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

[mbell75]

As a factual claim that is very bold. As is the inference that the Class D offerings from the likes of Aguilar, Bergantino, Genzler and Mesa are somehow not top-end or first class is laughable.

Talking about Ampeg and Fender. The two brands you see on 90% of concert stages...

 

[mcnach]

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

not quite, I thought it was a hybrid of a citron (ancestor of most if not all citrus fruits that we use) and some bitter orange species, not a lime?

I'm by no means an expert, but I grew up around lemons so I heard a few things but never really researched them. My maternal family comes from this area in the North of Spain by the mountains, where a valley just happened to have a microclimate that was especially good for citrus trees in general. They grow the largest lemons I have ever seen, some as big as midsize melons.

I've seen quite a lot bigger than these:

aaaanyway, enough lemony distractions!

 

[mbell75]

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here's one that ain't…
It's class D

Ok, thats probably why I dont think Ive ever seen one aside from at a Guitar Center. Nearly every time Ive seen an Ampeg on a stage, its a classic SVT or CL.

 

[Ric Vice]

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 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".

Interesting, thank you for providing that detail. I've owned three Walter Woods Amplifiers original MI/100/8 a MI/400/8 and a Electroacoustic Ultra High Power. Now admittedly, by today's standards a 100 watt amp ( 8 ohms) with a SMPS power supply is not a powerful
bass amp. At the time I got it in 1979 it was compared to anything but an SVT. I had the opportunity to do a head to head comparison between the MI/400/8 and an STV into the SVT 8x10 cabinet. Their was very little difference between the SVT and the Woods, they're
analog amplifiers (rated into 8 Ohms?). The Woods MI/400/8 weighed 9 lbs, My Walter Woods Electroacoustic Ultra (600 watts RMS into 8 ohms) weighs 7.5 lbs. I played all of those amps for years, sometimes at outdoor festivals and never lacked for power or tone quality or
flexibility. Just my take. I know many folks have never played a Walter Woods. My Jule Monique M700 will do the same thing with a decent preamp sitting in front of it. Once again, just my take and my experience.

 

[Passinwind]

Reaching for some mushrooms now to help me handle this thread better...

The pre-CBS cyanescens had more heft.

 

[agedhorse]

Not sure if this has already been said but:
1. Class D is NOT digital. However, many Class D amps use a digital Switching POWER SUPPLY. I believe this is the origin of confusion (well, this and because people regurgitate marketing BS as a means to falsely portray a modicum of technical understanding).

Two very popular forms of power supplies are: a) Linear Power supplies - they use a (relatively) big transformer mated to a series of capacitors and resistors, and b) Digital switching power supplies that perform voltage adjustment and AC/DC rectification via tiny microprocessors (not big transformers or capacitors, etc.)

No, almost all switching power supplier (SMPS) are analog PWM with a conventional control loop. SMPS could be done with digital control, but the process is more expensive and less forgiving.

2) A Watt IS a Watt. The perception of more power from Class A/B likely has to do with a) higher distortion levels, and b) the fact that Class D are overwhelmingly mated to Digital Switching Power supplies. Remember, I said Digital Switching power supplies do NOT have the big capacitors? Well, the benefit of large capacitors is that they have the capacity to temporarily store electricity. This means that a linear supply that has a bunch of big capacitors has the ability to deliver very large amounts of current for millisecond long, instant transient spikes. A digital power supply can not do this to the same extent. In practice, it means an amp with a linear supply can provide 100 watts continuous power into an 8 ohm load, but extremely short burst power (dynamic headroom) of over 200 watts. Conversely, that same gain stage paired with a digital supply can provide the same 100 watts continuously into an 8 ohm load, but only 125 watts of transient spike power.

This is not true as well. ENERGY storage is a function of the square of the voltage, so the value of the cap must be taken in conjunction of the applied voltage. On the typical primary side of an SMPS, the voltage is ~350V and on the secondary side it's typically 100V (for the size of amp we are discussing here).

For 100V and 10,000uF (common values for an amp), the energy stored is 50J. At 350V (primary side bulk storage), to store 50J of energy only requires 800uF. This value is then added to the secondary side storage (which gets recharged at a MUCH faster rate than the primary side, typically 50,000 times per second) of typically 5000uF at 100V for a total of 75J. In reality, most SMPS that are used in the amps we are talking use primary bulk caps of between 1,000 and 2,000uF which makes an SMPS FAR superior in terms of energy storage, and explains why you can't just compare the values of caps and draw valid conclusions without knowing a whole lot more about the circuit. I know comparing cap values or comparing transformer weight or any number of hair-brain internet ideas is a popular theory, but it's simply wrong.

It probably depends how you define loudness. Loudness, as in perceived volume and power calculations based on waveform amplitude alone are not the same thing. What matters is the power factor of the output waveform. A 50W tube amp flat out at full saturation will sound louder than a notional 50W (i.e the same peak to peak voltage into the same speaker) of clean class D power because compression, 'sag' and other harmonic distortion artefacts of the 'starved' tube amp change the power factor of the waveform - it becomes 'squared off' top and bottom, which not only increases the power factor (area under the curve) by the addition of harmonics, but also creates faster slew rates which add to the percieved intensity. It is also why compressors are used to add thickness and heft, and why there really is no such thing as a truly transparent compressor - they all change the waveform which must, by necessity, change the tone.

