Stewart 1.2 Buzzing

Discussion in 'Amps and Cabs [BG]' started by Joe Beets, May 7, 2005.

  1. Joe Beets

    Joe Beets Guest

    Nov 21, 2004
    Finally decided to do a little practicing this morning instead of reading the forum. I'm running a passive bass directly into a bridged Stewart 1.2, then into some Eden cabs. The volume and tone coming out sound normal. Except when a note is played there is a strange buzzing along with it. As the volume of a sustained note fades the buzzing is more noticable. It only buzzes when a note is being played. The sound is like a hand full of BB's in a glass bowl sitting inside the speaker cabinet. Or like there was a snare drum sitting in front of it with the wires vibrating.

    My first thought was that there was something loose inside one of the cabs, so I took it out of the bridge mode and hooked up one channel to each cab. Same thing. Buzzing coming out of each separate channel. So then I tried the cabs with the PLX3002. A little weak because of no preamp, but no buzz. So now I'm starting to feel a little sick because it looks like it is coming from the Stewart. Not something simple like loose hardware in the bottom of a speaker cabinet.

    What a mess. It's still on warrantee. But to send it back first I have to drive twenty miles, pay to have it boxed up and shipped back to Stewart, then wait a few weeks to get it fixed. Then pay the return shipping. This unit has never gigged, in fact it has never left the house.

    On the other hand, when you get back about 15 feet from the speaker cabinets, the buzzing and slight distortion give my bass an overdriven sound sort of like Jack Bruce on "Crossroads" or Mel Schacher with Grand Funk. Maybe I should just get an AB box and use the PLX for the clean channel and the Stewart for the fuzzed out distortion channel? No.

    Have any of you Stewart guys had a buzzing 1.2? :meh:
  2. burk48237

    burk48237 Supporting Member

    Nov 22, 2004
    Oak Park, MI
    I don't own the Stewart but have heard nothing bit good about them. I question running a passive bass direct ? Most power amps have pretty low input sensitivity and your S/N ratio could get quite high. First try the Stewart with a pre amp, that is the way it is desighned to run. Some active basses are sending a pretty hot signal, but I wouldn't recomend any passive bass directly into a power amp. Even a Sans Amp or a small PA mixer( be sure the lines or balenced ) and you could test it. The only negetive I've heard about the Stewart is you don't want to "over cab: it, in some cases they'll overheat if your using let's say cabs rated for 700 watts with 400 watts of stewart power. But I have a feeling a Preamp will solve your problem quickly.
  3. Joe Beets

    Joe Beets Guest

    Nov 21, 2004
    Into the Stewart power amp the passive signal is loud enough to gig with. Without a preamp it is only putting out part of it's 1200 watts, but it will still put out more volume than a combo amp. I'm running it bridged into 4 ohms and it has a half a rack space above and below it. So it gets just slightly warm. With a boosted signal and putting out full wattage it would run hotter. Next week I'm going to try it with a different bass and cabinets just to make sure it is the Stewart causing the buzzing. Even without a preamp it shakes the floors and walls pretty good. So it could even be something loose in the wall behind the amp or maybe the house is shaking apart. It sounds like it is coming out of the speakers, but I will have to do some more investigating to find out. Thanks for the input. :meh:
  4. Bob Lee (QSC)

    Bob Lee (QSC) In case you missed it, I work for QSC Audio! Gold Supporting Member Commercial User

    Jul 3, 2001
    Costa Mesa, Calif.
    Technical Communications Developer, QSC Audio
    :confused: That doesn't make sense.

    An amp could overheat if you push it hard into an excessively low load impedance, but its power rating won't have anything to do with it.
  5. Akito


    Dec 1, 2003
    Ok dumb suggestion, but are you sure you aren't hearing vibration from something in the room? It can really fool your ears sometimes into thinking it is part of the audible signal. Maybe at the lower level of your other amp, the room element isn't vibrating?
  6. Joe Beets

    Joe Beets Guest

    Nov 21, 2004
    Well, I dragged my rig into the living room and set up there. Cranked the Stewart up all the way and let it rip. No buzzing. The silverware in the kitchen drawer 20 feet away was rattling quite a bit, but no buzz out of the speakers. So I set up again back in the bedroom and got out an automotive type stethoscope to pinpoint the source of the buzzing. Apparently something has shaken loose inside the wall behind the speaker cabinets. They don't build houses like they used to. What a relief. I thought the Stewart had fried. In fact, I was so depressed last night that I decided to order an Aguilar AG500SC to cheer myself up. And now that nothing is wrong I think I will order the Aguilar anyway just to celebrate my good fortune. Jeez, buying new gear is fun. :hyper: