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Passive preamp?

Discussion in 'Amps, Mics & Pickups [DB]' started by bassteban, Feb 26, 2005.

  1. Is there such a thing as a passive(no batteries or wall wart, please)preamp or at the very least an impedance matching device? I have a radio shack piezo-equipped DB that sounds decent- thanks to Jeff Sahs of Sacramento- but I would like not to need to worry about a battery crapping out mid-song. I'm aware some amps sound good w/a preamp before the bass, but that's not in the budget, so I'm trying to make it sound good through a Hartke Kickback 12. Any suggestions would be highly appreciated. Thanks.
  2. JonB


    May 27, 2003
    An impedence-matching transformer maybe?
    In line ones are available.
  3. Can you tell me where? In the meantime, I'll try to clog google's bandwidth. Thanks, JonB!
  4. A matching transformer with a piezo pickup? Forget it!
    You need at least 1 Megohm to get proper piezo loading.
    You'll never get that with a passive transformer design, and furthermore, the inductance of the transfo is likely to behave quite bad with the highly capacitive reactance of the piezo pickup.

    Someone was selling a Fishman preamp for cheap in the DB Sales forum.

    You can also check Bob Gollihur's site:
  5. fdeck

    fdeck Supporting Member Commercial User

    Mar 20, 2004
    Madison WI
    HPF Technology LLC
    Sad but true. Some sort of active circuit is a necessary evil. If you are a DIY'er, it can be done with a 9-Volt battery and exactly 3 electronic parts, the thing draws roughly a milli-amp, resulting in 500 hour battery lifetime. If there is any interest, I will post the design at my website.
  6. - My goal is decent tone withOUT that stinking 9 volt gig killing leech. I have a K&K pure preamp- which sounds fine, but the thought of changing batteries mid-gig scares me. I realize I may be asking too much, but I'm asking anyway. I do appreciate the info.
  7. How about a small AC adapter to replace the battery?
    I understand the fear of battery failure at the wrong moment!
  8. Chasarms

    Chasarms Casual Observer

    May 24, 2001
    Bettendorf, IA USA
    There is nothing on the market that I am aware of that will work passively. A "passive" preamp is an oxymoron, in fact.

    If you are really freaked out about a 9V, just get something like a Baggs Paracoustic DI that runs on phantom. Or buy a bass amp that will accept a piezo. (Like a contra)

    It seems really a little paranoid. Batteries are only a couple bucks. If you are really that worried. Just change it every month or so. That's what I do with my EBG.

    I have a K&K preamp/blender with my trinity acoustic guitar rig. I only have to change the battery about once every few months and it even powers the mic.
  9. or if you are extremely paranoid just change them before each gig...
  10. SteveC

    SteveC Moderator Staff Member Supporting Member

    Nov 12, 2004
    North Dakota
    much ado about nothing.....
  11. That doesn't mean you guys are NOT out to get me, though. Likewise, I'm not trippin over a $5.00 battery, it's more that I don't want it to go out on me mid-tune(again). It's a huge hassle , & very distracting(mind you, this is in Church) to unplug(POP), pull out a screwdriver, ask around for a good 9V, & button it all back together. So I just dropped out. I don't want to do that again if I can help it. I realize the best thing may be to make battery swapping easier, I'm just finally at the point of, at least while playing live, less is best- less potential failures, less distraction, etc.
  12. Monte


    Jan 9, 2001
    DFW Area, Tejas
    If you can find a way to make swapping easier, than a rechargable 9v would be a good thing.

    I used to do this years ago when I used a preamp that I was paranoid about going out. I would recharge the battery every 2-3 times I used it and never worry about it.
  13. I think making it easier to swap will effectively shut me up. Batteries last long enough & I'd likely lose a recharger, but that's a good idea, Monte. Thanks.
  14. PB+J


    Mar 9, 2000
    arlington va
    I also hate batteries and want my signal chain to be as "passive" as possible. But you can't have it--any preamp is an "active" device in that it's boosting the signal. For a while I used a raven labs PMB with a wall wart adaptor, sometimes with the batteries. Currently I use the gorgeous sounding avalon u5 as my only preamp with both upright and electric. But it has to be plugged in.

    The best bet, it seems to me, woulld be to just get an amp with a high input impedance option, like maybe one of the swr strawberry blond acoustic amps--actually, alot of people are making acoustic instrument amps now that would sound at least as good as the hartke, probably better
  15. basss

    basss Supporting Member

    Aug 27, 2001
    In my experience with battery driven preamps they don't just "turn off" when the battery goes. You begin to hear some subtle distortion in the sound when they begin to die. I think you could finish a set or at least a tune after you begin to hear the distortion and before the battery totally dies. There are a lot of pros out there using battery driven pres in their basses. As stated above you just have to change it regularly.
  16. PB+J


    Mar 9, 2000
    arlington va
    that's actually exactly what I hate about them--that they don't go all at once--I'm at a gig, i start hearing what might be some distortion, I start wondering where it's coming from, I start trying to remember when i last changed the battery, I wonder if there's a blown speaker, a bad power tube, short somewhere, bad cable, etc etc. The I start fiddling with gear between tunes, or during the tune I'm listening for battery problmes instead of listening to the singer. It just adds to the distractions.

    Many pros use battery powered equipment, but they often have spare equipment and a tech on hand--I don't. I'm usually heading out to a gig in a hurry, after coming from work or from some family obligation: i like to throw the gear in the car and not worry--when was the last time I changed the battery? I think I have a spare in the gig bag--Do I have time to stop at the7/11 and get a new battery, or will that make me late for sound check and setup? Do I have a screwdriver, to open the battery compartment? You get the idea.
  17. My problems, exactly(as well as the posts above)!
  18. PB+J


    Mar 9, 2000
    arlington va
    I just rememebered--there are passive, impedance matching transformers that step mics down to 1/4 input. But that's taking low impedance (mic) to high impedance (1/4 inch). And I think it's high in the sens eof magnetic pickups, not in the sense of piezos, which are really high
  19. Yeah, I think I'll just graft a battery box into my K&K pure and shut up. I just had Jeff Sahs go through my bass so I'm pretty stinkin' happy- batteries, schmatteries!
  20. Bob Gollihur

    Bob Gollihur GollihurMusic.com

    Mar 22, 2000
    New Joisey Shore
    Big Cheese Emeritus: Gollihur Music
    Batteries are a necessary evil, portability but fewer wires and extension cords are the reward.

    I buy batteries in bunches at Sam's Club, IMHO name brand alkalines are the only way to go. And I always have a couple new batteries stashed in my boy scout gig bag.

    Little white labels are available at Staples and such, the type that are not permanent and can be peeled off. I put them on each of my battery powered toys, preamps, the plastic control panel on active planks, and write the date I installed the battery (on planks I'll also note the string type and date installed, especially if they are a new set I'm auditioning). I used to add a little mark after each gig, to track the # of gigs used, so I could have a good idea when to automatically replace the battery, but got away from that slightly obsessive behavior... though it certainly is a good way to track usage and send up the battery replacement red flag.

    If I grab a plank or pre that I don't often play to take to a gig, I follow my own simple recipe: One Phillips Head Screwdriver + One $10 Multimeter = a meter reading that tells me the battery is plenty alive or on its last legs.