Members Lucius Posted December 21, 2005 Members Share Posted December 21, 2005 Anyone can explain why. Please, don't respond if you don't know what you are talking about (I already have that position ) Ie: 150watts with 4 ohms, 120watts with 8 ohms etc... Cheers Lucius Link to comment Share on other sites More sharing options...
Members tlbonehead Posted December 22, 2005 Members Share Posted December 22, 2005 Because it is resistance. Link to comment Share on other sites More sharing options...
Members DirtyChains Posted December 22, 2005 Members Share Posted December 22, 2005 The resistance comment is correct. If you are wondering why tube amps do not do the same (well as noticable) it is because of the higher current most of them supply. With tons of current on tap the amp can overcome the resistance better than a lower current SS amp. There are plenty of formulas and all that crap, but that is it in a nutshell. This is also one of the reasons tube amps must see a proper load or they will burnup. Link to comment Share on other sites More sharing options...
Members tommythelurker Posted December 22, 2005 Members Share Posted December 22, 2005 SS amps act like voltage sources. V=IR, V stays constant, R goes up -> I goes down. P=VI, V stays constant, I goes down -> P goes down. Tubes amps maintain a constant power because the transformer matches the load impedence to the output tubes impedence, so in essence the tubes always see the same load. SS amps generally don't have OT's, they are connected directly to the load so there is nothing to match the different load impedences to the transistors. Link to comment Share on other sites More sharing options...
Members DirtyChains Posted December 22, 2005 Members Share Posted December 22, 2005 ^^^^^ Up there are all those formulas I was talking about:D Link to comment Share on other sites More sharing options...
Members GCDEF Posted December 22, 2005 Members Share Posted December 22, 2005 A commonly used analogy is a water hose. Think of voltage as being water pressure, impedance being the thickness of the hose, and current as the amount of water that flows. Your amplifier will supply a voltage. Your speakers are the hose, their impedance restricts the amount of water that can flow. If you lower the impedance (make the hose bigger) you can get more water flowing from the same water pressure. Electricity works in a similar fashion. Ohm's law says that if you lower the resistance (impedance in an AC circuit) and keep the voltage current increases as there is less resistance restricting it's flow. Link to comment Share on other sites More sharing options...
Members SuperStrat Posted December 22, 2005 Members Share Posted December 22, 2005 Ohm's law. Link to comment Share on other sites More sharing options...
Members Lucius Posted December 23, 2005 Author Members Share Posted December 23, 2005 Thanks Tommy and DirtyChains for checking into the question. And thanks everyone else for the basic engineering class but there must be something else going on here. My Rh200SC puts out 100watts @ 8 ohms and 120@ 4 ohms these calculations don't add up. If it is a constant Voltage then P=EE/R. If I am sounding like a {censored} then I appoligize right now it is not my intention. Anyone care to try again. Cheers Lucius Link to comment Share on other sites More sharing options...
Members tommythelurker Posted December 23, 2005 Members Share Posted December 23, 2005 Originally posted by Lucius Thanks Tommy and DirtyChains for checking into the question. And thanks everyone else for the basic engineering class but there must be something else going on here. My Rh200SC puts out 100watts @ 8 ohms and 120@ 4 ohms these calculations don't add up. If it is a constant Voltage then P=EE/R. If I am sounding like a {censored} then I appoligize right now it is not my intention. Anyone care to try again. Cheers Lucius Ha ha, that's actually a very good question, I haven't quite figured that one out either, but I think it has to do with the fact that impedence varies with frequency and power ratings are given for a specific signal. The 4 and 8 ohms are "nominal" impedences and may not reflect the actual impedence for the signal that is used to measure the power. A lot of hocus pocus goes with published amp specs, you can't always take them at face value. Link to comment Share on other sites More sharing options...
Members ThomasD Posted December 23, 2005 Members Share Posted December 23, 2005 Tommy has given you the best answers. As he mentioned, SS amps act like voltage sources, but only remain relatively constant within specified operating parameters. In other words reducing the inductance to zero (aka shorting the speaker) will not result in infinite output. Fire maybe, but not alot of output. Not to mention all the plain BS that amp manufacturers spew. Remember power output is not volume and perceived volume is another matter entirely and is highly frequency dependent. Link to comment Share on other sites More sharing options...
Members SuperStrat Posted December 23, 2005 Members Share Posted December 23, 2005 Originally posted by Lucius Thanks Tommy and DirtyChains for checking into the question. And thanks everyone else for the basic engineering class but there must be something else going on here. My Rh200SC puts out 100watts @ 8 ohms and 120@ 4 ohms these calculations don't add up. If it is a constant Voltage then P=EE/R. If I am sounding like a {censored} then I appoligize right now it is not my intention. Anyone care to try again. Cheers Lucius I don't know the "proper" answer, but consider this.... Ohms, in terms of a speaker, is measuring impedance which is a quantity of the reactive load and not the same as resistance. The power ratings are also given at a specific frequency when we know that the frequencies being amplified are never constant.... I still believe that it's ohm's law at play, we're just trying to define the formula in static terms when, in fact, it's all about a moving target. Link to comment Share on other sites More sharing options...
Members GCDEF Posted December 23, 2005 Members Share Posted December 23, 2005 Originally posted by Lucius Thanks Tommy and DirtyChains for checking into the question. And thanks everyone else for the basic engineering class but there must be something else going on here. My Rh200SC puts out 100watts @ 8 ohms and 120@ 4 ohms these calculations don't add up. If it is a constant Voltage then P=EE/R. If I am sounding like a {censored} then I appoligize right now it is not my intention. Anyone care to try again. Cheers Lucius Ohm's law holds in a perfect world. However, an amplifier's ability to deliver current is limited. At some point it's components are going to limit the amount of current it can produce. Better amps will come closer to following Ohm's law. Others will generally produce more current into lower impedances, but will likely not follow Ohm's law precisely. Link to comment Share on other sites More sharing options...
Members Lucius Posted December 23, 2005 Author Members Share Posted December 23, 2005 Awesome, thanks alot guys. You helped a poor schmuck like me understand SS output section. Cheers and Happy hollidays to all. Cheers Lucius Link to comment Share on other sites More sharing options...
Members GuitArtMan Posted December 23, 2005 Members Share Posted December 23, 2005 Originally posted by DirtyChains The resistance comment is correct. If you are wondering why tube amps do not do the same (well as noticable) it is because of the higher current most of them supply. With tons of current on tap the amp can overcome the resistance better than a lower current SS amp. There are plenty of formulas and all that crap, but that is it in a nutshell. This is also one of the reasons tube amps must see a proper load or they will burnup. Actually you have this bass ackwards. Ohms law states that I (current) = E(voltage) / R (resistance). If you lower the resistance, the current goes up. Current = heat, this is what burns things up. This is how toasters work - lots of current = lots of heat, or electric blankets. Many top end PA amps (solid state) will have power rating something like this:800 watts into 2 ohms400 watts into 4 ohms200 watts into 8 ohmsThe reason they can drive 800 watts into 2 ohms is that they can supply the current necessary to generate that kind of power without burning up. Link to comment Share on other sites More sharing options...
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