Tone position in circuit, PTB vs 50s wiring

Discussion in 'Tele-Technical' started by gdvsbp, May 18, 2021.

  1. gdvsbp

    gdvsbp TDPRI Member

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    Hi, folks. I've been looking around for this info for a while, and I guess the fact is I just don't have the electrical knowledge that I need to answer it myself. That said, I'm hoping some of you might be able to point out what I misunderstand here, and that I can come out of it with a little more knowledge under my belt.


    Background: I have a Squier tele I'm looking to add a version of a PTB (passive treble and bass) control to as part of a full rewiring. I also intended to use '50s wiring on the guitar, which would have the tone control branching off from the output lug of the volume pot.


    The question: When I look up schematics for PTB circuits for 3-knob guitars, the order of components is:

    1. Pickups
    2. Switch
    3. Treble roll-off (usually a pot branching off the circuit, bleeding treble to ground in parallel as resistance accumulates)
    4. Bass roll-off (usually a pot wired pass-thru, adding some sort of series resistance)
    5. Volume pot (nothing special, but apparently needed after bass roll-off to make that control effective)
    6. Output
    On the other hand, '50s wiring in a Tele-like guitar would look like:

    1. Pickups
    2. Switch
    3. Volume pot
    4. Tone pot (branching off volume pot output lug, bleeding treble to ground)
    5. Output

    So here's what I am: I'd like to keep my tone (or treble roll-off, if I'm using PTB parlance) in the '50s position (parallel with output, post-volume), because the tone loss that rolling down volume brings on a pre-volume tone pot has been the reason I've avoided the volume control on guitar for my whole life. So that's important to me (and I so far haven't loved treble-bleed circuits as a solution either). But, I also understand that the volume pot's position after the bass-cut is essential to the bass-cut control actually doing something (series... resistance? capacitance? I don't know). Would a post-volume tone pot limit the effectiveness of the bass-cut? Should I just plan for my volume/treble/bass controls to be "very interactive," but otherwise expect things to work?


    My guess is the answer is "very interactive, but functional." I really hope I'm right.


    Anyway, please let me know if I'm wrong, and if so why I'm wrong. Or maybe even why I'm right?


    References:

    • 50s wiring
      [​IMG]
    • PTB circuit
      [​IMG]
     
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  2. moosie

    moosie Doctor of Teleocity Silver Supporter

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    First, a bass cut control has little to do with the pot / resistance. Like the treble cut, the active ingredient is the cap. The pot is just there to allow some signal to bypass the filter, thus making it a variable control.

    Treble cut is cap in parallel with signal, and bass cut is cap in series with signal. Caps pass highs: starting at the very upper end of the spectrum, increasing the size of the cap widens the band that gets past the cap, which means including more lower frequencies. The biggest cap in the world :rolleyes: would pass all audible signal. In a bass cut circuit, a larger cap allows most of the frequency to get past it, and to the output. Smaller cap, more bass cut. In a treble cut circuit, it's the opposite. Larger cap allows more past it (as always), but in this case it's getting dumped to ground. So larger cap cuts more treble.


    Now, to your question. You can wire it thus: pickups --> switch --> variable bass cut --> vol pot --> 50s treble cut (and output to amp).
     
  3. beanluc

    beanluc Tele-Afflicted

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    You're right, if you're talking about treble and volume.

    Basically, the presence of the bass-cut control doesn't have anything to do with the location of the treble-cut wiring. They're totally independent and not interactive with each other. The interactivity is between the treble control and the volume control, just as expected in 50s wiring without any bass-cut control.

    Also 10000 likes for trying out PTB/focusknob/bass-contour control (3 different names for the same thing). You will discover many useful applications.
     
    Last edited: May 19, 2021
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  4. beninma

    beninma Friend of Leo's

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    Just keep it simple and follow one of Leo Fender's wiring setups for PTB.

    PTB has a treble bleed that works flawlessly, it is not at all the same thing as injecting a treble bleed into one of the earlier circuits.

    The bigger question is where are you going to mount a 3rd knob on a Tele.

    My Reverend has a Tele control plate and then throws the 3rd knob up on the upper bout. It's a great position for it but would require significant routing on your part and then building a cover.

    Alternately you could drill the pickguard somewhere and mount a 3rd pot to that, but a Tele pickguard doesn't have a lot of room for that.

