Psst... Ready to join TalkBass and start posting, make new friends, sell your gear, and more?  Register your free account in 30 seconds.

Stewart World Acme advice?

Discussion in 'Amps and Cabs [BG]' started by martens-koop, Apr 29, 2004.


  1. martens-koop

    martens-koop

    Oct 10, 2002
    Saskatoon
    hey there... I've got a Stewart World 1.2 running bridged into an 8 ohm Acme Low B2. So far, I really really love the whole setup and tone and everything, but as this is my first foray into anything approaching the "decent" category, I've got a few questions and concerns:

    1.) when the power amp is at about 1/2 way up, and I really dig into the b string on my dingwall, sometimes I hear a sort of popping or snapping sound right at the beginning of the attack. it doesn't sound like distortion but I don't know what it is... Am I wrecking my cabinet? is my cabinet already wrecked? I have really tried not to do this (its only happened 5 or so times) in case it makes it worse... -its scaring the heck out of me!

    2.) how much should the speaker cones be moving when I play? if I hit even a low E, it looks like the speakers are moving back and forth in the neighbourhood of an inch. i've never had an amp that did anything like this... is this normal? it seems pretty excessive considering I'm not playing heavy metal volumes...

    3.) one idea I had: a kid from church pressed the stereo / bridge button on the amp while it was on... it says in the manual not to do this... could some sort of internal circuitry have been fried because of this?


    does anybody have any advice? its starting to really freak me out!!! (everyone I've talked to has said "oh yeah... bridge the stewart into the acme! you'll love it!) but now I'm hearing things that I'm not certain are supposed to be there, and I don't seem to be playing terribly loud... -i play hard, but not loud...

    thanks for any ideas you guys have in advance!!!
    jeff

    JMK
     
  2. alexclaber

    alexclaber Commercial User

    Jun 19, 2001
    Brighton, UK
    Director - Barefaced Ltd
    If it's a growling snarling sound it's the speakers moving beyond their Xmax (but not Xmech). You're simply running out of LF capability. If it's not that, then I'm not sure. Could it be that the amp's clipping? (I doubt it because of the power you've got, though).

    The cones really shouldn't be moving that much. How much bass boost are you using? Could you add a simple high pass filter to put between the preamp and power amp, to filter out lows below 30Hz? That would add a lot of headroom and keep your speakers happy.

    FWIW I use a QSC PLX3002 with my Acme Low-B2s, running 900W into each. I keep the 30Hz filters switched on and can get a lot of volume out of a single cab without that loose growl you get from exceeding Xmax.

    Alex
     
  3. martens-koop

    martens-koop

    Oct 10, 2002
    Saskatoon
    I'm not sure I'd call it growly or snarling... its more like a very quiet balloon popping... just one quick pop right when after my finger releases the string.... (and its not the string hitting the pickup -I've checked that...)

    is a pass filter something I could build, or do I have to buy one? In my head what you describe sort of works the opposite of a passive bass tone control? cutting lows instead of highs?



    jmk
     
  4. Jerrold Tiers

    Jerrold Tiers

    Nov 14, 2003
    St Louis
    Snapping sounds are very often from protection circuits. You should not get that at a load within the capabilities of the amp as advertised.

    Or, if your speakers are moving that much, it could be the speaker voice coil actually hitting some part of the magnet structure. That can make a sort of "dull snap" noise. I don't think I'd let that happen very much.......
     
  5. jokerjkny

    jokerjkny

    Jan 19, 2002
    NY / NJ / PA
    marten,

    the best thing to do is run the power amp at its fullest. just turn the power amp's volume as high as it goes, then use the volume on your preamp, to control the overall rig volume. acme's need as much wattage as possible for the best performance. hopefully, all these little quirks will go away.

    also, how are you running it in bridged mode? are you using banana clips on the "red" inserts only? important that you do so this way.
     
  6. martens-koop

    martens-koop

    Oct 10, 2002
    Saskatoon
    I've got a bannana to speakon cable. I use the two red posts for mono. unfortunately, they posts are not labelled which is + and which is - during mono mode... so I may have the phase reversed... but I don't see that as having a large effect on things... I'll try that full on thing...

    jmk
     
  7. jokerjkny

    jokerjkny

    Jan 19, 2002
    NY / NJ / PA
    FYI, channel one's red post should be the positive.

    good luck!
     
  8. Nightbass

    Nightbass

    May 1, 2001
    Seattle, WA
    Jokers advice is all spot-on.

    Also, in bridged mode, the Channel 2 front-panel attenuator must be fully off (CCW).

    And make sure the Speakon end of your cable is wired +1 and -1.

    Acme cones do move a lot when properly powered. That's normal (to a point...)

    Nightbass
     
  9. Lonnybass

    Lonnybass Supporting Member

    Jul 19, 2000
    Minneapolis by way of Chicago
    Endorsing Artist: Pedulla Basses
    Interestingly, I had a similar problem (snap crackling sound on the initial attack whenever I played a low G) with a Crown Power Tech that I was using to power my pair of B2s.

    According to my tech, the problem was the result of a capacitor that within the amp that somehow slightly changed its resistance value and was putting out the clipped signal from the load of the Acme. If you can, try it with a different power amp and listen for a difference. Also, you might want to check out your speaker cones for over-excursion - tilt the enclosure so you can clearly see through the grilles and look for any wear lines around the circumference of the cone. These speaker cones are designed to really move physically (and move some air!) but if they aren't broken in properly, the surrounds (which are somewhat stiff out of the box) will crease.

