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Amp Shutdown – Overloading The Input Stage?

Discussion in 'Amps and Cabs [BG]' started by mrjim123, Apr 21, 2018.

  1. mrjim123

    mrjim123 Supporting Member

    May 17, 2008
    The Gene Deer Band
    I just received an Ashdown RM-800 (not the EVO) head from GC a few days ago. It was discounted to $299 and I would hate to have to return it, but, the amp shut down twice and I have concerns. The only thing my TB search turned up was a similar issue that occurs with some GK MB series heads when the gain is set higher than the master volume. I’m wondering if this is related.

    Here is my test setup: A speaker was connected to the output but the master volume was set to 0 because I am DI’ing out to a Behringer mixer and listening through headphones connected to the mixer (I live in an apartment :(). I plugged my passive G&L JB-2 into the amp. I *THINK* these may be the two key causes of the shutdown:
    1. The amp “Input” knob was all the way up. The only reason it was set that way was because the VU meter needle was barely moving when I played (the bass volumes were both dimed) and I was simply wondering if I could ever get the needle anywhere close to the red zone. That is a separate issue, about which I have emailed Ashdown tech support; no reply yet.

    2. The compressor was turned all the way up (not that I ever intend to play that way, just testing it). Within one minute the amp shut down as if I had turned the power, twice. Each time I cycled power the amp came back on. Right before shutdown it seemed that the audible level was sagging, and I did hear some distortion, as I recall.
    I have since dialed back both the compressor and the gain to about 12 o’clock and the shutdowns have failed to recur. In a live situation I never dime anything, so maybe the amp will never shut down again, but can I be sure? I know that amps can thermally shut down, but in this case the speaker was not being driven. So, did I simply overload the input into the power amp, and was the shut down a built in feature or a sign of a defect in the amp?
    Last edited: Apr 21, 2018
  2. Rick James

    Rick James Inactive

    Feb 24, 2007
    New Jersey
    Unless you do something really dumb, like plugging the speaker output of another amp into the input, you can't overload an amp input. The only thing that should cause an SS amp to shut down is overheating the output stage, usually caused by too low an impedance load. Since you've ruled that out it may well be a defect.
    BassmanPaul likes this.
  3. bwildt


    Mar 21, 2017
    Wichita, Kansas
    I don't think the meter on Ashdown stuff is accurate enough to use for setting levels. It is mostly a gimmick, and it may be that they always read low. My only Ashdown experience is my Mag300 head. If I can get the meter to the middle of the gauge (hard to do), distortion starts. I usually run it with the meter never going above 1/4.
  4. I agree about the uselessness of a meter in places like this.
    If it was an important thing for playing, all amps would have them.
    Put some tape over the darn thing so you can ignore it and just play the amp how you'd play any other.
    Aqualung60 likes this.
  5. mrjim123

    mrjim123 Supporting Member

    May 17, 2008
    The Gene Deer Band
    But I love to watch things that bounce. :smug:
    SoulReflection, Loring, Jewce and 3 others like this.
  6. BassmanPaul

    BassmanPaul Inactive

    I’m confused. In what way did the amp shut down?
  7. mrjim123

    mrjim123 Supporting Member

    May 17, 2008
    The Gene Deer Band
    It shut down as if I had turned the power switch off.
    Loring and Aqualung60 like this.
  9. mmbongo

    mmbongo Regular Human Bartender Supporting Member

    Aug 5, 2009
    Nothing you’re doing should cause an amp to shut down. It sounds defective.
  10. Agreed. Normal play, and everything hooked up properly should not cause amp problems.
    It's tech time.
  11. BassmanPaul

    BassmanPaul Inactive

    I cannot see how that can be connected to the input level unless you drove the amp into severe clipping and activated a protection circuit.
    Old Garage-Bander likes this.
  12. Mowbro


    Jul 6, 2015
    I would see what Ashdown has to say about this. But be prepared to return it if need be. There’s probably a reason why that amp was discounted so much and there was a new version released shortly after (EVO series).
  13. Is this another class D amp shutting down?
  14. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa, Product Support-Genz Benz
    Let's not go down this road, there are plenty of examples to disprove "this is a class D problem" myth.

    It may be an amp problem unrelated to class D, or simply a design without the necessary robustness.
  15. Yeah! Then he'd see that meter bouncing for sure!
  16. Haha! I knew you'd respond quickly, I'm not saying that there is a problem with them just that they seem kind of finicky so far, there's also a thread about an Ampeg Class D shutting down today. I've never owned one and probably won't until people stop posting threads about them shutting down.
  17. BadExample


    Jan 21, 2016
    I wonder if it was not hot enough playing it, but too hot to get through the power up sequence. Leaving it on with the fan cooling it might have been a better option if it's just going to be off for a few minutes.
  18. Wood and Wire

    Wood and Wire

    Jul 15, 2017
    Are you sure it shut down / went in to protect mode?

    If you've got the input gain maxed (particularly with the powerful kind of output G&L basses typically have), you're going to be exceeding the threshold of the compressor, even with very light playing.

    The compressor threshold is typically fixed at an optimal signal level (amp, and pedal compressors, tend to behave more like opto-compressors, than fully featured studio compressors). If you've also got the compression knob maxed, it's highly likely that your hi-gain input has the compressor pegged, and it's taking forever for the compressor to recover, so you're hearing the release phase of the envelope...

    Without hearing it, it's just a guess - though it might be worth reading some of the posts about the Trace Elliot ELF, as I seem to remember some people discussing triggering the protection shut down mode, perhaps relative to input gain (I have no personal experience with those amps).
  19. That would be a pretty crappy way to design a thing. IMHO.
    Fan should run at startup and then after powering up and it is determined the amp doesn't need the additional cooling slow or shut down.
  20. BadExample


    Jan 21, 2016
    Thermals do some funny things when you shut off. The heat source is gone, but the stored heat continues to travel. Without a fan, water pump, etc., it wants to spread out depending on (following the best path of) thermal conductivity. It's usually harmless, but it can be a problem on start up hot, especially when the sensor is not very close (thermally) to the heat source. This behavior should be thought out in the design if it is intended to be used this way, and it should have been caught during destructive testing. That doesn't mean either happened. Or it may have been determined not worth it to go back into development. I am not at all familiar with how protections circuitry applies to amps, or what other protection may be at play.

    Regardless of what caused that amp to shut down, it seems to be a design or build flaw. It doesn't matter to the owner of the amp. It just leaves them with a new, expensive boat anchor and a sour taste in the mouth.
  21. Primary

    Primary TB Assistant

    Here are some related products that TB members are talking about. Clicking on a product will take you to TB’s partner, Primary, where you can find links to TB discussions about these products.

    May 9, 2021

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