Passive Pots and Capacitors Help

Discussion in 'Pickups & Electronics [BG]' started by Matthew_84, Feb 13, 2014.


  1. Matthew_84

    Matthew_84

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    I'm debating re-wiring my jazz bass into a pretty diverse system using split coil humcancelling pickups. I know what I want, but I don't know what the different terms and values of tone, volume pots, tone capacitors, etc, actually mean. If someone could shine some light on these questions that would be very much appreciated.

    1) what is the difference between linear and audio taper pots?

    2) is the answer for number 1, the same for tone and volume pots?

    3) what's the difference in tone/volume between a 500k TONE pot from a 250k TONE pot?

    4) what's the difference in tone/volume between a 500k VOLUME pot from a 250k VOLUME pot?

    5) if I were to chose say 500k TONE pots, is it advisable to also go with 500k VOLUME pots?

    6) what is the difference in tone/volume between 0.47 mf capacitors and 1 mf capacitors?

    7) if I had the possibility to wire each split coil pickup with independent series/parallel switches, is there an added advantage to include an additional series/parrallel switch to switch the wiring configuration between the two pickups?

    8) is there a difference in signal quality between a Volume-Volume setup and a Volume-Blend setup?

    I think that's all for now, but I'm sure more questions will come up.

    Thanks!
     
  2. line6man

    line6man

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    All pots and capacitors are passive.

    1. Audio taper pots follow an approximate logarithmic taper. Linear taper pots follow a linear taper. This changes the way they behave when adjusted.

    2. Yes. (Though there are functional differences that make different tapers more or less suitable for different applications.)

    3. 500k pots allow you to retain a bypassed setting at the end of the rotation, for most passive pickups' impedances, because there is an additional 250k worth of resistance available to place between the signal and capacitor, when you want it.

    4. 500k pots are brighter. 250k shifts the resonant frequency down a tad.

    5. That's personal preference. There is no technical reason to match or not match volume and tone values.

    6. Both of those values are far too high for standard high impedance, or even low impedance magnetic pickups. You want 0.047uF or 0.1uF, which are an order of magnitude less capacitive. In any case, higher capacitances cause a lower frequency cutoff point, while lower capacitances cause a higher frequency cutoff point.

    7. That's personal preference. Some people like versatility, while others do not find various options practical.

    8. There are functional differences and the practicality of each is subjective.
     
  3. Matthew_84

    Matthew_84

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    Thanks Line6man. I was hoping you would chime in here. I'd just like to add some follow up questions if I may.

    Makes sense, just to clarify. A linear taper volume pot at 100% open will allow 100% of the available volume through. If it was 63% open, it would only allow 63% of the volume through, and at 21% open, it would only allow 21% of its volume through?

    Audio taper would not taper in this same way, they would act as per manufacturer's design?

    Are there different kinds of audio taper pots, or do they generally all allow relatively the same amount of pass-through at relatively the same positions?

    Can you please elaborate?

    If my understanding of linear taper is correct. I would think that would make adjustment more easily approximated by the end-user.

    Can you please give different examples of when different tapers may be more suitable in one application, and when the same may be less suitable for different applications?

    So basically, a 500k pot fully open (no taper), will nearly bypass this pot, but a 250k pot fully open (no taper), would still restrict the signal path a bit?

    Using a 250k tone pot over a 500k tone pot, would give you a slightly less bright tone even with the pot fully open (no taper)?

    Using a 250k volume pot over a 500k volume pot, would give you slightly less output even with the pot fully open (no taper)?

    Gotcha. Thanks.

    Thanks for clarifying the values. I had a feeling I would get those wrong.

    I don't think I fully understand your explanation here though. Please pretend like you're talking to a 5 year old (because in many ways, you are ;)).

    If the tone pot is wide open (no taper) there will be no tonal difference between a 0.047uF and a 0.1uF capacitor?

    Using a 0.047uF capacitor on a tone pot and closing/tapering the pot, would cause the higher frequencies (such as treble range) to be cut off?

    Using a 0.1uF capacitor on a tone pot and closing/tapering the pot, would cause the lower frequencies (such as the bass range) to be cut off?

    Understood, but let's say I had the neck and bridge pickup each in their respective series mode, but I switched them to be wired parallel with each other. Would the tone, volume, or output be any different then if I had just put them each in parallel to begin with?

