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Class D Micro Heads: Brownouts or Protect Mode on the Gig

Discussion in 'Amps and Cabs [BG]' started by bucephylus, Mar 19, 2018.

  1. bucephylus

    bucephylus Supporting Member Commercial User

    Aug 18, 2002
    General Manager TecPadz LLC
    It seems we need to start compiling experiences with Class D powered amp heads going into Protect Mode or experiencing brownouts on the gig.

    Ground Rules
    1. ABSOLUTELY NO CLASS D BASHING FROM AB OR TUBE USERS. You’ve been asked NOT to do it. If you comment along those lines, I will report to the mods.

    2. Experiences on the gig at normal gig volumes.

    3. Please list the head, estimate of dB level you were at, approximate stage temperature, and how often it happened.

    4. Also, which heads have given you no problems of this sort.

    My experiences so far are that this is extremely infrequent, and only seems to happen with the Class D micro heads. I’ve never had the behavior with a Class D power amp; so, seems to be the Class D micro modules. It is so infrequent, it’s tempting to ignore it. Yet, when it happens, it can be like the floor suddenly fell out from under you. That’s not acceptable. Here are my experiences.

    Shuttle 6.0, normal 75F stage temp, probably 105 -110 dB’s, happened twice. I just stopped using that head for higher volume gigs. IIRC, the protect mode was intentionally set low in this head.

    Demeter VTBP-201 with internal 250ASX2, 105F outside gig, probably 110 dB. Only happened that once. Gigged that head regularly for another two years + with no problems whatsoever. Still use it. Just have lingering lack of confidence.

    Heads with zero issues:
    GB Shuttle 9.0, tons of gigs
    GB Shuttle 12.0, numerous gigs
    Bergantino B|Amp, numerous gigs.

    The Class D micros offer a lot of promise for players happy with the voicings; but, this kind of behavior in the middle of a tune is unacceptable. So, please share your experiences +/-. Only way I can see whether we are looking at design issues or something fundamental to the modules being used. Apologies to the fine amp makers, who are working hard to improve things for us.
  2. waveman


    Sep 25, 2008
    I think each time this has happened to me, the power was very questionable, and had nothing to with other parameters. That's why I carry two amps to every gig, each a different brand, since one may be able to handle whatever condition the other cannot.

    The amp that I experienced this the most with is my favorite, Little Mark III, but it is my best sounding amp. Each time this happened (which was years ago last time it happened), I had my GK MB 500 ready, and it performed with no issue.
    kartiste, bucephylus and jthisdell like this.
  3. jthisdell

    jthisdell Supporting Member

    Jun 12, 2014
    Roanoke, VA
    I had one experience which I believe was 100% due to the electrical power supply at the gig and no fault of the amp at all.

    I was playing in a barn at a mini festival last year, running my Tonehammer 500 at about 12:00 master, gain zero so loudish but nothing extreme. Midway through the first song the keyboard player from the next band was setting up behind me and plugging things in and the TH cuts off completely. My power strip showed power but the head was off. I turned the head off and back on and it came back fine. A couple songs later someone is messing with the lights and the same thing happened again. Again I got it back on. The rest of the night no one messed with the power and I had no more problems. I believe the voltage was dropping to the point the TH saw a problem and went into protect mode.

    As I said this was in a barn and I suspect the wiring was nowhere near adequate for a band (or really anything). I've had the TH three years and used a Rumble 150 v2 for several years and never had any other issues, so 5+ years using class D and a couple hundred gigs and only the one problem that I'm certain was due to faulty wiring.
    kartiste, mikewalker and bucephylus like this.
  4. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa, Product Support-Genz Benz
    I can give you information on the Shuttle 6.0, the low line voltage protect threshold is between 100 and 105 volts, which is really low. I wouldn't want to be operating my (expensive) gear under these conditions, because of the added risk of damage.

    The reason that class D amps include such under-voltage protection circuits is because the output drivers under PWM control can become unstable as the voltage falls, causing cross-conduction and spectacular failure. As a designer who must also consider the impact on warranty claims, when presented with the two choices, protection always wins. It's better for the player as well, because once the amp is out of warranty the cost of repairing such (costly) damage becomes the responsibility of the player. The threshold on the ShuttleMax 12.0 and the Shuttle 9.0 are identical, so I think your experience was specific to the conditions at that gig. Your amp didn't blow up did it? If not, the protection did its job.

