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Acme Low B2 attenuator knobs not working?

Discussion in 'Amps and Cabs [BG]' started by thejumpcat, Mar 15, 2008.

  1. thejumpcat

    thejumpcat thejumpcat

    Sep 30, 2007
    I bought a used Acme Low B2 on ebay and gigged with it once. It sounded really good, and I had the high and mid attenuator knobs set at 12 o'clock. I didn't goof with them at all.

    At rehearsal today, I decided to fiddle with both knobs and see how they affected the sound. But, the drummer, guitarist, singer and myself could not hear any change in sound when either knob was wide open or off.

    Granted, we were not cranking at gig volume, but even when it was just me playing and the drummer adjusting the knobs, nobody could hear any difference.

    Could the attenuators be disconnected or broke? Is the effect supposed to be subtle? Does it make a difference that I'm playing an upright? I didn't have my P bass to try it.

    Any thoughts?
  2. Folmeister

    Folmeister Knowledge is Good - Emile Faber Supporting Member

    May 7, 2003
    Tomball, Texas
    Unless you have a relatively new cab, the most likely culprit is the light bulb that functions as a fuse on the crossover. You will need to remove one driver and take a look. If the lightbulb is not burned out, try making sure it's seated correctly. If it is burned out, I suggest that you contact Andy at Acme and get one of his new polyswitches (they replace the bulb) to install/have installed instead. They self-reset so you don't have to worry about dismantling the cab. Check the crossover for loose wires and scortching if it's not the bulb.
  3. thejumpcat

    thejumpcat thejumpcat

    Sep 30, 2007
    So the cabinet will still function if the bulb is burnt out? Can I cause any damage playing it like this?
  4. alexclaber

    alexclaber Commercial User

    Jun 19, 2001
    Brighton, UK
    Director - Barefaced Ltd
    Yes it functions, you just don't get much output above 1kHz. You won't damage anything playing with a blown bulb. With the mid and tweeter back in action and a good pickup on your upright you will be astounded by the smooth, open and clear sound through the mids and highs in addition to the deep bottom and fat lower mids you're already enjoying.

  5. thejumpcat

    thejumpcat thejumpcat

    Sep 30, 2007
    Thanks, Alex. I think this cabinet sounds great now. If that is the problem, and the highs and mids kick in with a new bulb, I'll be Acme's #1 cheerleader.
  6. thejumpcat

    thejumpcat thejumpcat

    Sep 30, 2007
    Well, I just spent a half hour taking the grill off, removing a driver, inspecting the bulb and putting it back together. Not the most user-friendly design. And the bulb was fine, as were the connections. This cabinet is built like tank, by the way.

    So now what? I can't believe that all four musicians in my band wouldn't hear SOME difference in tone when turning either attenuator all the way on and off.

    Like I stated before, the cabinet sounds great now. I'm just curious as to what I MIGHT be missing.
  7. mothra2

    mothra2 Supporting Member

    Dec 23, 2006
    B4 you start tearing it down, power it up and just turn up the gain and listen (up close...ear on grill) for a bit of hiss thru the mid/highs without playing...then you'll know. I noticed also that you mentioned a 12' oclock setting. You probably know this, but that is cutting the mid/highs so be sure to turn it all the way clockwise first for a flat response.

    Good luck
  8. thejumpcat

    thejumpcat thejumpcat

    Sep 30, 2007
    You, my friend, are a part-time genius!!

    That worked. I can definitely hear the hissing through the tweeter and the midrange when I turn the knobs with the gain cranked.

    Any thoughts on why we're not hearing a difference when I'm playing my upright through the LMII? Again, we don't rehearse very loud. I had the master wide open but the gain only at 8 or 9 o'clock.
  9. mothra2

    mothra2 Supporting Member

    Dec 23, 2006

    I'm thinking you are actually muting the overall sound with the above settings, and not maximizing the amps power either. I believe the settings shoud be reversed. Gain as high as you can get it without distortion, and then Master for whatever volume level you need. (Perhaps a LM2 owner could chime in here to verify).

    Keep in mind also that the mid/highs thru the Acme are indeed subtle (most are used to a sqwaukie tweeter, less than seemless driver integration and such - good for cut, but hyped - Acme does not hype the sound) and perhaps the Upright has too much acoustic output of its own for your testing environ. Kick over to EB if you can in order to lower the acoustic to amplified sound ratio.
  10. Whew.... turn the filters off, adjust the preamp to optimal setting (just below clip at your loudest, lowest notes) and then use the master to adjust your volume. This will give you optimal signal to noise, and IMO the best tone.

