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"Myths"
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<blockquote data-quote="Plater" data-source="post: 63600" data-attributes="member: 541625"><p>The original speakers used for the 200W per channel amp so really 400W was 2 ohm loads not 4 ohm</p><p></p><p>So</p><p></p><p>200W=I^2*R</p><p></p><p>200/2=I^2</p><p></p><p>sqrt(100)=I which is 10amps</p><p></p><p>A 2ohm stable 2channel 400W amp 200W per channel is not uncommon</p><p></p><p>As the impedance of the speakers is dropped the less voltage gain is needed and more current gain is needed.</p><p></p><p>Watch this</p><p></p><p>200=V^2/R which is</p><p></p><p>200*2=V^2</p><p></p><p>400=V^2</p><p></p><p>SQRT(400)=V</p><p></p><p>V=20</p><p></p><p>Or</p><p></p><p>P=20*10(I*E)</p><p></p><p>P=200W</p><p></p><p>Or</p><p></p><p>P=I^2*R</p><p></p><p>P=10^2*2</p><p></p><p>P=200W</p><p></p><p>Or</p><p></p><p>P=V^2/2</p><p></p><p>P=20^2/2</p><p></p><p>P=200W</p><p></p><p>P=I*V is the main eq'n subbing in ohms law solved for I or V in terms of R gives the other equ.</p><p></p><p>All three variations of the power eq'n will work.</p><p></p><p>The fact is as the load impedance goes down the current draw goes up and the voltage needed across the load lowers to have the same power at the load.</p><p></p><p>This is why it is hard to make a power supply the will work well under different loading conditions. IE. An amp that can run loads from 1ohm to 16ohms. Because the current needs and voltage needs to get the same amount of power to the speaker differ greatly.</p><p></p><p>Anyways I would say that we are both right but we are getting caught up in the wording of things. Oh and you where right about current services to houses. But mine is 110amps used to be 50A old farmhouse the 100A and 200A service are more common but a difference of 10A come on. LOL.</p><p></p><p>One more thing most car audio amplifiers use BJT's as output devices and MOSFET's for the switching power supply part of the amp. I do know that higher power amps use MOSFET's for the outputs (because of easier paralleling positive temperature co etc.) but in general most amps are BJT's because they are cheaper and easier to get complementary pairs, when the are used in lower power apps.</p><p></p><p>When you built the amp you where talking about how did it work?</p><p></p><p>Was it a home or audio amp?</p></blockquote><p></p>
[QUOTE="Plater, post: 63600, member: 541625"] The original speakers used for the 200W per channel amp so really 400W was 2 ohm loads not 4 ohm So 200W=I^2*R 200/2=I^2 sqrt(100)=I which is 10amps A 2ohm stable 2channel 400W amp 200W per channel is not uncommon As the impedance of the speakers is dropped the less voltage gain is needed and more current gain is needed. Watch this 200=V^2/R which is 200*2=V^2 400=V^2 SQRT(400)=V V=20 Or P=20*10(I*E) P=200W Or P=I^2*R P=10^2*2 P=200W Or P=V^2/2 P=20^2/2 P=200W P=I*V is the main eq'n subbing in ohms law solved for I or V in terms of R gives the other equ. All three variations of the power eq'n will work. The fact is as the load impedance goes down the current draw goes up and the voltage needed across the load lowers to have the same power at the load. This is why it is hard to make a power supply the will work well under different loading conditions. IE. An amp that can run loads from 1ohm to 16ohms. Because the current needs and voltage needs to get the same amount of power to the speaker differ greatly. Anyways I would say that we are both right but we are getting caught up in the wording of things. Oh and you where right about current services to houses. But mine is 110amps used to be 50A old farmhouse the 100A and 200A service are more common but a difference of 10A come on. LOL. One more thing most car audio amplifiers use BJT's as output devices and MOSFET's for the switching power supply part of the amp. I do know that higher power amps use MOSFET's for the outputs (because of easier paralleling positive temperature co etc.) but in general most amps are BJT's because they are cheaper and easier to get complementary pairs, when the are used in lower power apps. When you built the amp you where talking about how did it work? Was it a home or audio amp? [/QUOTE]
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