Epiphone 57CH technical analysis

Discussion in 'Pickups' started by Antigua, Mar 4, 2017.

  1. Antigua

    Antigua Senior Member

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    There was a post a month or two ago comparing Epiphone's old stock pickups with Probuckers and better alternatives. I bought some 57CH's to test them and see what they're all about. I'm posting this here since the topic came up recently, and the topic of import versus domestic PAF knock offs comes up often.

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    These humbuckers come stock in many Epiphone guitars, including the Les Paul and and Dot. The poor reviews of these pickups no doubt fuel many aftermarket pickup purchases. I've bought a set off eBay in order to analyze them and determine how they compare to the new Epiphone Probuckers and or the Gibson 57 Classic. I did a comparison of those pickups here http://guitarnuts2.*********.com/thread/7748/gibson-classic-stock-epiphone-humbucker , and I'll post some of those measurements below in order to more easily contrast them.



    Electrical Measurements

    Epiphone 57CH "Bridge"
    - DC Resistance: 8.75K ohms
    - Measured L: 4.972H
    - Calculated C: 101pF (111 - 10)
    - Gauss: 190G screw, 190G slug

    Bridge unloaded: dV: -1.9dB f: 6.66kHz (black)
    Bridge loaded (200k & 470pF): dV: -1.6dB f: 2.50kHz (red)


    Epiphone 57CH Neck
    - DC Resistance: 8.77K ohms
    - Measured L: 4.972H
    - Calculated C: 105pF (115 - 10)
    - Gauss: 260G screw, 250G slug

    Neck unloaded: dV: -2.1dB f: 6.89kHz (green)
    Neck loaded (200k & 470pF): dV: -1.6dB f: 2.50kHz (gray)


    Apparently the two pickups I received have near identical electrical measures. One pickup has a sticker indicating that it's a neck pickup, but the other has no sticker. it wouldn't surprise me if they actually sent me two "neck" pickups. I know that there also exists a "HOTCH", or "hot classic humbucker" with a DC resistance around 14k. Even without a HOTCH to test, the neck pickup is representative enough to compare to other Gibson / Epiphone pickups.


    Bode Plots


    These bode plots are created with a Velleman oscilloscope with a built in function generator, and exciter coil, and an integrator device made by Ken Willmott that imposes a -6dB/oct slope on the response in order to make the frequency response curve more apparent.

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    The 57 Classic neck, Probucker 2 and the 57CH all have loaded (470pF parallel) peaks around 2.5kHz, so they are similar in terms LC resonance. Where they really differ is in the quality of the covers. The CH57 uses a cheap brass cover, where as the 57 Classis and the PB2 use nickel silver. Notice in the plot below how the frequency where the inductance losses out to capacitance is about the same for all three models, around 2.5kHz with a chosen 470pF parallel load. But that while the Classic 57 and PB2 has a mostly flat response and mild boost at the resonance, the 57CH drops off almost right away, and with load, has no resonant peak (no Q factor).


    Gibson 57 Classic and Epiphone Probucker 2:
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    Here is how the 57CH performs with the cover removed:

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    The taller peaks show a higher Q factor as a result of having removed the covers, which cause eddy currents.

    The loaded (200k parallel resistance) uncovered peak of the 57CH is similar to the 57 Classic below (gray line in both plots). The 57CH has a much higher unloaded Q factor (green line in both plots) than the 57 Classic, which is interesting, and might say something about the quality of steel used for the screws and pole pieces, but since a pickup is almost always used with tone and volume pots, the unloaded characteristics (meaning no tone or volume pots in parallel) aren't all that meaningful to the tone.

    Gibson 57 Classic, with and without cover:
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    That dramatic roll off of high end seen with the 57CH isn't by itself a bad thing. A Filter'tron has a very similar roll off due to the thick filister screws used, but the difference there is that a loaded Filter'tron has a resonant peak close to 5kHz, where as a PAFs tend to roll off around 2.5kHz. It's the combination of that low peak frequency and high eddy current attenuation that makes a 57CH trend muddy, while a Filter'tron is heard as being bright and clear.





    Base Plates


    It can also be seen that the 57CH have brass base plates instead of nickel silver, and the Gibson 57 and Probucker 2 have, but I've previously studied that and found it to be almost entirely irrelevant http://guitarnuts2.*********.com/thread/7861/humbucker-base-plates-eddy-currents





    Wax Potting

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    It can be seen here that the CH57 has a lot of wax, and I've seen opinions out there that this wax must be detrimental to the tone. To the extent that microphonics are desirable, that is it true, but it should be noted that many (maybe most) premium pickups have a similar amount of wax in them, for example, this DiMarzio Air Classic looks similarly submerged:

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    Under the Hood

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    Unlike the Gibson 57 Classic and the PB2, the CH57 uses plastic spacers instead of maple (or Asian mystery wood).

    There are a few other "made in China" characteristics that differ from most domestic PAF knock offs; the hookup wire enters on the same side as the where the coil connections are made, necessitating two spacers instead of one. The screws have smooth, unthreaded ends, and of course the use of brass metals in place of nickel silver.

