Deleted. I typed before reading the rest of the thread.
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I'm sorry I listened.....
- Thread starter ShawnStones
- Start date
You'd be surprised but that makes for another thread.
Thanks to all for the explanations, links, etc.
Riis
yeah really when you have guys like bill who know their stuff saying you shouldnt run bridged @ 4ohms I would be stupid to overlook the advice along with the OP having this problem and buying one. especially with a company that runs totally mail order. Im actually looking towards the GB shuttle 6 or 9 in the future since they should be stable at a 4ohm load.
I find it quite interesting that for years all the talk was finding an amp that was stable down to 2 ohms. My amphead handles the 2 ohm load without issues, barely even getting warm, much less hot over an entire gig. I've run amps down to 2 ohms for years without issue (Peavey's have had reliable 2 ohm capable heads for years).
Now we're talking about finding amps stable down to 4 ohms?
F'in ridiculous. I've been running amps down to 2 ohm loads for years and NEVER had a single issue with either my amps or cabs. One thread and the whole bass world starts getting crazy worried that they'll fry their amps.
What's next? Is the next new fad after this going to be about finding amps stable down to 8 ohms?
Now we're talking about finding amps stable down to 4 ohms?
F'in ridiculous. I've been running amps down to 2 ohm loads for years and NEVER had a single issue with either my amps or cabs. One thread and the whole bass world starts getting crazy worried that they'll fry their amps.
What's next? Is the next new fad after this going to be about finding amps stable down to 8 ohms?
Actually, IIRC, we're referencing bridged power amps with 4 ohm loads (2 ohm per side) which may suffer thermal consequences if plagued by cost-driven design and/or construction limitations. Or that's how I read it.
OTOH, I'm one of the aforementioned jolly jokers who's driven daisy-chained main enclosures (4 ohm load) with a bridged QSC amp and never hit a snag. FTR, there is an upside to "hot" amps....you can stick a foil-wrapped sandwich on top and by the end of the first set, the cheese will be nice and melty.
Riis
And how long have power amps been available that can be bridged and run at a 4 ohm load? Quite a long time I do believe. I mean the whole point of bridging was to get more power from the amp and all of them were designed to handle a 4 ohm load. In all the years of gigging, we have always had our own PA and always had amps we could/did bridge and I have never, not once run into a problem doing so.
I've run my Carvin BX1200 with two 2 ohm cabs (one on each side) as well as running it bridged in 4 ohms and not once did my amp even get hot, much less shut down.
But...my amp is older than the OP's and apparently Carvin switched over to a lighter design. Perhaps the old "lead sled" amps do not have these issues that the new switching power supplies have. By that I don't mean ALL amps using this, but certainly there is a fair share of these lightweight heads (of which mine is not) exhibiting some problems that were not common with older, heavier heads.
I have one lightweight head (Ashdown Superfly) but mainly I'm still in the old style, heavier power supply heads camp mainly because I know they are built like tanks and reliable.
Here's at least part of the answer to this riddle. The tech exists to produce more "modern" (not AB) amp designs with SMPS capable of loading down to two ohms, but apparently it's not inexpensive to do. MI-grade bass amps are a fraction of the cost of pro-grade audio amps and it's likely that the tech (knowledge, components, etc?) have not trickled down yet to allow production of products with these features.
Same here...one newer PLX 3102 but everything else is "old iron". Heavier than hell (I have 4 in one rack box) but that's why cavemen invented the wheel. Saw it on "The Flintstones".
Riis
My lightweight (8 lbs. without the stupid metal, redundant case around it) Ashdown Superfly runs stable at 4 ohms each side. But it always ran hot, even though it never crapped out on me.
One of the reasons I went back to older style heads. I know the technology exists to make lightweight, yet powerful, stable down to 2 ohms heads but like most newer technology, I think I'll wait until it is more commonplace to go that route. I realize some manufacturers are already there, but until it's the norm I'm in no rush to jump on the lightweight bandwagon.
Because of my usage, I want a head that safely and reliably goes down to 2 ohms. If it can't, it's already off my radar. But with my Carvin BX1200's versatility I've got no GAS for another head. I'd rather put my money and efforts into lightweight cab design because while some ampheads are on the heavier side, they are small (and thus easier to carry) compared to larger/bulkier cabs.
I'm wondering, since the OP really liked the sound of the BX1200, if he could find a used one in the classifieds that was built earlier before they started having these issues. It would be cheaper than new anyway.
Dear Mr. Horse,
As usual, thanks you for the education.
Had no idea that there could be as much as a 30 ohm swing in speaker impedance over a pretty reasonable frequency spectrum.
For the rest of you deadbeats; get back to your cage and practice your instruments or the management will turn the power down to 90 volts and all the amps will overheat.
As usual, thanks you for the education.
Had no idea that there could be as much as a 30 ohm swing in speaker impedance over a pretty reasonable frequency spectrum.
