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treble bleed question

Discussion in 'Tele-Technical' started by old_picker, Nov 26, 2020.

  1. old_picker

    old_picker Tele-Afflicted

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    I have found using a small value cap (.00039uf) gives a good natural roll off. The treble holds up and doesn't become overly predominant at the lower end of the sweep. I find with higher value caps, eg .001uf, the treble becomes predominant towards the bottom of the sweep. I've tried various cap values without and with resistors both inline and parallel and found the lower value caps sound sweeter to my ears.

    I get the cap and how the values shape the tone but I never really understood what role the resistor is taking in the circuit.

    Hopefully someone can explain it in numpty terms for me
    thanks
     
  2. tubelectron

    tubelectron Tele-Afflicted

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    Hi @old_picker,

    It's rather simple : more or less it obeys to the well known equation of a RC filter F=1/(2PiRC), where :

    - The capacitor (in Farads) defines the cut-off frequency of the treble bleed (the lower the cap, the higher the cut-off frequency).

    - The resistor (in Ohms) defines the efficiency level of the treble bleed (the lower the R, the higher the volume of the treble bleed effect).

    Note : I speak about the Kinman-type RC serie treble bleed.

    The values that I use are 100K to 150K and 1nF to 1.5nF, and I found it working satisfactorily with SC and HB, 250 or 500K pots.

    But it's me, OK ? :D
     
    2manyteles likes this.
  3. AAT65

    AAT65 Friend of Leo's

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    For a very simple analysis, think about what is happening at 2 or 3 different frequencies:

    1) 0Hz, in other words DC. At this point the capacitor is an open circuit and no current flows through it (or any other component in series with it).

    2) ♾ Hz, in other words higher than the highest frequency you can imagine. At this point the capacitor is a short circuit so you can imagine it is just a piece of wire.

    If you want more detail then look at
    3) the corner frequency, where the impedance of the capacitor is equal in magnitude to the associated resistor. That frequency is f = 1/(2.pi.RC), and there the effect will be somewhere between the DC and Very High Frequency cases.
     
  4. old_picker

    old_picker Tele-Afflicted

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    Melbourne Australia
    To expand on tubelectrons post:

    A .001mf cap with a 100k resistor will pass more high frequency than a .001 cap with a 150k resistor.

    In other words as the volume sweeps down with .001uf 100k Resistor the treble will be more predominant than the .001 cap and 150k resistor combo.
    Correct?

    Cap values define the cut off frequency ie
    .001uf allows more high frequencies to flow as the sweep progress down than..00039uf
    Is this correct?

    I'll get to the effect on the taper question possibly in another thread
     
    Last edited: Nov 26, 2020
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