    As many point out, the upper mids and treble of the Acme cabs can be quite subtle if you are used to a more traditionally voiced two way bass cab. With some basses (i.e., a mid voiced bass with flatwound strings like a PBass) there is literally no difference in tone with the tweeter attenuator turned all the way on or off, and even the mid driver can have a subtle impact.

    Also, with some DB pickup systems like, for example, the Realist, it seems that there is an impedance mismatch with some heads, which can result in a very dark tone that would result in not much sound making it to the mid driver and tweeter of the Acme. This seems to be the case with the AI amps... I have not heard a Realist through the LMII though. That could also be an issue.... not sure what you are using with your DB.

    With the LMII and the Acme, there should be A LOT of sound in that upper mid control. With the amp set flat (maybe with the bass control rolled back just a touch) and the pre gain set correctly, and the filters off (flat), that upper mid control centered around 800hz or so should be great at dialing in some upper mid and lower treble clarity and a bit of growl if you want it.
  11. thejumpcat

    thejumpcat thejumpcat

    Sep 30, 2007
    Maybe this is a question for the the DB Forum, but I was always told that the best way to get as clean and undistorted tone as possible (which is USUALLY what we want on DB) is to crank the master and then bring up the gain, no? I'm after as close to an acoustic sound as possible without growl.

    My settings at practice were (these are O'CLOCK) gain, 8; low, 10; mid low 10; mid hi, 9; treble, 11; VLE, off; VPF, 9; master 5 -- and it sounded gorgeous. I had no complaints about the mids and highs. And from what Kjung stated about the possible impedance mismatch using my Realist / LMII, that may be why the attenuators had little effect.

    My apartment neighbors should be up by now, so I'll go in and give the P a run through.

    Kjung, I see you're in Detroit. We're at Dick O'Dows this Thursday. If you're in the area, come by for some blues and beer.

    Thanks for all the help, guys!! TalkBass is an unbelievable tool for musicians.


  12. I may stop by... I would enjoy meeting you.

    Regarding the pre versus master, I think the confusion comes from using separate pre's and PA type power amps. With those set-ups, you typically have a pre gain, a master on the pre, and then a master amp volume. In that sort of set-up, most agree the best way to manage that is to optimally set the pre gain to the best signal to noise ratio on a SS head, or to the amount of 'warmth/drive/distortion' you want in the signal with a tube pre, and then control the volume of the rig with the preamp master, running the amp wide open. (this isn't even that cut and dry, because of the issue of matching the preamp output to the optimal input level of differen power amps)

    With an integrated solid state head like the Markbass, running the master all the way open and adjusting the volume using the pre doesn't make much sense to me. That's why these types of heads typically have a 'clip indicator' light on the preamp, since both noise-wise and tone-wise, the 'optimal' setting of the pre gain control (again on a SS pre) is to have it as hot as you can get it without distorting the preamp, and then control your volume with the master. This results in, IMO and IME, quiet operation and the fattest, punchiest tone from the amp (while still keeping it totally clean and pure... just watch for the clip light at the hardest playing level at the lowest notes, and then back it off a touch).

    With my basses and touch/technique, with my moderate output EB's, the setting on the LMII is typically around 1 or 2 o'clock on the pre gain, and then between 8 and 10 o'clock on the master depending on the volume I need. With my very hot output piezo loaded Rob Allen bass, my pre gain is typically set at about 8 o'clock (i.e., that's the level with the Rob Allen where the input clip light barely comes on at the lowest, hardest hits).

    This way, no matter what bass you are playing, the preamp always sees the same 'optimal' signal strength, and you can adjust the volume with the master. IMO and IME!!!!

  13. Nick Kay

    Nick Kay

    Jul 26, 2007
    Toronto, Ontario
    If you have a dirt box of some sort, put that in your signal chain, crank up the distortion, and THEN see what the attenuator knob does. It's possible that there just isn't that much content in your signal above the crossover point. Overdrive will add tons of harmonics up there, making it easier to hear the difference.
  14. thejumpcat

    thejumpcat thejumpcat

    Sep 30, 2007
    I will definitely try that method again. This head is borrowed from my drummer (he's got killer bass equipment in addition to his 10 or 11 drum sets), and didn't come with a manual. I downloaded it online and it, too, suggests turning up the gain till it clips, backing it off and then bringing the master up to the appropriate volume for the gig.

    I tried that on the first gig, and it was really hard to keep my Kay from howling, so I went back to wide open master, gain around 8 or 9. But I'll try it again Thursday.

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