Basic amp questions!! i should know this stuff!

Discussion in 'Amps and Cabs [BG]' started by j b scott, Jul 7, 2003.

  1. Ok so i admit i dont much about amps or cabs or setting up speakers and whatnot

    all i have and have ever had is a 70 watt combo thing from cash converters, kind of a plug and play thing!

    so now i am looking into the furture and i need more, much more power, and i hear combos are to be kept away from! so then it comes to this head and cab deal i suppose!

    i read alot here and basically get very confused because there are HUGE holes in my knowledge!

    1)like matching heads with cabs? how is that done? how do you know what is the right power and compatibility and such? can just add as many and whatever type you want?
    2)ohm levels? what differnce does it make? how do you change it? which is the best? :meh:
    3)all this tube and solid state stuff, like an ampeg head from has the following under specs:<i>
    Preamp (Tube or Solid State): T (2 x 12AX7)
    Driver Tubes: 2 x 12AU7, 12AX7
    Power Amp (Tube or MOSFET): T (6 x 6550)</i>
    -> i dont get that at all except that is has '2X12' so does that mean thats the speakers needed? from what ive heard tube is the way to go.
    4)and whats this difference between pre-amp and power amp? you need em both? :confused:

    ok so there is alot of stuff i dont know about heads and cabs and if you guys help me out here i will be very grateful! and i will understand some stuff people are actually talking about!
  2. adouglas


    Jun 23, 2003
    Bridgeport, CT
    Okay, I'll see if I can help with the basics. What you wind up with depends a whole lot on your budget, how loud you need to be, what tone you're looking for, etc. etc. If you've got $2000 to spend on a rig you're going to wind up with something different than if you only have $300. So with that in mind...

    There's nothing intrinsically wrong with combos. There are some great combos out there (Eden Metro, SWR Super Redhead, etc.). A combo is nothing more than an amp head that's permanently attached to a cabinet. The Eden Metro is an Eden WT400 head on a 2x10. The SWR Super Redhead is an SWR 350 on a 2x10. If you had those heads and separate 2x10 cabs your results would be identical.

    No, you can't just add cabinets endlessly. This has to do with impedance (ohms). All cabinets have a given impedance (usually 8 or 4 ohms). This may be marked on the cabinet. A weird thing happens if you plug in more than one cabinet... if you plug two 8 ohm cabinets together, you wind up with a 4 ohm system. If you plug two 4 ohm cabinets together, you get a 2 ohm system. (I'm leaving some points out here for simplicity... the point is that if you plug in multiple cabinets you'll wind up with lower impedance.)

    This is important because lower impedance draws more current out of the amp. Most amps cannot handle impedance lower than 4 ohms. So, if you were to buy, say, four 8 ohm cabinets and plug them all in you'd wind up with an impedance too low for the amp, and the amp would go up in smoke.

    Regarding compatibility, worry not. Any given cabinet should work fine with any given amp. Just make sure you don't wind up with too low an impedance if you use multiple cabinets. Most rock players wind up with two cabinets, so if you buy 8 ohm cabs you'll be safe (two 8 ohm cabinets plugged in gives you 4 ohms, right?).

    Regarding power, check the rating of the cabinet and make sure it's equal to or greater than the output of the amp. For example, I have a 4 ohm Avatar B212, which is rated at 1000 watts. The amp I'm driving it with puts out 260 watts at 4 ohms. No problem.

    You can get all this information from the manufacturers. Cruise around the websites and look at specs. The amp will say what the minimum impedance is (if it doesn't say "ohms" it will probably have the symbol for ohms, the Greek letter Omega).

    A more important question to ask is what configuration of cabinet you want (1x15, 4x10, etc.). Generally speaking, larger drivers (e.g. 15 inch) will produce low frequencies better, but are too large and massive to reproduce high frequencies well (that's why woofers are big and tweeters are small). So smaller drivers will give you more definition at midrange and higher frequencies, but may lack the bottom end. This can be compensated for by using a lot of small drivers (like four 10 inchers). A typical rig is a 2x10 cabinet (which gives you that nicely defined midrange) and a 1x15 cabinet (which gives you that nice low end). My cabinet is a good compromise... it's got two 12 inch drivers and a horn tweeter. It handles the low B on my 5 string really well.

    Again, this is oversimplified... not all cabinets are created equal. A 2x10 from one manufacturer will sound very different from a 2x10 from another manufacturer. But it gives you something to start with.

    See above about impedance (that's the term, so use it... if you walk into a store and ask about "ohm levels" the salesperson will immediately peg you as someone who doesn't know anything... if you wind up getting hosed it's your own fault).

    You can't change it, and there is no "best." Just make sure the combination of cabinets you choose isn't too low.

    No, no, 12AX7 is just the type of tube...nothing whatsoever to do with speakers. What that says is that there are two 12AX7 tubes in the preamp.

    Tube amps have a different sound from solid state amps. Usually described as "warmer" or "richer." If this is what you're looking for, then yes, tubes are the way to go. If all you've ever known is a 70-watt combo, you probably wouldn't be able to tell much of a difference for a while. Tube preamps are much more common than tube power amps, mostly because tube power amps are large and heavy. The typical amp head will have a tube preamp and a solid-state power amp (Eden, SWR, etc.)

