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Power Amp Question

Discussion in 'Amps and Cabs [BG]' started by PollyBass, Jan 19, 2002.


  1. PollyBass

    PollyBass ******

    Jun 25, 2001
    Shreveport, LA
    Ok. i was going to ask if i could hook up a power amp to my already existing head, And the new bass player "Bass Gear" told me i could, by hooking it up to my head out,,, or in. If i added a 1000 watt carvin power amp (PA style) and i had a 350 watt head, i would have 1350 watts. right? or just the 1000? no way am i getting a 1000 watt power amp, I just used that figure. Anything i need to know when hooking up a power amp to my head?
     
  2. djbyron

    djbyron

    Jan 18, 2002
    Saratoga, NY
    I don't think that can be done... Are you sure the article wasn't refering to using you present head as a preamp, THEN going out the "head out" to a larger power amp??

    Of course I could be wrong... Someone else help us out!
     
  3. Steve

    Steve

    Aug 10, 2001
    You can do it but.... it's all about gain structure and input voltage. The wattage is not cumulative. the wattage you have will be the wattage of the amp you're using to drive the cabinets with.

    If the amp you want to use as a preamp is transistor (and for some reason you don't want to use a line out) you can come out of the speaker out into the input of the second power amp.

    HOWEVER!!!!!!! you'll only be able to just barely crack the volume so that it's only putting out a couple of volts. This is hugely risky as it is very easy to completely burn the front end of a power amp by feeding 30-40+ volts to an input that designed for less than 5 or 10.

    That's the long answer.

    The short answer is don't do it. It's strictly
    Old Timers get through the gig patch.
     
  4. PollyBass

    PollyBass ******

    Jun 25, 2001
    Shreveport, LA
    Why would bass player recomend something dangrous? It said id just need a power amp and a head, no pre amp power amp thing, just the head i had. Why would they do that? you sure its really dangrous? The reason i ask is this, i have a cab that can handle 350 watts RMS, With a head that puts out 350 watts, 200 in this case, due to the fact its an 8ohm cab. If i ever wanted a new cab, i would like some more power. This seemed like the way out of my problems, rather than buying a new head.
     
  5. notduane

    notduane

    Nov 24, 2000
    Location
    bikertrash~ is right. Avoid running your Crate head's 'amp out' or
    'speaker out' into the INPUT of another amp.

    Options...

    Run the 'preamp out' or 'line out' of your current amp into
    the input of the power amp. You could run the 'speaker out'
    of the power amp (1Kw) into your current cab, but if the cab's
    rated at 350w you'd be running the risk of blowin' that up.

    Ideally, keep your current setup, i.e. crate head speaker out
    into your current cab, then the crate head's preamp/line out
    into the 1KW amp's input, and then the 1KW's speaker out
    into a cab that can handle 1,000 watts.
     
  6. geshel

    geshel

    Oct 2, 2001
    Seattle
    The 1000w was just for an example, notduane. :)

    Polly - your bass head has a preamp section and a power amp section. If it has a "preamp out" output, which is the output after the volume control and EQ, you could run this to the input on a new power amp. If you hooked your speakers to the new amp (again say 1000w just for example), you'd be pushing 1000w. The power amp section of the head would be idle.

    It would also be possible to hook additional speakers up to the "speaker out" on the head and use it's power as well.

    What you don't want to do (what it sounded like at first, although you're definitely right BP would never recommend this, they were suggesting what I mentioned above) would be to connect the "speaker out" output on the head to the input on the new amp. It would definitely sound horrible and probably break something.
     
  7. Brendan

    Brendan

    Jun 18, 2000
    Austin, TX
    So (general Q, not just to geshel), in Theory *coughchough*...if I had, say, an Eden WT-300 head, and oh, say an 8 ohm D-410XLT...I could:

    Hook up the 410 to the head. Then get an 18' (8 ohm) and hook it also up to the head. Giving me 300 watts RMS @ 4 ohms. Then, I could buy a poweramp, and send the DI ("Recording") XLR out to a poweramp, and have the poweramp feeding a 4 ohm 8x10 cab...all without blowing the head with the odd impedances...right? Remember, this is strictly hypothetical....

