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swr sm500 problem

Discussion in 'Amps and Cabs [BG]' started by jr47foam, Dec 23, 2004.

  1. jr47foam


    Dec 15, 2003
    Hatboro, PA
    I seem to be having a problem with my SWR SM500 head. Right now I'm playing into Avatar cabinets and the sound is real good. Problem happens about an hour or so into the night. All of a sudden the sound disappears for about 5 to 10 seconds.
    I've tried jiggling cords, turning knobs but it still happens. Anyone have any experience with this?
    I should tell you that the amp is in a two space rack and it just fits. Is it overheating and shutting down? I know there are a slew of possibilities here but I thought maybe someone had this problem and could advise me. Thanks.
  2. andruca


    Mar 31, 2004
    Madrid (Spain)
    I experienced a similar problem with my Hartke gear. It could be an overheat protection. There's one way to check this. If this is a temperature protection, the only thing that should be cut is the output to the speakers (power amp stage). This means your balanced out/preamp out/effects loop should still work. Connect the pream out/direct out/effects send to another amp and just check out if it still sounds even when power to the cabs has been cut. In my Hartke rig this happened just once (and live -holy crap!-) and it was due to stage lightning (two 1000W spotlights) pointing directly at it from a short distance (4ft., and the amp was not rackmounted at that time) for more than 3 hours (being used by previous bands). They didn't experiment any cut. As I walked onstage I turned volume up a little bit and I think that was too much for the amps already critical temperature situation. One of the cuts took place in a moment I played alone and I could clearly hear the PA sound for the audience with my bass still sounding (although nothing came out of my cabs) but until that moment I was totally desperate. I asked Hartke (who told me the whole heat protection story) and reproduced the situation at our rehearsal place by applying a hairdryer to the fan breathing port just to confirm. Just in case I changed the fan for one with double it's thermal capacity. Never happened again, but I rackmounted it and also take care not to put it under direct exposure to short distance lightning. Hope this helps!

  3. Sparkie


    Nov 15, 2004
    Any time you have a problem with an amp always start the process of elimination. Start with the simple, easy access things i.e. cable/connections. Sounds like you did that. If your amp worked fine for a long time and then started acting up the next move for you would be to change out the tube, (on hybrid and tube amps). If that fixes it, great. Sometimes tubes overheat or fail which would short out your pre-amp even though hybrid tubes typically idle along at low voltages. (3-6v) If the shut-down still happens, take it to the best amp tech you can find in your area. It's too expensive of an investment to mess with if you aren't qualified/have trouble shooting skills. Any attempt to repair it yourself will void your warranty if it's still in effect. The cost to repair well intended fix-it efforts will double or triple repair bills. Maybe worse.....

    Another route to travel would be to post your trouble shooting question over on Ampage @www.firebottle.com

    Good luck with it
  4. Finger Blister

    Finger Blister

    Jul 8, 2003
    Sounds like heat IMHO.

    Just point a "Clip-On" fan at the rear of the amp.

    A little extra air circulation can go a long way.
  5. IvanMike

    IvanMike Player Characters fear me... Supporting Member

    Nov 10, 2002
    Middletown CT, USA
    i don't think it's a shutdown intended by swr, as those typically last for a while. It does sound like it may be heat related. What Is the Impedance (in ohms) of the avatar cabs, how many are you using, and how do you have them connected to the amp? and is the amp running bridge mono or stereo?