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Why does my onboard pre reduce "punch"?

Discussion in 'Pickups & Electronics [BG]' started by The Thinker, Dec 17, 2004.


  1. The Thinker

    The Thinker Supporting Member

    Sep 17, 2003
    Chicago, IL
    I found some reference to this in one of luknfur's (sp?) posts via search, but I'd like more info if possible. :help:

    My bass has an EMG BTC preamp that I can bypass. PUPs are DiMarzio Ultrajazz.

    When the pre is engaged, I notice that the initial attack of each note is "smoothed" compared to when I bypass the pre. I notice that this effect seems more pronounced as I boost the bass on the BTC. Nice when slapping, but not sure I like it for fingerstyle.

    I played a Skyline 44-02 w/the USA Bart pre, and noticed a similar result when switching between passive/active on the pre.

    Is this "smoothing" present in all onboards? Are any significantly less prounounced? Am I just imagining things? :help:
     
  2. luknfur

    luknfur

    Jan 14, 2004
    DIXIE
    FWIW:

    Don't remember punch specifically but it flows in terms of the "smoothing" effect which to me seems an accurate general effect. As you mentioned, this can have a positive effect as well, the most useful I found was noise reduction. The following thread wasn't done till after the 2 bands (including a BTC) were gone. But it is across the board with any onboard I've had and not an isolated condition. In the end, there was nothing an onboard would do I couldn't do with my amp or a set of quiet pups so I got rid of the preamps.

    In any of my older pup reviews you'll see comments regarding running them through a preamp, 95% of the time the comments are along the lines of your experience (the reduction in volume mentioned was due to the lo gain active input).

    Here's an endless shpiele if you're interested:

    http://www.talkbass.com/forum/showthread.php?t=128756&highlight=experiment
     
  3. The Thinker

    The Thinker Supporting Member

    Sep 17, 2003
    Chicago, IL
    Interesting. Thanks!

    My research is leading me to believe maybe it wouldn't be worth it to replace the pre with a different model. Maybe I'll just leave the pre in there and use it as a preset for slap, or if I need to make some on-the-fly adjustments.
     
  4. luknfur

    luknfur

    Jan 14, 2004
    DIXIE
    FWIW:

    I personally wouldn't bother with it cause I'd say it's such a low probability shot, but that doesn't mean an Aggie (whatever) may not be a just the ticket. As mentioned at the beginning of that thread (harmonics), even something that makes a slight difference can have a dramatic effect if it's the right combination.
     
  5. brianrost

    brianrost Gold Supporting Member

    Apr 26, 2000
    Boston, Taxachusetts
    The "smoothing" you are hearing is the effect of the preamp buffering the pickups from the input impedance of the amplifier.
     
  6. Tim__x

    Tim__x

    Aug 13, 2002
    Alberta, Canada
    There is one more possibility, it could be that your pickups have a fairly high output and your attack is clipping the pre, the fact that bass boost makes it worse points to this.
     
  7. A9X

    A9X

    Dec 27, 2003
    Sinny, Oztraya
    I've certainly found this is true with the experiments I've done in designing my own onboard pre's, trying others (borrowed) and replicating as much as possible some commercial designs (don't have the cash to buy them)*. Some pickups can put out several volts easily on peaks especially if you're digging in. Most pre's can't swing right up to the rail or down to earth, so their dynamic range is limited, and if you add in some boost then they will clip or in some cases slew limit.
    Two things generally change when you add in a preamp apart from gain and some frequency shaping capabilities;
    - the impedance seen by the pickup usually goes up, and can (depends on the design of the pre and location/layout of volume controls) remain relatively constant at differening volume settings, whereas a normal passive will vary markedly in the impedance the pickup sees. This moves around and changes the damping of the resonant peak that all coils produce, hence different sounds.
    - the preamp, if well designed, will actually give a lot better high end because it's lower output impedance and better drive current capabilities will more easily drive the cable capacitance and the input capacitance of the amp. However, most designs are very limited in what they can actually do because they're low current designs to give good battery life, so they increase in distortion at higher frequencies.

    Rick Turner once said here (paraphrasing) that all you're doing adding a preamp onboard is moving the first amplification stage to the instrument. True, but I've never seen an amp input as limited (sonically) in their design as every onboard preamp I've seen, and I doubt most of you would buy an amp with the same circuit designs as onboards in the front end of your amp.
    Most people are particularly poor in their perception of distortion and in describing it consistently too.

    * my experiments are not exhaustive nor definitive, solely based upon my experience and what I've heard and measured.
     
  8. The Thinker

    The Thinker Supporting Member

    Sep 17, 2003
    Chicago, IL
    You know, I wondered if it was a headroom issue. Would wiring the system for 18v make a significant difference if clipping is the problem?
     
  9. luknfur

    luknfur

    Jan 14, 2004
    DIXIE
    Seems every case I've read that's primarily what it does. The EMG site will state and has the 18V wiring if you don't already know. Also, I don't know if it would make any difference but you have the dip switches on the BTC that alter the knee frequency on the treble. Those settings are also specified on the site.
     
  10. The Thinker

    The Thinker Supporting Member

    Sep 17, 2003
    Chicago, IL
    Might be worth a shot on the 18V. Thanks again!
     
  11. Rick Turner

    Rick Turner Commercial User

    Jul 14, 2004
    I design and build electric basses and pickups under the Turner, Renaissance, and Electroline brand names.
    I think too many designers try to pack too many features into on-board electronics with too little voltage and current at their disposal. You can do a very good job of buffering and preamplifying pickup signals with 18 volt on-board electronics. I just don't think you can do a great job of that and then adding all kinds of excessive EQ. That job is better done elsewhere in the signal chain.

    I think the bass of the future may have simple on-board preamplification along with assignable knobs that control off-board EQ and effects that aren't constrained by voltage/current issues. Then you could also upgrade your off-board gear without making the bass itself obsolete. That could extend to pickup switching and balance as well as true master volume. Signals could be multiplexed for simple 1/4" cable usage or you could use multi-conductor cords. All signals (for as many pickups as you had) going out would be buffered, all blending/switching/effects would take place off-board, and basic controls would be remote on-board assignalble knobs and switches.

    It's going to take a miracle for that to happen as an industry standard, though....
     
  12. luknfur

    luknfur

    Jan 14, 2004
    DIXIE
    Some cool cutting edge comment as well as a little fortuitous synchronicity. I just recently pulled an old TBL post of yours regarding Alnico/ceramic mags to lend some credibility to a response. Think it's still on the first page of this forum.