    [​IMG]
     
  8. The theory of the two 8 ohm cabs being fed 300 watts at 4 ohms is correct. However, I am not sure that the "Line-Out" will produce a hot enough signal to trigger the power amp. In that hypothetical set-up you may still need some sort of power amp in front of the power amp.
     
  9. PollyBass

    PollyBass ******

    Jun 25, 2001
    Shreveport, LA
    Ok, so, let me see if i got this right. i can hook up a 1000 watt head to my head, making the power amp in my head idle, and since my amp has to speaker outs, i could hook them up, and have 1000 watts going to two cabs. What input am i looking for on my head? a balenced out? unbalanced? i dont think it has a "Pre-amp Out".
     
  10. Balanced or Unbalanced really would not matter. Most power amps will accept either kind of input. However, that will still be "line-level", and not hot enough to trigger the power amp.

    Your best bet is to look for a reasonable pre-amp. One good suggestion is the SansAmp. You could also use it as a DI box when recording.
     
  11. geshel

    geshel

    Oct 2, 2001
    Seattle
    I assume you meant "some sort of preamp in front of the power amp".
     
  12. geshel

    geshel

    Oct 2, 2001
    Seattle
    Generally I'm with you on this. But the SansAmp isn't a preamp - it's a direct box. It's got more beef than a line-out but not as much as a preamp level output. Word on the streed is that it is enough to drive at least some amps (I think it was the Mackies). But you might have to push it to get that.
     
  13. geshel

    geshel

    Oct 2, 2001
    Seattle
    You're starting to mix some things up. A "head" has a preamp and a power amp all in one unit. So hooking another head up to your head, while possible, is an altogether different thing. But back to what you originally said, and I think you mean, hooking an additional power amp up to your head.

    As far as if your head has the right kind of outputs, I'd recommend a new thread that specifically asks for info on that head, where you ask if it has outputs you can send to a power amp (or you could try here first of course - my knowledge of specific heads is pretty slim so I can't help you there :) ).
     
  14. PollyBass

    PollyBass ******

    Jun 25, 2001
    Shreveport, LA
    Im sorry, thats not what i ment to say, a head to my head? jez, i must have been somking somthing. I ment a 1000 watt power amp. to my head. Well darn, that bass gear mag is really misleading. all it says is that i can hook up a power amp to my existing heads "out". O well. i have a balanced, and un blanced, outs, as well as two bi amp outputs(lows, highs). I dont think youve heard of my head. a crate bt 350. pretty decent for crate.
     
  15. I pulled up the Crate site. They did not have the BT350 in there. However, the bass amps listed had a pre-amp out specifically designed to drive an external amp. If you have that on your amp, that would be the output to use. You can also try the balanced out, any line-outs or the effects send. Whether it will have enough power to drive the amp will depend on the level of the signal from the output and the input sensitivity of the power amp. I would think the one (or more) of the outputs on the amp will drive a power amp without any problems.

    Try it first before you buy.
     
  16. PollyBass

    PollyBass ******

    Jun 25, 2001
    Shreveport, LA
    Ok guys. check this out. i read the thing again. it says, ahem "You can use the power amp to power the more power hungry low end cabs (15' and so on) And use your HEAD to power the more midrange voiced cabs." Then it says all i need a out, on my head. And this i have. are people mistaken? or is bass player? Im scared to do any thing. seems like the people on here have been around the block a few times. but would bass player be wrong? Ugh, my brain.
     
  17. Steve

    Steve

    Aug 10, 2001
    "Out's" on the back of an amp come in different flavors. Speaker out, Line out, Balanced out, D.I. out, Effects out, Pre-out, Post-out, and others I'm sure.

    Your amp may have all of them, some of them, or none of them (It will have a speaker out).

    All but the speaker out will work. The speaker out is a high voltage output and should not, for all practical intents and purposes, be used.
     
  18. Richard Lindsey

    Richard Lindsey

    Mar 25, 2000
    Metro NYC
    I don't think this is quite correct. That is, I don't think that distinction you're drawing between line level and preamp level is right. AFAIK, a preamp output, at least for practical purposes, IS line level. Are you thinking of "instrument level"--which indeed is usually insufficient to drive a power amp?

    A line level output ought to be fine to drive most power amps.
     
  19. Yes, you are right. My bad.

    Typically the instrument level, such as plugging the bass directly into the power amp will not work.

    I have heard in some cases that active pups will drive a power amp, but cannot confirm.