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Power Amps Spec Guide


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What specs should we pay more attention to when buying a power amp (damping factor comes to mind)? Are there certain values we should look out for and what sounds should we expect based on them.


Yes, I know, I know, listen to them, see which one "feels" right. I guess I'm trying to establish a relation between qualitative and quantitative data, so prediction will be easier. Knowledge is power. :idea:


I've already done some research on the web, but I'm interested in feedback from Bassplayers that will hopefully produce a useful thread for future reference in the tradition of the Green One and Robb.


Not that I know 1/100th of what they do.

Does it hurt?


Only when I'm awake.

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Back in the 80's is when I went to engineering school so I'm pretty dated, but in labs and projects where we built amplifiers the overriding concern was slew rate. What comes out of the amp should be exactly what went in, except with greater amplitude. small changes in input voltage result in big changes in output voltage; the output wave should be an exact copy but larger in the same amount of time and theres the rub. If I remember right the Slew Rate is measured in volts/microsecond, so while the input signal may swing a few millivolts going in, to be accurate the output may need to swing say 50 volts in the same small amount of time. How well the amp can "follow" the input signal determines how loud you can get without distorting. Were his greeness here you would get a much better explanation, hope this helps.
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When I took my Acoustics class in music school, I seem to remember the prof saying the slew rate lets you know how rapidly an amplifier can respond to changes in voltage...i.e. notes. Slower slew rates mean that you can put signal in more quickly than the amp could adjust to. But I dunno.


I do also remember these things, but in name only:


Watts measured in RMS, to compare apples to apples. Peak output means little.


Total Harmonic Distortion...the lower the better.


Signal to Noise ratio...the higher the better.


Like most everybody else, I plug in and play!

"Let's raise the level of this conversation" -- Jeremy Cohen, in the Picasso Thread.


Still spendin' that political capital far faster than I can earn it...stretched way out on a limb here and looking for a better interest rate.

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Slew rate..hmmm. Didn't know what it was. Not often listed though. Can it be determined from other specs? Is it implied by other specs? I checked and Crest, Crown, QSC and Samson (to name a few) don't list it. Hafler and Stewart do, explicitly anyway.


The Hafler P7000 and the Stewart World 1.6 have slew rates of 100V/micro sec. and 30V/micro sec. respectively. I guess this means the Hafler responds better, right? I guess the issue is how much better and how big a difference will it make in a bass rig?


Usually unlisted specs are crappy specs. Does this mean the brands I mentioned above have poor slew rates (response?)?


Another thing I found intriguing was the non-uniform listing of damping factor specs. For example:


Crest V/Vs 650 -(10Hz-400Hz @ 8 Ohms) 800:1

Stewart World 1.6 - >500

Hafler P7000 - 600 (to 1kHz)

200 (to 10kHz)

25 (to 100kHz)


This looks like apples, bananas and tomatoes to me.


I'd intuitively guess that the Crest has the tightest bass. If so, how come their more expensive models don't have such high DF at similar of even higher RMS power ratings. In fact that's the highest DF I've seen so far for similarly rated power amps.

Does it hurt?


Only when I'm awake.

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