Geeks/Experts teach me some physics, please

[Cam 10+ year member]

Ok, I have an assload of questions, but I'll try to be succinct and hopefully get the info I want.

1) Wattage... how exactly is an amplifier rated/measured? does one simply give it a non clipped signal, with a passive load and measure the line voltage*amperage in the output leads? I ask because a 1ohm speaker may be 1ohm nominal, but the impedence changes depending on what you're doing to the sub... just wondering if any of that is taken into account, or if it's just a big ol' resistor, or some kind of rectifier circuit.

2) How exactly does an amp put out it's power?? I mean, I'm familliar with power electronics and MOSfets, and usually in my experience a mosfet is just a switch, where you can vary the duty cycle to obtain an output that is effectively a certain percentage of the input voltage. So, even at 100%duty cycle, and 100% efficiency, the mosfet puts out 12v, at 1ohm, P=VI, I=V/R=12A, so you get 144W. What am I missing? do big amps step up the voltage internally? Does a bigass amp throw down 30-50 volts to put out that 1000-2000W into 1ohm? Can I zap the f*** out of my buddy with a 2500W amp, cuz it throws down 50 VAC?

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[mtdewelf 10+ year member]

Ok, I have an assload of questions, but I'll try to be succinct and hopefully get the info I want.
1) Wattage... how exactly is an amplifier rated/measured? does one simply give it a non clipped signal, with a passive load and measure the line voltage*amperage in the output leads? I ask because a 1ohm speaker may be 1ohm nominal, but the impedence changes depending on what you're doing to the sub... just wondering if any of that is taken into account, or if it's just a big ol' resistor, or some kind of rectifier circuit.

that is imp rise, and you loose power as your impedence rises. so yeah if you have a dual 2ohm sub wired at 1 ohm and your amp is rated 1000@1ohm then after rise you are getting less power.

 

[supraman1379 10+ year member]

that is imp rise, and you loose power as your impedence rises. so yeah if you have a dual 2ohm sub wired at 1 ohm and your amp is rated 1000@1ohm then after rise you are getting less power.

And if it is not 1 ohm stable, It would put out its max power at 2ohms.

 

[Buckshot 10+ year member]

And if it is not 1 ohm stable, It would put out its max power at 2ohms.

This is not necesarilly true. I may still put out more power at 1 ohm, its just a matter of how long it will do this for...

 

[nauc 10+ year member]

if you need a 100 watts rms for your sub, just get an amp that puts out 100 watts rms while matching the impedance

use #3 to set your gain http://www.resnet.trinity.edu/areynol1/gain.htm

unless you have a scope

realm has tones in the download section http://www.realmofexcursion.com/main.html

 

[Cam 10+ year member]

Nauc, thanks for the input, but I think you're missing the gist of my question. I have a pretty good idea how to set the stuff up, I'm just trying to understand in more detail the how and why of Amps.

Anyone got an answer for the voltage question? I'm thinking it *has* to be a step up transformer circuit in the amp.

 

[FoxPro5 5,000+ posts]

Any and all questions should be addressed here

 

[Cam 10+ year member]

Wicked, exactly what I wanted. Thanks!

 

[thch 10+ year member]

Ok, I have an assload of questions, but I'll try to be succinct and hopefully get the info I want.
1) Wattage... how exactly is an amplifier rated/measured? does one simply give it a non clipped signal, with a passive load and measure the line voltage*amperage in the output leads? I ask because a 1ohm speaker may be 1ohm nominal, but the impedence changes depending on what you're doing to the sub... just wondering if any of that is taken into account, or if it's just a big ol' resistor, or some kind of rectifier circuit.

the test IIRC, is based upon a resistive load and measured with a 1khz sine wave (if possible) after the amp has been running for a long period of time. for this measurement, only a voltage measurement is needed (if the resistance is known).

2) How exactly does an amp put out it's power?? I mean, I'm familliar with power electronics and MOSfets, and usually in my experience a mosfet is just a switch, where you can vary the duty cycle to obtain an output that is effectively a certain percentage of the input voltage. So, even at 100%duty cycle, and 100% efficiency, the mosfet puts out 12v, at 1ohm, P=VI, I=V/R=12A, so you get 144W. What am I missing? do big amps step up the voltage internally? Does a bigass amp throw down 30-50 volts to put out that 1000-2000W into 1ohm? Can I zap the f*** out of my buddy with a 2500W amp, cuz it throws down 50 VAC?

Mosfets typically are just switches. i have a very good deal of experience in this area. Mosfets typically only are used in car audio amps for the DC-DC conversion. for analog use, Mosfets have a lower transconductance, higher capacitance, larger threshold, and worse noise specs then "bipolar junction transistors". More importantly, the P-Channel FET is lacking. in CMOS, people often try to go for ANT or "all N-Channel Transistors".

Let me explain a simple DC-DC converter. the obvious example is the "Buck Topology". in this topology, the device switches on and off. the output is based upon the time on vs the total time per period. i think you explain some of this in the post.

now lets put a transformer in there. now the output voltage is based upon the input voltage multiplied by the turn ratio of the transformer, and the time on vs total period. This isn't the only way to do things. and there are some intricacies involved.

amps are typically devided into 3 parts. the power supply, the actual amplifier, and the signal processing.

edit--

and if you're wondering why you even need the mosfet vs just the transformer. well, sorry. to work at DC, the transformer would need infinate inductance, and would need to be insaturable. one issue in magnetics is that the iron (or ferrite) can only support some maximum feild strength. if the feild would be required to be higher, the device stops acting like an inductor/transformer, and acts as a short. in a switching supply with a transformer, some method is used to reset the core. an example is a push-pull or a bridge design. in this design current is run through the primary until the core gets near saturation. then the connections are switched and current is run the other way through the primary, which reverses the feild, eventually it gets near saturation and the connections are flipped again. there were actually mechanical versions of this "DC transformer" back in the early part of the 20th century.

 

[Lakota 5,000+ posts]

if you need a 100 watts rms for your sub, just get an amp that puts out 100 watts rms while matching the impedance
use #3 to set your gain http://www.resnet.trinity.edu/areynol1/gain.htm

unless you have a scope

realm has tones in the download section http://www.realmofexcursion.com/main.html

IMO it's better to have a bigger amp than what the speakers are rated for.

 

[Cam 10+ year member]

Lakota, I've heard that before, but no-one ever explained to me why, or how MUCH bigger is a good idea. I'm considering a pair of IDQ12's, (350wrms) and the price difference between a 1000wrms amp and a 1600wrms amp is making me itch for the bigger one, but I'm not sure it's a good idea. Can you give me more insight?