    Okay, but is there a difference in signal loss/quality between the two. Putting personal preferences aside, would one ultimately put out a better quality signal no matter the position of the two respective pots?

    I understand that answering these may be a daunting task, but I would really like to have a complete understanding of all of this stuff.

    Thanks again.
     
  4. BruceWane

    BruceWane

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    Audio taper pots attempt to compensate for the way human ears perceive volume changes. Linear changes in signal levels do not translate as linear changes in loudness to our ears - this difference is documented and often referred to as the Fletcher-Munson curve. More info here.

    Since this primarily affects volume perception, you might want to use audio taper pots for volume control, and linear taper pots for tone control. But pots are pretty cheap, so I'd really recommend just trying them to see what works best for you.

    Of course, if we're talking about any kind of active electronics, either active pickups (EMG) or active preamp/EQ, you need to use the pot types and values recommended by the manufacturer. These circuits are designed to work with specific potentiometer types/values.

    The basic difference between standard passive volume-volume circuits and balance-volume........ balance pots are actually two volume pots stacked, one of them being reverse taper. So technically, a volume-volume circuit has two pots and a balance-volume has three, which affects the total impedance of the overall circuit. But it's avery subtle difference, depending on your ears and/or pickups you might not hear the difference, especially if you're working with higher value (500K or 1M ohm) pots.

    Also, there are multiple ways to wire a blend pot - you can have the blend pot grounded or ungrounded, and then also there's buffered (aka active) blending. Lots of reading here if you'll do a search here in the pickups/electronics forum for "blend".
     
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  6. line6man

    line6man

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    This is going to be a long post, so I might come back and edit it later, if I skipped something, or copied/pasted wrong.

    Yes.
    Yes. There are graphs to describe the resistance as a function of rotational position, and they are available on some manufacturers' spec sheets. Here is a general idea of how it works:
    [​IMG]

    Tapers are subject to considerable variation. As you can see in the above graph, it is common for inexpensive and poorly-made log tapers to be constructed from two or more linear segments joined in an approximation to the log curve, in order to cut manufacturing costs.
    There is fierce debate on the use of log versus linear taper pots on this forum. Do a search on this, as it’s highly subjective, and I don’t care to rehash my opinions. (Though I'll be explaining tone control tapers at the end of this post.)
    Yes.
    Yes.
    Yes.
    Tone controls are filters that shunt higher frequencies to ground, and leave lower frequencies untouched. The frequency at which the filter begins to cut off is determined, amongst other things, by the capacitance chosen; the higher the capacitance, the lower the cutoff point, and vice versa. This means that lower values give you a perceptible brighter tone, as more treble is retained, while higher values are noticeably darker.

    Whether or not you will be able to hear the difference between capacitors when the tone control is turned all the way up is dependent on the value of the pot, and to a lesser degree, the impedance of the pickups. With a 250k pots the tone control will still be in the circuit, cutting high frequencies, so you may still be able to hear it. However, many people are unable to hear the difference between a 500k tone pot turned all the way up, and removed from the circuit entirely.

    Yes.
    There are many threads on this. The main differences between the two setups are related to functionality, however, a VBT setup is the equivalent of a VVT setup with an additional master volume pot. This third volume pot reduces the signal impedance, causing the same effect as using lower value pots. This can be compensated for by choosing higher value pots. On the other hand, ungrounded blends are becoming popular. This is equivalent to a master volume and tone only setup.

    Volume pot tapers are very subjective, but linear taper pots should never be used for tone controls. The reason why is that the ideal tone control has an infinite resistance at the end of the rotation for when the control is to be bypassed, and a much lower range of resistance throughout the sweep, for when the control is to be used. Log taper pots are better suited to this, as the resistance drops off very steeply toward the end of the rotation. For example, the 50% point in the resistance range is typically found at around four-fifths of the rotation on a log taper pot, versus half of the rotation on a linear taper pot. This means that you would have to turn a linear taper tone pot down halfway to get the same effect as a log taper pot that is rolled down a fifth. The result of this is that the usable range of control is squashed down into a very small portion of the rotation, instead of spread out over the greatest area possible. Linear taper tone controls tend to behave more like on/off switches, with large portions of the sweep having little effect, and the filter quickly kicking in toward the end of the rotation.
     
