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help please...


clashcityrocker
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So 3 songs into our set tonight my amp (hartke lh1000) started smoking and cut out,this has never happened before and I'm shitting my pants as my ashdown died on me two months ago. I was on bridge mode,full 1000w,into a 2x15 laney cab (not mine),any ideas?I have a gig tomorrow night so bit pissed off and worried! Thanks a lot in advance,Simon

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I presume so as its a feature on the amp as standard and was made to go with my harkte 810 which is 4 ohms. Would putting a 4ohms load into an 8 ohm cab damage the amp? On the back of the laney cab it had like 4 inputs (but no writing) so just plugged into one of the 2 jack inputs. The cab also had a XLR input,could it of been a PA cab?! Thanks Simon

Edited by clashcityrocker
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Bridging should almost never be employed into a low impedance load. There's nothing to be gained except damaging the head by driving too low an impedance load or blowing the drivers with too much voltage swing, or both. Bridging should only be used into a high impedance load, say 16 ohms, which the amp would otherwise not be capable of driving to full output. The mechanics of what bridging does isn't about watts, it's about voltage swing. An instructive paragraph in the owner's manual about when to bridge, and more important when not to, should be SOP, but IME it's a topic that's seldom, if ever, addressed.

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According to the manual for the LH1000, the minimum impedance for bridge mode is 4 ohms. You say you were using a jack socket on the cab - how did you hook it up - a Speakon > Jack cable? The bridge output on an LH1000 is only supposed to come out of the Speakon, I think.

You "assumed" the cab was 4 ohm? So you don't know what the impedance was for definite?

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[quote name='LukeFRC' timestamp='1345226302' post='1775314']
theres a trend here then. these amps are getting enough air?
[/quote]
Yeah both have working fans,the ashdown was sat for 3 months untouched then died on first start up. The hartke has been fine for the 6 or so months I have owned it. I think it must be running it on bridge thru an 8 ohm cab that has done it,does anyone know the damage this may cause? Thanks a lot everyone for their advice and thoughts,Si

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If memory serves, if you run an amp into a cab at too low an impedance then the amp can overheat (which is what it sounds like has happened) as the cab is drawing more power than the amp is designed to handle - I'm sure someone with more knowledge than me can confirm / refute this and explain why.

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[quote name='Graham' timestamp='1345371609' post='1776669']
If memory serves, if you run an amp into a cab at too low an impedance then the amp can overheat (which is what it sounds like has happened) as the cab is drawing more power than the amp is designed to handle - I'm sure someone with more knowledge than me can confirm / refute this and explain why.
[/quote]

As far as solid state amps are concerned, yes. The key is in the word "impede". A high impedance cab impedes the flow of current from the amp. A low impedance cab impedes it less. A bit like pouring water down a thin pipe compared to a fat one.

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