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1 ohm amplifier


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aznboi3644 
Gold - Posts: 2,600
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Joined: May 01, 2006
Location: United States
Posted: July 06, 2006 at 9:17 PM / IP Logged  
Raven, what did they use to run subs BEFORE class d technology came out?? Class AB amps. And yes I know you were just generalizing.
Ravendarat 
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Joined: February 23, 2004
Location: Canada
Posted: July 06, 2006 at 9:21 PM / IP Logged  
Class AB amps were the norm for along time. I still use class AB for my subs in my current set up
double-secret reverse-osmosis speaker-cone-induced high-level interference distortion, Its a killer
bazzgazm 
Copper - Posts: 113
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Joined: June 06, 2004
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Posted: July 06, 2006 at 9:57 PM / IP Logged  
ohms law
CURRENT = square root of power/resistance.
bend that!
haemphyst 
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Joined: January 19, 2003
Location: Michigan, Bouvet Island
Posted: July 06, 2006 at 10:27 PM / IP Logged  
bazzgazm wrote:
ohms law
CURRENT = square root of power/resistance.
bend that!
What the hell does that mean? And I am asking because there is much hostility in that, and it's aimed directly at me...
If you look at what you just wrote, it is a mathematical formula. Can you bend mathematical formulae? No, that's why the USE them... there is no "ummmmm... maybe I can do this with it... fudge a little here, and it'll still come up with the right answer" so you just stuck your own foot in your own mouth.
Now, if you'd like to defend your statement, I'll listen to whatever you have to say.
It all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice. You should write it down."
Ravendarat 
Platinum - Posts: 2,806
Platinum spacespace
Joined: February 23, 2004
Location: Canada
Posted: July 06, 2006 at 10:32 PM / IP Logged  
I didnt get that either so I just left it alone man
double-secret reverse-osmosis speaker-cone-induced high-level interference distortion, Its a killer
bazzgazm 
Copper - Posts: 113
Copper spacespace
Joined: June 06, 2004
Location: United States
Posted: July 07, 2006 at 9:37 AM / IP Logged  
If your mathematical formula is
current = square root(power/resistance)
then when resistance is cut in half, current is doubled.
hence the idea of the high current amplifier
now, if you read most test reports from independant companies on class a/b amplifiers, many reliable, decent amps are now 55-60% Efficient @ their 4ohm mono load
now when your class d's (90% in real life.. @ 1/3 power maybe) then you will see more likely 70-75%
now calculate your 4ohm load vs. your 1ohm load.
haemphyst 
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Joined: January 19, 2003
Location: Michigan, Bouvet Island
Posted: July 07, 2006 at 11:09 AM / IP Logged  
THAT'S your defense?
OK... Let's do that, shall we?
I dont care about the load... 1000 watts out is 1000 watts out. We agree on that, right? 1000 watts into 4 ohms just requires a higher output voltage to achieve than it would at one ohm. Anybody on this board should know that. (NO offense intended to those of you who don't, or possibly don't understand)
What I am referrring to is EFFICIENCY. How effectively does the amplifier, and all of it's associated circuitry (including power supply DC-DC conversion, and output stages), transfer 1000 watts of energy to the load. How much heat is wasted?
A Class D amplifier, and I'll use your worst case number of 70%, OK? (This'll be like running it at a 1 ohm load...)
1000/.70=1428.6 watts INPUT
1428.6/14.4=98.75 AMPS IN
428.6 watts blown off in the heatsink as wasted heat.
Now, your Class A/B, and I'll give you the benefit of the doubt again, and use your BEST case scenario of 60%... (This'll be like running it at a 4 ohm load)
1000/.60=1666.7 watts INPUT
1666.7/14.4=115.74 AMPS IN
666.7 watts blown off in the heatsink as wasted heat... 55% MORE wasted energy in a Class A/B amplifier, and that is comparing a WORST case Class D to a BEST case Class A/B.
I will also give you the benefit of the doubt that both amplifiers are loaded optimally... I don't care, again, about the speaker impedance... The lower the impedance, the less efficient any amplifier will run. Those numbers above will not likely change much, relative to each other, and the input currents will only get higher, as the efficiency decreases across the board... Also, as every amplifier will have component tolerance variations, these are not necessarily EXACT numbers, but again, all the formulae above are sound, well known, and proven. Was I able to bend any laws? Didn't think so...
:::::EDIT:::::
I forgot I wanted to add this example, earlier...
