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WHAT EXACTLY DOES AN ONBOARD PREAMP BUFFER DO?

Discussion in 'Pickups & Electronics [BG]' started by luknfur, Apr 1, 2004.


  1. luknfur

    luknfur

    Jan 14, 2004
    DIXIE
    Does anybody know what these things actually do. Somehow I've gotten the impression they boost the signal but they have bass boosters/expanders so I'm assuming a buffer is something different. The expander I assume is for broader frequency range of 4+ strings. Many people associate buffers with Piezos so they must have some boosting affect since piezos put out weak signal.
     
  2. Passinwind

    Passinwind I Know Nothing Supporting Member

    The idea of a buffer is to prevent signal loss, rather than to boost signal. Since a piezo element is very high impedance, plugging it straight into an amp or preamp designed for a lower impedance input device (like, say a magnetic pickup) results in a lot of signal loss and degraded tone. Ever try plugging a low impedance mike into your instrument amp? Then using a matching transformer? A buffer serves essentially the same function as that transformer, although the impedance mismatch is in the other direction.
     
  3. luknfur

    luknfur

    Jan 14, 2004
    DIXIE
    Okay, so let's see if I've deciphered this half accurately (skipping the piezo thing cause it's not actually a piezo in question), a buffer between the pups and preamp is essentially acting as a step down transformer? If so then how broad a spectrum will a buffer cover. That is, there's going to be considerable difference between say a passive Duncan hotstack and EMG actives.
     
  4. Passinwind

    Passinwind I Know Nothing Supporting Member

    My bad if it's not for a piezo, I just picked up on your mention a piezos and ran with it. That's a specific case, not the general one.

    So what specifically are you looking to do? A buffer could be making gain too in some circuits, or could be for impedance matching the other way. In any case, most buffers have lots of headroom, but the impedance matching (of the buffer input) to the pickup needs to be reasonably close for best results, but reasonably close might mean within a factor of ten or so. Active pickups already are buffered, by definition. They're happy driving all sorts of loads. That Duncan wants to see a high impedance load though, so a buffer would allow you to run it through a low impedance tone network, like say the ones you commonly see for active pickups. If you used independent buffers on a pair of high impedance pickups, they might no longer interact in the usual fashion when you adjusted the volume controls. I used this approach for one of my basses, and like it a lot.

    This Warmoth tutorial could be helpful: http://www.warmoth.com/Bass/Gecko/ActivePassive.htm
     
  5. luknfur

    luknfur

    Jan 14, 2004
    DIXIE
    Yeh, I'd been to that site before but a refresher was at hand anyway.
     
  6. Passinwind

    Passinwind I Know Nothing Supporting Member

    If you used independent buffers on a pair of high impedance pickups, they might no longer interact in the usual fashion when you adjusted the volume controls. I used this approach for one of my basses, and like it a lot.

    So what was the outcome from this that worked so well?

    I can now turn one pickup way down, without dragging the other one with it. No need for a pickup selector or blend pot either. The pickups still interact, but only as a function of their different phsyical locations. No hum cancelling "sweet spot", it's all good in my particular case. It took a lot of rebuilds of the preamp to get there though.


    Which brings to mind a still unanswered question, what affect on sound in general does a buffer have: increase volume, clarity, fullness?

    Can be all of those, but especially improved signal to noise ratio, and lack of lost highs, epecially over a long cable run. However, many pickups are compensated for the losses inherent in passive circuitry, and sound "better" run that way. IOW, buffering may not be a panacea. As you probably know, lots of amps are also similarly compensated for cable losses and so on.