Are Class D amps really 5 times less powerful than A/B?

[Boneless]

Yes I think these things can be measured, but I am not completely versed on all of the relevant factors...although I think I probably have a better understanding than some.

From what I have seen, the biggest complaint about class D seems to be in the delivery of lows. They get plenty loud, but many of them lack the quality some of us call heft and slam. IMHO part of what gives us a sense of heft and slam is a certain frequency response profile. But there are other factors as well. I don't think it's necessarily about getting enough of certain factors. Rather there needs to be a balance, not too little and not too much. Also I think there is some interaction between factors that can confound our perceptions. If one factor is present in a certain amount, you may need to vary another factor too taste.

Between the three class D amps in my collection, I would say the Jule Monique 700 has the most heft and slam, but also the least headroom. The lowest headroom is not totally unexpected since it has the lowest power rating of the class-D amps in my collection.

A lot of people describe Monique 700 as compressed or squishy, but I believe that has a lot to do with the Monique preamp. I have not tried running another preamp into the M700 output module. Also I have not done any sort of measurements to document the power level where the M700 hits the wall. I don't know how much continuous power it can make, and I don't know how much burst power it can make.

I have not really done any sort of AB comparisons between the Monique 700 and any of my other amps. I only noted how good it sounds and that it seems to hit the limit of it's power before I start worrying about the health of my cabs. I have not really explored the power limits of several amps in my collection. When they reach a certain SPL, I don't really see any point in turning up further. I do like big power though.

While the Monique 700 is capable of playing significantly louder than I generally require, some of my more powerful amps can easily play loud enough where I start worrying about destroying drivers in my cabs. Although it does not have the highest power rating, my Genz Benz GBE1200 seems the stoutest amp in my collection.

I am not familiar with any of these amps, but bear in mind that many of the amps basically package an Icepower power amp, complete with power supply.

 

[red_rhino]

How come a lemon gets soft and juicy as it ages and a lime gets hard and dry and physically smaller as it ages? Shouldn't they age the same since they are both sour citrus tree fruits? Asking for a friend.

I wouldn't know. All the limes I buy don't seem to hang around long enough to age more than a day or so before I put them to good use.

However, I can state categorically that lemons have more heft than limes.

 

[Michael Favata]

Ok, that might be true but can you name any Class D bass amps with analog power sections? I can't think of a single one. Most every Class D is digital.

Gallien-Krueger Fusion 112 1x12" 400-watt Bass Combo Amp

this has tubes and class D. Hence "Fusion".
Is that what you mean?

 

[agedhorse]

So, basically and in very simple terms. Class D amps are, by virtue of the way they work, very efficient but this comes at the cost of little to no headroom once they start being pushed. In other words, they tend to have abrupt clipping behaviour. You get a 700W Class D amp, and it *will* give you 700 "clean" watts. Usually they are 700W @ 1% THD (essentially clean for bass or even electric guitar purposes; 3% starts maybe getting noticeable on bass as some sort of mild thickening, you generally need to go beyond 5-6% to actually hear some clear distortion), beyond this power figure distortion increases comparatively rapidly. AFAIK, Class D amps tend to also be aggressively limited for this reason too. Class AB amps (both tube and solid-state) may have better clipping behaviour, but this still depends on the design, the use of negative feedback (and how much of it), if there is a limiter and whether it is defeatable, whether it is actually desirable to do so, and it also depends on how aggressive the protection is on the power devices, on the dimensioning of the power supply, on the voltage amplifier stage possibly. Sometimes there is soft clipping built into the power amplifier (and that may also be true of Class D amps), something that essentially lowers the available clean power but sounds nicer. Too many variables. That said, those 700W that many of those Class D amps the size of a textbook can deliver aren't a scam, they are actual measurements. What may mislead is that many of these amps tend to lean towards the "hifi" side of things, therefore they reserve those 700W to allowing clean transients to be reproduced quite faithfully. And that doesn't sound loud. If you feel your big-watt head sounds a bit weak, try buying a compressor first (one that you can set with lowish attack times preferably, lower yet if it's a feedback topology) and see if that helps.