Now, going back to my earlier statements of previous posts, IF you have a Class A/B amplifier with, say 100A worth of fusing, (to go with the above example of the Class D amplifier, at 98.75A input) how much output power can it REALLY make, on a continuous basis? Let's do the math, shall we?
14.4*100=1440 watts IN
1440 watts in, * 60% efficiency = 864 watts out.
Now, is that a 1000 watt amplifier? Short and simple answer? No. So, to reiterate, the Class A/B amplifer, CALLED a 1000 watt amplifier is simply over-rated, isn't it? It's NOT a 1000 watt amplifer.
Please read my posts, regarding choosing an amplifier, if you have any further questions regarding this...
It all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice. You should write it down."
bazzgazm 
Copper - Posts: 113
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Joined: June 06, 2004
Location: United States
Posted: July 07, 2006 at 10:43 PM / IP Logged  
if the resistive load on an amplifier has nothing to do with current draw then i should just quit installing.
I wonder why it is when you try to run a 4ohm stable amp @ 1ohm mono that the amp overheats and the fuses blow?
if the same 40 amps is being drawn through the power wire from the alternator to create the 40x13=520*.6=312watts at 1ohm, as the same as 4ohm.. then? I'm really lost? please explain this theory you corrected me with.
when resistance is cut in half, current consumption doubles.
that's simple
haemphyst 
Platinum - Posts: 5,054
Platinum spaceThis member has been recognized as an authority in Electrical Theory. Click here for more info.spaceThis member has been recognized as an authority in Mobile Audio and Video. Click here for more info.spacespace
Joined: January 19, 2003
Location: Michigan, Bouvet Island
Posted: July 07, 2006 at 11:24 PM / IP Logged  
bazzgazm wrote:
I wonder why it is when you try to run a 4ohm stable amp @ 1ohm mono that the amp overheats and the fuses blow?
if the same 40 amps is being drawn through the power wire from the alternator to create the 40x13=520*.6=312watts at 1ohm, as the same as 4ohm.. then? I'm really lost? please explain this theory you corrected me with.
If you have, for your example, an amplifier that is one ohm stable, and it can produce 312 watts into that one ohm load, into 4 ohms, it will only produce (around) 78 watts, NOT 312 watts. It's NOT the same 40 amps into a 4 ohm load... It's more like 10 amps.
Input current consumption doubles, because you are trying to produce MORE OUTPUT POWER. When you halve the load, yes, you WILL pull more power on the input side, but that is because you are not ONLY making X watts anymore, your are making (or trying to make) X*2 watts...
WHEN two different amplifiers are producing IDENTICAL OUTPUT POWERS, in my example above, 1000 watts, the LOAD MEANS NOTHING... it is inconsequential. The output power is 1000 watts, whether it is into 4 ohms or a dead short... 1000 watts is 1000 watts, and 1000 watts out, in the case of Class D requires 1400 watts in, and in the case of Class A/B, requires 1700 watts in - WHATEVER THE LOAD. The efficiency of the amplifier is still maintained based on its topology, and Class A/B will ALWAYS be less efficient than a Class D.
In ANY ONE GIVEN amplifier, in order to produce 1000 watts, an amplifier must make X voltage at Y current. The power supply does this on the power supply rails. If you halve the load, ON THAT SAME AMPLIFIER, now the power supply must try to make Y*2 current, to maintain X voltage. It can't do this without demanding more INPUT power from the battery. Because the voltage from the battery does not change, it must demand more CURRENT... Twice as much, to be exact. That is why the fuses blow... Because you are trying to make more power than the input fuses, provided by the manufacturer to keep the amplifier operating in a safe range, will allow. IF you were to increase the current capacity of the input fuses (don't do it, but IF) the power supply will continue to try to make the necessary power, until A: the protection circuitry stops it from running away, or 2: the amp overheats to an untimely DEATH... i.e. ya let the smoke out.
It all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice. You should write it down."
12vdeej 
Member - Posts: 26
Member spacespace
Joined: July 04, 2006
Location: United Kingdom
Posted: July 08, 2006 at 10:54 AM / IP Logged  
While trying to avoid what may sound like some serious ass kissing, I would like to second everything that haemphyst has said so far in this thread, this dude knows his stuff. From everything I have learned as an electrical & electronic engineering student, I would say that it is entirely correct and the arguements that some people are making are not based on the solid, basic physics and maths arguements such as those above, and can definately learn something from them.
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