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Amp goes into protect mode too easily

Discussion in 'Amps and Cabs [BG]' started by Rockin Mike, Nov 11, 2012.

  1. Rockin Mike

    Rockin Mike

    May 27, 2011
    I have an amp that shuts down almost everywhere I take it. I think this is related to undervoltage. It works OK on one circuit in my bandroom but on another circuit it shuts down every few minutes. I have had it cut out at gigs, and last week it cut out during an audition.

    I understand protection mode is supposed to be a Good Thing (tm) and folks will say this is normal behavior, but I have a backup amp that has never done this. In fact, every time my main amp cuts out, I whip my backup out of my gig bag and it runs fine all night.

    Both are good quality name brands.

    Is there any way to set the sensitivity of the undervoltage protection circuit?
  2. 1958Bassman


    Oct 20, 2007
    Have you actually measured the voltage?

    I would bet that it has leaky outputs or maybe the bias is set too high. Have it checked for DC offset at the output, too.
  3. Bassmec


    May 9, 2008
    Ipswich UK
    Proprietor Springvale Studios
    We need more info than this to give sound advice, we need name rank and serial number.
    So just a guess, its a modern lightweight transistor amp with an SMPS instead of big old heavy transformer.:bassist:
  4. Rockin Mike

    Rockin Mike

    May 27, 2011
    Closest I have come to measuring the voltage is to notice the reading on my power conditioner:
    Furman P-1800 PF

    On the weak circuit in my house it regularly drops into the red, I think around 104v. The flaky amp cuts out every day on that circuit. Haven't measured the good circuit, just glad it works there. I haven't measured it at any of the clubs or people's houses where it cuts out.

    The stable amp is a lightweight, Genz-Benz Streamliner 600.
    The amp that cuts out is an Eden WT-550.

    Both are hybrid, tube preamp and solid state power section.
    I would guess by the weight that the Eden has some iron in the transformer.
    The Eden is 30 lbs, the Streamliner is 6 lbs.
  5. Bassmec


    May 9, 2008
    Ipswich UK
    Proprietor Springvale Studios
    Now there's a turn up for the books.
    Well you could check the Eden output transistor bias, move to Europe to avoid half arsed electricity, decide that perhaps the Eden is running into less ohms than its really happy with, replace the caps and rectifier in the Eden power supply, or all of the above.:bassist:
  6. Rockin Mike

    Rockin Mike

    May 27, 2011
    Eden is going into 4 ohms, and it's rated OK down to 2 ohms so I don't think it's that.
    It's only a couple of years old so components are probably not aged out.

    The rest of what you said is amp tech stuff. I was hoping to avoid spending money on it.
  7. Bassmann1968


    Feb 17, 2009
    Hi Mike,
    This is not normal.
    Have your big resistors on the preamp board checked out.
    Resold er will help.
  8. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa, Product Support-Genz Benz
    104 volts is getting pretty low. The Strewamliner (and most of our amps) are rated down to slightly below 100V (for the non-Japanese versions) but each manufacturer makes a choice on low voltage protection threshold (assuming that this is in fact the cause) based on their own particular product's sensitivity to low voltage damage.

    I suggest that you discuss this with Eden, perhaps they have an idea as to what is going on and some helpful suggestions as to how you can resolve this.
  9. Bassmec


    May 9, 2008
    Ipswich UK
    Proprietor Springvale Studios
    I am afraid it is home tech time because it is not working correctly, something
    Is causing a significant voltage drop in the power supply and so if the loudspeaker cable is in good order and not slightly shorted by damage.
    You are going to have to find the voltage drop, so you need to have a mate who knows how to use a multimeter and measure the DC rail voltages all the way back from the output transistors back to the caps in the power supply, measure across all joints (solder or otherwise) with it plugged into the mains circuit that will keep it running, load the amp with a strong steady signal level (signal generator or sine wave sample from a computer or cd player) and look for the high resistance joint.
    with the DC voltmeter.
    The chances are its just a big component like a big electrolytic cap in the power supply has dry jointed its self due to vibration as was suggested
    by Bassman 1968, chase all big resistor solder joints with fresh solder and flux.
    You will find it if you look methodically through it, if none of that works just ask an engineer to test the output transistor bias for excessive quiescent current. Not a big job.:bassist:
  10. 1958Bassman


    Oct 20, 2007
    Where are you, that yousee voltages as low as 104VAC? That's outside of the 10% range the power companies are supposed to be held to. I would have them some out and make sure everything is OK- the condition of the cables going to the meter box are their responsibility and I have seen buildings with three or four splices between the power company's cable and the cable going to the meter.