    That said, things are changing a bit with the evolution of some of the newer SMPS that are being used, there is an additional regulation circuit that holds the class D amp rails under tighter control which lessens this under-voltage effect. Of course, this costs more to design and incorporate, but is overall a better approach for most players (except those on a tight budget), and this typically extends the under-voltage threshold to 85V with no damage to the amp. The Shuttle 3.0 had this circuit, works great but was in part responsible for the higher cost of this unit compared to much of the competition. The Subways also have this circuit.
    steelin4u, brutalron, ak56 and 21 others like this.
  5. In my opinion, it is not fair to:

    1) Estimate db level for the purpose of this thread.
    People make lousy db meters.
    db levels are something that should be measured under controlled circumstances to be at all meaningful.

    2) Have this discussion without including the load on the amp.
    If you are running an amp rated to operate safely at 4 Ohms and only using an 8 Ohm load that should be noted.
    Likewise if you are running the same amp at 4 or 2.6 Ohms it is noteworthy.
    Also what cabs are in use as loudness can be very different between two cabs of similar configuration.
    In other words how well do the cabs in use convert Power into sound?

    I agree that stage temperature, measured, not guesstimated, once things are going, the lights are on, the room is packed, would be something to include.

    Amps fail under gig conditions. If you don't know what those conditions are, you can't really say if the conditions contributed to the failure, or if it was defective and bound to fail anyway. The gigging conditions may exacerbate the situation, but may not be the underlying cause.

    If people just report that amp X failed while gigging, that may actually lead to an unintended "bashing" of one brand based on insufficient data.
    As long as everyone understands that, then a gig report failure thread can be a good idea.
  6. Most of my amps are now Class D. I have yet to have any sort of a problem with any of them.
    Plectrum72, pudgychef, Zbysek and 3 others like this.
  7. bucephylus

    bucephylus Supporting Member Commercial User

    Aug 18, 2002
    General Manager TecPadz LLC
    Thanks, comments appreciated. Intent of the thread is just to start tracking actual experiences. As Andy (@agedhorse) described, there are both structural and design aspects. I just think it is better that we have a civil and up front discussion about where and how this is happening. NO BASHING intended or wanted. In fact, I'll report bashing to the mods. My intent is purely to collect data in one place. Otherwise, we end up with scattered perceptions; which, I can't eliminate it, but, hopefully we minimize it. Make sense?

    Oh, and regarding estimating dB's, can you think of a better estimate for how hard the head is being driven? IME, that seems to matter. Agree that cab load may make sense to include.
    AlexanderB likes this.
  8. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa, Product Support-Genz Benz
    For how hard the head is being driven, the combination of load (2/4/8 ohms) and if the output limit, peak or clip LED is flashing and how much might be a more objective way.
  9. Passinwind

    Passinwind I know nothing. Supporting Member Commercial User

    Dec 3, 2003
    Columbia River Gorge, WA.
    Owner/Designer &Toaster Tech Passinwind Electronics
    At one tine or another I've experienced crippling brownouts with tube amps, Class A/B SS, Class H SS, Class D SS, and various lighting gear.
    agedhorse likes this.
  10. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa, Product Support-Genz Benz
    DBX-160's were a challenge too, as were some crossovers (BSS IIRC), Carver PM-1500's, and such.
  11. Passinwind

    Passinwind I know nothing. Supporting Member Commercial User

    Dec 3, 2003
    Columbia River Gorge, WA.
    Owner/Designer &Toaster Tech Passinwind Electronics
    Old analog synths were no bonus that way either. Or_wink.
    AlexanderB, climber, jerry and 2 others like this.
  12. Al Kraft

    Al Kraft Supporting Member

    May 2, 2016
    Northern Virginia
    I've never experienced this issue with my Mesa D-800, Aguilar TH500, or GK MB's (200, 500, 800). However, I'm very careful to not overload circuits or use questionable power, expose my gear to direct sunlight while in operation, or operate in high heat conditions without making sure I have a fan providing some additional air flow around the gear.

