STEvil Posted March 1, 2011 Report Share Posted March 1, 2011 Low voltage doesn't blow amps. That's a myth. i believe you, but i really would like to hear your explanation for this. hmmm not excatly true. having low voltage doesn't really blow amps its the current being drawn to produce 4k at lower voltage is what kills amps power supply. as voltage goes down current goes up, FET's get hot and then pop! *anti nut hug device activated* boon is probably one of the smartest if not THE smartest man on the forum when it comes to amplifiers...just sayin maybe be he is, but as far as i know running amps at a lower voltage like low 11s often results in blown power supply parts. also the power supplys work harder at lower voltages to produce the same amount of power as it would say 14V. The only solution i can come up with is the excess current being drawn to produce the 4kW. I guess boon with school me about this in a bit....its all good. alot of ppl will like to know the answer to blown power supplys. Its not the low voltage that kills them, its the clipping. If the amp is rated at 4KW at 14 volts, what makes you think it will still do 4KW unclipped at 12v? MickyMcD - "Capable of making some serious trouser flapping volumes at where's-my-testicles frequencies, the Servo-Drives used to be fairly jaw dropping..." Any time you have have a power wire next to your frame put some rubber hosing (or cut up an innertube) around it. The wire is bound to wiggle (due to driving or flex) and the casing will eventually wear through. Hammerdown... 1% no links to outside websites, business related FB/YT pages allowed. Link to comment Share on other sites More sharing options...
loki Posted March 1, 2011 Report Share Posted March 1, 2011 clipping doesnt kill the power supply of an amp. waiting on boon to chime in and explain this low voltage myth. 05 Ford F150 Single Cab Audio: -Pioneer DEH-3200DVD -Hertz Hi-energy 5x7 Front -RE Audio 5x7 Rear -DD 2512 in Custom 40 Hz Box -Eclipse EA4100 High/Mid amp -Eclipes XA1000 Sub amp -Audison Connnection RCAs -Random wire:Kicker,RF,Lightning Audio Link to comment Share on other sites More sharing options...
Boon Posted March 2, 2011 Report Share Posted March 2, 2011 Okies - most amp power supplies are unregulated - they just make as much voltage as they can with a given input voltage. They use a fixed multiplication transformer, say 10:1 - so you feed them 14.4v, they turn it into a square, then 10:1 it to get 144v rails. Or you feed it 12v, it gets turned into a square, you get 120v rails. Less rail voltage = less current across the load = less wattage = less power = less heat. The duty cycle of the power supply is fixed, most of them run really dumb PWM controllers like TL474 which just makes a square wave of fixed duration and that's about it. Some of the more cunning amps (JL, Soundigital) use an intelligent controller that will increase the duty cycle of the PWM on the power supply when the input voltage drops. These are the amps that you will pop from low voltage because in this case less voltage = more current = more voltage drop due to Rds(on) in the FET = more heat. But these very same intelligent controllers usually have some pretty badass protection circuits that will shut down the amp or limit the output before this is allowed to happen. The rail voltage becomes important because say you are driving the amp with a 5v signal and you're asking for 12x gain for a 60v output. If the rail voltage sags because of input voltage drop and the amp can only deliver 45v at the output then obviously you get clipping. When you get clipping 2 things happen - the output FETs are running continuously rather than pulsed (pulsed rating is usually ~70% more than continuous) and the inductive load from the woofer disappears since it's working as a DC resistor rather than a reactive AC load. So the resistance plummets and the output current spikes. Then you have a race between 4 things: the output FETs overheating and blowing up, the power FETs overheating and blowing up, and the over-current protection kicking in and stopping it. Thermal protect won't save you because it takes a long time for the entire heatsink to warm up and trip the thermister that provides thermal protection - this is extreme, localised heating. The last thing is the wave falling again, dropping the voltage hence the current hence the heat. The lower the frequency the longer the wave will stay clipped hence the more chance you'll pop the amp. So, long story short - it's not voltage drop that kills amps. The whole 'less voltage means more current' thing is a myth, the amp just produces a voltage across a resistance and pulls as much current as it needs to cause that voltage drop. Basic ohms law blah blah. What kills the amp, is the clipping generated when your voltage drops with too much gain. Likewise you can kill an amp if you clip the sh!t out of it with perfectly good voltage - in fact it'll die faster, because it's producing more rail voltage so there will be more current People often see low voltage just before their amp dies - usually it's a massive current spike in their system that causes the voltage to drop - this spike is usually caused by either the clipping mentioned above, or the fact that their amp has already started to fail and the shorting-out components are presenting a near-zero resistance so the battery is dumping current. 10.x volts fo' life! Link to comment Share on other sites More sharing options...
ahoz28 Posted March 2, 2011 Author Report Share Posted March 2, 2011 Damm Boon that is a lot of info had to read it a couple of times. I did open the other amps and they do show signs of rubbing on the caps. Makes me feel better knowing it was not low voltage. Link to comment Share on other sites More sharing options...
STEvil Posted March 2, 2011 Report Share Posted March 2, 2011 props to boon for specific info I'm no EE, just learn bits and pieces as I go Would be nice if amps came with current sensing capabilities for the input and output stages, right on the legs of one or two mosfets. MickyMcD - "Capable of making some serious trouser flapping volumes at where's-my-testicles frequencies, the Servo-Drives used to be fairly jaw dropping..." Any time you have have a power wire next to your frame put some rubber hosing (or cut up an innertube) around it. The wire is bound to wiggle (due to driving or flex) and the casing will eventually wear through. Hammerdown... 1% no links to outside websites, business related FB/YT pages allowed. Link to comment Share on other sites More sharing options...
Boon Posted March 2, 2011 Report Share Posted March 2, 2011 A lot of Class D amps have current sensing on every single output FET... the question is, is it fast enough to shut the amp down before it kills itself? 10.x volts fo' life! Link to comment Share on other sites More sharing options...
STEvil Posted March 3, 2011 Report Share Posted March 3, 2011 Probably, if it is designed well enough to function correctly. How many people bother testing that, though? MickyMcD - "Capable of making some serious trouser flapping volumes at where's-my-testicles frequencies, the Servo-Drives used to be fairly jaw dropping..." Any time you have have a power wire next to your frame put some rubber hosing (or cut up an innertube) around it. The wire is bound to wiggle (due to driving or flex) and the casing will eventually wear through. Hammerdown... 1% no links to outside websites, business related FB/YT pages allowed. Link to comment Share on other sites More sharing options...
Recommended Posts
Archived
This topic is now archived and is closed to further replies.