sfellini Posted April 14, 2007 Share Posted April 14, 2007 Hi All, I've got a question about power specifications for solid-state amps. Amp A doubles it's power output from 8 ohms to 4 ohms, let's say 75W to 150W. Amp B doesn't: 75W at 8 ohms, but only 125 at 4 ohms. Is it correct to say that the reason amp B can't double its power output when the impedance halves, is that it can't double its current output? Thanks, Steve. Quote Link to comment Share on other sites More sharing options...
Guest " " Posted April 14, 2007 Share Posted April 14, 2007 I'd like to pose a thought about a reason that is often over looked. Heat. It maybe that the sum of all devices can contribute to the numbers needed to produce the output expected, but perhaps due to the lack of a cooling solution, i.e. heat sink to small, componet failure may result. Common problem with output and driver transistors. It is very common in electronics to publish spec's based on different levels of operating temperture. Quote Link to comment Share on other sites More sharing options...
WMcD Posted April 15, 2007 Share Posted April 15, 2007 Steve, I'm quite sure you're correct in the basics. Others here are probably sick of hearing me explaining basic (all I can explain is the basics) amplifier theory. But you'd be surpised how difficult it is to find an explanation of the basics. Essentially, the tube or transistor acts as a valve (British term for a vacuum tube but transistors act the same way) which is controlled by voltage at the input to the amplifier. The input works the handle on the valve. The "power supply" section of the amplifier produces the electrical power which the valve sends to the speaker. Of course the power supply converts 60 Hz alternating voltage and current from the wall sockets to direct current (constant voltage) which is like what a battery creates by chemicals. So, what we are really listening to is the power supply as valved by valves in time to the music input to the amp. On the electrical side, any power supply like the one used, has a limit because of the internal resistance of the transformer windings. Same too with a battery (a battery has an internal resistance). When you apply more of a load (lower resistance down through 4 or 2 ohms) the voltage sags in the power supply. This is a way of saying the current capability is not high enough. Granted, it is possible to apply regulation to parts of the circuit. Still, there is always a limit. Otherwise we could light up New Jersey by using a very, very, very low impedance speaker. Smile. Gil Quote Link to comment Share on other sites More sharing options...
jacksonbart Posted April 15, 2007 Share Posted April 15, 2007 forget the watt ratings, just buy the one that advertises that it sounds best. Quote Link to comment Share on other sites More sharing options...
mas Posted April 15, 2007 Share Posted April 15, 2007 Gil...et. al. You may find this interesting... HowBigIsYrWallWart.pdf Quote Link to comment Share on other sites More sharing options...
pauln Posted April 16, 2007 Share Posted April 16, 2007 I might find it interesting if my viewer could decrypt it... Quote Link to comment Share on other sites More sharing options...
mas Posted April 16, 2007 Share Posted April 16, 2007 Its just a PDF. My Adobe v7 reader displays it fine after a short wait. If you continue to have problems PM me with an email address and I will send you a copy. But you will still need Adobe or an equivalent reader. Quote Link to comment Share on other sites More sharing options...
mas Posted April 16, 2007 Share Posted April 16, 2007 Quote Link to comment Share on other sites More sharing options...
mas Posted April 16, 2007 Share Posted April 16, 2007 . Quote Link to comment Share on other sites More sharing options...
DrWho Posted April 17, 2007 Share Posted April 17, 2007 Amp A doubles it's power output from 8 ohms to 4 ohms, let's say 75W to 150W. Amp B doesn't: 75W at 8 ohms, but only 125 at 4 ohms. Is it correct to say that the reason amp B can't double its power output when the impedance halves, is that it can't double its current output? Or it has a high output impedance - which would mean variations in the frequency response and all sorts of other nasties.What are the two amps that you're looking at? Quote Link to comment Share on other sites More sharing options...
sfellini Posted April 17, 2007 Author Share Posted April 17, 2007 Or it has a high output impedance - which would mean variations in the frequency response and all sorts of other nasties.What are the two amps that you're looking at? Mike, One amp is a Bedini, the other a Boulder. Both have very high damping factors. Steve. Quote Link to comment Share on other sites More sharing options...
mas Posted April 17, 2007 Share Posted April 17, 2007 Page 2 of the article (in particular) explains the 'problem'. Quote Link to comment Share on other sites More sharing options...
LarryC Posted April 17, 2007 Share Posted April 17, 2007 One amp is a Bedini, the other a Boulder. Both have very high damping factors.What models, Steve? Thanks, Larry Quote Link to comment Share on other sites More sharing options...
Spkrdctr Posted April 21, 2007 Share Posted April 21, 2007 You do not need to worry about current unless you are putting a heavy load (low impedance) speaker set on an amp. The amplifier will allow enough current to pass up until it pops a fuse.This happens (usually) during severe clipping when the speaker shorts out from a burnt voice coil. BUT, the ratings on the amp or recievers do mean that the manufacturer has determined that the power output transistors will only take so much heat before they check out. On high efficiency speakers like Klipsch, you can use small output transistors that are in your typical Sony, Pioneer etc unit. They will not however, handle a 2 ohm load without frying quite quickly. Take the transistors on a big amp like a Sunfire or Adcom etc, and the transistors are huge. They will play with low loads associated with high end speakers other than Klipsch. In other words, you get what you pay for. The big amps will put out a lot of voltage usually around 125 volts and lots of current without frying the transistors. A Sony for example will offer around 60 volts and if asked for too much current, will deliver it until the transistors fry. This can happen VERY quick if the impedance is real low around two ohms. Remember, you get volume with voltage. It is the #1 issue for playing loud which also by its nature and Ohms Law means more current too! So, you can hook up a 4 ohm speaker set to an 8 ohm amp IF, and it is a big IF, you keep the volume down which will keep current and therefor heat down too. I hope I haven't confused anyone..... Quote Link to comment Share on other sites More sharing options...
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