    The Probucker is a combination of domestic and Chinese attention to detail, it uses wood spacers and nickel silver, but the lead wire enters at the connection end, so it too has two wood spacers to fill the voids instead of one. The mechanical drawback to having the wire enter at the side where the connection is made is that the solder joint is slightly more susceptible to pulling and breaking, since the length of the pickup is not serving to secure the hookup wire.

    Gibson 57 Classic and PB2; notice the spacers and where the wire enters the base plates, as well the fact that the base plates are silver in appearance, rather than brass / yellow in color.

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    Hookup Cable

    Another thing that sets the 57CH apart from a 57 Classic is the insulated hookup wire. I disconnected the hookup wire from the coil to get a measurement, and found that the 57CH has just shy of twice as much capacitance as the vintage style hookup wire at 129pF:

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    A good guitar cable has around 30pF capacitance per foot, and the lower value helps maintain a resonant peak that delivers good treble clarity. These smaller hookup cables show higher capacitance because the shielding layer is much closer to the inner lead wire. The thicker construction of a guitar cable is a big reason they have lower capacitance. Therefore, the Gibson vintage style hookup wire is equivalent to about 2 1/2 feet of guitar cable for every 1 foot, while the Epiphone CH57 hookup wire is closer to 4 feet of guitar cable for every 1 foot.

    If this same lower grade of wire is also used for the run from the tone controls to the selector switch in a Les Paul, that might represent an additional two feet of wiring with this especially high capacitance. If two feet of this grade of wire is like eight feet of guitar cable, then it's like you've added eight feet to your guitar cable and have nothing to show for it, tonewise. If you value treble clarity, it might be a good idea to replace the wiring in an Epiphone Les Paul with a lower capacitance shielded hookup wire.

    The real problem with having this much capacitance between the volume pot and the pickup by virtue of intrinsic coil capacitance and hookup wire capacitance is that, the volume knob is wired as a voltage divider, and as such, when you turn down the volume, the cable capacitance is actually removed from the pickup, improving the brightness a little bit. If you have a lot of capacitance within the pickup, or between the pickup and the volume knob, this capacitance is always there even when you turn down the volume, causing the pickup to become especially dark as you roll back on the volume.




    In Conclusion

    Based on the evidence, it looks like the most likely reason the 57CH gets bad reviews compared to other PAF knock offs is 1) the brass cover damping the high end response, and 2) the hookup wire of not only the pickup, but probably the Epiphones they come in, adding a large amount of capacitance, further reducing the high end.

    I also believe that the inclusion of a "HOTCH" 14k DC resistance pickup in stock Epiphone Les Pauls also contribute to a poor view of Epiphones, because Gibsons generally do not have such a hot pickup in the bridge, and it's not a bad thing if you play with high gain and like pickups such as a "JB", but if you want a good clean bridge tone, a "HOTCH" bridge pickup is probably heard as detrimental to the overall tone of the guitar.
     
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  2. Oldskoolrob

    Oldskoolrob Member

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    Thanks for the review. So if I understand correctly, the Epiphone 57 would benefit from having the covers removed and a better connector wire. What magnets do they use? Would they benefit from a magnet swap?
     
  3. Zipslack

    Zipslack Member

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    I believe the 57ch used A5 magnets.

    BTW, the Dot and (I think) SG models used the 57ch in both positions. The HOTCH was bridge on the LP models (dunno why).

    Thanks for the technical analysis!
     
  4. copperheadroad

    copperheadroad Senior Member

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    Correct , I've had a bunch in to replace the pickups & the HOTCH are only in the Bridge of a les paul
    SG's & Dots have 57ch in all positions
     
  5. Oldskoolrob

    Oldskoolrob Member

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    Yep my Broadway had '57 neck and bridge. Underneath it even specified LP neck, even though the bridge is clearly bridge spacing. Magnets, wax and connector wire aside - do you think these pickups are worth saving/modifying?
     
  6. LtKojak

    LtKojak Senior Member

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    I thought both has 50mm of polepiece spread. You say that's not the case and the bridge one measures 52mm of polepiece spread? Are you sure about that?
     
  7. Oldskoolrob

    Oldskoolrob Member

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    Yes, the two I have are definitely different spacing. I don't know the exact measurements but when you put the pole pieces in line one's more spread than the other. I'll measure them when I get home tonight. :)
     
  8. Antigua

    Antigua Senior Member

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    Ditching the brass cover, and possibly replacing it with a nickel silver cover will improve the high end clarity by reducing eddy current damping, giving the resonant drop off a "hard knee" rather than a soft roll off.

    Replacing the hookup wire would have more subtle benefit. Reducing the overall capacitance by ~60pF is like removing 18 inches of guitar cable, which increases the resonant peak by a 200Hz, give or take, but it also increases the amount of brightness that is retained as you roll back on the volume knob, becuase the volume knob isolates the capacitance of the pickup and it's hookup wire, so the lower that isolated capacitance, the higher the resonance, and the brighter the pickup is as you roll off the volume.
     
  9. Oldskoolrob

    Oldskoolrob Member

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    Ok thanks. My computer at home died (using work computer now shhhh!) so I couldn't upload a photo of the bridge V neck spacing but there's about 2/3mm difference overall between E-e pole screws. On the back they have the same sticker (Epi dot neck/bridge, LP neck.)
     

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