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

[Ric Vice]

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.

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.

 

[mbell75]

Not in my experience, not the manufacturers I worked for, and other quality manufacturers used the same ratings for the same class D sections.

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.

 

[fdeck]

"Analog" means that information is represented by continuous physical quantities such as voltage, time, pressure, etc. Analog systems are capable of computation, transmission, and storage of information, but only to an extent limited the propagation of noise.

"Digital" means that information is represented by pure numbers. Digital computation, transmission, and storage, can be done without noise. This, combined with the miniaturization of electronics, has allowed digital systems to reach levels of complexity and reliability unimaginable with analog systems.

How I think about switchmode (Class-D) amplifiers: If you put the same signal through two of them at the same time, their output voltage / current waveforms will be measurably different. If you chain enough amplifiers together, the signal will eventually be lost in noise. This is exactly the same state of affairs as with Class-AB amplifiers.

In contrast, e-mail a digital audio recording such as an MP3 to two friends in different cities, and the files that they receive will be exactly and utterly identical. Perform a complicated calculation with a spreadsheet program on two computers, and both will get exactly the same answer.

Digital systems have something called "noise immunity," where a signal is prepared and received according to rules that allow it to be assigned to a specific sequence of pure numbers, even if a bit of noise creeps into the process. You can look up oscillscope displays of signals such as "eye diagrams" for USB and Ethernet interfaces, and they look like a horror show, but the rules ensure perfect data recovery.

People have tried to make Class-D amplifiers with digital signal processing inside the feedback loop, but the pitfall is that those systems have turned out to be more expensive and no better performing than purely analog designs.

 

[Killing Floor]

Because a lemon is a hybrid of a lime and a citron and was bred for its juiciness.

Then what is a lymon?

 

[Boneless]

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.

The Little Mark II was a Class AB amp with a switching mode power supply. Also, if you think about it, many of those distortion pedals you power with a switching mode power supply are basically class A amplifiers. (Mostly irrelevant but funny).

 

[5StringBlues]

Jocko didn't need to be a bad influence on him

Lukather uses high value Watts.

 

[Razman]

I do believe what we are talking about can be measured/quantified, but doing this is over my head. I believe we are actually talking about multiple factors that can be measured, so they are objective. But my understanding of the various related factors is too incomplete and shallow for me to really go too far down the rabbit hole.

Also, I believe our perception and taste plays a role, so some aspects are subjective. Our perceptions and the measurements will not always agree. This may seem counterintuitive, but the idea is some things happens in a way that the test equipment picks it up, but not our senses. Our senses may interpret two transients with the exact same magnitude in different ways, perhaps depending on how fast the transition occurs and the duration at max amplitude?

If we limited the discussion to a couple of specific amps, I could give my perception, which I generally try to do as objectively as possible. But describing how something sounds in a way that communicates what I am hearing with 100% accuracy is not really possible. Ultimately the best thing to do is try amps for yourself and draw your own conclusions.

I do think reading what other thinks about an amp can be helpful for suggesting gear to try. But in my experience, the results frequently don't match our interpretation of what we have read. I also find value in reading specs, but the specs don't necessarily tell me everything I need to know.

Sorry...wish I could give you a better answer.

Thanks - I get what you are saying, but my experience with class D amps is that they seem compressed, as Boneless (below) explains (they seem to run out of headroom). Whereas, another topology may provide more power in transients albiet with higher levels of THD as volume is increased.

Totally agree that numbers aren't everything. Like with motorcycles, you have to ride them to see what fits and feels the best. I would have never known that a Yamaha FJR1300 would have been the wrong choice for me until I sat on it and discovered that the outside edge/angle of the fairing matched perfectly with my kneecap and hits it in the right spot when my leg is close to it (while seated) to cause no small amount of pain.

There's also a difference in how a v-twin delivers 150 hp and an inline four delivers 150 hp. But there is a way to measure it.

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, 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.

My non-class D heads seem to maintain more headroom as they are turned up and don't sound as compressed. Can this be measured? Like dampening factor is?

 

[JeezyMcNuggles]

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.

Yeah, on some. The ampeg pro series amps are solid state, and they're very warm, compared to the pf series amps. The 7 pro being the least hifi amp I've ever played through. The 3 sounds the best, 4 has the best features. But, they are all full of life. Again, once you turn them up. The pf amps need to be at about 2 o'clock, with the gain set correctly, for them to get past that neutral, weakness, and start pushing speakers. Yes, even my 800 doesn't really start pushing speakers till past half.

Same with my Veyron.

Same with my mini mega.

Same with my BH500

Same with my RH750

Same with my old Headliner.

Same with my nuke.

Same with my old BT1000

Same with my RB combos.

Same with my Bugera 15 combo.

