Linear volume pot with center detent

Discussion in 'Pickups & Electronics [BG]' started by loadedthorn, Oct 11, 2016.

  1. loadedthorn

    loadedthorn

    Apr 7, 2015
    I have a bass with an audio taper volume pot and would like to replace it with a linear pot. Easy so far. I frequently pull my volume down to 50-75% and back to 100%, so a center detent would be really helpful to keep that lower level consistent. However, the only pots I can find from parts outlets with a center detent happen to be blend pots. Is there a secret 250k or 500k linear pot with center detent out there? Or is there a creative way to wire up a MN blend pot so it behaves like a volume pot with 50% signal in the center? I'm considering using an AC blend pot, which I think gives me a 75% signal at center. But I'm guessing it would be a drop from 100 to 75 at the center, and then taper from 75 - 0 after that? Thanks in advance for any advice! Clearly I'm a beginner, so the answer may be really obvious.

    (and yes, the alternatives of using a regular linear pot, using a volume pedal, or doing nothing are all options... I was just hoping to get more functionality out of the one pot replacement)
     
  2. testing1two

    testing1two Supporting Member

    Feb 25, 2009
    Southern California
    You may have better luck taking a 50k or 100k linear pot (like used on active EQ circuits) and adding a resistor across the terminals to get you in the ballpark of 250k. This affects the pot's taper so no guarantee it will function adequately for your application or if the detente will occur at the output level you want.

    Noble - EQ Pot - 50K EQ - Best Bass Gear

    A cheap workaround in the meantime would be a volume knob with numbers on it or a chickenhead knob (anything with a pointer) that you can turn to a specific position without looking.
     
  3. I'm afraid you can only reduce the effective value of a pot this way, not increase it.

    An AC blend will give you two options. One (the A taper) will be exactly like the audio taper pot you currently have. The C taper (reverse audio) will be hopeless for volume. At half rotation, you'll have about 85% voltage. This equates to only 1-2 dB of attenuation.

    It sounds like a linear pot is definitely what you want. This will give you around 6dB of attenuation at half rotation.

    Actually, yes! I haven't tried this, but I can't see why it wouldn't work. Simply tie the centre lugs together, then use the outside diagonally opposite lugs. (Make sure you use the lugs that aren't short to the centre lug of course. Check this with a multimeter.) This will effectively give you a 500K linear pot with centre click.

    Be aware that comparing a 250K linear to a 500K linear as volume control in a passive bass, you'll have a slightly brighter tone at full and a slightly darker tone at half rotation. Also, half rotation will likely be slightly quieter with the 500K compared to the 250K due to the interaction of the control with the input z of your amp/pedal/DI etc.
     
  4. loadedthorn

    loadedthorn

    Apr 7, 2015
    Thanks RobbieK, this is really helpful! I'll experiment with this. I originally assumed that wiring it this way would give me no discernible volume change since I'd would have the same signal at 100% on both sides of the center detent.

    I was hoping to avoid changing the look/feel of the knobs, but it's such an easy thing to change that it will probably be my interim solution. Thanks!
     
  5. Clark Dark

    Clark Dark

    Mar 3, 2005
    earth
    I've seen blends/pans with a center detent but not volume pots.
     
  6. No, you use the other lugs. Here's a standard MN pot wired as a blend:

    blend pot.gif

    To work as a linear vol pot, leave the two "output" lugs disconnected. Tie the two "source" lugs together. This is the output (to the jack). The two lugs that are usually connected to earth (as in this diagram) are now treated as either end of the volume pot. Top left is earth, bottom right is hot (from the pickup).

    Like this:

    blend for vol.gif

    This is for the Stewmac blend pots. It's possible that there are MN blend pots out there that work opposite to this.

    Ha! There you go. Or just buy one of these! It will be electronically identical to the 250K MN pot wired the way I've shown. (The resistor tracks are in series, so it becomes a 500K pot.)

    The other option is to get a 16mm alpha blend pot (like the stewmac ones) plus a regular alpha pot and swap the lower wafer. It's super easy. This would be the way to get 250K if you really want that.
     
    loadedthorn likes this.
  7. walterw

    walterw Supportive Fender Commercial User

    Feb 20, 2009
    alpha-music.com
    50% of what?

    if you mean 50% of the knob travel, then a center detent on a linear wouldn't work anyway, the level would be way different (higher) at the detent than the audio taper you're using now.

    if you mean 50% of the perceived loudness, well there's no guarantee that would be found at the detent either.

    i suggest not bothering, just get a good linear volume pot; you'll have no trouble setting it where it needs to be.
     
    wcriley likes this.
  8. loadedthorn

    loadedthorn

    Apr 7, 2015
    This makes perfect sense, thanks! I ordered some via the link BassLife77 posted, but if they don't work out I'll try this next. Thanks to all who contributed!
     
  9. TheMarkSide

    TheMarkSide Supporting Member

    Jan 6, 2023
    Chicago
    I have the same issue/need and just came across these, which I think will allow for more precise/incremental/consistent adjustments. As a bonus, these should fit on your existing pots, so the upgrade should be quick/easy - D'Addario LokNob Pro Small - Black. Not necessarily center detented, but should allow you to move the knob incrementally and I would assume you’d get to a point where you’d just bump it “2 clicks” one way or another.

    Personally, I see a center detent volume knob as valuable so I can dial in my amp with all controls on my bass (active) at 50% (except tone). This will give a consistent starting point for gain staging, but allow me to compensate for boosts/cuts to the onboard EQ, as needed. For example, if you boost the bass control on your bass, it’s likely that you’ll push your amp/pedals into breakup/distortion, so you’d back off the volume on the bass to compensate. Overall, I’m going to try these detented knobs on all my controls. Depending on the various tapers/ranges, this should essentially allow me to make 1:1 adjustments (boost the bass 2 clicks, cut the volume 2 clicks), or at least find combinations to keep output relatively even. It’ll def be better than guessing!
     
  10. Oh gosh... last time I checked with Georg Ohm, he said that adding a resistor across another resistor resulted in a lower total resistance value. But old Georg hasn't chimed in on this in a long time, so maybe someone repealed Ohm's law.

    FWIW... What you propose does work with capacitors. So not all is lost. C for the effort, but shoulda showed the math for a shot at a B. :thumbsup: