Advice from Pre Amp owners

Discussion in 'Amps and Cabs [BG]' started by Mohter, Nov 4, 2004.

  1. :) Hi GuysnGals how's it hangin',

    I'm a recent convert to things bass, picked it up helping someone finish some originals ended up :bassist: with 'em
    for three years :D I had an Ampeg SVT3P/Classic 4x10.

    Anyway, I'm looking for a another amp and I'm leaning towards a pre amp set up and would like some advice/opinions
    on a few things.

    In thinking about power amp/speaker set up I realised I don't
    know that much about 'em - they were always in a road box,
    set up, and the bass players toys or the sound guy's tool :eyebrow: or is that the other way round .... er ......

    Anyway, do power amps have many features in common of
    equal value eg: full power at 4 ohms, bridged full power at 8 ohms, or are there different choices. Do any run full power 4
    ohms in both stereo and bridged mono, or am I stuck with making the chioce between 4 ohm stereo - 8 ohms bridged mono :confused:

    My old '69 Marshall JMP guitar amp had a rotary switch on the back - 4,8,&16 ohm, it sure made speaker coice easy :help:

    Is it better to have one stereo amp or two monos of differing power lows/highs. What is the difference in sound character running stero as to mono if you don't run your speakers

    What are the pre amp rigs like to live with in comparison to an integrated amp style. I'm trying to decide between getting an Eden WP100 or a 550 Traveller which, at the moment I can get for within $200Aust. each other ( WP with a 2nd hand amp) I think I 'd get more bang out of the WP100, but I'm a loooong way from any dealer with higher end equip. on hand to try and the Manual for the WP on the Eden site won't display :scowl:

    I don't really need 1400 watts or anything so I wont need a huge rack to lug and even with an intergrated amp you'd end up putting it in a rack or some sort of hardcase, is the difference in weight that much :confused:

    :oops: Just realised how long I've been rabbitting on, sorry.
    Any advice will be greatly appreciated, thanks ..... Moh
  2. Tim__x


    Aug 13, 2002
    Alberta, Canada
    Most modern power amps will run down to 2 ohms a channel or 4 ohms bridged. With any solidstate (non-tube) amp you can run a speaker with a higher impedance (ohms) than the amp is rated for, so a 2 ohms minimum amp can handle a 4 ohm cabinet.

    A stereo amp is basically two mono amps in one case.
  3. IvanMike

    IvanMike Player Characters fear me... Staff Member Supporting Member

    Nov 10, 2002
    Middletown CT, USA
    a lot of power amps will run at 2 ohms a side (4 ohms bridged), but many only run at 4 ohms a side and 8 ohms bridged. I prefer the former. Amps like Stewart 1.6/2.1 and the QSC PLX series are lightweight and run at 2 ohms. A good stereo power amp should be all you need. Running the same mono signals thru both sides sounds fine, (most of the world does it that way). Biamping (sperating the lows and highs) works fine with a stereo amp with equal power ratings on each side, but you may find you like the sound of your cabinets all run full range better.
    Size wise with a preamp/poweramp setup you're usually talking a 4 space rack vs the normal 2 space integrated head.
    With a lightweight power amp you can generally count on the pre/power setup being about twice as heavy as a head.
    The rotary switch on your marshall is a tube amp feature. On tube amps the setting has to match the impedance of the cabinet used. On solid state amps this type of switching is impossible, but you can use any impedance as long as it's not lower than the minimum safe load specified on the amp.

    more info on amps and speakers
  4. Thanks Tim - Ivanmike, okay - so I do have to decide between stereo/
    mono - 4 or 8ohm for the cabinets, fair enough.
    Not too sure about the ohm switch HAVING to be set the same as the cabinet for the valve amps though Ivanmike - one of the things I used it for was to set it at 4 and run it into my 8ohm quad for small rooms,
    pushing the amp for a little grit while keeping the volume resonable for the sound guy. Worked a treat, every person who ever played that amp want to buy it of me, plus a lot that just heard it! Didn't seem to hurt it either - I owned & used it for 15 totally reliable years - only selling it to set up with bass gear. Hard decision that was.
    back in the mid '70's an Aust. band we knew was going nutso trying for a particular starting sound. Stomp boxes wouldn't do it, they even tried hanging carpet over the front of the boxes to hold the stage volume down while pushing the amps to distortion. They ended up putting a similar thing only in their boxes not the amps.
    Thanks for the advice guys......regards Moh.
  5. IvanMike

    IvanMike Player Characters fear me... Staff Member Supporting Member

    Nov 10, 2002
    Middletown CT, USA
    running a tube amp set for 4 ohms CAN work ok but it will shorten tube life at the least, and at worst will raise the plate voltage to the point where components of the tube amp can get fried
  6. troll


    Aug 31, 2000
    Chicago area
    I prefer just sticking to 4 ohm cabs. That way you can end up with a 'smaller' amp and use more of the available power, and if need be, even run it at 2 ohms to get the power you need to it.

    I am running a plx1602 (was rmx1450 until recently, which worked splendidly as well, but too heavy) to two 4 ohm cabs, but made a cable to run both inputs of the 4x10 to give it more juice that it requires.

    Most modern amps can and will run 2ohm safely, cool, and without any noticable quality loss for bass guitar reproduction :) Make your amp work, not your pocketbook.

    Getting a huge amp just to run 8 ohm speakers properly seems like a waste.

  7. Thanks guys, I geuss the main thing I'm tring to figure is which will give more options eg with a stereo amp that runs full pwer at 4 & 8 brgd I could only get full power brgd and one quarter power stereo with an 8 ohm box. whereas with 4's I could run stereo full power or one side only full power mono/