"Vocal" tone from closed ton pot...Why?

Discussion in 'Luthier's Guitar & Bass Technical Discussion' started by JingleJungle, Aug 29, 2006.

  1. JingleJungle

    JingleJungle Member

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    I'm just in love with the sound of a coupla old Hamers.
    Specifically I'm talking about some kind of "resonance" that develops when the pot is closed all the way - it's the most beautiful OD sound on the face of planet earth (IMHO of course).

    But what exacly accounts for it? I'm very curious.
    The two Hamers are doublecut.. one is a '79 Sunburst w/ original DiMarzios, the other is a 90s Mirage w/ 2 Seth Lover puppies.
    Two different guitas and different electronics as well. Both these guitars have this kind of tone, and as far as I recollect none of the other humbucking equipped ones.

    Thank you,

    JJ
     
  2. Clorenzo

    Clorenzo Member

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    Most likely it's the value of the tone capacitor. This is what happens to the frequency response of a typical PAF with 500k pots, a 0.022 uF tone cap and a 500 pF cable as you turn the tone down:

    [​IMG]

    Same thing but with a 0.047 uF cap:

    [​IMG]

    As you can see, initially you kill the main resonant peak of the pickup and roll off the treble, with no significant differences between both caps. But towards the end of the pot range, a new resonance appears, with different amplitude and frequency depending on the cap value. It's likely that Hamer uses one cap value (which gives a resonance that you like) and your other HB guitars use a different one.
     
  3. JingleJungle

    JingleJungle Member

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    Carlos, thank you for the info.
    What do you mean by the 500pf cable? It's the capacitance of the guitar cable itself or of the internal cabling of the guitar??

    By the looks of it, it appears that lower cap values are the way to go in order to achieve tis kinda tone. Hmm.
    Experiments are called for :) !!

    JJ
     
  4. Clorenzo

    Clorenzo Member

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    It would be the total capacitance of anything connected after the vol. and tone controls and before the amp, but it's a good approximation to consider just the guitar cable, which is by far the most significant contribution.

    I made those plots with this spreadsheet:

    www.harryj.net/voltone.xls

    Which you can download and play with to see the effect of different cables, pot values, etc. I'm currently working on an updated and tidied up version with some more options and a better user interface. Watch this space.
     
  5. Junior

    Junior Member

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    Very cool, Clorenzo.

    As I don't have Excel, might I ask a favor? Would you please post another graph showing the effect of a .01 cap? I'm curious as to how low the cap value would have to be to get that resonance above the fundamentals.


    PS: A few years ago, an engineering student posted similar graphs on the LPF. I think he used SPICE, or something similar. That wouldn't have been you, would it?
     
  6. LaXu

    LaXu Member

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    If you don't have Excel, download OpenOffice. It's free and works perfectly fine with Microsoft Office formats.
     
  7. Clorenzo

    Clorenzo Member

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    Here it is:

    [​IMG]

    Nope, I never did anything like this with SPICE (which BTW I happen to use a lot for simulation of active circuits).
     
  8. JingleJungle

    JingleJungle Member

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    So basically, the LOWER the value, the steeper the cutoff slope and the peakier the resonance, right?

    The only thing I must lament is that there appears to be a lot of confusion on websites between MICR and PICO Farads, and the respective decimal notations. Stuff like a 0.22 cap...
    OK - chill pill, back to Tone Lab 101
    JJ
     
  9. Junior

    Junior Member

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    The peakier, and perhaps more importantly, the higher, for the resonance. The steep cutoff might be a problem for some, causing a "honky" sound. Personally, I like it.

    JJ, keep in mind you can put caps in series to decrease their values. It's one of those inverse things, like speakers in parallel. Two .022s will give you .011, a .022 and a .047 is about .015 (by measurement, not math), so you might have more cap values in your parts box than you think.

    This doesn't jive with what I've thought I've heard in the past, but I've been doing this long enough to realise that we tend to hear what we expect. So, I'll have to test everything again with different expectations. ;)

    Thank you, Clorenzo, for the extra chart, and thanks to LaXu I might not have to bother you again. :)
     
  10. finom1

    finom1 Member

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    The link does not work??? Can you please send me the XLS link again that will work?
     

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