my DIY Resistocaster:

Has anyone else noticed this quirky characteristic?

13 comments to The One Weird Thing About Gold Foil Pickups

  • Matt Diehl

    Huh! I tested this on my Gold Foil-equipped Partscaster – & you’re completely right! I do use my volume knob expressively often – especially because I use a Fuzz Face as a significant part of my pedalboard, which I’ve found is really built for this approach (Sam McCrae actually instructed me to dime the FF & adjust the amount of distorted tone with the volume knob. However, I apparently do this more on my P-90-equipped guitars (where the cleans are sweet & ringing). On the Partscaster, I don’t think I ever noticed because the Gold Foil there is on the neck, where if I engage usually have/want a higher-gain, non-clean situation going. (I had played Teiscos with original GFs but didn’t play clean ever – I get too garagiste excited!) My other, non-installed GF (a Lollar) is going on a neck as well. Useful!

    • joe

      So I’m not crazy! I had the experience, though not with a FF, but with my Cult pedal, which like the FF, relies on the capacitive relationship between guitar and amp. FWIW, I second Sam McCrae’s method 100%. It just doesn’t work very well with these pickups. (Though the full-on FF distortion is pretty epic with gold foils.)

  • Matt Diehl

    Actually meant to include a shot of my guitar, not pedalboard…

  • Digital Larry

    I hope someone can explain more than “rubber magnets” because I find this behavior baffling.

    I think about guitar circuits in terms of impedance – which generally means that if something is inductive or capacitive then impedance changes with frequency. If you have an inductance and a capacitance interacting directly, you get a peak. Resistance is the case of an impedance which does not change with frequency. They are both measured in ohms. Other than that there is not much to say!

    An impedance which is low tends to load down a connected impedance which is high, whereas as high impedance has relatively little effect on a connected low impedance. This is more about pickup impedance than normal people can handle: https://courses.physics.illinois.edu/phys406/Lab_Handouts/Electric_Guitar_Pickup_Measurements.pdf

    So what the *&@#$(!$*& is the model for a gold foil pickup? If it has measurable DC resistance then it is not a series capacitance (e.g. a piezo pickup).

    A guitar volume control’s fixed part hangs off the end of the pickup. If you have a low impedance hanging off the adjustable wiper, then the load on the pickup itself will be maximum when volume is cranked. When volume is low then the pickup itself is less loaded. Whether the pickup impedance is low or high, I would not expect this behavior.

    Joe are you aware of any patent drawings about these showing what the “gold foil” itself does or where it is structurally?

    Does it only happen when you use it with a heavy load e.g. grounded emitter input with capacitor to base? Or does it also happen when you use it with a high impedance buffer or effect?

    • joe

      Hah! I was hoping YOU would explain it for everyone, man! I am utterly stumped. But it’s 100% repeatable, and lots of folks have chimed in here and on my YouTube channel seconding the observation. I’ll plug in a buffer and see what happens …

      • Digital Larry

        I’m a little hesitant to make pronouncements here after blowing lots of theoretical BS smoke over the years, the kind that I instantly regret. Even though I was using the best words!

        It’s better just to ask questions and act confused, because I am. Terry’s description is nice but it doesn’t help me too much. I do like the tone of those pickups however!

  • I’m pretty sure the ‘capacitance’ of the magnet has nothing to do with it. The construction of a Gold Foil pickup is broadly like any other electromagnetic guitar pickup – a coil of copper wire and a magnet.

    A Gold Foil pickup of the Teisco/Lollar type has a fairly wide flat coil of 44awg insulated copper wire with the ‘rubber’ magnet in the middle. This sits on top of a metal plate (I believe it is a nickel plated steel plate) which extends past the coil on one long edge and has a fold in it. Like a Strat saddle this fold or crease is drilled and tapped for six small steel screws. Several commentators have said that these pole screws have no effect on the pickup and are purely cosmetic. While may be true that they do not allow much in the way of string to string output balancing, they are made of a magnetic material and are next to the pickup magnet so I suspect they do influence the output of the pickup. The pickups have metal base plates and top covers. I do not know what these are made of, probably plated brass or maybe nickel.

