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ok to use 400 watt 4 ohm amp head with 800 watt 8 ohm 4 x 12????

Discussion in 'Amps and Cabs [BG]' started by gareth, Dec 27, 2003.


  1. gareth

    gareth

    Jun 9, 2002
    UK
    I've got a 400 watt trace elliot V6 all valve amp head that operates at either 4 or 2 ohms

    I've seen a 800 watt 4x12 trace elliot cabinet rated at 8 ohms for sale which i'm tempted to buy.

    My questions are:-

    1. Is it "safe" to use the amp head set at 4 ohms with the cabinet - will this cause damage to either the amp head or speakers in the cabinet.

    2. Will the amp produce less power/output.

    3. Currently i use trace elliot 4x10 and 1x15 cabinets both rated at about 300 watts each and both 8 ohms, so together they produce 4 ohms. Will this rig produce more power than using the 4x12 mentioned above?

    What do you think?
     
  2. Nick Gann

    Nick Gann Talkbass' Tubist in Residence

    Mar 24, 2002
    Silver Spring, MD
    Sell either the 410 or the 115, and use the other along with the 412, so you'll have 4 ohms.
     
  3. gareth

    gareth

    Jun 9, 2002
    UK
    which one should i sell
     
  4. Nick Gann

    Nick Gann Talkbass' Tubist in Residence

    Mar 24, 2002
    Silver Spring, MD
    I would probably sell the 10s, the 12's would cover the highs and mids, and the 15 would do mids and lows. Does either cab have a tweeter? That would help produce a full sonic spectrum as well.
     
  5. Scott D

    Scott D

    Apr 21, 2003
    Minneapolis, MN
    The ohm mismatch should be fine. I believe that a 4 ohm + 8 ohm = something like 2.666667 ohms, which the amp reads as 2 ohms. But, i'm not totally sure.
     
  6. The level of "safety" depends on the quality of the output tubes (which stock are Chinese KT88's; they're decent) and how conservatively biased they are. Using a higher than rated output impedance causes a plate voltage rise in your outputs. If the amp's bias current is not sufficeint to hold the rise in check, they could short and do some SERIOUS damage to your amp. I strongly do NOT reccomend you use a single 8 ohm cab if you're planning on playing regularly at any kind of appreciable volume.

    Yes, but not like a s/s amp. A tube amp "expects" an output impedance coupled through its output transformer at a voltage/current ratio determined by the primary impedance of all the tubes vs the output impedance (speaker cab). Theoretically, higher impedance on the secondary (speaker) should cause an INCREASE in power, but it does so at the expense of exceeding the stable operational paramaters of the outoput tubes. In addition, output transformers are rated by voltage, so a voltage rise above what the transformer can cunduct will be wasted as heat in its core and you end up with a net loss of power.

    That's the long way of saying if you're running your output tubes near their limit to start with (and most bass amps do so for max clean power) do NOT run a higher impedance cabinet than the amp calls for. I know you'll hear guitar guys saying [stoner idiot voice] "Use what sounds the best, man, ratings don't mean squat,"[/stoner idiot voice] but that's because their amps have MUCH larger margin for error because, well, most guitar players are idiots.

    My answer to #2 should exlain it. If you're still not clear and need more clarification, I'll gladly eloborate further.
     
  7. Petebass

    Petebass

    Dec 22, 2002
    QLD Australia
    Without hearing the 12's in action, it's hard to say. Some 12's sound like biggish 10's and that's the assumption that Nick has made here. Other 12's sound more like smallish 15's. I suspect it's the latter, but I could be wrong. You really do need to listen to it.
     
  8. According to Bass Player's review of the cabs when they were new, the Trace 4x12 sounded more like 15's with less bottom than 10's with more. The specs are VERY similar to SWR's new 4x12 cabs. I'd say it's for more of a wooly old-school bass vibe and if the cabs had better bottom, I'd want one.
     
  9. Nick Gann

    Nick Gann Talkbass' Tubist in Residence

    Mar 24, 2002
    Silver Spring, MD
    Meh, I took a guess :)
     
  10. Nick,
    FWIW, I agree with your earlier post!
     
  11. Nick Gann

    Nick Gann Talkbass' Tubist in Residence

    Mar 24, 2002
    Silver Spring, MD
    It's worth something :D lol
     
  12. xyllion

    xyllion Commercial User

    Jan 14, 2003
    San Jose, CA, USA
    Owner, Looperlative Audio Products
    My question is why? Why do you want to buy the 4x12? 4x10 and 1x15 are an excellent combination.

    No you can't run that amp with an 8 ohm load. Tube amps like that are designed for specific loads and give them a load too high or too low will cause excessive stress on the output stage. The amp may continue to work, but odds are you will shorten its life.
     
  13. Scott D

    Scott D

    Apr 21, 2003
    Minneapolis, MN
    If you really wanted to, you could wire it in paralell. Each driver is 8 ohms. What they do, is wire each 2 in series, giving it a 16 ohm load, and then the wire both of those in paralell so it gets to 8 ohms. What you can do is wire them all together, so each group of speakers is 4 ohms, which them two combined is a 2 ohm load, and that'll be safe for your amp.