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a different question on power amps...


Scoot

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...well, at least I haven't found any info on this.

 

I've read threads about trying different combinations of power and pre-amps to get a different sound which makes me wonder: "why would power amp A sound better than power amp B even though the wattage and the pre-amp are the same?"

 

How much can one 1000W power amp differ from another 1000W power amp as far as sound quality? And why would it?

Ah, nice marmot.
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Same reason one preamp sounds different from another.

 

I have no greenboy-skillz in this area, but different amplification circuts and power transformers do sound different.

 

The difference is slight, though. You mainly want to make sure that the amp is coloring YOUR sound (ie: your hands) the way you want it to.

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I can't speak about the why's in detail, but they do/will sound different. Quality of components and overall signal to noise ratio has a lot to do with it. Generally speaking, the more expensive it is, the better it's going to sound... but not always. It's best to listen to as many different combinations as you can.

 

OK, I'm worthless, please move along. :D

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for example...

 

a crest CA-12 is rated for 1400W/channel into 2 ohms when driven in stereo. that's 2800W total. factor in efficiency of both the amplifier circuits and power supply, and you're looking at the potential for about 3600W of power draw. if you want to actually put that kind of power out for any appreciable amount of time (i.e. longer than a few milliseconds), you'd need 30A from a 120V socket, which just doesn't happen.

 

the crest designers knew this, so the CA-12 has a 125V/30A plug, which is severely more stout than a 120V/15A IEC plug like almost everything we see has. that is just enough, and it will actually put 1400W into a 2 ohm load for a long time.

 

by comparison, a QSC PLX-2402 is rated for 1200W/channel into 2 ohms when driven in stereo. ignoring that the QSC THD for this rating is 1% compared to crest's .03%, that's 2400W total. with a generously efficient power supply and amplifier circuitry, we might say it takes 2800W total to actually create 2400W for the load, which would draw over 23A from 120V. that also won't happen, but you'll notice the 2402 still has a 120V/15A IEC cord, anyway, limiting its total power consumption to 1800W continuous. (and good luck not tripping breakers trying to draw that current....)

 

does this make QSC liars? no. their amp can create 2400W, but for only a short duration before its power supply can no longer supply sufficient charge to do so.

 

so even though 2400W and 2800W aren't incredibly far off from each other in number, the execution of them is decidedly different.

 

that's just for pure power differences, though. as far as sound quality differences, think in terms of cars. how many 150hp cars are there in the world among honda, mazda, toyota, chevy, ford, audi, acura, mitsubishi, etc. how many of them are V6? how many turbo 4 cylinders? how is the gas mileage?

 

every transistor is different, and there are literally thousands of different models of transistor. there is also no standard way to create power, so any decisions as to how the power is created can affect sound quality. i've demonstrated the difference a power supply can make in an amp, so let's think of all the different ways we can make a different power supply, and all the different components we can use. also, how do we put them all together to minimize noise and maximize heat dissipation inside the box.

 

there is a lot to designing and building an amplifier, and a lot of ways to get lucky or go wrong.

 

what was the question? how can two 1000W amplifiers differ? how can two 6'0" 180lb. men differ in appearance?

 

robb.

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Damn Robb., I feel so childish after reading that way-over-my-head technical speak. But thanks, the part about "there is also no standard way to create power" summed it up for me actually.

 

And thanks for the other thread, gave some good info. I have a Crown MT1200 on the way (to go w/ the Ashdown RPM1 pre), and by what I've read about Crown's I've picked a pretty good one I hope. No mention of the MT's though, just the MA's. Any opinions on the Microtech's?

 

thanks again,

 

s.d.

Ah, nice marmot.
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Originally posted by music-man:

Scoot -

 

I'll be interested to hear YOUR opinions on the MT.

I'm sure I'll be back sometime next week w/ a nice grin on my face telling you all about it. ;)
Ah, nice marmot.
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Originally posted by Scootdog:

Damn Robb., I feel so childish after reading that way-over-my-head technical speak.

oh. i'm terribly sorry.

 

i get wrapped up in reasoning through things, and i often forget that not everyone is an engineer like i am.

 

my intent is always to make things understandable to everyone. i guess in this case i fell far short of that.

 

i'm really sorry. i hope i didn't come off as trying to impress with my knowledge, or appear condescending in any way.

 

let me know if you need a more plain english explanation of the technical details. i think the ideas are important, or at least helpful; i've already re-read the post and thought of different ways to say it.

 

robb.

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Originally posted by robb.:

Originally posted by Scootdog:

Damn Robb., I feel so childish after reading that way-over-my-head technical speak.

oh. i'm terribly sorry.

 

i get wrapped up in reasoning through things, and i often forget that not everyone is an engineer like i am.

 

my intent is always to make things understandable to everyone. i guess in this case i fell far short of that.

 

i'm really sorry. i hope i didn't come off as trying to impress with my knowledge, or appear condescending in any way.

 

let me know if you need a more plain english explanation of the technical details. i think the ideas are important, or at least helpful; i've already re-read the post and thought of different ways to say it.

 

robb.

lol. Don't apologize robb. You actually explained it probably as good as it can be explained. It actually made more sense than I probably let on. Besides, it doesn't take much technical talk to get over my head, I'm only just now understanding the concept of ohms. :rolleyes:

 

Actually, your response was the type of answer that I was expecting to the "how" part of my question. And your comment about "different ways to make power" made perfect sense.

 

thanks (really!),

s.d.

 

I just re-read your first post (makes even more sense today) and have a question: what does the "...THD for this rating is 1% compared to crest's .03%" part mean? I'm guessing this has to do w/ the part in my MT1200 manual near the power ratings that says "1 kHz Power: refers to maximum average power in watts at 1 kHz with 0.1% THD."?? What is THD?

Ah, nice marmot.
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THD = Total Harmonic Distortion

 

The lower the % at which the power is quoted, the more accurate the power rating.

 

Here's a quote from stereophile magazine which may help: It's a common mistake to consider a single THD figure an indicator of distortion audibility. The THD+N figures in the previous graph sum all harmonics and noise for a single figure and ignore which harmonics are present and in what ratios. As you can demonstrate for yourself with the second Stereophile Test CD, 0.3% of seventh-harmonic distortion is more annoying than 10% of second-harmonic distortion. Generally, lower-order harmonics are less audible, as are even-order harmonics (second, fourth, sixth). The most benign harmonic distortion is thus second-harmonic.

 

So, THD is just a useful indicator as to the cleanliness of any given power amp.

 

Alex

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:idea: Very cool. Thanks.

 

So, to put all this into practice for me...if my power amp is rated at 970W (bridged-mono @ 8 ohms), and below the ratings it says:

 

"1 kHz Power: refers to maximum average power in watts at 1 kHz with 0.1% THD",

 

then in layman's terms (my language) it means something like: "The amp can push a 1kHz signal with up to 970W w/ less than 0.1% THD."? Or in other words, "Loud and clean."

 

coming soon...damping questions...

 

thanks again

sd-apprentice gearhead

Ah, nice marmot.
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yup.

 

.1% is pretty decent. some manufacturers go down to .03% or even .01%. although bridged-mono tends to distort more than dual-channel. check the single-channel specs of your MT and realize that, though less powerful alone, they are much cleaner.

 

to use my example above, the QSC PLX at 1%THD produces 33 times the distortion that

the crest CA-12 does (.03%). that is how 1000W can be different.

 

robb.

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