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how to add a passive tone to a preamp ?

Discussion in 'Pickups & Electronics [BG]' started by giuseppecaporus, Dec 31, 2013.

  1. giuseppecaporus

    giuseppecaporus

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  2. line6man

    line6man

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    You can add a passive tone control to any preamp. Put it parallel to the input.
  3. ReidK

    ReidK Jst sy n t lssy cmprsn. Supporting Member

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    The auction text says there's an active/passive toggle switch, but I don't see one in the photo. You might ask about that before paying. The best approach would be a push/pull switch on the volume pot rather than a toggle - maybe that's what they meant, since the wholesaler they're getting these pieces from sells those as well.

    They also don't know what a "full-blown parametric equalizer" is, but that's not surprising.

    For this price, this looks like a nice little unit. Please keep us posted.

    Reid
  4. JustForSport

    JustForSport

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    Didn't see an a/p switch in that one, but it can be added, on the pre input side with tone pot as 'line6man' said. One side of a DPDT switch can bypass the pre, and the other side can be used to bypass the power to the pre at the same time if using passive pots.
  5. line6man

    line6man

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    No, you need two poles for active/passive switching. If the input of the preamp is not switched, its input impedance will load the pickups in passive mode, reducing output/treble. If the output of the preamp is not switched, its output impedance will cause extreme loading on the pickups, reducing almost all output. Thus, both the input and output need to be switched, for best performance.

    It's not a good idea to switch the battery, as there are usually loud pops, and a DC offset, when power is applied to the preamp. There is no reason for power switching, anyway, as current draw is not significant.

    Also, all pots are passive.
  6. walterw

    walterw Supportive Fender Gold Supporting Member

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    +1, you need all the lugs of a DPDT to do proper true-bypass switching.

    as for a tone pot, put it with the volume and any pickup switching/blending, before the preamp (before the bypass switch, really).
  7. giuseppecaporus

    giuseppecaporus

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    what do you mean for Put it parallel to the input ? do you have a wiring diagram for that ?
  8. line6man

    line6man

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    [​IMG][​IMG]
  9. walterw

    walterw Supportive Fender Gold Supporting Member

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    IOW, connect the tone pot to the volume pot, before you even get to the preamp.
  10. giuseppecaporus

    giuseppecaporus

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    thank you so much!
  11. RobbieK

    RobbieK

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    You can also wire the tone pot to the switch. This way it has no effect in active mode. I've had a lot of guys ask for this, plus an attenuator on the preamp's output, prior to the bypass switch, so you can switch between the two very different tones easily, without adjusting volume.

    Yeah I run true bypass whenever possible, but in practise, it's not the end of the world if you have to run a bypass on the output only. I've done this many times (with some switching I've designed, you simply run out of poles on your switch) and the effect of a 1meg+ input Z is often barely audible, especially if the amp is not very modern sounding and the customer doesn't use brand new strings all the time. Besides, generally, you switch to the active setting for modern bright tones, and the player usually is happy for the passive setting to be a warm contrast to this.

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