Except that the headroom is in large part defined by the compliance of the power supply. We used to have to over-specify the power supply in order to achieve the steady state power rating because as the output power increased, the supply sagged and the power decreased. It was a stumbling block, and though several manufacturers tried to use linear regulated power supplies (ferro-resonant) to get around this, it didn't work all that well. With SMPS, this is not the case, we can regulate the voltage so that it doesn't sag under load and in this case the lack of sag is in fact added headroom. Some class d (and class AB) amps use regulated SMPS, some use unregulated, it's simply the choice of the designer.

One HUGE advantage of a regulated supply is that under low or sagging line voltage, the SMPS will automatically self correct. In the good 'ol days of unregulated supplies, an amp under load driven from an "average" power source might actually deliver 20% UNDER rated power, whereas a regulated supply will maintain the ratings.

Solid state to me means hi-fi. Sterile if you wish. Depending on EQ more volume gives a buzz saw effect. Call it an irrational perception. But it's there.

I would call it a massive generalization, though there are exceptions... just like there are sterile tube amps as well.

The entire Walter Woods MI series of amplifiers (MI-100-8, MI-400-8, and MI-600-8) were analog power amplifiers with a SMPS. (Switch mode power supply) So did several others from that period. It's my understanding that Class D power amps mostly have SMPS power supply's. Just my take and I could be incorrect.

They started off using (line frequency) linear supplies, but there was so much advantage to using SMPS that once the technology matured, it was a no brainer for most power supplies to transition (provided cost was not the major concern).

Thanks. So a 160 watt bass amp with an A/B power section is not equal to an 800 watt bass amp with a Class D power section? Thats what Boss is claiming in that interview.

Not in my world.

While that is true about perceptions, I mean master. With gain set just under clipping.

If you haven't done so before, turn the master knob on your class D amp all the way up, and use your gain knob for volume. It's different. Back it up to half, and set your gain correctly. Then, turn up your master by "hour increments" while you play for a bit. It gets different.

Not my observations, over many different amps and in many highly controlled listening sessions, including double-blind. It's quite possible that you are experiencing confirmation bias, where you are simply set up to confirm what you already believe is true. Debunking a massive confirmation bias marketing firm back when I was designing high end Hi-Fi (cork sniffer stuff), that's how I was fired from my first design job (though technically I had already resigned). I rigged the tests so folks THOUGHT they knew what they were listening to yet intentionally reversed the selections without their knowledge. Good learning experience in marketing gullibility.

I am not familiar with any of these amps, but bear in mind that many of the amps basically package an Icepower power amp, complete with power supply.

Sure, and they all sound, play and feel differently in spite of using the same power module. It shows how important everything else in the design is.

 

[Razman]

Yes. I have a rule of thumb, that if it's real, then it can be measured. Contemporary measurement equipment is more sensitive than human hearing. If it were me, I'd set up the two amps to reproduce what I'm experiencing, and then measure the input and output signals. Then analyze away. The only limitation for me is that I'm not equipped to deal with the big signals produced by amps, and my test gear is homemade, which means any conclusion I draw would always call into question whether my measurement technique was any good.

By day, I mess around with analog measurement systems, but not for audio.

Understood, and thanks for the reply Fdeck. For now I'm left with the "seat of my pants" measurement system. I'm okay with that, but it would be nice to have some numbers that explain what I experience so that I can tell if an amp I can't test in person would suit me or not.

 

[HelpImaRock]

Then what is a lymon?

Bad 80s marketing. Which is redundant.

 

[byacey]

Class D is NOT digital. It means it uses Transistors instead of the older component type of Tubes/Valves. Transistors are PRE digital tech, common post WW2 electronics. Integrated Circuits (which is where things get "digital") are a later tech way of miniturizing and replacing many networked transistors (and the massive heat problems they would cause).

Transistors have nothing to do with it. A class D amplifier can be made using tubes as the series pass element, although any power saving benefit of class D go out the window.
Edit: I see Andy beat me to the draw again!

