Most power efficient poweramp

I've never used one myselft, but a friend said they were just about the best your could get. Although, I just read a review on bgra.net and it was BAD!

 

I just posted this at a different forum, so I'll pass it along.
Crown was bought out by Harmon about a year- year and a half ago. Since then the company I work for has been having huge problems with their whole product line burning up. I don't mean just stop working, I mean smoke pouring out.

Had a comtech 2000 burn up monday, took the pip module with it. Brand new amp, brand new install, everything checked out perfect. Ran two hours then burnt to a crisp. Crowns whole thing is "ultra reliable" and "indestructable". That amp shouldn't have burnt even with the outputs dead shorted.

We...have just about had it and are looking for a new supplier, which really sux because we all loved Crown.

 

I think those class H power amps are all pretty efficient. Just ask about the Stewart World series. Lotsa fans here.

 

Besides the fact that you have a contradiction there, why care about THD on a musician's amp? That about the same as care about the interior fan noise on a 400 hp hotrod.

 

Correct me if I'm wrong, but I think Joris and Bigbohn are in what we call "violent agreement".

 

I think if you cut the power on the Carvin by 5 watts, the distortion will fall far below that of the QSC. It's just how things are measured. Carvin specs their max power rating at 1%, QSC at .03% So really, this only says something about HOW the max power is measured, not about the distortion figure itself.

1% distortion on a bass amp is inaudible. 10% you may be able to hear if you're playing solo. Now 40-50% that's audible. 90% is annoyingly bad. But you would be surprised at how many people will not hear 50% distortion.

 

Yeah, Joris - Bob Lee made some very eloquent posts on this subject (wattage measurement vs. THD) several months ago. It's worth a read for anyone interested.
- Mike

 

Not everything you hear is true.

 

Bob,

Would my lead-sled MX-3000a have any power storage advantages over the PLX in a lousy voltage environment? Such as playing outdoors where everything electrical is plugged into a single power cord.

I guess I'm trying to find out if there is ANY upside to my 69 pound wonder, other than it always works, and is paid for.

 

Now that were on the subject of amp specs...

What is signal to noise ratio? My amp's specifications are "75dB typical" signal to noise ratio.

Is this good? Bad? Impressive? Average? Someone explain please.

 

Good point that numbers can't be meaningfully compared unless you know the circumstances in which they were obtained. Just for fun, here's what a Carvin person had to say about their amp ratings (his > should be <, as a look at their published specs indicates):

"The power section of the R1000 is the same as our DCM1000 power amp. All RMS - all the time. The >1% THD rating is a full power, full freq. response spec. (unlike other companies that rate at 50% power). At 50% power, our spec is > 0.03% THD. "Net lore" should be flushed with the rest of the BS."

I also checked the QSC site. They give a THD figure for the PLX series of <0.01%--BUT this is not 20 Hz-20kHz at full rated power, as Carvin's claim to be. It's (1) 1 kHz and below at full rated power and (2) 20 Hz-20 kHz at 10 dB BELOW full rated power.

So here you have two sets of THD figures that are derived by slightly different means and thus aren't directly comparable. This is NOT in the least to say that QSC or anybody else is doing anything even remotely wrong by doing this. They are very upfront about how they get their figures--that's why I could find them so easily!

The point is that you just can't compare two numbers you get without knowing how they were derived.

 

Hi Bruce,

The MX 3000a, of course, has a conventional power supply, so its maximum output voltage drops as the AC line voltage does. And the amp's maximum power is proportional to the square of its maximum output voltage.

It has a massive amount of reservoir capacitance on the power supply rails, and that's where the energy storage is. However, storage in a power amp is really for providing enough power for peaks, because the audio signal is not synchronous with the AC power. It also smoothes out the amp's current demand.

A couple things the MX 3000a really has going for it are the 3-step Class H output (more efficient than 2-step, and much more efficient than plain Class AB) and the 3-RU chassis, which allow big heat sinks and a big fan (about twice as big in cross-sectional area as a 2-RU fan) for effective cooling. If you're driving 2-ohm-per-channel loads really hard, that's a good thing to have.

The PLX amps use a switch-mode power supply that regulates the rail voltages somewhat and can partially compensate for dips in the AC voltage. However, if the AC line dips too far down (into the low 80's, for a 120V model) for more than a fraction of a second, the supply shuts down as a protective measure until the AC line gets back up to a usuable level. We can modify how quickly the low-voltage detection circuit reacts, but it's there to keep the supply from burning out trying to compensate for a hopelessly low AC line.

 

Yeah, there is no end of heat sink and fan in the MX-3000a for sure. 69 pounds worth of it. But... it works, and it's paid for.

It's good to know that this amp will drive 2.0 ohm loads well. I don't run that low, but might in the future.

 

Hi Richard,

Distortion specs should never be confused with the distortion mentioned in a power spec.

In a power spec, the distortion figure is purely an arbitrary definition of the onset of clipping on a sine wave test signal, and not a description of the amplifier's linearity.

Any amplifier will clip a signal that exceeds its maximum output voltage. Let's say you had an amp that was perfectly linear--that is, its THD would be zero--and its maximum output voltage when driving an 8-ohm load was ±50 volts peak. The amp would produce zero distortion as long as the output voltage was below 50 volts.

If you put a sine wave into the amp and had it drive an 8-ohm load, you could increase the level and watch the waveform on an oscilloscope. As the sine wave peaks reach 50 volts, they would start to flatten; this is the onset of clipping. But it's a gradual thing; you have to define your "onset of clipping" for repeatability. So maybe you'll decide to define it as the point where the THD reaches 0.1%, or 0.03%, or 0.05%, or 1%, or if you really want really unscrupulously inflated specs, 10%.

Let's assume you go with a reasonably low number. You measure the RMS voltage of the output sine wave, which would be 0.707 of its peak voltage, and you'd get a value of about 35.36 volts. You can then calculate the maximum output voltage: E^2/R = (35.36^2)/8 = 156 watts.

Obviously, the deeper into clipping you go on an amp, the higher the measured RMS voltage goes, and the higher the calculated power. But the THD starts climbing very quickly.

 

Interesting stuff, Bob. It's good to have somebody here who really has a handle on the technical side of things. I always get something to chew on out of your posts.