Question on Preamp

Discussion in 'Amps and Cabs [BG]' started by Hofbrauhaus, Jul 20, 2003.

  1. Hofbrauhaus


    Feb 10, 2002
    Upton, MA
    Hey everyone...I'm interested in finally purchasing my first bass rig. I'm looking at a QSC RMX850 power amp and mating it to either an Avatar 4X10 or 2X12 cab. My question is if the rig would function like this, or if I would need a preamp as well (I guess the real question is if I could plug into the poweramp directly or not). I play a Stingray5 (if that means anything) and just want to know if a preamp is simply for tone shaping or if it is needed for more than that. Thanks!
  2. David Wilson

    David Wilson Administrator Staff Member Administrator Supporting Member

    Oct 14, 2002
    Lower Westchester, NY
    you'll need a preamp. Preamp tone shapes as well as bringing your instrument level signal up to a level suitable for a poweramp.
  3. lo-freq

    lo-freq aka UFO

    Jan 19, 2003
    The Republic of Texas
    I would highly recommend a Demeter VTBP-201S.

    I have an SR5 -> Dem 201S -> PLX1602 -> Berg HT322.

    Awesome sound!
  4. redneck2wild


    Nov 27, 2002
    Memphis, TN
    There are 3 primary things I look for in a preamp:
    1) Tone Shaping ability
    - Multiple knobs such as Low, Mid, High - the more knobs, the more tones one may produce
    - Parametric Mids are nice if there are few knobs - allows one to change the frequency of Mid level
    - Graphic EQ is helpful if there is a lack of knobs or no parametric Mid
    - Tube preamps can add color and nice harmonics to tone
    2) Compression
    - Compression can help smooth the sound and help protect speaker drivers
    - Tube preamps may not necessarily need a separate compressor as the Tubes themselves will compress the signal as the gain increases
    3) Crossover
    - allows one to run a biamp rig - sending the highs to one amp and the lows to another - something helpful if one wants to run larger rigs
  5. Hofbrauhaus


    Feb 10, 2002
    Upton, MA
    Thanks for the advice. I'll look into some preamps and follow up later on what I decided to get. Hopefully the funds will allow it!
  6. xyllion

    xyllion Commercial User

    Jan 14, 2003
    San Jose, CA, USA
    Owner, Looperlative Audio Products
    There are lots of choices for preamps, and preamps have a huge effect on your sound. Try to play through as many as you can get your hands on before you buy. Also consider unusual choices. I currently use an ART Tube Channel preamp in my bass rig. It is not strictly a bass preamp but I like the result that I get.

    If you have the money, Ashdown, Kern, Demeter and Alembic all make really nice preamps. If you don't there are many other lower priced preamps that have a good sound to them.
  7. To make your rig complete you should have some type of pre-amp to tie the whole thing together. As far as what to buy? About the least expensive fully functional preamp I can think of would be the SansAmp Bass Driver DI. They are under $200. They look like a stomp box with a bunch of knobs. You can get a rackmout version with a few more features for around $300. Many folks on this forum swear by them. I've got the little stomp box and I think it is the perfect backup pre-amp. Personally I use a Ampeg SVP-Pro or an Alembic F1-X with my rig. Pre-amps are kinda like Scotch, the more you pay the smoother they go down.
  8. Ahhhson

    Ahhhson Guest

    Jun 5, 2003
    ALBANY NY 518
    my preamp is a bottle of henny
  9. Hofbrauhaus


    Feb 10, 2002
    Upton, MA
    Hey guys...for a cheaper alternative would an Aguilar DB 924 or Sadowsky Outboard Preamp/DI pedal work? I'm more concerned about getting the boost I need for the poweramp rather than my tone shaping capabilities just because my Stingray5 sounds just how I want it to sound with my current amp set flat, so I don't think I would be doing much shaping with the new one either, although i am aware that this rig will sound different from the Marshall I currently play out of. Let me know if either the Aguilar or Sadowsky would work for this purpose, thanks
  10. lo-freq

    lo-freq aka UFO

    Jan 19, 2003
    The Republic of Texas
    RMX850 Input Sensitivity @ 8 ohms = 1.15v (+3.4 dBu). You might need to check with the manufacturers of the outboard preamps to find what their output is.

    Some people use SansAmp BDDIs for preamps, but I don't know if it will drive the RMX850 or not.
  11. Hofbrauhaus


    Feb 10, 2002
    Upton, MA
    Well I'd be running thee RMX850 bridged at 4 ohms, not 8 ohms. I do know that the Sadowsky and Aguilar provide a boost of 13dBu and 18dBu respectively, so my understanding is this would be more than enough to drive the RMX850. Am I right or is there anything I'm missing?
  12. lo-freq

    lo-freq aka UFO

    Jan 19, 2003
    The Republic of Texas
    Assuming those values are correct, you should be fine; the amp sensitivity should need a little less input voltage at 4 ohm to produce full rated power output.
  13. BillyB_from_LZ

    BillyB_from_LZ Supporting Member

    Sep 7, 2000
    As Davidwilson wrote, besides EQ, the preamp also provides the voltage gain that you need to properly drive your power amp.

    If you are totally happy with the tone shaping abilities of your bass and just want a voltage boost, you could try an Ebtech Level Shifter. It's a passive device that converts an instrument level signal to a line level, or vice versa.

    They're about $70 from Musicians Friend.

    If you live near a Guitar Center or similar, they should have them too...and you'll have 30 days to try it out and see if all goes well. You have 45 with MF but you'd eat shipping both ways.

    If you're electronically inclined and want to build your own, Walter Harley offers up a schematic of his bare-bones bass preamp (he's satisfied with the EQ power of his onboard preamp) at