cheap preamp?

Discussion in 'Amps, Mics & Pickups [DB]' started by snowdan, Mar 7, 2006.

  1. snowdan


    Feb 27, 2006
    well now the WM 10 combo is there and it is what i expected. but the fishman piezo i am using is not loud enough for the SWR.

    which would be the cheapest suitable preamp to buy? fishman cost around 100 euros here, that is too much. EQ is not that important.
    even though a notch filter wouldn't hurt either.

    thanks for any ideas.

    DIY is possible by the way.
  2. mje


    Aug 1, 2002
    Southeast Michigan
    I built fdeck's preamp into my Azola, and it works very well.

    Lately, though, I've been experimenting with J. Donald Tillman's design, which trades some headroom for a little bit (3dB) of gain. His neatest idea is building it into a cable:

    I did a prototype of this the other night, and it works exceptionally well with the Fishman I glued to the bridge of my UB. If you can solder tiny parts, this is a great system. I'm going to build a bunch of them along with some battery boxes with volume pots built in.
  3. robgrow

    robgrow Supporting Member

    May 1, 2004
    Cincinnati, Ohio
    Technically, the circuit on fdeck's site is actually a buffer circuit that provides no gain. The circuit on Don Tillman's site, , does provide some gain, however it introduces a new problem, since it inverts the phase (or to be more technically correct, the polarity) of the signal.

    Connecting two of the FET preamp circuits on the Don Tillman site in series with a 50K audio taper pot in place of R4 in the first stage would provide a fair amount of gain and the absolute polarity of the signal would be maintained. This could be built for very little money by anyone with reasonable DIY skills.
  4. mje


    Aug 1, 2002
    Southeast Michigan
    Right, fdeck's source follower actually has a slight insertion loss.

    I question how much absolute polarity matters, especially as:

    1. The signal from the pickup may not be in phase with the acoustic output of the instrument;

    2. The amp may not maintain polarity

    3. Unless the speaker cabinet is inside the instrument, you're gonna get phase differences that vary with frequency anyway. There's no way you can ever get the amplified sound in phase with the instrument.

    The G string fundamental is 98 Hz; that's a wavelength of 10'. An amp 5' away from your ear is going to deliver a signal 180 degrees out of phase from the acoustric output of the instrument, even if you maintain the polarity of the entire system.

    Some maintain that it's critical to get the polarity right on the leading edge of the sound wave, but experiments have not shown that to be distinguishable in most cases unless you're dealing with sharp impulse noise (like a gunshot in an enechoic chamber) that has no similarly to the kinds of sounds we're talking about.
  5. larry

    larry Supporting Member

    Apr 11, 2004
    For those who are soldering-challenged, Studio Projects VTB-1is a mic pre that also has a line in and can function as a DI. It is awesome as a bass preamp. No EQ, but good sound for under $100 USD. Has a tube that can be dialed in or out in any amount. Not it's best feature, but it offers different flavors. Good bang for the buck.
  6. seamonkey


    Aug 6, 2004
    (If you can stomach the guilt)
    Behringer V-TONE ACOUSTIC ADI21
    $30 USD

    Quiet, Clean
    Be aware the "blend" control is a distortion like control. I leave mine off.
  7. snowdan


    Feb 27, 2006

    40 euros here. anybody else to comment on this device?
  8. snowdan


    Feb 27, 2006
    order placed, 38 euros shipping included.

    i will report here how the behringer performs.
  9. A good DIY option with loads of gain is Jack Orman's Mosfet Booster:
    I bought one of his good quality circuit boards and built it into a friend's EUB with excellent results.
  10. snowdan


    Feb 27, 2006

    the unit seems to be reasonably well built.

    it provides very little gain. the sounds gets quite a bit better though. the EQ sounds musical indeed. the amp simulation is crap for DB.

    if it had a little more gain it would be awesome.

    can anybody tell me wether the behringer is any louder when run with a 9v adapter?
  11. drurb

    drurb Oracle, Ancient Order of Rass Hattur; Mem. #1, EPC

    Apr 17, 2004

    CORRECT! Absolute phase does not matter! Thanks for getting to this before I did! :)
  12. seamonkey


    Aug 6, 2004
    What are you running it into? Balanced or unbalanced?
  13. snowdan


    Feb 27, 2006

    i am running the behringer into the workingman 10. i can tell from camparison w/ BG that the behringer is not as loud as it could be w/o overdriving the WM.