Telecaster bridge plate testing; brass, steel, thin, thick

Discussion in 'Just Pickups' started by Antigua Tele, Feb 4, 2019.

  1. Antigua Tele

    Antigua Tele Friend of Leo's

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    One of the aspects of vintage guitar pickups that gives their their characteristic tone is LC resonance. Resonance causes there to be a bump in the treble range, which is often the cause of "ice pick" tones when it's too great, but also makes for "dull" sounding pickups when it's too low. The reason 1 meg ohm pots make pickups sounds brighter is because they increase resonance, while low value pots decrease resonance. Another cause of low resonance is eddy currents, such as those caused by cheap metal covers. But it can also be caused by any other conductive metal, such as AlNiCo magnets and steel pole pieces. Since virtually all pickups have conductive metal parts (not counting the coil itself), some degree of eddy current related resonance loss is inherent in all guitar pickups.

    One definite cause of eddy current attenuation is the metal bridge of a Telecaster. I've analyzed three actual Tele bridges, as well a piece of aluminium foil cut to the shape of a Tele bridge in order to compare the differences they cause with respect to eddy current attenuation.

    The test subject are:

    Fender vintage style bridge plate, made of steel, is magnetic, thickness is 1.10mm
    Fender modern style bridge plate, made of brass, is not magnetic, thickness is 2.32mm
    Reynolds Wrap, made of aluminum, is not magnetic, thickness is 0.022mm
    Fender Standard Series steel bridge plate, made of steel, is magnetic, thickness is 2.50mm

    Obviously the foil is the thinnest, followed by the vintage ashtray bridge at about 1mm, and then the modern style bridges which are over 2mm thick. You can see their thickness by looking at the lower lip where the intonation screws pass through.

    The ashtray and Standard Series bridges are made of steel, the Reynolds Wrap is aluminum, and the late 90's stock bridge is made of brass.

    [​IMG]



    The test pickup is a Fender NoCaster bridge with the base plate still attached underneath the pickup.

    The first plot is without added load. The only load is that of the USB oscilloscope, which is far lower than that of a guitar setup.

    The plots shows that all of the base plates cause only a slight reduction in resonance, except one, the Fender brass bridge plate, the second bridge plate in the pictures above. The bridge was taken from an American made Telecaster, built in the late 90's or early 00's. The eddy currents cause the resonance to drop by a whopping 4.7dBV, as well as causing the inductance of the pickup to drop and the resonant peak to rise by about 700Hz.

    The Fender Standard Series steel bridge plate, fourth in the picture, is actually thicker than the Fender brass bridge, and it shows almost as little eddy current attenuation as the much thinner steel ashtray style bridge.

    Telecaster Bridge Plate Test

    No plate: dV: 14.1dB f: 7.46kHz black
    Fender vintage: dV: 11.5dB f: 7.54kHz blue
    Fender brass: dV: 9.4dB f: 8.17kHz red
    Reynolds Wrap: dV: 12.2dB f: 7.37kHz green
    Fender Std. Ser.: dV: 11.1dB f: 7.54kHz pink


    [​IMG]




    ~*~*~*~*~



    Here is a plot that adds a representative load of 470pF capacitance and 200k ohms across the pickup to mimic the effects of a guitar cable and control pots. This causes the resonant peak and the peak amplitude to drop significantly.

    In this context, the Reynold Wrap bridge plate becomes indistinguishable from no bridge plate at all. The vintage ashtray style bridge and the thicker steel bridge overlap very closely, while the brass modern style Fender bridge once again shows significant attenuation.

    For the vintage ash tray and the thick, unknown steel bridge, the reduction at resonance is only 1dB, which is right at the threshold of what human hearing can detect. The modern Fender , on the other hand, shows an amplitude drop of 3.2dB, and a peak frequnecy increase of almost 300Hz, both of which make for audible differences.


    Telecaster Bridge Plate Test w/470pF & 200k ohm load

    No plate: dV: 5.4dB f: 3.24kHz black
    Fender vintage: dV: 4.4dB f: 3.24kHz blue
    Fender brass dV: 2.2dB f: 3.51kHz red
    Reynolds Wrap: dV: 5.4dB f: 3.24kHz green
    Fender Std. Ser. dV: 4.4dB f: 3.24kHz pink



    [​IMG]


    This is not to say the tested brass bridge plate sounds bad. The taller resonance creates a distinct sound, a pointed treble that is sometimes described as "shrill", where as the flatter response, caused by the eddy currents, causes the treble to sound a bit darker overall, but at the same time clearer, like an acoustic guitar. Rolling back on the tone knob slightly has a near identical function. If you have this brass bridge in your Tele, it's as though the tone knob is maxed out at 8 or 9, instead of 10. Since a lot of players like the tone knob rolled off anyway, some intrinsic attenuation can be a welcome feature.

    Given that the aluminum and brass are similar, both being non-magnetic, and highly conductive, this result shows that thickness matters to some extent, otherwise the foil and brass would have shown similar plots. On the other hand, the 1mm and 2.5mm Fender steel bridge plates showed very similar plots, suggesting that in that context, where the material is both conductive and highly permeable, the thickness doesn't matter nearly as much.