    Yes, you need both and if you buy an amp head or a combo you'll get both.

    The preamp is the part with all the knobs on it. It controls your tone (bass, treble, etc.). A preamp alters the signal, but only puts out a tiny amount of power, far too little to drive a speaker. The power amp is just the part that makes lots of watts. It takes the tiny signal from the preamp and boosts it up to ear-bleeding levels before sending it to the speaker cabinets. A typical power amp will have just an on/off switch and level controls. No EQ (bass, treble, etc.)... that's what the preamp does.

    Power amps don't alter the tone (well, they do, but for a discussion at this level just assume that the power amp does nothing but boost power). Preamps do. So if you get a tube preamp, you'll get a tube sound even if your power amp is solid state (by the way, MOSFET means solid state).

    The reason you're confused is that it's possible to buy separate preamps and power amps. A regular amp head (e.g. Ampeg SVT) is both in one box.

    Your little 70 watt combo has both a preamp and a power amp in it. The preamp is the part you see.

    Hope this helps...
  3. snailplow

    snailplow Leon Phelps Wanna Be

    [PART 1]
    I'm assuming that you're a player who's just beginning to jam with other people,so I'll word this as simple as I can to avoid added confusion.
    You're definately ganna want to get at least 300 watts of power,and make sure there's an output on the back of the amp that you'd plug a microphone cord into.
    This is called the D.I.("direct interface")output.It's there to run a mic cord from the amp,to a P.A. mixer/head.It sends your bass signal through the P.A. so the people in the audience can hear you if you're playing a large place,or outdoors.You don't really HAVE to use it if you're band is rehearsing or gigging in a small place.Your rig should be loud enough on it's own in this environment.
    As for tube vs.solid state vs. mosfet,etc.,etc.,just play through as many amps as possible that's in your price range,and let your ears decide for you.
    What's the "best" for somebody that responds to your post here,may not be the "best" for you.Just be sure to use YOUR bass when you try out an amp and/or cabinets,and if you can afford it,put new strings on it before you do so.
  4. snailplow

    snailplow Leon Phelps Wanna Be

    [Part 2]
    When it comes to cabinets,think of ohms (also refered to at times as impedance) as resistance to the power an amp is sending to it/them.When you're trying out cabinets,look on the back,where you plug the speaker cable in,and most of the time you'll see a 4 or an 8 with a symbol that looks like an up-side-down horseshoe.That's the symbol for impedance.The smaller the number is;the less the resistance is to the amp's power,so it will sound louder,and more dynamic.
    Most amp companies make heads that puts out it's maximum power into a 4 ohm impedance,and it will say so on the back of the amp.Try to find one that does.
    To make the cabinet(s) delemma easier for you to understand,just do this and please trust me.
    If you decide to buy just one cabinet,get a 4 ohm cab.In this case you'd run one speaker cable(NOT AN INSTRUMENT CABLE)from one of the speaker outputs on the back of the amp,into one of the speaker's inputs.Done.You don't need to use the other speaker output on the amp.
    WARNING!!!!If you run two 4 ohm cabs with an amp that's rated to run at 4 ohms minimum,you will probably overheat the amp,and that's NOT good for it.
    If you decide to buy two cabinets,make sure they are both 8 ohm cabs.Then you'd run a speaker cable from each of the speaker outputs,to a speaker input on each cab.Done.
  5. snailplow

    snailplow Leon Phelps Wanna Be

    [Part 3]
    As for speaker configurations like 2x10s vs. 4x10s vs. 2x12s vs. 1x15,again,just try them all out in multiple configurations and let your ears and taste guide you.Nobody knows what you like better than yourself,but do the exprimenting BEFORE you buy anything.
    Preamps and power amps.When you buy a bass "head",you get the preamp,(sometimes a compressor),the eq,and the power amp all in one package.This is definately the cheapest way to go comparitavely,and I'm assuming you're working on a budget,so I'd just get a head if I were you.
    Hope this helped.
  6. i cannot thank both of you guys enough! :)

    it most certainly did help! and i really appreciate the time that was spent helping me out.

    Things are so much clearer now!

    i am no longer afraid to try amps at shops since now i know some stuff and i wont look like a complete idiot.

    this forum is a very good place and i am glad people are willing to help others out!


  7. unharmed

    unharmed Iron Fishes

    May 19, 2003
    London, England
    Yay! Melbourne!:D
  8. kirbywrx

    kirbywrx formerly James Hetfield

    Jul 27, 2000
    Melbourne, Australia.

    Where are you 2 guys from?
  9. unharmed

    unharmed Iron Fishes

    May 19, 2003
    London, England
  10. im in glen waverley if that means anything to ya!
    right at the end of the melbourne - glen waverley train line (who would have thought)

    you near luna park or something?
  11. unharmed

    unharmed Iron Fishes

    May 19, 2003
    London, England
    <BR><BR> :p Not really. Other side of St Kilda, over Nepean Hwy. A small but select crowd of Melbourne TB'ers is emerging :D
  12. when hooking things up in the store make sure you watch the ohms so you dont end up blowing up an amp. rember 2x8ohms is 4ohms and 2x4ohms is 2ohms and some amps cant take 2 ohms!