Power amp, preamp and head explanation.

Discussion in 'Amps and Cabs [BG]' started by dudemeister, May 23, 2002.

  1. Hi,
    Could you either direct me to a thread where the concepts and their differences are explained or kindly enlighten me on the subject in this thread?
    I've played bass for quite a while but never checked these things out since I've always played with a combo. I only know that a combo is a head and cabinet in one and I think a head is a power amp and a preamp in one.
    Could you also explain advantages and dissadvantages of combos and head+cabs.

    Thank you!
  2. chucko58


    Jan 17, 2002
    Silicon Valley, CA, USA
    I paid for all my gear myself. Well, me and MasterCard.
    You're exactly right, a head is just a power amp and a preamp combined in one box.

    Small combos are nice in that you only have one box to haul around, and no cables to futz with. This is a great setup for recording, and for small, low volume performances.

    Some combos try to do too much. An extreme example is the Carvin RL6815 "Cyclops", which packs a 15" speaker and a pair of 8" speakers as well as a tweeter, in a cabinet that also holds an R600 head. The Cyclops weighs over 100 lbs (45 kg for those of you in civilized countries :) ). I don't know about you, but I wouldn't want to haul that around without help!

    For me, a practical limit is a single 15 or a pair of 10s. Any more and I think you're better off with a separate head and cab.

    If you need more volume, the best way to get it (transportation permitting) is to add more speakers. Some combos let you hook up an extension speaker. Others don't, like my old Peavey TNT 130. A combo that doesn't have an external speaker hookup is rather limiting.

    A head and a single cab can be easier to haul around than a single large combo. Owning a head and two or more cabs gives you lots of flexibility for different performance requirements. You can choose to haul only one cab to rehearsals and small gigs, use different combinations of cabs to get a particular tone, etc.

    When you need the ultimate in flexibility, the "rack rig" is the way to go. Separate preamps and power amps give lots of control over your sound, at the cost of more stuff to lug, more complexity to deal with, and of course more cost! Most folks who go the rack route add effects boxes, power conditioners, and the like. All this gear can weigh a ton.
  3. jokerjkny


    Jan 19, 2002
    NY / NJ / PA
    just wanna echo alot of chuckie's sentiments.

    portability is an advantage as chuckie alluded to. I've got a nice 2 space rack, along with a pair of 1x12 cabs. if they were glued together in a single combo, it would have weighed about 95 lbs. but they're separate so the rack weighs only 15 lbs. while each cab is a more managable 40 lbs.

    to be able to carry each cab in each hand while strapping my rack on my back is much easier. it is costly, however, yet worth the portability considering my many taxi cab rides.

    also, usually separate components are better quality cause they've been engineered for a specific purpose. rather than a bunch of stuff slapped together into one box. again, this can be a pricey route.

    good luck!
  4. Ok, thanks alot!
    What is is the difference between preamp and power amp and in what ways to they affect the sound?

    Btw, I'm going to play my first gig with my new EBS 210 combo tomorrow night and it's going to be exciting to see how it sounds live. I've only played it at home with the volume knob at between 10% and 20% of maximum and it still sounds quite loud so it should manage delivering enough volume at the gig.
  5. jokerjkny


    Jan 19, 2002
    NY / NJ / PA

    The sole purpose of the preamp is to allow you manipulate the overall sound using good ol' treble, mids, bass, and other goodies to help enhance and shape your bass' tone. some are built with just transitors. these are known as "solid state". other preamp designs employ the use of vacuum tubes, which many agree, impart a juicy "warmth" and other positive characteristics to your tone that make tube preamps highly desirable. yet, these "tube" amps are pricey, whereas SS is relatively inexpensive. for instance my Demeter VTBP-201s is an all tube preamp.


    Yet, preamps by themselves cannot pump sound into a speaker cab. you need a power amp. The job of the power amp is to amplify your signal so it can be pumped thru your speaker cabs. it doesnt really shape your tone at all. it shouldnt cause you'd want a power amp that is as transparent as possible, so all the tone from your preamp is accurately translated to your speakers. for example, this QSC PLX2402.


    some basses have "onboard" active preamps, which are like mini preamps powered by 9 volt batteries hidden inside the bass' cavity. they serve to further enhance a bass' tone, and to give the player even more tone shaping options. it sounds redundant, and it can be, but also, its purpose is to make sure a nice clean signal is reaching your rack preamp over a long instrument cable. for instance, this J-Retro onboard pre.


    there are also "outboard" versions of these mini onboard preamps that come in boxes you place at your feet for easy access. these are used for basses without the onboard pre. these boxes serve the same purpose as the onboard pre's. an example is Sadowsky's Outboard preamp.


    hope this helps. i'm sort of generalizing here, but you get the jist. if anything check out this FAQ on this old post. it'll help you with anymore amp questions.

  6. That isn't entirely true because if it were nobody would buy tube poweramps
  7. jokerjkny


    Jan 19, 2002
    NY / NJ / PA
    yea, i know, but i wanted to keep things general, so Dude would understand the gist.