Les Paul mods: “treble bleed”

Hi folks. Another post about Les Paul circuitry customization: this time I’ll show the effect on the tone of the so-called “treble bleed”, a mod that many people consider a good enhancement.
The rationale for this mod is that when you turn down the volume, you hear what many consider a loss of treble. Looking at the graph it seems that this description is inaccurate, because as you turn the volume knob, initially the resonant peak get smoothed (and here there is actually some treble loss), but then the frequency response extends a bit, with a resonant peak that is less pronounced but higher in frequency than the one at full volume. So I think the ear just get just “tricked” a bit. Or maybe the real-world components just behave different enough from the ideal ones of these simulations to arise the bad volume behavior.
Whatever the truth, the “cure” is to add a small capacitor between the pickup pin and the middle pin of the volume potentiometer to let some treble “bleed” straight to the output. Many people advocate to add a resistor in series or parallel.
The problem is that the values of the capacitor and the resistor and their configuration are pretty critical. In general the bigger the cap the more dramatic the effect, while the resistor smooths somewhat the effect.

I chose here to show a parallel configuration, with values matching ones from this forum thread. It seems, looking at the plots, to be a nice combo, with a distinct but not overkill effect on the sound.
The graphs shown are logarithmic plots of the frequency response from 20 Hz to 20 kHz between the pickup ideal signal and the output, for the standard wiring and for the one with the treble bleed, and for different positions of the volume potentiometer (I set ten values of a logarithmic sweep from 1 Ohm to 500 kOhm). The first plot is for the tone knob fully on bright (on “10”), and the second one is for the tone knob fully on dark (on “0”).

You can clearly see the effect: with the tone on bright and partial volume, the resonant peak is lower in frequency (and, with this cap value, in a position close to the one at full volume) but more pronounced, and with both of the tone positions, the roll-off of the high frequencies is less steep, as expected, giving a brighter tone.
Note, however, that there’s no effect at full volume, where the steeper roll-off is retained; this implies a more or less pronounced timbre change as you turn the volume knob.
The effect of the volume knob is also a bit slower near the full volume and faster near the lower end.
For a more in-depth analysis, you can check this excellent thread.

Of course, this is just a circuit simulation with ideal components; if you want to know how this translates in reality just open your axe, check some different caps and resistors, and – as always – let your ears be the judge!

PS:
The software I used for the simulation is Qucs on Linux, but on the website you can find downloads for Windows and Mac OS X as well.
There’s no potentiometer component in Qucs, so I just used two resistors with the values bound together by the equation Rvb=500k-Rva.
For the pickup I chose values that, combining various sources, seem to be good representatives of a standard Gibson PAF pickup.

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3 Responses to Les Paul mods: “treble bleed”

  1. Sycomore says:

    Hello from France,
    I would like to test my LP with theorical components values and after test the real response but i have a syntax error with Qucs.
    Could you please provide me your .sch file ?
    Thank you in advance

    # Qucs 0.0.10 C:/Users/Phil/Desktop/guitares/g1.sch

    Vac:V1 _net0 gnd U=”1 V” f=”1 GHz” Phase=”0″ Theta=”0″
    R:Rtone1 _net2 _net3 R=”Rt” Temp=”26.85″ Tc1=”0.0″ Tc2=”0.0″ Tnom=”26.85″
    R:Rvol_a2 out1 gnd R=”Rva” Temp=”26.85″ Tc1=”0.0″ Tc2=”0.0″ Tnom=”26.85″
    R:Rvol_b1 out1 _net2 R=”Rvb” Temp=”26.85″ Tc1=”0.0″ Tc2=”0.0″ Tnom=”26.85″
    R:Rl1 gnd out1 R=”1M” Temp=”26.85″ Tc1=”0.0″ Tc2=”0.0″ Tnom=”26.85″
    L:Lpu _net0 _net1 L=”4.5″ I=””
    .AC:AC1 Type=”log” Start=”20 Hz” Stop=”20000 Hz” Points=”500″ Noise=”no”
    R:Rpu1 _net1 _net2 R=”8k” Temp=”26.85″ Tc1=”0.0″ Tc2=”0.0″ Tnom=”26.85″
    C:Cpu1 gnd _net2 C=”130p” V=””
    C:Ctone1 gnd _net3 C=”22n” V=””
    C:Cl1 gnd out1 C=”0.5n” V=””
    Eqn:R_vol_b Rvb=”500k-Rva” Export=”yes”
    Eqn:R_tone Rt=”500k” Export=”yes”
    Eqn:R_vol_a Rva=”Rs” Export=”yes”
    .SW:SW1 Sim=”AC1″ Type=”log” Param=”Rs” Start=”1″ Stop=”500k” Points=”10″

  2. emarsk says:

    Hi, I uploaded my sch files here:
    https://drive.google.com/folderview?id=0B6rIPreVMNRZMDNrZS13c2V6Skk&usp=sharing
    They’ve been created with qucs 0.0.15, I just tested with 0.0.17 and seem to work fine.

  3. TonyKL says:

    I modified my Les Paul and removed the .047 Cap and replaced with 0.22 and added in the treble bleed using 150K resistor and .001 cap in parallel,. Brilliant! my guitar feels like it has a new lease on life. I also had a hum issue which was a loose earth on the bridge. Now fixed and I think the change from 0.47 to 0.22 also helped clear up the mud. I also relocated the cap from the 2nd lug of the tone which was just earthed to the cap. The 0.22 connected between the tone cap and the volume cap at the input from the pickup. Common diagram. Well worth the effort and for me a dramatic change with so few dollars spent.

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