For the rest of you deadbeats; get back to your cage and practice your instruments or the management will turn the power down to 90 volts and all the amps will overheat.
- Feb 12, 2006
- 61,024
- 5
- 220,897
- Disclosures
- Development Engineer-Mesa Boogie, Development Engineer-Genzler (pedals), Product Support-Genz Benz
The whole reason for designing (linear) amps to be bridged is that is allows for a wider range of power ratings with lower internal supply voltages from a single amp model. Power output is a function of the SQUARE of the output voltage, and there's additional stress placed on the output transistors as the supply voltages increase. Either bridging or class G/H solutions are used when power levels go beyond about 1200 watts per channel into 2 ohms, both for voltage stress and thermal efficiency reasons.
It's quite common to run 4 ohms bridged in the pro audio world (better be sure your speakers are rated for the power though) and with quality products there are no problems.
It should be noted though, that a shorted speaker cable can cause greater damage to an amp operating in bridged mode due to the way the internal feedback paths work. Oscillation can be one of the byproducts, causing greater (possibly terminal) damage. ALWAYS be sure that your speakers cables are in good condition (no intermittents and no shorted connectors) if you intend to operate your amps in bridge mode.
It's quite common to run 4 ohms bridged in the pro audio world (better be sure your speakers are rated for the power though) and with quality products there are no problems.
It should be noted though, that a shorted speaker cable can cause greater damage to an amp operating in bridged mode due to the way the internal feedback paths work. Oscillation can be one of the byproducts, causing greater (possibly terminal) damage. ALWAYS be sure that your speakers cables are in good condition (no intermittents and no shorted connectors) if you intend to operate your amps in bridge mode.
- Feb 12, 2006
- 61,024
- 5
- 220,897
- Disclosures
- Development Engineer-Mesa Boogie, Development Engineer-Genzler (pedals), Product Support-Genz Benz
Indeed, this gets right back to my previous comments that robustness costs money, and in this market and for many customers, price is THE most important feature. Unfortunately for those companies who make the more expensive, more robust product, the failures of less expensive products poison the well for the rest of us.
It all comes down to the quality of the design, the quality of components and quality of fabrication, which cost money, real money.
I'll also throw into the mix the thought that an amp with a switch-mode power supply is generally more sensitive to problems with the mains voltage than an old-school linear supply. I'm guessing there's a combination of issues going on here and maybe an amp that's less tolerant of being pushed to the edge of it's operating limits than some other designs.
(Disclaimer: happy BX1200 owner here, but everyone's mileage varies...)
(Disclaimer: happy BX1200 owner here, but everyone's mileage varies...)
- Feb 12, 2006
- 61,024
- 5
- 220,897
- Disclosures
- Development Engineer-Mesa Boogie, Development Engineer-Genzler (pedals), Product Support-Genz Benz
As a general rule, there's no reason why a SMPS can't be just as robust and just as reliable (though there are more parts) but one thing that's forgotten is that it's much easier to design fault protection into an SMPS which keeps catastrophic amp failures to a minimum. This includes over-voltage and under-voltage protection. An amp that shuts down at say 95 volts is far preferable to an amp that eventually blows up under those conditions don't you think? This is in part why some manufacturers are able to offer much longer warranties and even transferrable warranties, both of which have value to the customer.
I'm not so sure about the "easier" part - a linear psu without protection circuitry will just sag if the input voltage drops, won't it?
But, yes, proper protection is a good idea, especially if there's some indication to the user as to why the shutdown happened.
(Note, my previous post wasn't intended to say that I'm certain that this would be why some people seem to have much more problems with the BX1200 than others, just throwing it out there as a hypothesis worth checking out).
I would respectfully request the OP to return to post some specific details about the 4 ohm cab that he is using.
- Feb 12, 2006
- 61,024
- 5
- 220,897
- Disclosures
- Development Engineer-Mesa Boogie, Development Engineer-Genzler (pedals), Product Support-Genz Benz
The problem is that with some circuit topologies, strange things can happen when the supply voltages drop to very low levels, things like oscillations, chattering and sticking to the rails when the amp is driven into clipping (that occurs at much lower levels due to the power relationship to the V-squared factor), these are things that can damage an amp under the right conditions. Better to avoid them at all costs rather than failure.
I was only thinking of the input voltage/current relationship at the PSU stage - linear is roughly proportional, switcher is inverse, correct? Hadn't thought about downstream from there.
Thanks. Once again I learned something today
Thanks. Once again I learned something today
Is Carvin rated to go down to a 4 ohm load in bridged mode? That's pretty tough. I wouldn't doubt its hot as heck and thermalling if you're driving it hard in that configuration even if it is rated to handle that low of a load. There are plenty of Crown and QSC power amps that are NOT rated to drive 4 ohm loads bridged.
Randy
