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An Amp / Pre-Amp Primer

Discussion in 'Amps and Cabs [BG]' started by Althius, Jul 28, 2004.

  1. Althius


    Jul 25, 2004
    I know NOTHING about amps and pre-amps. I grew up playing Upright, and only messed around a bit with electric.

    Now its really all I do... BUT... I know NOTHING about amps and pre-amps.

    What is a good amp? How powerful does it need to be? What the hell does 2x100 or 8x10 or whatever mean? What is a pre-amp? How does it work? Is it necessary? What are some good ones?

    I know its seems hard to believe that I am this ignorant after playing EB for 10 years... but its true. I never knew anyone who knew about amps and pre-amps, who could show me the ropes, so to speak.

    I bought a Behringer 600BX not too long ago (60 watt, 12"). Is it crap? Would a pre-amp like the SansAmp help?

    To reiterate... I know NOTHING about amps and pre-amps. A short primer would be most appreciated.

    I play mostly at church and in small bar-like spaces, where loudness tends not to be such a factor.
  2. Hollow Man

    Hollow Man Supporting Member

    Apr 28, 2003
    Springfield, VA
    Those 2x15 and 6x10 (and so on) notations are cab configurations. The first number indicates the number of speakers in the cab, and the second number tells the size of the speakers. The bigger the speaker size, the louder it goes and the deeper it goes; however, bigger speakers tend to have poor treble response.

    There are plenty of good amps; a good amp is determined at least as much by taste as it is by construction. Good players can make lousy amps sing, and lousy players make great amps look like overpriced paperweights. They don't "need" to be a particular volume, per se, as long as you can be heard over whoever (if anyone) you're playing with. The rule of thumb around here is that if you're playing with an electric guitar in any kind of aggressive rock-ish situation, you want about four times the power that the guitarist is using (i.e. if he has a 100 watt amp cranked all the way up, you'll want at least a 400 watt amp). The physics behind this is that it takes more power to make low frequencies equally as audible to the human ear as higher frequencies.

    Briefly, preamps control the shape of your sound, and power amps control the volume. Your Behringer already has both (thus you don't need a Sansamp). Some people prefer to buy two separate units (one preamp and one power amp) because if they decide to change their sound, they can swap preamps while maintaining their overall volume with the power amp. Similarly, they can change their power without losing their sound.

    Hope this helps. For more detailed explanations, do forum searches here on TB... there's more info than you could ever absorb on these pages.
  3. DaveDeVille

    DaveDeVille ... you talkin' to me ?? Supporting Member

    HollowMan227 ,
    excellent post , short and to the point :D

    Althius , nothing to be embarrased about , we all can learn something on this forum ...
    always try the search feature , it most likley will have at least part of the answer to your questions ... this is a great learning place !!
  4. Althius


    Jul 25, 2004
    For the record, I did some forum searching... I may be a EB n00b, but I'm a forum pro! :D

    Sometimes the search can be TOO powerful, especially when your knowledge is so minimal like mine. I really needed somewhere to start so I knew WHAT to search for. Thanks a lot for the information HollowMan, now I have somewhere to go from here!

    Of course if anyone else would like to chime in, I would appreciate it.
  5. A9X


    Dec 27, 2003
    Sinny, Oztraya
    Starting at the bass and following the signal chain through to the speaker, we have

    <b>pickup</b> this consists of a magnet(s) with a coill of wire wrapped around it. As the steel strings vibrate in the magnetic field of the magnet, they cause a current to flow in the pickup, which is the 'sound' of the bass. The signal here is about 1/10 of a volt.
    Some basses have a preamp on board, which may or may not boost the signal level or add equalisers on board. Onboard preamps also have the advantage that they usually have a much lower output resistance, which means that less high frequencies (overtones) are lost through the cable. These are often called 'active' basses because they have electroncs in them, whereas the first example would be called a passive bass, because it has no active (amplifiers) in it.