    Alnico magnets and steel poles are electrically conductive so induced eddy currents can flow through them, they also have a magnetic permeability which is greater than that of free space (air). So when inserted in a coil the inductance of the coil goes up. As far as I understand it because both ceramic and ‘rubber’ magnets consist of powdered magnet particles embedded in clay or plastic, they both have low eddy current losses and a low permeability. This would mean that a Gold Foil should have a relatively low inductance and measurements of the Lollar Gold foils show that it is on the low side, around 1.9H (typical Strat single coils are 3H and above).

    The Gold Foil has a low flat coil with not a great number of turns so you would expect the COIL to have low capacitance and combined with the low inductance that should mean a low Q. Measured Q at 1000Hz is indeed quite low, 1.3 compared to 2.5 to 3 or so for a typical Strat single coil.

    With a typical Strat pickup the inductance of the pickup, combined mostly with the capacitance of the instrument cable (into a 1Meg load) results in a resonant peak of at least 3 or 4db at around 4kHz with the volume at max. As you turn the volume down this peak reduces. You wont get such a pronounced peak with a Gold Foil and the response won’t change much as you dial down.
    When plugged in to a Fuzz Face or similar then any guitar / pickup is heavily loaded by the low impedance of the Fuzz Face input.

    I have recently fitted a Lollar Gold Foil to a clients Telecaster. I did wonder if Gold Foils had a ‘preferred’ control resistance and tone capacitor value. A quick internet search yielded nothing conclusive, other than the possibility that the old Teisco guitars may have used 100K controls. I fitted the pickup with the existing 250K controls and 0.022uF tone cap and I did notice that the tone control didn’t have much effect on the Gold Foil and I only started to get a little treble roll off at the extreme anti-clockwise of the tone control.

  • joe

    Terry = my hero.

    Thanks for so much interesting detail. (And fair warning: I have another video coming in the next few days featuring a different historic pickup with its own set of oddball behaviors.)

    Interesting about the tone caps. I never even checked that out on my guitar, ’cause I used a ToneStyler for top cut, and a 3-position bass-cut switch, rather than pots running to ground.

  • How about this for a theory –

    I have simulated the guitar pickup driving a Fuzz Face in LTSpice. With ‘normal tone controls this shows that the gain of the Fuzz Face is greatly dependent on the impedance of the guitars volume control. Gain drops off very rapidly as the control is turned down.

    However with a Tonestyler in circuit the resonant peak from the pickup inductance in parallel with the Tonestyler capacitance increases (output at certain frequencies goes up) because the volume control gradually isolates the resonant circuit – pickup inductance in parallel with the Tonestyler capacitance – from loading by the low impedance of the Fuzz Face input.

    In effect although the volume control is reducing signal and decreasing the gain of the Fuzz Face, at the same time the output of the pickup is increasing. However it shouldn’t make any difference what the pickup is, this behavior should occur with any pickup.

  • Mark Hammer

    The original gold foils I’ve seen do have fairly low DCR and used 100k volume pots.

    One of the quirks of the gold foils comes via the folded base-plate which I understood to be soft iron and that this loaded down the coil in a way, increasing the inductance. I add the qualification here that electromagnetism baffles me completely, so treat this info gingerly.

    The old Epiphone New Yorker pickups are similar. They LOOK like a minihumbucker, but are actually just another single-coil in HB clothing, with the “adjustable screws” very close to the edge of the pickup and contributing very little to the tone or string levels. before I gave it to Mark Knopfler in the late 80’s, I took one apart to see, and it is very similar to the construction of a gold foil, albeit higher quality and a bigger coil.

    I have been slowly rewinding a busted original GF with a ceramic magnet. Once I’m done, I’ll have to see if it exhibits this behaviour. But my undereducated guess is that the effect is largely related to the pot value. Someone should try it out with other pot values and see.

    • joe

      Thanks for more smart insights, Mark! I don’t have time this week to swap the pot (’cause I have some work that actually, you know, pays). But I did a quickie experiment, running the output from the guitar’s wide-open A250K pot through an additional A100K in series on breadboard. (It’s not exactly the same thing, I know.) The result was similar: level attenuation about as you expect, but the A100K pot never delivers a clean tone on its way to silence. Tones are cleaner, but not clean, and always with an ugly/farty quaility that few players would enjoy.

  • Might be worth disconnecting the Tonestyler just to see if it is the resonance peak it introduces.

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