 

[Leigh Semmens]

As has been commented ad nauseum a Watt is not a measure of sound pressure. My 100watt driving lights do not out perform my 1 watt transistor radio in the sound stakes, as far as lighting up the road, however. Read the Wiki link a=back on page 1 of this thread.

 

[/\/\3phist0]

Ok, that might be true but can you name any Class D bass amps with analog power sections? I can't think of a single one. Most every Class D is digital.

Incorrect.
Class-D amplifier
A class-D amplifier or switching amplifier is an electronic amplifier in which the amplifying devices operate as electronic switches, and not as linear gain devices as in other amplifiers. They operate by rapidly switching back and forth between the supply rails, being fed by a modulator using pulse width, pulse density, or related techniques to encode the audio input into a pulse train. The audio escapes through a simple low-pass filter into the loudspeaker. The high-frequency pulses are blocked. Since the pairs of output transistors are never conducting at the same time, there is no other path for current flow apart from the low-pass filter/loudspeaker. For this reason, efficiency can exceed 90%.

 

[JimmyM]

This thread is a laff riot! We've been exposed to these types of amps for decades now and still the myths persist.

 

[bucephylus]

For those promoting a view that Class D power sections are digital, and who do not want to read the Wikipedia article on Page 1, I will offer this more mundane evidence that these power sections are analog, not digital.

First Digital means that there are two states - on and off. The power section drives the drivers. A digital output would cause the drivers to either be at rest (0) or energized (1).

But, what we see and hear is that the drivers are driven with ANALOG mechanical motion. Here is what I mean:

Some time back, I made some measurements of stage coupling using various damping methods. My measurements used an analog signal generator set at 200 Hz driving an analog signal into a Class D amplifier connected to a JBL 15" driver in a cab placed on a 5/8" plywood stage plate. A vibration sensor was placed on the stage plate.

Here is the image of the oscilloscope trace of the input analog waveform superposed against the vibration of the stage plate.

What you see is that both signal AND cabinet output are ANALOG. So, if one chooses to believe that the Class D output is digital, then one also has to believe that some kind of magic happens between the power section and the driver.

I don't happen to believe in magic.

The Class D output is Analog. Therefore, the Class D power section is analog. QED.

 

[fdeck]

This thread is a laff riot! We've been exposed to these types of amps for decades now and still the myths persist.

One of my bosses used to say that repetition was a principle of education. Of course it was usually when he had to tell me something more than once, and he was being sarcastic. But also usually right.

 

[dbsfgyd1]

The real question is does aged horse ever get tired of being summoned to these threads to sort us all out?

All I know is I plug my bass in and heavy metal comes out on my Mb200 and my 700rbii

Good enough for me

Re: The real question

Boy, isn't that the truth? LOL!! He's roasted this (me) knucklehead more than a few times..LOL!!

 

[seamonkey]

It's my understanding that Class D power amps mostly have SMPS

FWIW - SMPS is also A....ah-never-mind!

 

[LBS-bass]

OMG. This reminds me of the time I went to a store to buy speakers for my home stereo system in the early 90s. There was a nice older set on the shelf and I asked the salesman to A/B them. They were cheaper, but they sounded great. He then steered me to this other pair that sounded nasty and said, "but these are better, 'cause they're DIGITAL."

I would have bought the first pair from him but he pissed me off so badly with this misinformation that I just walked out.

Can't believe this tripe is still getting put out there.

 

[Ric Vice]

I purchased my first Walter Woods amp (MI-100-8) circa 1980. At a time when the Ampeg B-15 weighed 75 lbs and produced 25 Watts the Walter Woods MI-100-8 weighed 7.5 lbs. and produced 100 watts RMS. Once you have the advantage of a smaller, better sounding, more powerful amplifier never look back. Just my take of course.

