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Eden WT300 question: ultra-loud fan coming on at moderate volume

Discussion in 'Amps and Cabs [BG]' started by Lia_G, Oct 23, 2013.


  1. Lia_G

    Lia_G

    Oct 27, 2005
    Hey folks,

    I took in an Eden WT300 on trade recently and am liking it. However, when warming up for a gig last night, the fan came on extremely loudly at what I thought was pretty moderate volume. I had EQ mostly centered at noon, with just slight deviations here and there. Master was at about 12:30, and pre-gain was at 9:00. It was pretty loud, but not what I would consider really pushing the head. The fan came on and sounded like a jet or something. Led me to believe the head was overheating, so I didn't take it to the gig. Took the BX500 instead (which performed admirably).


    Anyway, do these settings seem extreme to you or anything? Should I take it to my amp tech for a lookover? I'm thinking yes.

    Cheers,
    Liam
     
  2. Did it sound like a fast fan or like something is hitting the fan blades?
     
  3. Lia_G

    Lia_G

    Oct 27, 2005
    Just sounded like a really fast loud fan, not like something hitting the fan blades.

    Liam
     
  4. Hi.

    Since the amp is used, check if there's dust buildup on the blades that causes inbalance.
    Also check the bearings on the fan. Most don't quite get much past the warranty period.
    Usually cheap and easy to replace.

    If those check out, find out whether the fan has a variable speed control, it may be malfunctioning and as soon as the fan kicks in, it's on full speed.

    Lastly, the worst scenario IMO, check the bias, the amp may run too hot.
    That should cause audible problems as well though.

    Regards
    Sam
     
  5. Lia_G

    Lia_G

    Oct 27, 2005
    Cool, thanks for the tips.

    Liam
     
  6. Munjibunga

    Munjibunga Retired Member

    May 6, 2000
    San Diego (when not at Groom Lake)
    Independent Contractor to Bass San Diego
    The WT-300 is a solid state amp.
     
  7. Hi.

    Yes, of course it is.

    It's a discretes amp though?
    No personal experience, but judging by the pics, the WT series amps are real Eden's, not rebadged Smarvo's.

    I'm just an enthusiastic hobbyist, not a pro by any means, but AFAIK there's no self biasing discretes used in MI amp construction.
    AFAIK again, the only output devices that don't need outside biasing circuit are some of the TDA family hybrid amp chips and IIRC the STK chips.
    But the former are found usually only on entry level amps (and SWR WM10 ;)) and the latter on 80's vintage (cheapo) SS amps.


    Regards
    Sam
     
  8. Munjibunga

    Munjibunga Retired Member

    May 6, 2000
    San Diego (when not at Groom Lake)
    Independent Contractor to Bass San Diego
    Have you ever adjusted the bias on a solid state amp? I've never even heard of it.
     
  9. Lia_G

    Lia_G

    Oct 27, 2005
    I know the SVT 3 Pro's mosfets need biasing periodically. That's the only ss amp I've ever heard of needing biasing though. But I'm ignorant of these things.

    Liam
     
  10. Hi.

    Yes.

    On both SWR discretes amps I've had SM400 & ST220 and on the few A/B SS amps I've built.
    Plus on some that I have repaired.

    You haven't seen all the "My SWR SM400 or ST220 runs hot threads" on TB?

    Really?

    And the replies to get it biased?

    Or the instructions to do so?

    Or the relieved OP's reply when their beloved amp sounds "like new" even though they can't cook eggs for a snack on top of it on a break between the sets anymore?


    The following is just a laymans explanation, and barely scratch the surface of the subject, but here goes.

    Biasing is necessary for any device that has an operating curve, to ensure that the operating point either stays fixed (class A for example), or moves at a certain point from one class to another (class A/B) for example.
    For distortion free operation, the operation of the device should be also limited to the linear portion of that operating curve.
    The bias circuit may or may not handle that task as well.

    Classes G&H may or may not require the bias to change when the rails switch.

    On some designs, a part of the bias circuit is kept at the same temperature (attached to the same heat sink) as the device it biases, so the bias stays optimal on all the operating temperatures.


    Only if the amp is a class D SS, and the output devices act like switches, the traditional biasing may not apply. You have to set the operating parameters and limits to the devices somehow though.

    Much trickier than biasing "old school" amps, and if something goes wrong, it usually goes terribly wrong.
    Removes any doubt what to repair though ;).
    On traditional amps the efficiency just goes down (towards class A usually) and as a result the devices heat up until the protective circuits (hopefully) kick in.


    Next You're probably going to reveal me that the WT series are class D even though there's a fan in there, and all my rambling has been in vain :).

    If so, well played sir.

    Regards
    Sam
     
  11. Munjibunga

    Munjibunga Retired Member

    May 6, 2000
    San Diego (when not at Groom Lake)
    Independent Contractor to Bass San Diego
    Nope.

    Yep.

    Nope.

    Nope.

    Nope.

    I'd be more interested in what's entailed in the process. Do these amps have pots in the biasing circuits and test points on the PCB? And the WT-300 is not class D.
     
  12. Matthijs

    Matthijs

    Jul 3, 2006
    Amsterdam
    IME the fan of the WT300 does not kick in until I push it seriously hard and even then the fan does not make a lot of noise. Cleaning up sounds like sensible thing to do, but if the problem remains you should take it to a tech.

    Did the amp feel hot to you? If not, it might very well be the trigger circuit for the fan. I don't think it's a variable speed fan, but I'm not sure since I hardly ever notice the fan.
     
  13. Hi.

    I haven't biased the MosFet Ampegs liam_g remembered (and I didn't), but I have the instructions to do so somewhere, should the need arise.
    Mr. Tiers or another Ampeg rep. has posted them on several occasions IIRC.

    The SM400 and ST220 have a trimmer on the power amp PCB(s), and I could swear that I have seen a "test point" method for just a signal generator and DMM for them in the 90's, but sure haven't been able to find it anymore.
    Those amps are biased with the so called "cross-over method" where the o-scope trace shows a cross-over notch when a test signal is applied. When that notch disappears as the trimmer is turned, the bias is correct.

    On some amps You monitor the idle current of the module and use a trimmer to adjust the idle to the specs.

    On some amps there's test points and a trimmer.

    Some amps that don't have a trimmer to control the bias, certain components are swapped.

    Not much unlike how one would bias different tube amps.
    For the same reason as well.

    The key is to know what topology the amp is though, and how exactly the bias is controlled and adjusted. The manufacturer is usually the most accurate source for such information.
    A know-it-all tech quickly fries the output devices.

    While bias adjustment on an SS amp is usually very DIY friendly procedure, it's also important to be able to tell whether the bias drift is caused by component malfunction -either the output device or the bias circuit itself- or if it's just the nature of the circuit as the components age.

    In OP's case the need for biasing is IMO unlikely though since he's liking the tone and doesn't report overheating.
    Like I said in my first reply, out of whack bias usually results weak performance and audible problems.
    IME anyway.

    Regards
    Sam
     
  14. Matthijs

    Matthijs

    Jul 3, 2006
    Amsterdam
    As far as I know offset bias is not very common for wt amps, but it is possible. I think it would change the sound before it causes overheating though.
     

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