    I would also look inside the breaker panel for evidence of moisture. If you see this, have an electrician check all connections for corrosion.
  11. fdeck

    fdeck Supporting Member Commercial User

    Mar 20, 2004
    Madison WI
    HPF Technology LLC
    I'll second or third the motion that 104 V is low. Is it that low on all of the outlets in your house? There should be two "sides" to the 220 coming into the house, and it would be interesting to know if they both have equal voltage. If you're getting weak juice coming from the pole, the electric company can fix that, hopefully on their nickel.
  12. 1958Bassman


    Oct 20, 2007
    The meter is sometimes used as the demarcation point between their responsibility and the homeowner's responsibility. Usually, if damage occurs to the feed from the splice above the meter, the homeowner is responsible because the power utility doesn't install that part.

    I wouldn't hesitate to call the utility about this- they don't charge for it unless physical damage has occurred to their feed.
  13. Zooberwerx

    Zooberwerx Gold Supporting Member

    Dec 21, 2002
    Virginia Beach, VA
    Keep in mind that this anomoly is occurring at home, gigs, auditions, etc.

  14. teemuk


    Mar 1, 2011
    AFAIK, there is no undervoltage protection in WT550 since it's a generic class AB amp with a generic linear power supply. Such will basically work with any voltage unless it's ridiculously low and undervoltage is not damaging anything like in class D amps or in SMPS.

    Those amps do have a thermal breaker so I'd suggest you check if it's tripping. I'm quite certain we are discussing about more severe issues than low mains voltage.
  15. Rockin Mike

    Rockin Mike

    May 27, 2011
    Sounds like time to talk to Eden.

    Bassmec I would love to learn to get in there and troubleshoot amps but knowing nothing about them I'm concerned I might fry something or get electrocuted.

    For example, what's a DC rail voltage?
  16. Bassmann1968


    Feb 17, 2009
    As I said, have the ceramic resistors on the preamp board checked.
    Easy fix.
  17. Bob Lee (QSC)

    Bob Lee (QSC) In case you missed it, I work for QSC Audio! Gold Supporting Member Commercial User

    Jul 3, 2001
    Costa Mesa, Calif.
    Technical Communications Developer, QSC Audio
    It's actucally a conventional line-frequency power supply, which is non-linear due to its use of peak rectification.

    You have two problems: 104V is way low, and as fdeck said, you should have equal voltage on both sides of the 220-240V legs coming into the house. If a neutral is in bad condition or even open, the proportion of the two voltages could drift so that one side is low and the other is high. This could be dangerous to anything plugged into the AC mains. If the voltage is low because of an excessively high resistance somewhere in the AC wiring, you could have a lot of heat being produced, which is a potential fire hazard.

    The second is the Eden amp. You need to have a tech check it out. We don't have any real clues in this thread why it's cutting out or in what way, what the symptoms are. Contact Eden or bring it to a qualified service facitility.
  18. lowfreq33


    Jan 27, 2010
    Endorsing Artist: Genz Benz Amplification
    Question: is the amp always plugged into the power conditioner? If so, try plugging straight into the wall outlet.
  19. Rockin Mike

    Rockin Mike

    May 27, 2011
    I sent Eden an email and they responded right away. Their amp tech will be in tomorrow and they will see what they can do for it.

    104v is low, and I should mention it ranges between 104v and 120v depending on whether the window-unit A/C is running. I know, an A/C should be on its own circuit with nothing else running, but I don't have that luxury. If I put everything on the other circuit it will (quite rightly) trip the circuit breaker.

    As far as heat, I have checked all the outlets and switches by touching the covers and nothing feels warm. I think it's OK. I have had electricians out for various things but they have all said they can't get to the wiring in that room because it's an enclosed patio with a flat roof. No attic space above it and the wire-carrying walls are brick, formerly exterior walls.

    In the over 10 years I've lived here I haven't had any problems with short lifespan of any other gear plugged into that circuit including computers, stereos, flatscreen TVs, mixing board, fluorescent lights, or effects pedals.

    It's just the Eden amp that cuts out on that circuit and the circuits at various clubs and peoples' houses. My other amp works just fine in all the scenarios that cause the Eden to cut out. It's saved my butt on numerous occasions. I'm pretty clear it's a problem with the Eden.

    Just wanted to know if it's due to a malfunction in the amp or some kind of sensitivity adjustment.