 

[Boneless]

Except that the headroom is in large part defined by the compliance of the power supply. We used to have to over-specify the power supply in order to achieve the steady state power rating because as the output power increased, the supply sagged and the power decreased. It was a stumbling block, and though several manufacturers tried to use linear regulated power supplies (ferro-resonant) to get around this, it didn't work all that well. With SMPS, this is not the case, we can regulate the voltage so that it doesn't sag under load and in this case the lack of sag is in fact added headroom. Some class d (and class AB) amps use regulated SMPS, some use unregulated, it's simply the choice of the designer.

One HUGE advantage of a regulated supply is that under low or sagging line voltage, the SMPS will automatically self correct. In the good 'ol days of unregulated supplies, an amp under load driven from an "average" power source might actually deliver 20% UNDER rated power, whereas a regulated supply will maintain the ratings.

Of course, that's why "good amps" (even solid state ones) "weigh a ton". For a 300W RMS amp you might pack, dunno, a 600 or even a 700VA transformer? An amplifier might be able to eventually output up to even 200% its rated "clean" continuous power (of course, terribly distorted, but still) and you also need to account for its dissipation. But maybe you don't and under heavy load the voltage sags and the amp struggles (or that sag gives it some sort of character when slight? It all adds up).But my understanding is that the filtering you need with Class D power amps only works well up to a certain point, so even if you have SMPS power supplies that are well regulated etc. and the voltage doesn't sag, once you get past a certain point heavy enharmonic distortion starts to become apparent. But I'm not a power amp designer (nor a true designer of any sort, I'm mostly a hobbyist sound engineer). Still, I also do know that "Class AB" (or even Class A) doesn't necessarily mean much, even if you have a good power supply (maybe even a good SMPS power supply, why not? It's actually quite sensible these days), if the amp is not designed to recover gracefully from clipping, you get all sorts of terrible artifacts such as "rail sticking". Also, I do know that there is a whole amp around the Icepower modules, and that not necessarily using an Icepower module will yield the same results.

 

[lyralain]

Im sure you prefer streaming music to vinyl too

the virgin 'format that is incredibly toxic to humans with a terrible SNR & band-limiting that wears out over time'
the chad 'infinitely duplicable high quality format available everywhere'

if I wanted a vinyl frequency response, machine whir / crackles / hum and such on my record, I'd mix that into the master. No need to rely on some breakable toxic disc. If I'm listening to someone else's music, I'd rather do it lossless & digitally, so I can hear it exactly as the engineer wanted as best as my speakers can represent. Claiming you need to listen on vinyl for the best flavor is like salting your own food at a restaurant.

 

[DJ Bebop]

Then why does every Class D combo bass amp have a digital power section?

Show me one.

 

[TheSpinDoctor]

Caveat: It has been decades since I worked as an electronic test engineer. That said, I offer some personal observations.

I owned a blackface Fender Showman head. A tech spec'd it to produce 60W RMS at 1 % distortion, not the 85W RMS that Fender stated (which was true for a much higher distortion level). When integrated circuit operational amplifiers became fairly inexpensive there was an issue with slew rate distortion, basically how well the op amps handled transients. I never see this mentioned any more. This was a significant issue with 741 op amps used in some telecommunications test equipment. I preferred TL082 and TL084 op amps for signal circuits. Regarding distortion, I remarked during a Grateful Dead concert in December 1973 that I could carry on a conversation with the person next to me despite the volume of the music. Distortion produces many more frequencies than the original source. These frequencies can interfere with accurate speech comprehension.

I am not sure how much an amp's damping factor influences what some people hear. Again, this is usually only specified with hi-fi amps.

The pre-amp section can have a great influence on what one hears as output power. A potentiometer (pot) can come as either linear or audio taper. Commonly audio taper pots are used for volume controls and linear taper pots used for tone controls. A linear taper pot will be louder at lower settings while an audio taper pot will have a greater increase between 1/3 to 3/4. It might seem logical to assume that all amplifiers will use audio taper pots for volume controls. Unfortunately, cost containment can result in linear taper pots being used throughout.

The astute comments provided by agedhorse are greatly appreciated.