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Blend knob volume dip centered

Discussion in 'Pickups & Electronics [BG]' started by KablesP, Jan 24, 2014.

  1. KablesP


    Oct 29, 2013
    Basses that have a blend knob tend to lose a little bit of volume when centered and both pickups are 100%.

    Does this happen with a switch as well? I wanted to replace a 3 way switch with a blend knob.
  2. It happens any time two pickups are parallel to each other. The reason is that each pickup loads the other with its own impedance. That impedance is lowest at the center detent of a blend pot, and when the volumes are all the way up on dual-volume basses. It also happens with pickup selectors, but because there is no continuous volume control, most people don't tend to notice.

    Perhaps you should try switching some resistors/trim pots in the circuit, to fine tune the volume in each position.
  3. wmheilma


    Jan 5, 2010
    Or do what I do and never leave it exactly in the "dip". I had no idea there was a scientific reason why it always sounds better to favor one pickup or the other!
  4. walterw

    walterw Supportive Fender Gold Supporting Member Commercial User

    Feb 20, 2009
    use an M/N blend pot and don't connect the grounds and you'll have the exact same sound in the center as you do now.
  5. However I love the sound of two hbs in parallel... Gibson les paul guitar or Gibson ripper bass for example, amazing tone in that setting for rock rhythm playing.
  6. amana


    Oct 16, 2013
    First of all, it also happens to basses with two volumes. The reason, as you've been told, is that when you put the two coils together they "interfere" with each other. Take into account that when the balance is not in the center position, or the volumes are not both full, there is a resistor that is part of the circuit.

    Solution is simple. Use an active balance circuit. These normally introduce separate preamplification stages for each pick-up and then sum the signals, although there are different designs. Take into account that you may even keep the passive onboard eq because some of these circuits are available without the eq (that is, you add only the active balance control), so no change in sound. You'll need a battery though. And you must make sure that your volume and tone controls will work with the active balance control (not all of them will).

    See this one (where you also have a good explanation of the problem: http://www.emgpickups.com/accessories/bass-accessories/summing/abc.html
  7. It is worth noting that active blend controls change the tone. The pickups each see a constant input impedance, and that impedance is usually just a 500k or 1M Ohm resistor. This is not the same as being loaded with the resistance, inductance and capacitance of the other pickup. The entire nature of the resonant circuit changes, as a result.

    That's not a concern. Volume and tone controls are just pots and capacitors. They work fine in any circuit, if their value is appropriate for the signal impedance. If you need to move controls to a part of the signal path that is post-buffering, just replace the pots with a value appropriate for low impedances. Pots are inexpensive.
  8. amana


    Oct 16, 2013
    Totally agreed on the technical side, but in good ones, at least in my experience, the change is not noticeable to the ear. I have only tested the Glockenlang myself, but I can tell you that no one that has heard my bass passive and now with the preamp has told me they can notice a change in tone (and some "fine ears" are among these). I mentioned the EMG because they sell the balance control alone.

    In fact, being rigorous, as soon as you connect your bass to a pedal or an amp, this also introduces new components in the circuit and changes the tone a bit. That's inevitable.