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Mismatching tube heads and Ohms. (Trace gear)

Discussion in 'Amps and Cabs [BG]' started by protoz, Jul 18, 2005.


  1. protoz

    protoz

    Nov 30, 2000
    Iowa
    I have an offer for a Trace V6 for my Sunn 1200S but my main cab is my Sunn 2x15 cab which is rated at 8Ohm parallel wiring.

    The Trace only functions at 4 and 2Ohm.

    My question is: Would I damage the Trace running it at 8Ohm rather than 4 or 2Ohm? Is there any way to mod the Trace to run at 8Ohm naturally?
     
  2. Hmm. I don't see a problem. I run my V8 to two 8 ohm cabs in parallel. That makes 4 Ohm for the amp. Sometimes I only use one cabinet (8 ohm) on the 4 ohm setting. Imho the amp just has to work a little harder to push one 8 ohm cab.

    I always heard it's way more dangerous to push 'lower' (2 ohm) loads when your amp isn' t made for it it, than it is to push a 'higher' load.

    Feel free to tell me I'm wrong, though. :meh:
     
  3. Thats with SS amps, with tube amps im sure its the other way round because you fry the output transformer
     
  4. protoz

    protoz

    Nov 30, 2000
    Iowa
    That's what I was afraid of on not matching up the Ohms. I know Solid state can handle odd loads (like 2.6Ohm) but not tube amps...
     
  5. From the V8 manual:
    The OUTPUT IMPEDANCE switch allows the power stage to be set to drive either 2 or 4½ loads as indicated. These ratings are the preferred nominal impedance speaker loads that should be connected. However, it is OK to drive slightly higher value loads, i.e. driving an 8½ cabinet with the 4½ setting, without too much perceived difference in power transfer.
     
  6. protoz

    protoz

    Nov 30, 2000
    Iowa
    So I'll lose a little bit of power but I won't damage the tranny right?
     
  7. protoz

    protoz

    Nov 30, 2000
    Iowa
    anyone? bueller?
     
  8. HIGHER is more dangerous. I can't speak for a V8, but in a VR400 it would mean instant death for the output tubes, and they would take half the amp with them.

    That manual quote is wrong.

    As much as I love Trace tube amps, I have yet to seen an accurate schematic for the ones I've been in, and if they can't get a schematic right, don't assume their manual is any kind of accurate reference either.
     
  9. protoz

    protoz

    Nov 30, 2000
    Iowa
    Well that definately turns me off on the trade then...I can't go and blow up a great amp just by runnings a cab at 8Ohm when the amp is rated for 4Ohm...ah well this has great tone anyhow :)
     
  10. popinfresh

    popinfresh

    Dec 23, 2004
    Melbourne, Aus
    I say get the V6 and a new cab :p

    Also, you wouldn't get less output, tube amps stay the same, no matter what tap.
     
  11. Plain Old Me

    Plain Old Me

    Dec 14, 2004
    In my experience with tube amps (I currently own a 400+, but have played through many more at gigs and such), you can do up to about a 100% mismatch without damage as long as the volume isn't up too far. However, the tube life may be a tad shorter...
     
  12. woo, i was right :)
     
  13. I hadn't really noticed until now that the head in question is a V6, which I do have. I've never opened that head up to work on it, ( haven't needed to- bought it NOS) but its service manual and schematic are more in line with what it is supposed to be in terms of power. If its schematic is correct, it has "blowback" diodes on the plate lines of its output tubes, which are meant to protect the amp from voltage feedback caused by too high an impedance. So the amp shouldn't blow up with an 8 ohm cab, BUT if those diodes do blow up from a big enough voltage spike, the damage from having a plate line unconnected to the output transformer would be just as catastrophic. Moral of the story: use the proper impedance.

    While it is true that 100% mismatch is generally tolerable with most tube amps, the Trace runs its output tubes VERY hard for clean power and the margin is significantly lower, so much so that there is effectively NO margin, especially at high volume. Again, moral of the story: use the proper impedance.

    Finally, as a matter of personal opinion, the V6 is a FAR superior amp to the Sunn 1200s, and IMO, it would be well worth it to trade and get yourself either another 8 ohm cab or trade your cab for a 4 ohm cab.
     
  14. 43% burnt

    43% burnt an actor who wants to run the whole show

    May 4, 2004
    Bridgeport, CT
    Forgive my ignorance, but I've never owned an all tube bass amp.

    I'm getting a mesa 400+. Which is stable down to 2ohms. Can I run 3 8ohm cabinets? What would that make the total impedence? If so, how would I connect the three cabs, daisy chain 2 plug one in seperate?

    BTW, I would be all over that trade...I had a chance to play one once- Those amps are sick.
     
  15. protoz

    protoz

    Nov 30, 2000
    Iowa
    Well it was traded to someone else so, oh well.

    43% Burnt:

    If you ran 8Ohm cabs you would be getting 2.67Ohms. You would need another 8Ohm cab to get a proper 2Ohm so I would stick to using 2 8Ohm to get 4Ohm.
     
  16. 43% burnt

    43% burnt an actor who wants to run the whole show

    May 4, 2004
    Bridgeport, CT
    Thats too bad about the V6.

    hmm...so 4 8ohm cabs would give me 2ohms? :eyebrow:

    Would running 4 cabs be rediculous? push my amp to hard?
     
  17. Your amp puts out the power it puts out; so long as it "sees" the proper impedance it will be its rated power. It doesn't matter if you use four 8 ohm cabs, two 4 ohm cabs or one 2 ohm cab; the 2 ohm output puts out the same amount of power for all three.

    You CAN Use three 8 ohm cabs for a 2.67 ohm load, but you'll have to choose between the 2 ohm output or the 4 ohm output. The 4 ohm output is the SAFER option because you will be going lower than rated impedance. You'll lose some power, but your amp won't be harmed. It's still probably OK to use the 2 ohm tap; you'll get slightly more otuput power, but your amp will be more unstable. You'll be running it 'closer to the edge,' but the difference won't be so large as to cause any immediate damage. Many manufacturers, Aguilar and Mesa, come to mind, recommend the 2 ohm output for a 2.67 ohm load.

    Their is one HUGE caveat however; this assumes all your cabs are connected in parallel. If you try to run them in series with the special series cable, the rules change because you've changed the way your amp distributes its output wattage. Series wired cabinets will make an amp more unstable because they will exhibit much larger impedance resonances, so if you go with series wired cabs, make sure you have them set for the EXACT output impedance.

    BTW, in case you are concerned that you may be running your cabs in series and not knowing it, you cannot run cabs in series without making a special cable. If you're using a normal speaker cable, your connections will always be parallel.
     
  18. 43% burnt

    43% burnt an actor who wants to run the whole show

    May 4, 2004
    Bridgeport, CT
    Sweet! Looks like I might keep my cabs, and be able to post something respectable in the rig of doom thread ;)
     
  19. protoz

    protoz

    Nov 30, 2000
    Iowa
    Yea get a rig to best my Sunn stack of doom :)
     
  20. Get the V6, sell the cab, get another. Aside from ebay, where is it possible to find V6's or V8's? They're both pretty rare and I'd like to get one eventually.