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Really dumb GK Amp question

Discussion in 'Amps and Cabs [BG]' started by Flashback Bass, Mar 29, 2013.

  1. I see that a GK 800RB has two speaker outputs per channel, (2@100w & 2@300w) each rated at 8ohms.

    Do you have to use two 8ohm cabinets, (one per outlet) or can you just plug in one 8ohm cab?

  2. 1bassplayinfool

    1bassplayinfool -Nowhere Man- Supporting Member

    You can plug a single 8 ohm in the 100w or 300w output. Or two 8 ohm cabs into the 300w
    outputs. 8 ohm min. on the 100w side and 4 ohm min. on the 300w. GK went with one output plug for the 100w side to avoid OT failure. Hope you are not too confused now.
  3. Dave W

    Dave W Supporting Member

    Mar 1, 2007
    White Plains
    Personally, I wouldn't worry about the 100w side. Just use the 300w side. It can handle a 4 ohm minimum load, so...a single 4 ohm cab or two 8 ohm cabs. You can also use a single 8 ohm cab, you just won't get the full 300w into it.
  4. BassmanPaul

    BassmanPaul Gold Supporting Member

    Aug 25, 2007
    Toronto Ontario Canada
    Just be careful not to plug a 4Ω load into the high amp (100W) side. That's how many of the amps get damaged.
  5. Thanks for the replies!

    I purchased the amp and now I see that the "Hi" 100w has two 8ohm jacks and the "Lo" 300w has two 4ohm inputs. Why would they be different?

    I ended up getting a great deal on two 8ohm 1X15 no-name cabinets.

    I've tried some different combinations but I'm not seeing any volume difference between the 100w or 300w.

    I did the following:

    Set both the "Hi" and "Lo" volume knobs straight up at 12:00.

    1. Plugged both 8ohm cabinets into the 100w 8ohm input jacks.

    2. Then plugged them both into the 300w inputs (8ohms into 4ohms.)

    3. Then plugged both cabinets into a "Y" so they would be in parallel (now 4ohms) and plugged them into one 300w 4ohm input jack.

    All three combinations had the same volume although #3 did seem to have the best sound. But shouldn't the 300w's be louder? What am I missing?
  6. Dave W

    Dave W Supporting Member

    Mar 1, 2007
    White Plains
    Don't do that! You'll blow the 100w amp. It can only handle 8 ohms, not 4 like you give it when connecting both cabs.
  7. NEVER plug two 8 ohm cabs into the 100 watt amp! NEVER. You are lucky the 100 watt amp didn't blow. They had two jacks back then as 16 ohm cabs were in the product line.

    If you start adding some from the boost control you will notice more difference but even them more speakers will always make more difference than more watts.
    The 300 watt with one 8 ohm cab is 200 watts, with two 8 ohm (or ONE 4 ohm) it is 300 watts). You can use both 300 watt jacks with 8 ohm cabs (but never two 4 ohm cabs).
  8. So what you are saying is, (if I understand correctly) that the input jacks are in parallel so when you plug the two 8ohm speakers into them the amp is only seeing 4ohms which is too low of a resistance loading for it?

    That's interesting because the guy I bought the amp from said he almost always played with two 8ohm cabs plugged into the 100w for his small gigs and then just plugged them into the 300w for larger venues. That's why I got the two 8ohm 1X15's. He had the amp for like ten years!
  9. Probably should have mentioned that I had the boost also straight up at 12:00 during the testing.
  10. 1bassplayinfool

    1bassplayinfool -Nowhere Man- Supporting Member


    The speaker outputs show the MINIMUM load for each of the power amps. Hope this helps.:bassist:
  11. If he did he was the LUCKIEST person I have heard of. Yes the output jacks on both the 100 watt and 300 watt amps are wired parallel to their output amps.
  12. 1bassplayinfool

    1bassplayinfool -Nowhere Man- Supporting Member

    That would kill it in no time. I hardly ever use the 100w side unless the drummer needs a monitor. I'll plug an 8 ohm cab in there for that.
  13. I guess he was lucky, but that's what he told me!

    Well then it sounds like I'm plugging the two 8ohm 1X15's into the 300w inputs and I'm ready to rock!

    Thanks for all the answers!
  14. When I was working on the bench 98% of the 800RB failures were from running two 8 ohm cabs on the 100 watt or two 4 ohm cabs on the 300 watt. That is not a guess, that is from experience in a large volume repair center. ;)
  15. Dave W

    Dave W Supporting Member

    Mar 1, 2007
    White Plains
    It's already been said, but yeah...you definitely don't want to do that! The 100w amp can only handle 8 ohms. Newer 800RB's only have a single output on the 100w section because too many people plugged in more than it could handle.

    You can still use one or both cabs with the 300w amp. That's why I said to just to not worry about using the 100w amp originally.

    If you want to get nuts you can add a 3rd 8 ohm cab in the future, and plug that and only that into the 100w amp. Pretty much unnecessary, but it would be cool!
  16. AdamR

    AdamR Supporting Member

    Sep 24, 2007
    Bethel CT
    No need to use the 100 watt high side unless you want to bi amp.
  17. Yeah the "Bi-amp" thing is a whole new kettle of fish.

    I tracked down the user manual down on-line but it was a little sketchy. I was surprised to see there was no warning about two 8ohm cabs into the 100w. I guess they thought that if you purchased one of these amps you knew what the hell you were doing.
  18. From the owner's manual: "The
    upper set is for the 100W power amp and in the bi-amp mode is
    used for the high end. They deliver 100W rms into 8 ohms.
    Lower impedances should not be used. Higher impedances such
    as 8 ohms or above are okay."
  19. D'oh! Now I see what that means! When I was reading it I didn't know yet that the jacks were in parallel and that it would half the ohm-age.

    Thanks for the further definition!
  20. :D :cool:

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