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5F2-A volume & tone pots: audio (log) or linear taper

Discussion in 'Shock Brother's DIY Amps' started by chas.wahl, Dec 5, 2019.

  1. chas.wahl

    chas.wahl Tele-Meister

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    As I assemble parts for a 5F2-A (Tweed Princeton narrow panel) build, I am confused about the best taper to use for volume and tone control pots. Based on recent research:

    Vintage Fender schematic is non-specific, but their layout shows "LIN." for both volume and tone.
    Weber kit layout and schematic agree with the above.

    Hoffman and Mojotone kit layouts and schematics show audio for both pots.

    Merlin Blencowe's description/analysis of the Princeton tone stack in his "Designing Tube Preamps . . ." book calls out "log" by the volume pot, and doesn't for the tone. Since this seems to be a convention throughout the book, I presume that if there's no "log" a pot is linear. And TDPRI member @jimgchord has advised volume-audio / tone-linear in this thread and this one (nice amp-building!).

    Since this is a fairly popular build in these parts, I'd appreciate any feedback you folks can offer about what you did, and how you like it. Thanks.
     
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  2. drneilmb

    drneilmb Tele-Meister

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    Rob Robinette's Deluxe Micro also uses that tone/volume setup with both pots having audio taper: https://robrobinette.com/Deluxe_Micro.htm. I'm very happy with the smoothness of the adjustment on both the tone and volume pots.

    Remember a linear and audio taper pot cover the same range of resistances, but at different "rates". So what you are choosing is not the tones you'll get out but how much change you get from a little bit of turn at each particular point in the pot's travel. The picture on https://electronics.stackexchange.c...linear-and-audio-tapers-and-why-should-i-care was quite helpful for me.

    I'd pick one schematic and stick with it all the way through the build and if you don't like the result, buy the other kind of pot and swap it in and see if you like that adjustment rate better.

    -Neil
     
  3. cobaltu

    cobaltu Tele-Meister

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    I would pick audio taper for both.

    My reasoning being that linear controls are VERY twitchy for volumes. You would find it very difficult to fine tune the volume; at lower levels in particular. This isn't the worst thing for this amp since most people sort of view it as an 'overdrive pedal with a speaker', but it would still be annoying.

    The 'tone' control is also very interactive with the volume on this amp, and acts a bit like volume itself. So in the spirit of matching the controls and making the controls a bit more predicable, make the 'tone' audio as well.
     
  4. Mexitele Blues

    Mexitele Blues Tele-Afflicted

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    I would use 500k Linear for the 5F2-A tone since it is more or less a fader control between the treble bleed cap and the bright cap. An audio taper pot will put the center point of this fader nearly all the way up the knob travel.
     
  5. chas.wahl

    chas.wahl Tele-Meister

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    Thanks drneilmb, cobaltu, and Mexitele Blues. I should have added: this will be an "apartment amp" generally used at lower volumes, though I may employ attenuation to lower the speaker output. Does that make a difference?
     
  6. Tube Life

    Tube Life TDPRI Member Silver Supporter

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    I have a 5e3 proluxe and it’s the same way, all or nothing for the volume. I just tried the the Pre PI MV and did not care for it at all. I have a Fryette PS2 arriving tomorrow to use with it and my other amps too. I can let ya know how an attenuator works with the 5e3 if ya like. The majority of my playing happens when the wife and kids are sleeping so I need one no doubt!! Good luck!
     
  7. dan40

    dan40 Friend of Leo's

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    Linear volume will bunch up all of the "loudness" down on the low end of the dial. Audio will give you a smoother taper at the lower end. If you can spare the cash, the PEC audio pots have some of the smoothest tapers around for volume controls. As for tone, I have never tried a linear there so I can't give an honest opinion. Very easy to try both and see which one you prefer though.

    https://www.tubesandmore.com/products/potentiometers_0?filters=Brand=Precision Electronics
     
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  8. printer2

    printer2 Poster Extraordinaire

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    A log pot give you control of the amount of treble you let through and how much treble cut you want. Using a linear pot gives you fine control over the treble bleed but you have poor control of the tone cut, only the 10% of the rotation, at 1 it no longer acts to cut the treble. Mind you the range changes depending on where the volume control is. Both work but it depends on if you like more treble rather than cutting it.

    Get the program, Tone Stack Calculator.

    http://www.duncanamps.com/tsc/

    Use the James tab.

    The online calculator.

    https://www.guitarscience.net/tsc/james.htm

    Change these values in TSC to change the Bass control into a Volume control, the cap and pot values to normal Tweed values.

    R1 1Ω
    R3 1 Ω
    R4 1Ω

    RT 1000000 Ω
    C1 1pF
    C2 1pF
    C3 470pF
    C4 4700p

    Adjust the Bass/Volume control and the Tone control then change the log response to linear with the drop down list on the online version, right click on the pots with the download version. Adjust part values to see hove different values changes things.

    Hours of fun. Just noticed they included more tone control types in the online version. So much for me doing anything useful this evening.
     
  9. Corvus

    Corvus Tele-Meister

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    Built one or two 52A's - 1 meg log pots work best. The Tweed tone control is ok but any more sophisticated types do cut into the gain.
     
  10. theruley

    theruley TDPRI Member

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    I used linear in my build and i wish i had used audio. The first 90% of the amp’s volume comes in the first 1/3 turn of the knob.
     
  11. chas.wahl

    chas.wahl Tele-Meister

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    Thank you @printer2 (especially), for showing the ingenious method for getting a Princeton tone control from the DTSC. I did not intend to be the occasion of anybody wasting time that could have been spent more usefully.

    I started this thread feeling that it's pretty obvious that it would be better to use a log-type pot for volume; the real question is whether to use a log for tone; and I suspect the answer may lie in how much the tone and volume interact -- as @cobaltu observed above.

    I'm sort of interested in R.G. Keen's method in "The Secret Life of Pots" for turning a production linear pot into a log-like pot (with the ability to change the log-ness) by adding a fixed resistor. If that's a decent solution, it would make it relatively easy to go back and forth, with just a couple soldering alterations.

    Thanks to everyone!
     
  12. drneilmb

    drneilmb Tele-Meister

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    Rod Eliot also has a good page on paralleling linear pots to get log-like tapers (that are much better than A taper). https://sound-au.com/project01.htm

    I'm ordering parts for an amp project and seriously considering getting 1M linear pots and some 120k loading resistors.
     
  13. printer2

    printer2 Poster Extraordinaire

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    Now days I pick and choose where I want to waste my time, I felt answering this question was a reasonable use of it. My post count is above 6000 for a reason, above 5000 I started to tapper off and get more stuff done rather than answering questions. I might even get the Tele I have been building finished today!

    The Making A Linear Pot Log thing is a waste of time. While the response is more log like you have to keep in mind that the 12k resistor loads the source with 12k at full rotation. In our cases a 1M pot which would need a 120 k resistor. This would load the preceding stage as you turn up the volume. At half rotation you would have 512 k, not so bad. At 3/4 rotation 262 k. Starting to load the preceding stage.


    [​IMG]
    It even says in the page,


    Our stages are not low impedance, that is the reason we use high value pots. Better to just get a log pot.
     
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  14. chas.wahl

    chas.wahl Tele-Meister

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    I had pretty much come to that conclusion, but it's good to have confirmation from a reliable source. I will stick with KISS instead.
     
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