    Good luck.

    Lonnybass (Stewart World 2.1 + 2 x B'2s)
     
  10. notanaggie

    notanaggie Guest

    Sep 30, 2003
    I sure hope you garbled up his explanation.......(no offense intended), because otherwise it sounds a bit like he made up something!
     
  11. martens-koop

    martens-koop

    Oct 10, 2002
    Saskatoon
    thanks for the tip on channel one red being the positive binding post.

    I'm kind of stuck with the power amp that I have... I suppose I could test it out on a different cab to see if it still does it... maybe if there is something definately wrong with the amp, it'll be covered under warranty... -i bought it brand new...

    the cab I got used, but as near as I can tell, theres nothing wrong with it.... I actually just just took it to the local music store renowned for their speaker tech and he ran a "sweep" on it, but didn't find anything... - i assume he ran pink noise and sine waves at all freq's through it...

    thanks for all of the suggestions and advice so far! it helps alot and means alot too!!!



    jmk
     
  12. Aaron

    Aaron

    Jun 2, 2001
    Bellingham, WA
    My Acme speakers move a lot as well, so that seems normal. By running the poweramp on full, you have more clean power. It is a lot more harmful to be using an overdrivin signal with not much power than using way too much power (if there is such a thing.)
     
  13. Lonnybass

    Lonnybass Supporting Member

    Jul 19, 2000
    Minneapolis by way of Chicago
    Endorsing Artist: Pedulla Basses
    Nope, this is precisely the explanation he gave me. Of course, I don't know how trustworthy a source he was, considering he had the Crown on his bench for five months (seriously!) trying to figure out what the problem was. The only good thing is that he loaned me a more powerful Crown. ;)
     
  14. notanaggie

    notanaggie Guest

    Sep 30, 2003
    Hmmmmm....

    Speaking as one who has been a Crown-trained tech (starting in the old days.....DC300, M-600 etc, even the tape recorders, betcha don't remember those), you probably went to the wrong place.

    Crowns didn't seem hard to fix, but you need the Crown info. Trying to "get into" the things flying blind is not particularly productive....I have seen (and fixed) the results of that approach done elsewhere.

    Crown usually has lots of service notes and field notices, and you need them. Sometimes a very short serial number range would be different from all others. They kinda stopped doing that a while back, but still have service notes AFAIK (haven't been into one for a few years since I changed industries).
     
  15. martens-koop

    martens-koop

    Oct 10, 2002
    Saskatoon

    I was under the impression that it didn't matter whether or not the power amp was on full... the manual (or maybe Jack Read told me this) says that the amp is capable of putting out its full rated power regardless of what the control is set to, and that its all dependant on the source signal going in...

    is your suggestion then meant to keep me from overdriving my preamp on the bass and the preamp in the rack? or does it fulfill some other purpose?
     
  16. Aaron

    Aaron

    Jun 2, 2001
    Bellingham, WA
    I forgot where I got the information from, so be a bit wary...

    I think it is about clean power. I'm fairly sure it is possible to get the power amp's full potential when set on 1, but there will probably be a lot of clipping that is potentially harmful to speakers. That is what seems logical to me, but I forgot my source.
     
  17. martens-koop

    martens-koop

    Oct 10, 2002
    Saskatoon
    another thought I had: what are the chances of overloading the pickup with a really intense plucking? has anyone ever heard of this?

    Over the years I have developped an intensely bad playing technique... I would often hit a string a little too hard or too softly and my playing came out a bit sloppy... so I turned the volumes on the amp down a good ways and then played every note really really hard just to be heard... (like 11) maybe that technique is coming back to haunt me... maybe I should try to focus on turning the amp up and playing softer.... The only drawback is that I have really enjoyed the snappy attack and instant presence of those super aggressive plucks... (I guess it doesn't really matter though... I pretty much only play church music these days, and lets face it, no one is really listening to the bass player anyhow!!!)


    jmk
     
  18. g4string

    g4string Supporting Member

    Sep 19, 2002
    Melissa, TX

    This doesnt make any sense when you think about it. Why would a power amp have a volume control if it were to run full open all of the time regardless of volume control posistion. The sound/speaker symptoms you describe sounds like power amp clipping to me. I would agree with several previous posters to run the power amp full open and make all of your volume adjustments at your preamp. FWIW, I run my bass rig (PLX 1602) and PA (PLX 1602 - PLX 2402) this way.
     
  19. inazone

    inazone

    Apr 20, 2003
    Colorado
    Yes, I had some problems with this. With Q & A with Jim Bergantino, Bart,and EMG pups we fixed the problem. The 18volt preamps in my modulus basses are hot and I needed to lower my pups.
     
  20. MikeBass

    MikeBass Supporting Member

    Nov 4, 2003
    Ferndale MI.
    Artist: Xotic Basses/AccuGroove

    According to Stewart (I went through three 1.2 power amps) you should NEVER turn the amp up full like every other power amp on the planet.
    From Stewart: Turn up your pre and then use the front panel level control on the pwr-amp to adjust you overall volume.
    Sorta makes sense right? Use the power amp and pre-amp controls like you would on a head. You never turn up the master on your head all the way (at least most don't).
    Well, I told Mr. Stewart that by doing this it wasn't near loud enough and I don't play crazy loud, really I don't. So try as I might, I did what he said with no luck.
    I ran it like every other power amp I ever owned (Crown, Mackie, QSC) and it went into thermal shut down. Great sounding power amp. I'll never used one again.