Transitioning to a pre-amp/power amp

Discussion in 'Amps and Cabs [BG]' started by Beardsley, Sep 14, 2017.


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  1. Beardsley

    Beardsley

    Sep 5, 2016
    So I'm looking into switching from a dedicated bass head to a pre/power amp combo. I'm working with 2 600w 8ohm cabinets so I would like to find a power amp that pushes at least 500w @8 ohms to each cab. Now for example, the QSC gx5 States it can do 500w @8 ohms both channels driven vs 600w @8 ohms single channel driven. My confusion arises with the single & both channel driven. Does that mean 500w per channel, one channel per cabinet? Or perhaps 600w bridged into one 8 ohm cab?
     
  2. Ampslut

    Ampslut Supporting Member

    May 15, 2017
    It is 500 Watts per side at 8 ohms. It is 700 watts per side at 4 ohms. I don't see any provision for bridging.
     
  3. Johnny Crab

    Johnny Crab HELIX user & BOSE Abuser

    Feb 11, 2004
    Texas
    You would be better off going slightly higher than cab rating on power and putting a comp/limiter into your signal path.
    The original PLX series has the best options(dip switches, power, bridging) IMO.
    The least expensive one PLX1202 does do 1200W bridged at 4 ohms(run your 2 cabs in parallel to get 4 ohms)
    OR
    to run stereo(1 cab per amp channel) you could get the larger(more expensive) 3002(550W/CH @ 8 ohms) or 3402(700W/[email protected])
    https://www.qsc.com/resource-files/productresources/amp/discontinued/plx/q_amp_plxspec_specs.pdf
     
    Geri O likes this.
  4. jshinal

    jshinal

    May 28, 2013
    Raleigh, NC
    One extra item to check when looking at power amps is the input sensitivity. High power amps require a higher output voltage from your preamp to reach their stated max power. (see page two of this link https://www.qsc.com/resource-files/productresources/amp/discontinued/plx/q_amp_plxspec_specs.pdf).
    Double check what the max output voltage from your preamp is.

    My interpretation of your question is that yes, it means one channel per cabinet. They're just stating what the test conditions are, I don't see that as a restriction they're stating.
     
  5. Beardsley

    Beardsley

    Sep 5, 2016
    This sounds like a good option. Now I'd say 8 times outta 10 I'm gigging with both cabinets, so in your opinion what's the better route? 4ohms bridged or 8ohm through each channel?
     
  6. Doesn't really matter. Bridges will make a lot more power but stereo is enough with those specs
     
  7. jazzbass_5

    jazzbass_5

    Sep 1, 2007
    NY, Medina
    I do the preamp power amp thing exclusively. Get an amp thats rated for more than you need. Make sure it's bridgable. That way you will always have enough power and the ability to bridge it if needed.
    None of my amps are under 1000 watts and of course I never have to use that much power. They always run cool and always have enough head room. I'll give a quick kudos to the 1U Peavey DPC1400x (although it's a deep amp) it's a powerful, small and dependable amp found used online for a decent price.
     
    Gearhead17 likes this.
  8. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa Boogie, Development Engineer-Genzler (pedals), Product Support-Genz Benz
    What speakers? 600 watts "RMS" rating or undefined?

    I see a fair number of speakers damaged from too much power and not enough good judgement, or a misunderstanding of how the specific ratings are derived.

    Also, the GX-5 has non-defeatable limiting built in, engages at rated power. plus, there's a loss of feedback clipping indicator for when the user runs out of limiting.
     
    Last edited: Sep 15, 2017
    Pbassmanca likes this.
  9. Pbassmanca

    Pbassmanca In the pocket n' thumpy. So woody, so greasy...

    I'd like to have a separate Pre/Power amp rig. It would be nice to be able to be able to use of of those 2 or 3 way single 12 or 15 cabs that can take a lot of juice and throw 600-1000 watts at it @ 8 ohms, carefully I imagine........:D
     
  10. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa Boogie, Development Engineer-Genzler (pedals), Product Support-Genz Benz
    I would suggest very careful if you want them to last a long time.
     
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  11. Stranger Danger

    Stranger Danger Feel Like A Stranger Supporting Member

    Jan 3, 2010
    Texas
  12. Pbassmanca

    Pbassmanca In the pocket n' thumpy. So woody, so greasy...

    People seem to always suggest having a much more powerful amp than the speakers are rated for and then being judicious in your use of the power amp. Do you think this is the right way to go or is it playing with fire?
     
