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Need assistance with bass set up

Discussion in 'Amps and Cabs [BG]' started by CaptAbandon, Mar 13, 2018.

  1. CaptAbandon


    Mar 13, 2018
    First off, please excuse my ignorance.

    That said, I have a GK MB500 head (500W @ 4 ohms, 350W @ 8 ohms), an Acoustic B115 cab (250W power handling) and an Acoustic BN210 cab (600W @ 8 ohms).

    When I have it connected in parallel, the head switches off after playing a bit. I was told at a local music shop to connect them in series, and I have done that. It all works, however I'm not getting the volume I need.

    I'm assuming I need to change something out, but I don't know where to start.
    Again, I'm sure this is an obnoxious question to those of you who know the answer, so I apologize.
  2. bholder

    bholder Affable Sociopath Supporting Member

    Sep 2, 2001
    central NY state
    Received a gift from Sire* (see sig)
    need the impedance of the Acoustic B115 - if it's 8 ohms too, you should be fine, but if it's below 8 ohms, parallel may exceed the amp's capacity (not the right way of saying it I'm sure).
  3. The quickest solution would be to buy another BN210 & then you'd be operating at 4 Ohms & using the full power of your amp.
    By that I mean run two 2x10"s & leave the 15" at home.
    chip134 likes this.
  4. bholder

    bholder Affable Sociopath Supporting Member

    Sep 2, 2001
    central NY state
    Received a gift from Sire* (see sig)
    Looks like the B115 is 8 ohms, so it ought to work, not sure why the amp is cutting out.
  5. ctmullins

    ctmullins fueled by beer and coconut Gold Supporting Member

    Apr 18, 2008
    MS Gulf Coast
    I'm highly opinionated and extremely self-assured
    Either or both of those cabs might carry an 8 ohm rating, yet the actual impedance minima could be significantly less.
    bholder likes this.
  6. Stumbo

    Stumbo Wherever you go, there you are. Supporting Member Commercial User

    Feb 11, 2008
    the Cali Intergalctic Mind Space
    Song Surgeon slow downer software- full 4 hour demo
    Does the amp work okay with just one 8 ohm cab?

    Find another tech to take a look. Take both your cabs when you do.

    Did this just start happening?
    Spidey2112 likes this.
  7. Al Kraft

    Al Kraft Supporting Member

    May 2, 2016
    Northern Virginia
    First off welcome!

    Having done little research, it appears that both your cabs will present an 8 Ohm impedance load to whatever they connect to. This means that either one alone will look like an 8 ohm load to your GK MB500 and the head will be able to deliver 350 Watts of power.

    Now to the terms series and parallel as you've used them. Unless you use some very special cables or unique cab wiring on the two jacks (the odds of which are about the same as you being hit by a meteor while you read this...essentially one in a very, very big number) all your connections will be what are electrically referred to as parallel. And yes it would "visually appear" that the things are in a line or series (e.g amp to speaker cab to speaker cab).

    In parallel two 8 Ohm cabs will present a 4 Ohm load to the head. This means that the two cabs will share equally in the 500 Watts of power available and each get up to 250 Watts. This operating condition should not be a problem for a GK MB500.

    For reference only, if your were to electrically connect the two 8 ohm cabs in series (not a simple thing to do with how everything is wired now and typical speaker cables), the head would see a 16 Ohm load. My guess is that the GK head could probably operate in that mode, but you'd be limited in power output.

    So, as to your problems, are you using known good speaker cables to connect the head to the cabs or cab to cab (and not instrument cables)? If so, will the head drive each cab individually on its own, at volume, without a problem? There may be some answers that could surface from this first trouble shooting step.
    Last edited: Mar 14, 2018
    Spidey2112 likes this.
  8. Check the woofers in your cabs.

    Should be one 8ohm in the 15, likely two 16ohm in parallel in the 210. Parallel has both red connected together to one side of the input jack and likewise with the two black to the other side.

    One time I got a used cab that was supposed to be 8ohm. Turned out it had series 4 ohm drivers but someone had shorted a blown one while the other one still worked = 4 ohm cab.
    Spidey2112 and Al Kraft like this.
  9. Al Kraft

    Al Kraft Supporting Member

    May 2, 2016
    Northern Virginia
    Good point! My thoughts assumed the speakers were original or OEM/OEM equivalent replacements. When I checked the Acoustic website it didn't even appear that these cabs were available in anything other than 8 Ohm configurations.

    I guess the 210 could have two 4 Ohm 10's in series to get the cab to 8 Ohms???
  10. it could but I believe it's more common to parallel stuff so you don't blow up a tube amp every time you blow a woofer.
  11. Al Kraft

    Al Kraft Supporting Member

    May 2, 2016
    Northern Virginia
    ...yeah, tube amp with essentially nothing connected while running at power rarely ends well! :)
  12. "Not getting the volume I need." Maybe the cabs are out of phase with each other. Is there good bass response with just one cab? Does it diminish when connecting second? If so, Out of Phase.
    five7 and Al Kraft like this.
  13. CaptAbandon has gone for the day.
  14. Al Kraft

    Al Kraft Supporting Member

    May 2, 2016
    Northern Virginia
    This coupled with turning EQ and gain/master controls up to try to compensate could easily put an MB500 in shut-down/protect mode. Cabinets being wired incorrectly is not unheard of. I bought two brand new GK Neo 112 II's years ago and they were wired out of phase...I elected to simply have them replaced, but realize I could have just switched some wiring around.
    David Jayne likes this.
  15. Al Kraft

    Al Kraft Supporting Member

    May 2, 2016
    Northern Virginia
    True to his name! ;)
    Killed_by_Death likes this.
  16. Bob Clayton

    Bob Clayton Moderator Staff Member Supporting Member

    Aug 14, 2001
    Philly Suburbs
    What is your eq like? Can you post a picture of the amp with your normal playing (when this happens)

    Are you playing with an active or passive bass? Using the db pad?
  17. sxaxsx


    May 23, 2012
    Harrisburg PA
    Get a multimeter and always do this before buying used cabs.
  18. Ric5

    Ric5 Supporting Member Commercial User

    Jan 29, 2008
    I convert 4 string Rickenbackers to 5 string basses.

    Speakers and Power Amps: Don’t Blow That Cabinet

    OHMS & IMPEDANCE from the OUTPUT (speaker) perspective - FAQ courtesy of GollihurMusic.com

    Ohm cooking 101: understanding amps, speakers and impedance
  19. WardEarth

    WardEarth Supporting Member

    Feb 18, 2010
    Anchormanville, CA
    Ya I'd say you may have an issue w your amp. Not sure
  20. CaptAbandon


    Mar 13, 2018
    I didn't abandon the thread, I was under the impression I would get emails related to responses, so it's quite the surprise this morning. I didn't realize this forum was so timely with assistance.

    The amp works with a single cab, however my issue stems from not being loud enough. For background, I currently play in a metal band which includes a guitar player using a full stack and a drummer using a full double bass drum kit. I bought the 1x15 used and the 2x10 new from GC.

    I connect the head to the 2x10 cab with a Speakon Speaker Cable, and connect the 2x10 to the 1x15 with an appropriate 1/4in speaker cable. I play a Dean Edge 09 with a passive soapbar pickup.

    Here is a picture I took after practice of what seems to sound the best, but I feel like it's a bad idea to push the master volume that high. Full disclosure, I've spent much of my time playing in a crappy punk band using a used Randall RB-115 folded horn enclosure, with a Randall RB-120 head and Fender Standard Precision Bass, in which I mistreated in all aspects. I'm only now (very late in the game as it were) trying to educate myself on what seem like basics in bass equipment.

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