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Does A Stereo Power Amp Require A Separate Preamp?

Discussion in 'Amps and Cabs [BG]' started by john nam, Apr 1, 2009.


  1. I'm interested in getting the QSC GX5 power amp to power my 4x10 cab, but must I also get a preamp? This might sound dumb, but I really like the built-in preamp and pickups on my bass (Glockenklang and Delano) and I don't want to color it with anything else. I was planning on putting my bass through my DI (JDI) box straight into the QSC amp, which will be connected to my cab. Will this work? Thanks in advance.
     
  2. bongomania

    bongomania Gold Supporting Member Commercial User

    Oct 17, 2005
    PDX, OR
    owner, OVNIFX and OVNILabs
    Check out the "preamps explained" link in my sig. :)

    Edit: I just accidentally deleted almost a third of that article, and my backup copy is out of date! I'm re-writing the missing parts now.
     
  3. Mo'Phat

    Mo'Phat Supporting Member

    Oct 1, 2003
    San Diego, CA, USA
    Short answer: Yes, you still need a preamp to give the power amp enough input signal to be properly driven. Onboard bass preamps and/or DI's don't have that.

    Even a simple, cheap microphone preamp will do what you need and hardly color your sound at all.
     
  4. dougjwray

    dougjwray

    Jul 20, 2005
    On the other hand, I knew a fellow bass player who plugged a G&L L1000 directly into a Crown power amp (actually, he used a compressor/limiter, too) and sounded great. Maybe the G&L had enough output to make it work.
     
  5. Mo'Phat

    Mo'Phat Supporting Member

    Oct 1, 2003
    San Diego, CA, USA
    Well...sure, you'll get something out of that power amp when you plug a bass directly into it. Your bass has a preamp with some output voltage. But as bongomania's great link explains, you need to match preamp output voltages with amp sensitivity.

    Even some pedals would work directly into a power amp, but can they truly drive the power amp to their full potential?
     
  6. bobcruz

    bobcruz

    Mar 10, 2004
    CA
    QSC amps need a fairly hot signal to reach full power. For something really low volume you can sometimes get by plugging your bass straight into a power amp, especially if your bass has a strong onboard preamp. I can get adequate volume for my quiet church gig plugging my Peavey Cirrus with 18V onboard preamp directly into my Carvin T100 tube power amp bridged into a very efficient speaker, with master volume dials at about 2 o'clock. The Carvin is fairly unique in that it only requires 1/2 volt input to drive it to full power (100 tube watts).
     
  7. seamonkey

    seamonkey

    Aug 6, 2004
    You can open your active bass up and look to see if there's a trim pot. Many have them. You can usually tweak it to comfortable drive a power amp.
     
  8. CosmicRay

    CosmicRay Supporting Member

    You will most likely, more like definitely need a pre-amp. Even if you run the pre-amp flat as not to add any color to your tone, you will need to step up the signal.
    IMO - Alembic pre's are sweet, Tech 21 not bad either....I like tube pre-amps as opposed to solid state.
    Look around, there's quite a few out there...
     
  9. Yes you will need a pre-amp however it could just be something like an ART TubeMP. I too like how my basses sound right out of the jack. For a while I just used a TubeMP to drive my carvin and Mackie power amps. For around $40 it's pretty cheap to try one out.

    Paul
     
  10. 4Mal

    4Mal Supporting Member

    Jun 2, 2002
    Columbia River Gorge
    Something like the ART Studio MP - $50 at GC would do ya fine. You'll probably want the additional gain stage - in that case you might lose the JDI unless you also need to send a line to a house system or recorder...

    ART also makes a nice little box called the Tube PAC. It's a half rack item with a preamp and compressor. That one has an internal power supply as opposed to a wall wart. It's a pretty industrially built box. Last I knew, AMS had them for something like $110. You can find those in the GFS pretty often.
     
  11. bongomania

    bongomania Gold Supporting Member Commercial User

    Oct 17, 2005
    PDX, OR
    owner, OVNIFX and OVNILabs
    Also FWIW the JDI has a -12 dB drop from input to XLR output, so even if your bass had a hot-enough output to drive a given power amp by itself, it sure as heck won't be able to if you run it through the JDI.
     

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