Same with my Behringer 12 combo (that one actually needed to be maxed volume to get any life out of it. Sucker took it like a champ too. Pushed that thing 12 years before I finally sold it off. It's probably still going too.

 

[Killing Floor]

Jocko didn't need to be a bad influence on him

The We Are Devo song?

 

[esoxhntr]

Up next, what works best? Regular clothespins, or the springy kind?

Everyone knows that regular clothespins hold 5 times the weight in socks that springy ones do. Hereafter this will be known as the "Boss Ratio". Applies to amplifiers, socks, burritos, and just about anything else you care to name.

 

[ardgedee]

I have, every amp I've ever played through has a sweet spot. On every solid state amp (class D or otherwise) up to half, they're sterile. After half, they get meaty and open. Raw, if you will. Up to a point that it starts to suck.

On a tube amp, after half, it doesn't even really get louder. It just gets more saturated. Blurred, squished. Up to the point it starts to suck.

Sweet spots.

Without knowing more, it's possible that you're describing the behavior of the preamp section rather than the power section. Or possibly of the speakers. Or possibly of your ears, since an otherwise-identical excerpt of audio can sound differently to us at different volumes.

 

[ddnidd1]

Is it possible that the CEO for Boss has a financial interest in the products he's pushing.

 

[JeezyMcNuggles]

Without knowing more, it's possible that you're describing the behavior of the preamp section rather than the power section. Or possibly of the speakers. Or possibly of your ears, since an otherwise-identical excerpt of audio can sound differently to us at different volumes.

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.

 

[Stewie]

Some people can't hear a difference between analog and digital, you are clearly one of those people. Im sure you prefer streaming music to vinyl too

Actually, I listen to vinyl and CDs. Both my upright and my Fenders sound great through my new RB combo. Not quite as sweet as through my old Fender stuff, but mostly because of the cabinet. Maybe you should have a little more faith in others, or maybe not try to be such a smartass. Especially when you are dead wrong

 

[Boneless]

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.

It is sort of a bad methodology this, though. Also because who knows what is "correct gain", even in the presence of a clip LED. But mostly because you are doing things and expecting to see a result.

 

[JeezyMcNuggles]

It is sort of a bad methodology this, though. Also because who knows what is "correct gain", even in the presence of a clip LED.

Hit pre amp distortion, back it up til distortion stops. Set.

 

[Pings Bass]

Here's my handy amp guide I posted over a year ago, because people really get confused about wattage and ohmage and ampage.

• Class A: analog, must use analog speakers
• Class B: butane-powered (careful around open flame!)
• Class AB: analog wattage with butane ohmage, loads < 2 ohms are extremely flammable
  
• Class C: covid-resistant, mask still recommended indoors
  
• Class D: digital, must use digital speakers; divide wattage by two to get equivalent analog power; inferior sound when used with analog speakers
  
• Class Q: quantum power, infinite wattage but if you run a load under 2 ohms you may produce a singularity (not recommended)

 

[Wasnex]

Thanks - I get what you are saying, but my experience with class D amps is that they seem compressed, as Boneless (below) explains (they seem to run out of headroom). Whereas, another topology may provide more power in transients albiet with higher levels of THD as volume is increased.

Totally agree that numbers aren't everything. Like with motorcycles, you have to ride them to see what fits and feels the best. I would have never known that a Yamaha FJR1300 would have been the wrong choice for me until I sat on it and discovered that the outside edge/angle of the fairing matched perfectly with my kneecap and hits it in the right spot when my leg is close to it (while seated) to cause no small amount of pain.

There's also a difference in how a v-twin delivers 150 hp and an inline four delivers 150 hp. But there is a way to measure it.

My non-class D heads seem to maintain more headroom as they are turned up and don't sound as compressed. Can this be measured? Like dampening factor is?

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.

 

[Tim Skaggs]

Nothing to add, just glad to see the debate continue with more knowledgeable members starting to swing the discussion to one level of understanding. It hasn't devolved into name calling, blame for who is at fault (doesn't matter there is nothing for which anyone has to be "at fault"), threats, disparagement, calls for silencing those who have a particular belief, and many other negatives that plague most forms of text communication.

If this discussion would have occurred on Twitter, tribalism would have taken over long ago. One group would have been accused by the other group for anything that has ever been wrong with any amp, name calling would have been going on since page two, and who knows what all other nastiness would have ensued. Not saying there have been no disagreements, and not saying there have been no spirited posts, but it has remained civil.

Instead, there has been an adult discussion, corrections made, opinions expressed, and just general co-existence among humans communicating by text. TB is a forum of which I'm glad to be a member.

 

[fdeck]

My non-class D heads seem to maintain more headroom as they are turned up and don't sound as compressed. Can this be measured? Like dampening factor is?

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.