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Power Amp Confusion

Discussion in 'Amps and Cabs [BG]' started by Gingrilla1987, Nov 6, 2013.

  1. Gingrilla1987


    Jan 7, 2013
    Hey guys. Another rookie question, but last time you vets were super helpful.

    I was watching a rig rundown for Billy Sheehan and he was using some power amps in front of his Hartke HA5500s. Same thing with Justin Chancellor, using a Demeter in front of an amp.

    Why would you put a power amp in front of an amp that is a contained, stand alone amp?
  2. You wouldnt.
  3. "Slaving" a power amp off of a complete amp head uses the amp head's pre amp so you can drive additional cabs with the voicing control you have set.
  4. dmrogers

    dmrogers Supporting Member

    Jan 26, 2005
    Eastman, GA
    Like CL400Peavey said, you wouldn't.

    You could, however, take the output of an amp head and send it to a power amp.

    The reason: Let's say you like the pre amp of a stand-alone, but you need to run a large cabinet array and the stand-alone won't handle them. You could send the pre-amp out signal to the power amp and power a much larger group of cabinets.

    For instance, my current rig is using a power amp that will operate both sides at a 2 ohm load. I could run 4 8 ohm cabs on each channel for a total of 8 cabinets. (This is just an example, I don't think I would ever play a gig where I would need 8 cabs).
  5. Gingrilla1987


    Jan 7, 2013
    Okay, so basically you're just taking the tone from the complete amp and making it stronger so you can use it bigger applications?
  6. dmrogers

    dmrogers Supporting Member

    Jan 26, 2005
    Eastman, GA
    Sort of.
    You would take the signal after the pre-amp (and before the onboard power amp) and send it to the input of the external power amp.

    But yes, you are using the tone shaping of the amp (EQ etc....) and sending the signal to the power amp.
  7. tbirdsp


    Sep 18, 2012
    Omaha, NE
    Looking at Chancellor's rig rundown - he is using Demeter bass PREAMPs (not power amps) as a DI to the main PA which is mixed mic'd signals from both his cabs.

  8. Gingrilla1987


    Jan 7, 2013
    So in the case of Chancellor's, he goes into the preamp which then splits his signal to the GK heads, 1 running a clean signal and one running a dirty signal, and then those each go to the respective cabinets? And if that is the case, would he be using the Demeter as his tone shaping preamp and then the GK heads as power amps?
  9. dmrogers

    dmrogers Supporting Member

    Jan 26, 2005
    Eastman, GA
    That sounds likely.

    I also should clarify my earlier posts. You can also run a pre (such as the Demeter) into the front end of an amp head. As long as you don't overdrive the input signal.

    For instance, I have a Monique pre amp that I run into a Crest Power amp. I could take the Monique output signal and run it into the input of my Thunderfunk Bass Head to further shape the tone. I would just have to set the Monique output and the gain on the Thunderfunk for an optimal sound.
    Like I said, you can do it, but personally, I think my above example is kinda overkill.

    The Monique sounds great going into the Crest and the Thunderfunk doesn't need any help in the tone department.

    In short, there are many options when working with all of this equipment. Depends on your goals and how good it ultimately sounds.

    Hope this helps.
  10. Gingrilla1987


    Jan 7, 2013
    Definitely does. Just looking at options as I'm going to have to get my own bass "head" (I'm borrowing someone's) and seeing different things on rig rundowns, where they aren't fully explained, sometimes makes it confusing. I just don't like to box myself in and have nowhere to go, ie. Buy a small contained head and then need to buy a whole new rig for bigger stuff.
  11. tbirdsp


    Sep 18, 2012
    Omaha, NE
    I think the Demeter pre is just to send a clean-ish signal to the PA. Then the sound from the clean and dirty GK heads is also sent via mics from the respective speaker cabs and it's all blended together.
  12. dmrogers

    dmrogers Supporting Member

    Jan 26, 2005
    Eastman, GA

    I understand. All my life, I used bass amp heads and separate cabs. This year I put together a pre/power rig and I love it! I still have the regular heads, but the tone and flexibility of the pre/power rig is unreal.

    It's a real plus to do tons of research before making the purchase. You will be glad when it comes time to make a decision.

    Good luck!
  13. René_Julien


    Jun 26, 2008
    Since you are interested in Justin's amp setup here is an interesting thread in the effects forum in case you haven't seen it:


    It explains how his signals are split. I hope by now that you have an understanding of what a preamp, poweramp, "stand-alone amp" and DI is.

    Basicly it's starts with his tuner pedal splitting the signal in two.

    One of those goes: tuner --> some dirt pedals and eq --> GK2001RB ("stand-alone" amp) --> cabs --> mic --> mixing board of PA

    The other goes: tuner --> bunch of pedals --> Demeter preamp - Radial JD7

    The Radial JD7 then spits his signal again:

    JD7 --> GK2001RB --> cabs --> mic --> mixing board of PA


    JD7 (DI output) --> mixing board of PA

    There are also some great drawings somewhere that makes it a bit clearer how his signal flows.
    I'm no expert on Justin Chancellor's rig, just a fan of Tool and I hope my description was somewhat correct.
    In this case I hope it is safe to state that the Demeter preamp isn't used as a preamp per sé. It's used as a toneshaper. It isn't driving any poweramps. This might be confusing, a preamp can mean different things. I think bongomania has a great article on preamps on his ovnilabs website. (You definately should check that out as it is very informative to people who are new at effects and amps and any equipment in between.)

    But... to give you advice... setting up a rig like Justin Chancellor is overkill if you are just a weekend warrior. And I don't think your band mates are going to welcome it.

    It's fun to obsess what the pro's are using, I do it too, but for us regular Joe's what we use must be realistic.

    Advice: keep it simple. Avoid as many hassle as possible setting up your rig.

    I own several amp heads, preamps and poweramps. My favourite setup to use is a preamp/poweramp setup. A Sansamp RPM into a poweramp. I can get my most desired tone out of that one and it is a great DI.
    However, these days I mostly use an Ampeg PF-350. It's good and simple. It gets "my jobs" done.

    Big complicated rigs are usually for big needs, not necessarily for better tone. (I am weighing my words here, devoted pre/poweramp users might slam me for this. :))

    So right now you only need to aquire an amp head...
    Under the assumption you most like Justin Chancellor (sorry if I'm wrong) I would say Gallien Krueger.
    Even if you are not of his tone, you can't go wrong with Gallien Krueger either way.

    What cabs are you using?
    My opinion is that your cabs are even more important than your amp.
  14. Consider how much time you have for soundchecking bass before you go to multiple bass channels / mics to FOH.

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