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Overheating SWR SM900 bass head

Discussion in 'Amps and Cabs [BG]' started by david_l_perry, Feb 3, 2003.

  1. This is for any body who allready has or has owned an SWR SM900 bass head.

    I Have recently purchased this head used (its a 1998 model) I am running it into an SWR goliath senior cab set Bridged.

    The amp is housed in a 4 U flightcase wich has a single spare unit above it and the case has a built in fan mounted above the amp vent slots to direct cool air into the heat sinks.

    The amp front right hand side (input side) gets VERY HOT. Literally to hot to keep my finger on the rack handles. It actually starts heating up the flightcase it is housed in.

    The case is very well ventilated. Last night I ran the amp out of the flightcase to check if air circulation was the problem but it still got just as hot.

    I have just had the amp fully checked out and no problems have been found. The amp biasing was checked out and this was set correct. The inbuilt fan does come on when the amp is heating up.

    The Pre-amp tube has been changed.

    Does any body have any suggestions or similar experiances with the same model of amp (SM900) ?

    Cheers and thanks in advance

    Dave Perry
  2. I have a Bass 350. This amp has always run hot. The fan on mine is controlled by a switch rather than automatic.

    Even with the fan on and playing with the amp pushed to half way it runs hot. I've often wondered if this was nornal or not, but I've had a electronic engineer tell me it's nothing to worry about - apparently it's something to do with the fact that the amp uses a toroidal output transformer.

    My SWR is reliable as anything though.
  3. Cantstandsya


    Jul 27, 2001
    Fontana, CA
    SWR amps have an aluminum chassis which acts as a heatsink to draw heat away from internal components.This is why the outside gets so hot.......
  4. secretdonkey


    Oct 9, 2002
    Austin, TX
    Mine gets hot, too. All of my previous SWR amps would run pretty hot. I've only run the SM-900 at 8 ohms so far (second Goliath cab to be added soon), which might not heat it up the way a 4 ohm load would, but the front right does get nice and hot.

    You might email SWR support - they have been very responsive to my questions. I bet they will tell you this is normal, but they may have some suggestions for you.
  5. The amp is producing so much heat that the effects unit display is being effectd on my Boss VF1 unit that is set at the top of the flightcase (with one u of clear space below and fan cooled)
    I am just unsure that they should get this hot...
  6. At Last...somebody else with an SM900...

    Yep, I have no problems with the amp into an 8ohm cab (I use a Hartke 4.5XL for rehersals)
    Just wait until you get the other goliath 4x10...you could cook a pastie on the front end...

    SWR have been very good in responding, but I can't stop thinking that what one person thinks of HOT is not quite what this amp is kicking out..
  7. Brian Barrett

    Brian Barrett

    Nov 25, 2001
    Murfreesboro, TN (Nashville)
    Dealer LowEndBassShop.com, Builder LowEndBasses.com
    I see this a lot. Your lucky if so far it hasn't shut down on you during a show. This is an inherent problem with Head unit’s having the preamp and power amp in one. It one thing if your an endorser and the company gives you back up unit’s but it a big problem if your a regular working stiff and don’t have the money for an extra unit. I’ve seen this happened with allot of the top brand head unit’s and the biggest reason I don’t carry them. I tell people that if like the SWR sound or the eden sound buy the preamp new or used and then buy a really nice power amp. Heck in most cases you will actually save money on a power amp and preamp combo. The best part is if you get a quality power amp you can always change out preamp’s when you get tired of the old one.
    The fact that you have a great power amp that built for the road is a plus and makes thing a lot less expensive.

    Example is buying an eden Navigator used for 350-400 and then buying a crest LT1000 - 1200 watts at 4 ohm’s. This whole setup is under a grand!!!!
    Now go and price a WT800!
    It goes for any brand, and the fact that you will never get close to 800 watts or 900 watts out of the said head is a real downer to people.

    Good luck,
  8. Jon Burnet

    Jon Burnet

    Jan 21, 2001
    Memphis, TN
    i just clip a fan on my rack or make sure a fan is blowing on it. hasnt shut sown on me yet!
  9. I run my SM 900 at 4ohms and yes it cooks. I've never had a problem with a shutdown but I have the same concerns. I recently bought a Demeter 201s and Stewart 2.1 pre and I think the SWR head's days are numbered. I agree, preamp/power amp is the way to go. I may get a different preamp for different styles, Ampeg, IOD, Navagator, Aguilar....

    BTW--> I thought the SM 900 had power until I fired up the Stewart.....CLEAN THUNDER!!!!!!
  10. The problem does seem to be solved now, but it took some alterations to the flightcase and top panel of the amp

    1) The amp top panel has additional vent slots positioned directly over the amp fan to allow passage of air from outside of the amp to be drawn in

    2) The flight case fan which is positioned above the amp has had the air directed straight into the amp vent slots

    3) The rack case now has a fan and vent positioned in the side directly adacent to the vent slots of the amp. The fan is set so it is pulling air from the amp.

    So now air is being forced through the amp heat sinks and exits out of the side of the flightcase,
    It all runs a LOT cooler now.

    Incedently, it looks like SWR have remodeled the newer SM900's so the fan pulls air straight from the back of the amp casing, so clearly it must have been causing problems for them..

    Thanks for all the comments people

    Cheers, Dave

    Keep Music Live !
  11. secretdonkey


    Oct 9, 2002
    Austin, TX
    Interesting... when I first replied to this thread, I was using an older SM-900 loaner from GC while a brand new one was on order. FWIW, the new one seems to run much, much cooler. So far, it seems to run cooler at 4 ohms than the old one ran at 8. The fan comes on later and quits sooner.