    The other thing is that I usually use a HPF when pushing higher volumes and always have a head that is running with plenty of clean headroom. I also can't recall ever running any of my heads at less than a 4 Ohm load. I don't baby my gear on gigs, but at the same time I try to stay well within the safe operating envelope to ensure I'm nowhere near the limits.
    Last edited: Mar 19, 2018
  13. jthisdell

    jthisdell Supporting Member

    Jun 12, 2014
    Roanoke, VA
    Great name for my next band;)
  14. jthisdell

    jthisdell Supporting Member

    Jun 12, 2014
    Roanoke, VA
    But seriously @agedhorse thanks for the explanation of what happened to my TH, I think we talked on another thread about this and you said that it was probably due to under voltage but this explanation as to the danger of under voltage for class D is very helpful and informative.
    bucephylus and Al Kraft like this.
  15. Bob Lee (QSC)

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

    Jul 3, 2001
    Costa Mesa, Calif.
    Technical Communications Developer, QSC Audio
    While playing onstage at a church fair on local generator power the voltage dipped enough that my preamp latched up and stayed that way but my PLX amp kept going. To bring the rig back to life I switched the whole thing off and on again. The PLX amps will shut down at <75% of the nominal mains voltage, which for a 120V amp is 90V. I was surprised that it was the pre that misbehaved from the low voltage before the power amp did.

    I would expect that a more electrically efficient amp could help prevent abnormally severe mains voltage dips.
  16. Kro

    Kro Supporting Member

    May 7, 2003
    New Jersey
    Almost all of my experience with Class-D heads comes from the GK MB2-500 that I owned and gigged almost exclusively with between 2008 and 2015. By my estimate I probably put over 2,000 hours on it at-volume, competing with a very hard hitting drummer.

    My memory is a little fuzzy, but IIRC, in that entire time there were probably 3 or 4 shows where the amp went into protect mode - sometimes once, and sometimes more than once during a set. I also believe the amp needed to see bench time twice in that time-frame (not counting the couple of false starts out the gate that required work/replacement units from GK). One of those later repairs required a full power amp board replacement.

    I don't quite remember exact details for each situation, but I offer this experience up purely from a scientific standpoint without any hard feelings towards Class-D as a whole. In fact, it's a much better case study I'd say as to those granddaddy GK MB2-500 heads - I wouldn't be surprised if reliability has increased significantly since then.

    I've seen other amps blow up on stage being used by other bassists, but I've never had any other amp fail on me in any way personally. I'm not quite as active as I was back then, so it's not really a fair comparison though.
    bucephylus likes this.
  17. MrLenny1


    Jan 17, 2009
    2 Class D amps for 2 years.
    No issues.
  18. I get what you're trying to do and it's a good idea, except for one thing. Most people don't understand the correlation between a failure event and what caused the failure.

    I think those who would be reporting information here are more sophisticated than the average player. However the average player reading comments here may not get plast the amp model and that it failed. Even if all of the pertinent info is included, the reader sees "Brand X," then a lot of blah blah yadda yadda, and he glosses over and skips right to "failed during a gig."

    It's like reading a review of a microwave oven, "Brand X" blah blah... "melted my face off." The reader glosses over the blah blah part which tells how the owner defeats the safety switch so he could watch his food cook with the door open.

    How about if you were to include some type of a standard form that would be filled out that asks a number of pertinent questions about the failure and the events leading up to it? If someone can't answer the specifics, it would be noted that such and such information was unknown and may or may not have contributed to the failure. This at least puts the reporting player on notice that they'd better have all the facts. It might also serve to help the reporting player as well as other readers what to watch for when gigging to avoid future problems.

    It won't help with lazy readers, but it might be useful to those who care enough to want to use the information that was provided by answering the questions on the form.
    bucephylus likes this.
  19. pfschim

    pfschim Just a Skeleton with a Jazz bass Supporting Member

    Apr 26, 2006
    SF Bay Area
    Ampeg PF500
    3 shutdowns (now only used in rehearsal, and has not had a shutdown in several years of this kind of use).
    Running at 8ohms into 1 Ampeg 115HE cab
    Moderate volume (don't know the dB .. don't have a dB meter in my head ;);)), but Gain was set to just under clipping and Master was set at about 11:00
    temps were very moderate
    venue power is familiar and solid, never caused an issue with any other amp
    a third shutdown was in a bit warmer temps, upper 80's, but nothing that should be associated with thermal shutdown at the level the amp was being used.

    I have owned and gigged a TC RH450 (now long gone) and a Demeter VTBP-M-800DJ (my primary gigging amp all of last year).
    No issues with either of those amps.
    bucephylus likes this.
  20. bucephylus

    bucephylus Supporting Member Commercial User

    Aug 18, 2002
    General Manager TecPadz LLC
    Agreed. Not what is needed.

    Agreed. I actually tried to outline that. If you can come up with a better form for players to use to keep the discussion between the lines, I'm all for it.

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