    I'm not sure which Telecasters on the market today have a brass bridge plate, and I've only tested the one I have on hand, so I don't know if all modern Fender bridge plates are brass, but if the bridge plate looks like the one above, and a magnet will not stick to it, my guess would be that it is brass. If a magnet does stick to it, it must be made of steel, and it will perform like other steel bridge plates, regardless of whether it's vintage ashtray or the modern six saddle type.


    Pics:

    That's Ken Willmott's integrator in the back ground, v4 IIRC.

    Ashtray bridge:

    [​IMG]


    Reynolds Wrap:

    [​IMG]

    Brass bridge with some of the brass exposed:

    [​IMG]
     
    Last edited: Feb 5, 2019
  2. CFFF

    CFFF Tele-Meister

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    Thank you @Antigua Tele. The Reynolds Wrap and Fender brass plates do not have saddles affixed. Would this make any difference?
     
  3. Antigua Tele

    Antigua Tele Friend of Leo's

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    It's generally used in tandem with a cardboard body having imaginary strings, obviating the need for saddles.
     
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  4. CFFF

    CFFF Tele-Meister

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    My first guitar was like that. The second one was not much better :)
     
  5. Ringo

    Ringo Poster Extraordinaire

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    I don't know how much difference there is tonally but I do know that when I used the standard stamped steel Tele bridge with most bridge pickups, I got bad squeal , when I changed to a Callaham bridge which is thicker that problem went away.
     
  6. Antigua Tele

    Antigua Tele Friend of Leo's

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    If not secured well, the bridge plate can function as a crude microphone along with the pickup.
     
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  7. 11 Gauge

    11 Gauge Doctor of Teleocity

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    I mentioned in another post that I found a common reason reason that seems to occur has to with burrs or tiny "ledges" on the underside of the stamped plate, at its four screw holes.

    I use a drill bit that's about 30% bigger in diameter than the screw holes, and simply rotate it by hand, to bevel out any ledges and burrs.

    If the ledges/burrs are there, it may not matter how tight you crank down the screws, because the plate doesn't end up completely flush with the body.
     
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  8. Antigua Tele

    Antigua Tele Friend of Leo's

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    I havent had any problems, but if I did I would treat it like a PAF cover, either put some wax in there, or double sided sticky tape, to prevent the steel plate from acoustically resonating.
     
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  9. Zepfan

    Zepfan Poster Extraordinaire

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    Too bad you didn't have a thicker aluminum plate to use for this test.
     
  10. Antigua Tele

    Antigua Tele Friend of Leo's

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    How come?
     
  11. craigs63

    craigs63 Tele-Holic

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    I imagine an aluminum plate of comparable thickness to the brass and steel ones would have its own effect on the sound (and different than the thin piece of foil).
     
  12. Zepfan

    Zepfan Poster Extraordinaire

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    I think an aluminum plate with more mass would've been different than a piece of foil.

    The thick brass one certainly had big results.
     
  13. Antigua Tele

    Antigua Tele Friend of Leo's

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    An aluminum plate would essentially be "super brass", because both metals have no significant permeability, and they're both highly conductive, with aluminium being nearly twice as conductive as brass, so however lossy brass is, aluminium will be worse.
     
  14. Zepfan

    Zepfan Poster Extraordinaire

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    One thing aluminum offers that brass doesn't is that it will kill the 60 cycle hum if the plate is thick enough.
     
  15. Antigua Tele

    Antigua Tele Friend of Leo's

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    For electromagnetic interference, the penetration depth for aluminum at 60Hz is about 10mm, which is not practically achievable. For electrostatic shielding, the thickness virtually doesn't matter.
     
  16. dougstrum

    dougstrum Tele-Holic

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    I built this guitar about a year ago. It started out with a typical pressed steel tele bridge. For some reason it was very harsh/spikey. Had some .065" aluminum so I used it to make a new bridge. Really changed the sound, the guitar is still bright but not harsh. Nothing scientific like you Antigua. Just thought that aluminum was soft metal so it might take out the harshness. 15499160785441480305659.jpg 1549916228986417244244.jpg
     
  17. Zepfan

    Zepfan Poster Extraordinaire

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    DSCF0767.JPG 8" aluminum skillet that's maybe 2mm or 3mm thick killed the 60 cycle hum in this guitar for both pickups. You might get the same results with a regular sized bridge plate that's 2mm thick.
     
  18. Antigua Tele

    Antigua Tele Friend of Leo's

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    allegedly.

    BTW, kill that thing fire.
     
  19. Antigua Tele

    Antigua Tele Friend of Leo's

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    Based on the findings in the op, the eddy current activity would have picked way up after you switched to the aluminium. If you describe a high Q as harsh, which I think is very reasonable, then eddy currents reduce harshness, and in fact this was a point Bill Lawrence made when talking about these metals, comparing them to "salt in a soup". The thing is, there are simple electrical means of accomplishing the same outcome, such as lower resistance tone and volume pots, among others. The underlying reason being that a high Q arises from strong LC resonance, and there are a number of ways to diminish that resonance.
     
  20. Zepfan

    Zepfan Poster Extraordinaire

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    Allegedly?

    I don't even know why you bothered to test that flimsy piece of foil in the first place. How did you come up with the 10mm thick idea?
     
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