  7. Matthew_84

    Matthew_84

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    Thanks again. I really do appreciate your help. I understand a lot of these things more clearly now.

    So using a VBT setup with a ungrounded blend, is like only having one volume pot, as far as the signal impedance is concerned?

    If the blend is ungrounded, are there any added issues in regards the shielding, grounding, hums, things of that nature?

    This last sentence (bolded) confuses me, and seems to contradict the linearity of the taper. If a linear pot is truly linear, why would large portions of the sweep have little effect and the filter quickly kicking in toward the end of the rotation? Being linear, by definition, wouldn't the amount of effect be directly equal to the amount of the sweep?

    And another question altogether. What is really the difference in volume or tone from wiring pickups in series or parallel?

    I have read that pickups wired in series will have more output and will sound brighter, where as is parallel, they will have less output and be warmer. If a pickup was wired in series, could it sound like it was wired in parallel by simply turning down the volume pot a bit, and cutting the right higher frequencies, or does it change the characteristic of the output sound more than this? If the latter, can this please be explained to me in more detail?
     
  8. line6man

    line6man

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    Yes.

    Nothing of that nature. The only downside is the fact that it is not possible to completely solo a pickup, as a tiny bit of the opposite pickup's signal will still leak through, when one pickup is soloed.



    Think of it like this. Imagine that you are at a fashion show, where models strut down a long runway to show off clothing. Let's assume that part of the runway, by the stage, is obstructed from view in some way, and that each model has 10 seconds to walk to the end of the runway, by the crowd. If the models walk in a linear fashion, they will be hidden, and then far from the crowd for a considerable length of time. If, however, they run halfway down the runway in the first 2 seconds, they will have the remaining 8 seconds to cover the rest of the distance. This would ensure that they are seen for the most amount of time, since they are not wasting their time at the back of the runway. This is like an audio taper tone control. It has a high resistance at one end, to bypass the control when desired, but the resistance drops off quickly so that you don't waste so much of your sweep trying to get it down to the lower values needed to have a functional control.

    Of course, I don't know anything about fashion shows. They probably don't work that way, but the concept is valid.


    Indeed, series is louder and more midrangey, while parallel is quieter and more trebley. Turning down the volume is not enough to change the character of the sound. Series and parallel wirings tend to change the voicing of the pickups. Perhaps you can search up some soundclips of various pickups in both configurations.
     
  9. audioglenn

    audioglenn Gold Supporting Member

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    I'd like to thank you, too, line6man. You have taught me so much from reading your responses to various questions.
    Much appreciated!
     
  10. aphexafx

    aphexafx A mind is a terrible thing. Supporting Member

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    Lol :)

    This little thread is so much help. Great question set OP.
     
  11. Matthew_84

    Matthew_84

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    Gotcha. Thanks.

    Hmm, I'm assuming there's some electrical laws that are causing the linear tone pots to react this way.

    Also, just to clarify... Volume linear pots do not react this way correct? Whatever percentage they are open, is the percentage of available output volume you will get?

    Will do. Thanks a trillion line6man!

    +1. He's been tremendously helpful.

    EDIT TO ADD ANOTHER QUESTION: When buying pots, are there separate volume and tone pots, or are they just the same pot - it's the wiring/capacitors that differentiate its purpose?
     
  12. FunkyMan

    FunkyMan

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    line6man, all that info is absolutely pure gold for us who still don't understand well how those components work! The bad thing here is that in theory, everything seems nice but in reality, there is not much noticeable difference in all those aspects, plus sometimes placeo plays its game too
     
  13. Matthew_84

    Matthew_84

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    There may be some that there may not be a huge audible difference in some of these aspects, but I ultimately I do want the best sound quality and versatility that I can get. :bassist:
     
  14. Matthew_84

    Matthew_84

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    I think I just have these last few questions (as well as my two in post #10).

    I have read in a few different posts that wiring each pickup in series/parallel with itself is a little futile as the parallel option has a pretty weak signal. Is it a significant drop in output?

    Instead of wiring each pickup with this option, if I were to wire only one switch to switch between series/parallel between the two pickups, would there still be this output drop?

    If I wire them up the latter way, with one switch, and I solo a pickup, does the position of the series/parallel switch stiff effect the output and tone, with a Volume-Volume system? Or would it be preferable to wire it as a Volume-blend system for this switch?