    You could do a dual-ganged pot as well, but that might be hard to adjust on the fly while playing.
     
  5. moosie

    moosie Doctor of Teleocity Silver Supporter

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    Re the extra pot, I prefer to use a modified TBX. The caveat is that I can't use both cuts simultaneously. I don't see that as a problem, but some might.

    The mod is from Phostenix (google his youtube explanation). It converts a Fender TBX circuit to a control where it's out of the circuit at the center detent; turn it one way, bass cut, turn the other, treble cut. I don't see why the treble cut couldn't be placed in the 50s position.
     
  6. gdvsbp

    gdvsbp TDPRI Member

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    I appreciate the info, all!

    I’m actually going to be using a mini switch to toggle two levels of bass cut, no pot. I have a control plate with a mini switch hole, so that kinda solved itself. If I really like it and find I want more control, I’ll probably go with a concentric pot for treble/bass or TBX, but in the meantime it’s probably GOOD for me to have a liiiittle less tweakability in my setup while I’m finding my footing.

    I appreciate the reassurance re: placement in the circuit. Those were my feelings, but nice to know I’m not gonna be disappointed by the fruits of my “big plans.”
     
  7. gdvsbp

    gdvsbp TDPRI Member

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    I’ll consider the treble bleed on volume. For now, I’m into the concept of the linear reduction of volume without darkening (which is new territory for me) just so I can get comfortable with messing with volume. If the tone interactivity bugs me then I’ll for sure be investigating the treble bleed.
     
  8. moosie

    moosie Doctor of Teleocity Silver Supporter

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    Not using a pot, all signal will see the bass cut cap. So, spec it larger than you would for a variable bass cut control.

    Another thing you can do to tweak, is to mimic the pot with a certain value of fixed resistor. So, instead of shifting the frequencies affected, keep them at optimum, and allow some dry signal to bypass the cap/switch. While you're figuring it out, you could install a tiny trimpot, and then replace it with a fixed value resistor.


    I think you realize this, but you won't need a treble bleed with 50s wiring. That's one of the benefits.
     
  9. gdvsbp

    gdvsbp TDPRI Member

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    Much appreciated advice; trimpot’s a great idea. And yes, that bit (no TB w/ ‘50s) at least I’m pretty solid on.
     
  10. beanluc

    beanluc Tele-Afflicted

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    920D available in many colors and various retailers (Reverb for one) https://920dcustom.com/products/920d-custom-blank-3-hole-t-style-control-plate-chrome

    Rock Rabbit also available if you prefer the slanted switch slot, also at Reverb if you care https://rockrabbitguitars.com/shop/angled-piezo-telecaster-control-plate/

    Undersized knobs (about 16mm diameter, compare to the normal 19mm) to mitigate the crowding you'll get from full-size knobs, available in 6mm shaft size from MGB https://mgbguitars.com/collections/knobs/products/guitar-parts-knobs-knurl-flat-black It's a little bit less surface to grab if you like doing pinky-swells but on the other hand you are a lot less likely to contact the knob next door while you're doing it. They don't have 1/4" shaft size but I drilled mine out. I did find 1/4" undersize knobs on another site but they were more expensive and now I can't find them again.

    [​IMG]
     
    Last edited: May 20, 2021
  11. beninma

    beninma Friend of Leo's

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    Looks like a pretty decent setup.

    I might prefer the style of switch on a Jazzmaster to save a little more room then give the volume knob a little more space.

    I feel like the volume knob is the critical one to be sure you can adjust without looking.

    I like the Tele/Strat style switch but it takes up a lot of room.
     
  12. gdvsbp

    gdvsbp TDPRI Member

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    Yeah, I have the rock rabbit 2-pot / mini-toggle / slant-switch cover awaiting install. The blade really does take up a lot of room no matter how you turn it, though, and as an old Strat and LP player, a 3-way blade does feel pretty weird. Sorry, Tele folks — I’m new to this haha.
     
  13. beanluc

    beanluc Tele-Afflicted

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    If that's what you want, you don't want 50s wiring. Treble bleed CAN change the curve of the volume control, as well as it's depth, but here's a good resource for making these effects predictable including eliminating it. One thing I didn't talk about in there was the idea that you can change the taper of your vol. pot to adapt to the effect of the resistor in your TB.
     
  14. gdvsbp

    gdvsbp TDPRI Member

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    Oh, wow, that’s VERY useful. Thanks so much!
     
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