Fixed Resistor for Knobless Bass?

Discussion in 'Pickups & Electronics [BG]' started by funkmaster p, Jun 8, 2020.

  1. For an upcoming build, I am planning on going without volume or tone pots. Instead, I would like to use a fixed resistor in the control cavity. I want to have the sound of volume and tone pots maxed out, rather than wiring from pickup straight to jack.

    I will be using an EMG active P pickup. The pots that usually come with this pickup are 25k for both volume and tone.

    I measured the resistance of both pots on max and got 47.5k. Does this mean I need a 50k resistor?

    I realize the whole knobless scenario isn't for everyone, so I am not here to get involved in debates. Thanks!


    IMG-0807.jpg IMG-0808.jpg
     
  2. lz4005

    lz4005

    Oct 22, 2013
    Have you tried it with no resistor? The difference between the two is the equivalent to less than a 1/16th turn on the high or high mid EQ knob on your amp.
     
  3. A few years ago, I did try straight to jack with a passive Fender P pickup. The highs were rather strident to my ears. The EMG active P pickup would have even more high end on tap.

    You're right, though. It wouldn't hurt or cost me anything to try it.
     
    Last edited: Jun 8, 2020
    lz4005 likes this.
  4. lz4005, thanks again for the suggestion. Just got this email from EMG, and you were right.

    "I would just run it straight to the Jack. We use 25k pots and they are essentially bypassed when at 10. The pickups run at 10k Ohms so the pots don’t have any effect on them when open, it’s not like passive pickups that lose some top end through the pots."
     
    TrustRod likes this.
  5. walterw

    walterw Supportive Fender Commercial User

    Feb 20, 2009
    alpha-music.com
    if you did want the exact same circuit load as a 25k volume and 25k tone both dimed then you'd want a resistor to simulate the two pots in parallel, not series.

    that means about a 12k resistor between hot and ground.

    +1 to it not making much difference with EMGs, though some argue that a 10k output impedance is actually rather high for an active pickup and you could in fact hear a slight darkening with 25k pots and straight-out might be slightly brighter.
     
    miljoneir, 40Hz and funkmaster p like this.
  6. Thanks, Walter for the info. I happen to have a 12k resistor on order that will get here tomorrow.
     
  7. Pot resistance really isn't a thing with active EMG pickups - that was one of the big reasons for EMG making the pickups active in the first place - they are buffered so the pot resistance won't affect them (much).
     
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  8. thewildest

    thewildest

    May 25, 2011
    Florida, USA
    I like the absence of devices (knobs, switches, jacks) in the front of instruments; my only suggestion would be to add the pots inside the cavity, perhaps using some mini-potentiometers, as you may want to set it a the right spot and it could mean to have to adjust the controls at least once.
     
    Igor Porto, equill, edencab and 3 others like this.
  9. Thanks for the suggestion. This is a sound idea. I've thought about just using the stock EMG pots within the cavity and maybe even hacksaw the potshafts off of them. Maybe adjust them with pliers, pack foam against them so they don't move around. The advantage of this is that I could use the EMG Quick Connect system and not have to solder anything. I am horribly unskilled at soldering, and my soldering iron is crap.

    However, I have 2 basses that have the orginal EMG PJ active pickups installed. I mostly use just the P pickup with wide open pots. With flat eq settings on my amp and PA system, the sound and response is 100% to my liking. If the sound is comparable on my new build while using a fixed resistor, I wouldn't feel as though I painted myself into a corner.
     
    Last edited: Jun 8, 2020
  10. Tonally it shouldn't be necessary for an active pickup. Just wire it straight to the jack.

    The tone of a passive pickup depends on the capacitive and impedance loads it feeds, but an active pickup has its coil(s) feeding a constant load - that tiny inbuilt buffer preamp.

    Having said that, in some circuits, like the classic musicman preamps, the volume pot is also the earth reference for the (polarised) output coupling cap. But I'd be very surprised if EMG haven't thought of that already, and there's a resistor already in the pickup's buffer preamp that does this job.
     
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  11. Thank you and all others for your generous, informed input. Straight to jack will be the first course of action. I’m increasingly convinced this may be the simplest and best path to my goal. Thanks, everyone!

    It may be weeks later, but I will try to follow up with pics and/or video of the final build.
     
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  12. Real Soon

    Real Soon

    Aug 15, 2013
    Atlanta, GA
    I'm just here for the cool idea.

    I love me some knobs, don't get me wrong, but there's something liberating about not even having the option to turn one: either balls to the wall or yank the plug.

    Re: the internal trimpots with amputations, that reminds me of a custom Cog Effects pedal build someone had done wherein some of the pedal's pot shafts were hacked down to nubs, then flathead screwdriver grooves were cut into the nubs. That way, changes COULD be made, but not without premeditation and effort.

    Seeing as a course has been decided upon, the prior is academic but it might be good to know it's an existing practice. Doing it inside a bass might actually be pioneering, even.
     
    funkmaster p likes this.
  13. Something I feel confident to reply to!! The tone control simply cuts the upper frequencies. The thing is though, even set at its least effective, the capacitor is still in circuit so you still are cutting some of the upper frequencies, often what you want on a bass. On my homemade 6 string, I have a push/pull tone so I can remove the entire circuit to let all the upper frequencies through. The easiest way to test is to put a capacitor across the jack socket. You can try the original 0.01 MF everyone first but you could also try other values which raise or lower the cutoff frequency.
     
    funkmaster p likes this.
  14. darwin-bass

    darwin-bass

    Mar 29, 2013
    Salem OR
    In the most technical sense of the word, you cannot wire EMG pickup elements straight to the jack. The actual pickup elements (magnet & wire) are wired straight to their own built-in preamp to create a pickup system within the pickup shell. You can wire THAT to the jack but the actual pickups are buffered, isolated, behind the preamp and will be unaffected by the switch from 20k pots to direct wire.
     
  15. Thanks for the info. My confidence is really picking up now.
     
    n1as likes this.
  16. darwin-bass

    darwin-bass

    Mar 29, 2013
    Salem OR
    Well, yes you are right but there is a minor distinction you're missing. In a passive system the tone cap is not in the circuit by itself. It is in series with a tone pot. Signal must pass through the 250k pot then through the cap to ground. So doing a test by just adding a cap across the output does not duplicate the tone circuit.

    Also with passive pickups, their tone is affected by the impedance of the wide-open volume pot. Even with no tone circuit, having different volume pot values (500k, 250k) will affect the sound of the pickups.

    So it isn't just simply the presence of that capacitor.
     
  17. Along with other suggestions, I'd encourage you to just try it. A resistor hardly costs anything.

    That said, record yourself so you can compare between the two configurations. :)
     
  18. You are right, the tone circuit comprises the whole inductance of the circuit, from the pickup (s), resistor and capacitor. What I meant though is that with no resistor the cap and pickup still remove some of the upper frequencies which some people like in a bass guitar. By adding back the cap you do get some low-pass filtering if that is what you like hearing. Personally, I like the all-frequency output but opinions vary.
    Greg
     
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  19. Passinwind

    Passinwind I know nothing.

    Have you looked at @RobbieK's video on passive tone controls? It's pretty danged interesting and his conclusions were not exactly what many of us expected at first blush. Well worth a look IMO, perhaps Rob can post the link as I can't seem to find it right now.
     
    funkmaster p likes this.
  20. I would be interested in seeing this. Thanks!
     
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