    To my ears, from some of the audio clips I have listened to, the tone sounds warmer in series, and in parallel I don't quite hear the weaker signal, but I'm not sure if the recorder increased the volume to compensate.
     
  15. uOpt

    uOpt Supporting Member

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    There are a couple more specific things here.

    What exactly "logarithmic" means is highly vendor specific. If you measure how different log/audio pots actually measure on an ohmmeter you would be surprised how much difference there is. RSguitarworks does this, too, they have completely custom-designed the curve for the pots they sell.

    A lower resistance volume pot lowers the amplitude of the resonance peak, not the frequency of the resonance peak.

    If you want flexibility there is no need for a 250 Kohm tone pot. A 500 Kohm tone pot behaves precisely like a 250 Kohm pot would behave when you turn it down to where it reads 250 Kohm. The same trick does not work for volume.

    The tone pot control in a passive bass is not a low pass filter. You can look at the schematics of a 1st order LPF to tell instantly. What happens with the tone control in a passive bass is that instead of being it's own circuit it is adding/subtracting its electrical properties to the high-impedance pickup. The high-impedance passive pickup is very sensitive to having resistance, capacitance and inductance put at its end, and the values mix with the pickup's own values.

    The latter issue is also why active basses never sound like passive ones, the tone pot means something entirely different once the pickup has been isolated from the tone control via changing the impedance (e.g. with a preamp).
     
  16. line6man

    line6man

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    :D You're welcome.

    That's debatable. I personally think so, but not everyone agrees.

    The pots are the same.

    It tends to depend on the pickups. I recall SGD Lutherie had a pickup that had about the same volume in series, parallel and single coil modes. Other pickups have noticeable changes in volume for each mode.

    Yes. Think of it as a volume boost for series mode, versus normal volume for parallel, however, as pickups are usually wired parallel to each other. You can compensate for the boost with a switchable trim pot, if you want. Though this may cause a loss of high frequencies, to some degree.

    Master series/parallel switching on a bass with a blend pot is possible, but unusual. The control scheme is unrelated to the volume differences between modes.
     
  17. Matthew_84

    Matthew_84

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    I can't thank you enough line6man. This is great.

    I think I'll be going with 500k linear volumes and audio/log tones (I'm doing one tone pot per pickup).

    Is there a brand/model of audio/log tone pots you have found to be pretty even? I used CTS tone pots once, and they didn't seem to have big tone swings in a short sweep of the pot, but I sold that bass a week or two later, so I'm not too sure.

    I'm not really looking to turn down the boost of series, I'd rather turn up the output in parallel, particularly if I did decide to allow a switch for series/parallel of each pickup.

    I believe that if I did a series/parallel push-pull for how the pickups are wired together, and they were in series mode, then I would only have one master volume for both of the pickups and they would both be full on?

    I'd really like to be able to put it in Series but still be able to blend more towards one pickup - 90% of the time would be to emphasize the bridge in Series. Would any of these options allow for this?

    A - Volume-Blend setup) Could I focus on each pickup freely in series or would it cause any issues? Could there be an advantage to using either a grounded or ungrounded blend with this use in mind?

    B - Volume-Volume setup) Since most of the time in series, I'd want to emphasize the bridge pickup could I put the master series/parallel push-pull on the bridge volume pot, and then when it's pulled (series) use that to adjust the master volume, but if I wanted to lower the volume on the neck pickup only, wire it up so that if I then also pulled the neck volume pot out (the neck pickup only would run through this), I could lower the volume only on the neck to taste? I think it would lower the overall volume though, but only because I lowered the neck, the bridge would still output about the same?
     
  18. Ric5

    Ric5 Supporting Member

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  19. Matthew_84

    Matthew_84

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    Hate to be a bumper, but I'm still looking for some recommendations for a 500k audio/log pot that has a fairly even sweep, and anyway where I can put both pickups in series with eachother, but be able to emphasize one (please see post 16 for more details).

    Thanks in advance.
     
  20. Casablancas

    Casablancas

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    How significant is the difference between 500K and 250K VOLUME pots? And between 1M and 500K VOLUME pots? (Using 2 humbuckers in series mode)
     
  21. line6man

    line6man

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    Subtle. People worry too much about pot values.
     

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