    There's also another type of pickup called a peizo. this is basically a small crystal mounted under the bridge or saddles, and when you squeeze it, ie through the string vibrating, it produces an electical signal. Peizos almost always have an amplifier on board, and in acoustic instruments, are the most common types of pickup.

    <b>preamp</b> The preamp takes the signal from the bass, via the cable, and amplifies it a bit, to maybe 1 volt, or more, depends on the design. It also adds various equalisers and switching (for effects loops etc), compressors, distortion etc. At the output of the preamp, the signal is strong enough to drive a poweramp.

    <b>poweramp</b> All a poweramp does is take the signal from the preamp, and make it a lot larger, and capable of driving the low impdance of the speakers connected to it.
    In some amps, the preamp and poweramp are in the one case, and are often called a 'head'. There are advantages and disadvantages of doing it as either one or two components, including, size, weight, flexibility, cost and reliabilty mongst others.

    Both preamps and poweramps can change or colour the sound coming from your bass, intentionally or not.

    <b>speakers</b> These come in a huge variety of shapes, sizes and power ratings. Hollowman's post above gives some excellent information and rules of thumb. Speakers will generally have a big effect on the final sound you produce, and what you like and what you're trying to acheive sonically. As HollowMan mentioned, a larger speaker driver will generally have better bass than a smaller one, but not perform as well in the higher frequencies. For this reason, some rigs will have a larger driver handling the low frequencies, and then 'cross-over' to a smaller driver which will reproduce the higher frequencies (or overtones/harmonics). The lower the frequency you need a driver to produce, the more air it will physically have to move to sound equally as loud as a higher frequency.
    One point to note, the power rating of a speaker, ie how many 'watts' it will handle, is almost always NO indication of how good it will sound, or even of how loud it will go. That will take a longer explanation....

    A good amp is one that sounds good (to you and the listeners), is reliable, has enough power, is able to be moved easily and you can afford. Hollowmans tip about 4 x the guitarist's power is a good starting point. Add more power for larger venues, and less on the other end of the spectrum musically and size of the venue.
    As for what's a 'good' amp in terms of brands and models, do a search here and you'll get a few ideas I'm sure. I know what I like, but that might not suit what you need. Find a friendly store, and see if you can spend some time in there playing with a few different ones and you'll get a much better idea than I can ever express in print. Just beware of the dreaded "gear aquisition syndrome".

    I've been working on amps (and other audio gear) for a long time and I'm not amazes by some of the half truths and garbage about how they work that people tell me. So don't feel bad, you've obviously been doing OK if you've been heard and your gear has lasted.

    I've only ever played with one breifly, but it seemed OK. I have a BX300 with I use as my quiet practice amp, and the one I hump to work occaisionally to accompany a girl and her acoustic geetar. Works well for what I use it for, but I doubt I'd ever use it as a main amp in even a small venue, because it's a bit small, and the same <i>probably</i> goes for your BX600, but try it and if it starts to sound strained, then try something else larger. If it's suiting your requirements, them it's perfect as it's cheap and lightweight. If you get the opportunity, try other preamps/amps/speakers and see if they make much difference to you, especially if you can try them where you're normally playing. All the Behringer stuff I've used has been reasonably reliable in non pro-tour useage.
    I don't think a SansAmp will add much the the Behringer, except some tone shaping from it's EQ. By all means borrow one and try it, before you spend the $.

    I hope that helped some. Feel free to ask for clarification or any further questions you might have.
  6. Althius


    Jul 25, 2004
    That was awesome. Exactly what I was looking for. I never understood a lot of that, it helps a ton.

    Far be it from me to say so... but those two posts could be cut out and stickyed... IMHO. There have to be more ignorant people out there than just me... at least I hope so.
  7. Tim__x


    Aug 13, 2002
    Alberta, Canada
    Good idea. How 'bout a talkbass glossary, we could have a thread stickied in every forum. What do you think Notduane, Kirbywrx?

    Edit: or atleast a thread like the "NEWBIE LINKS" one in "basses"