  13. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa Boogie, Development Engineer-Genzler (pedals), Product Support-Genz Benz
    Depends on how much control you have over your judgement, and any accidents that you might have with your bass and/or signal path. I just tend to see when things go (expensively) wrong, so my recommendations tend to be more conservative. I usually recommend roughly matching the amplifier power to the speaker power (both rated using "RMS" metrics)

    Part of the reason is because speaker power handling falls quite a bit in the lowest octave of the speaker's response, most folks aren't aware of this and cause mechanical damage unintentionally. Also, speakers tend to be rated less conservatively these days, with "must survive" test lengths of only 2 hours, so when these tests are extended to 200 hours it's typical for the rated power handling to decrease to about 2/3 of the 2 hour test.

    This is why, after much discussion on TB, we expanded out rating data to include both thermal as well as mechanical power handling. It takes more work and a more comprehensive design to get good mechanical power handling while maintaining sensitivity (these specs. are at odds with each other)
     
    Jeff Scott likes this.
  14. DWBass

    DWBass The Funkfather

    My rig is a pre/power setup. I run mine in parallel mode. There is zero need to bridge power amps these days. You find one that matches your cabs power wise. My setup gives me 250w per channel into a set of 8ohm GK Neo112's. Same as a 500w standalone amp. I'm plenty loud with volume to spare. If I ever need more, I run the 2 GK's on one channel and I have a 4ohm Eden 2x12 cab I run on the other channel for a total of 1000w (500w per side). I'm pushing a lot of air. If you desire more power per channel, find a power amp to suit your needs.
     

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  15. scuzzy

    scuzzy

    Feb 15, 2006
    Troy, MO
    I have a Crowne xls1000. Lightweight, bridgeable to 1100 watts at 4ohm, or 215 watts per channel at 8 ohms each. Has built in filters if you wanna use em. I use the high pass at 50hz, I believe. Great lil amp, never had a problem.
    2s7e72e.jpg
     
  16. gelinas666

    gelinas666 Guest

    Sep 8, 2009
    20170817_181728.jpg I just pick a preamp and plug into my Qsc PLX 3402.. Runs cool and quiet! I use many cab setups .. Never needed more than one channel for volume . :thumbsup:
     
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  17. tom-g

    tom-g

    Oct 2, 2007
    Now, I wouldn't go that far. I, for example, only have one 8 ohm cab. With only one cab it doesn't make sense to not bridge the amp. You can get a less powerful and expensive model. Example Crown XLS 1000 bridged at 8 ohm at 700 Watts. 215 Watts with one single channel would not cut it.
     
  18. DWBass

    DWBass The Funkfather

    This is why I said to find an amp that matches your cabs power requirements. There's plenty out there. Why buy a lesser powered amp (in stereo) just to bridge it? I only need 250w per channel into each my GK cabs and I'm plenty loud. One of my amps bridges at 8ohms only. Won't work for me as I run a 4ohm load. I have another that bridges down to 4ohms. More power than my 4ohm cab needs. I'll stick with parallel mode. If I want more power, I'll find an amp that suits my needs.

    This works for me though. Do whatever works for you.
     
  19. Jeff Scott

    Jeff Scott Rickenbacker guru..........

    Apr 11, 2006
    What preamp are you planning to use with this rig, OP?

    I did the "rack gear thing" in the mid '90s into the very early part of this current century. Was fun as I kept trying different combinations of gear, but in reality (for my needs, anyway) it just got too expensive and unnecessary, really. There are so many great bass amps these days, I could not see going back to a rack outside of a preamp and my Korg DTR-1 tuner in my 2 space SKB rack. I have two empty 4 space SKB racks that have been pining for something to fill them; maybe they could make good planters for the garden. :smug:
     
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  20. somebrains

    somebrains

    Feb 7, 2017
    So you remember when GC had Ampeg, Demeter, SWR, Eden, and other preamps in a big display and either a guy plugged in what you wanted or you contemplated an expensive switching system too?

    Rack gear was way too expensive for a kid at Gilman St with guitar players that had to spray paint power chord progressions on the backs of their cabs.

    Also overpowering cabs 20 years ago was a problem as mentioned above.
    My buddy's commercial wood shed in Petaluma is literally filled on one side with lumber, the other side cabs our buddies have killed and left with him to pack rat.

    I'm particularly bothered by newer speakers having a very low test cycle to achieve rating. Reminds me of the Chevy 1500 transfer case problems of the 2004-2011.

    OP I wish you luck, there's so much extra work getting a rack setup that old timers remember rack "specialists" that would build out your rig.
     
    agedhorse likes this.
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