1. Please take 30 seconds to register your free account to remove most ads, post topics, make friends, earn reward points at our store, and more!  

SM 400S

Discussion in 'Amps and Cabs [BG]' started by Cantstandsya, May 30, 2002.

  1. Cantstandsya

    Cantstandsya Supporting Member

    Jul 27, 2001
    Fontana, CA
    Anyone have problems with their SM400 or 400S shutting down.Mine will go for about two hours at moderate volume(gain half way up-master 2 notches past half-Stingray 5 into the passive input with EQ flat on the amp and my bass.)into a Henry 8x8.I have the amp in bridged mode which is 500 watts @4ohms.After about two hours of playing the amp gets really hot and shuts down.It will come back on after cooling down,which takes about 30 minutes but most of the time we just call it after my amp shuts down.I'm thinking about getting the SM 500 because it seems to have a different system of cooling the amp.The vents are in different places than the 400S.Was this done due to a problem with the 400S?Any advice on this subject would be greatly appreciated
  2. stevekim


    Feb 11, 2000
    los angeles, ca
    no, that has never happend to my sm 400s. are you leaving one rack space free above the amp for ventilation?
  3. Cantstandsya

    Cantstandsya Supporting Member

    Jul 27, 2001
    Fontana, CA
    Yes I, have one empty rack space above my 400S.
  4. Nope. My SM 400-S has never shut down, even with the Gain at 12:00 and the Master at 3/4's for hours on end. AND of course you know that I run mine bridged with a Henry 8x8.

    All units manufactured after September 1993, having a serial # geater then #6125 have a cooling fan. Earlier models of the SM 400 had problems with over heating.

    One condition you should be aware of is when one or more of the power amplifiers in your unit becomes "over biased." This condition can be recognized by turning you amplifier on and letting it sit without speakers plugged in and withut playing it. If you amp becomes quite warm, it may be over biased.

    A power amp can become over biased through vibration or especially through a jolt received in shipping, etc...

    Your amp may have become over biased, the therefore run too hot when it was shipped to you.

    Improper packing or shipping procedures can easily cause this. Even happens when procedures are done right... the shipping monkeys may have thrown it around a bit.

    Take it in to a service tech. and have it checked out.
  5. Cantstandsya

    Cantstandsya Supporting Member

    Jul 27, 2001
    Fontana, CA
    My 400s was made in April 1998 so i'm pretty sure it has a cooling fan.I've done the test to check for overbiasing and it did not get hot at all.Do you think it could be the preamp tube or possibly bad power in our rehearsal space?
  6. brianrost

    brianrost Gold Supporting Member

    Apr 26, 2000
    Boston, Taxachusetts
    Make sure the fan is working and a local tech can do the (simple) factory bias procedure. Note this is not a TUBE biasing, it's adjusting voltages in the power amp.

    Bridged at 4 ohms does run hot so the shutdown circuit is at least protecting you from a smoked amp.

    Also you can talk/email to the service guys at SWR, they have been very helpful to me in the past.
  7. ihixulu

    ihixulu Supporting Member

    Mar 31, 2000
    South Shore MA
    I run my SM400 (400W, no fan) bridged into 4 ohm for hours on end with gain and master at both about 12 o'clock. I have never had it shut down on me like that.

    Of course, the bandmates love it that I can grill burgers on the thing at the end of practice.

    The only other thing I can think of is that the thermostatic sensor may have gone out of whack and is causing the heat protection circuitry to kick in.
  8. You would be absolutely sure if the fan was on.

    My fan comes on early and stays on.

    Actually the fan is kinda' loud.
  9. Cantstandsya

    Cantstandsya Supporting Member

    Jul 27, 2001
    Fontana, CA
    Yeah ,the fan comes on and stays on.
  10. FunkySpoo

    FunkySpoo Supporting Member

    Feb 6, 2002
    I have an old old sm400, probably around 1988 and it's been flawless. Gain usually set to about the 2 o'clock pos. and the master at about the 1 o'clock pos. I did go to radio shack and get a fan that I just sit on top of the amp so it sucks air through it and it doesn't even get hot.
  11. Cool Idea!
  12. FunkySpoo

    FunkySpoo Supporting Member

    Feb 6, 2002
    and cheap too
  13. tornadobass

    tornadobass Supporting Member

    Nov 20, 2000
    Iowa City, Iowa
    No problems shutting down on my 400S...I think it's run cooler since having the bias adjusted...the fan's on less now. Usually run one 4 ohm cab per side. It used to run for 15 minutes or more after a gig before stopping.

    I liked reading that a few of you use the amp with a Henry 8x8...I'm thinking of that route...any comments?
  14. IMHO the Henry 8x8 matches the SM 400-S perfectly. A 500 watt amp with a 480 watt cabinet (both at 4ohms).

    Each also seems voiced for each other and it'll really loud and punchy.

    I'm really happy with mine.

    Cantstandsya also has this set-up, but I think he needs his amp biased as well.
  15. tornadobass

    tornadobass Supporting Member

    Nov 20, 2000
    Iowa City, Iowa
    Sounds great! I'll start saving up the gig money :)

    It's hard to find much available locally, even used gear. I see used Henry's for about $500 on the Internet, once even for $400.

  16. Cantstandsya

    Cantstandsya Supporting Member

    Jul 27, 2001
    Fontana, CA
    I talked to Adam at SWR today and he told me that my amp was reacting fairly normal to an active five string.Two hours of hard playing at fairly loud volume is apparently all the 400S can handle.I guess reproducing the lower frequencies of the B string make the amp work a lot harder than a four string.He suggested a Bass 750 or 750X to push my Henry.He swears I wont blow my speakers with the 750 but will get the same volume I get out of my 400s at alower setting thus making the amp run alot cooler.He did offer to have one of the techs adjust the biasing for free if I want to bring it in.I think i'll try that first before I spend money on a new head.
  17. That could explain it.

    Keep us updated.

Share This Page

  1. This site uses cookies to help personalise content, tailor your experience and to keep you logged in if you register.
    By continuing to use this site, you are consenting to our use of cookies.