When operating at a given output in the clean 'linear' region, say both delivering 1W into the same cabinet and with plenty of headroom in reserve there should be very little difference provided the power supplies can keep up. Watts are always Watts. The power factor is a measure of how those Watts are distributed and delivered over time. Static analysis of power based on Ohms Law (P=IV) will not provide the answer.

YMMV

The area under the curve is very important to power measurement and perception. In reality, using this concept is part of how distortion and overdrive algorithms are developed, it's one variable in the check & balance equations.

If I have a STV CL plugged into a good cab like a Barefaced Big Twin I can be louder than anyone really needs to be. If I try to use a 300 watt GK MB or Aguilar TH SS head into the same cab, it will not perform well against a pair of 412 half stacks and a heavy drummer.
I think we are all also aware that the breakup of that SVT CL or AD200B is far more pleasant than the breakup of any SS amp. A 300 might reach the same volume as a tube amp but it will sound like butt in the process.

Try with an Ampeg SS amp, not another brand.
Last year I was interested in going all tube with an SVT 2. I made a several shootout against my SVT 7. Could see any reason to go full tube. Way heavier, less power, harder to maintain.... And they sounded the same for the tone I like.
I only play clean.

Agreed, there is so much perception of loudness associated with voicing of different amps (and speakers) that it's easy to develop opinions that do not generally apply (but may in some cases)

Don't get me wrong, I have absolutely zero interest in all tube amps. My hybrid Aguilar DB751 is heavy enough, thank you very much.
I just know that when you go to SS amps you have to aim up a little. I don't think it is a mistake that Darkglass starts their amps at 500w, and Mesa's Subway series are 800w.

No, it's not a mistake (for the Subway amps anyway). We were looking at the challenges of getting parts for the Carbine and Big Block models and the D-800/800+ were developed considering those platforms. Later, when developing the WD, I asked specifically what folks would want if we were to consider a re-imagination of the Walkabout and one of the most common needs was for more power since the Walkabout ran out of power too quickly for enough users that it was a real issue (for those applications). Even if I would have re-designed the Walkabout using class AB technology (which was one of the considerations), it would have been about the same power as it is in the current class configuration. This doesn't man that we won't do a smaller amp, but that was not a priority at the time.

In fact, most every high end bass amp uses an A/B power section rather than Class D. Why is that? Just a coincidence?

Name a high end bass amp released in the past 5 years that is class AB.

(Hint: there are a couple but pretty obscure)

 

[patrickhowell]

I still dont get this. A 100 watt, all tube Ampeg V-4B will absolutely blow the doors off a Class D 100 watt Fender Rumble, which is barely more than a practice amp. So how is a watt a watt? Seems to me its much more about the power section and how that watt is utilized.

A watt is a constant unit of measurement and that doesn't change for different classes of amplifiers. It's also not a good way to compare how loud two different amps will be because there are so many other factors involved in amplifier design.

 

[ardgedee]

I still dont get this. A 100 watt, all tube Ampeg V-4B will absolutely blow the doors off a Class D 100 watt Fender Rumble, which is barely more than a practice amp. So how is a watt a watt? Seems to me its much more about the power section and how that watt is utilized.

Power ratings are the product of a formula based on maximum amount of power the amp can output into a type of load below a threshold at which it generates a certain amount of distortion.

Most tube amps, particularly for musical instruments, distort in ways that people find pleasing. So musicians can (heck, they usually want to) drive tube amps harder than their advertised ratings.

Power is cheaper to come by out of solid state amps, so there's no reason not to make them more powerful. Your questions keep approaching this subject as if published power levels are qualitatively fixed phenomena, and that amps must be compared exclusively in terms of them, which is kind of weird.

Incidentally, almost all music amplifiers are either AB or D. There are probably some low-power amps that are purely class A but they would have to be limited to headphone amps or small boutique guitar amps because class A is way too inefficient for most purposes. If you haven't read the Wikipedia entry on power amplifier classes yet, you really should.

 

[paskisti]

We could even make class D amp with smps, display and processor and still keep the analogic signal path. So what the processor could do?

• Control front panel LEDs
• Control protections like over current, over temp, short circuit etc.
• Control output relays
• Control cooling fans and their speed depending on the duty cycle or semiconductor temp
• Reading input gain control pulse potentiometer and giving set value information of gain
• Controlling display

I'm sure this is not practical or cost effective but could be done. Maybe some protections need very fast DSP or FPGA to be fast enough, or maybe they need to be HW oriented.

I'm not amp designer but thinking that I have clue how class D amp works. Don't take this too seriously

 

[yodedude2]

Talking about Ampeg and Fender. The two brands you see on 90% of concert stages...

hmmm. if we're talking about bass amps, i see more aguilar than both of those other brands combined. so, less than 50% ... is what i see.

 

[Mingo Sanders]

I can sell my 500W Class D head and get a 33W Tube head and be done with it now

Are you insane? You're going to need headroom!

Better get 34 watts.

 

[socialleper]

No, almost all switching power supplier (SMPS) are analog PWM with a conventional control loop. SMPS could be done with digital control, but the process is more expensive and less forgiving.



This is not true as well. ENERGY storage is a function of the square of the voltage, so the value of the cap must be taken in conjunction of the applied voltage. On the typical primary side of an SMPS, the voltage is ~350V and on the secondary side it's typically 100V (for the size of amp we are discussing here).

For 100V and 10,000uF (common values for an amp), the energy stored is 50J. At 350V (primary side bulk storage), to store 50J of energy only requires 800uF. This value is then added to the secondary side storage (which gets recharged at a MUCH faster rate than the primary side, typically 50,000 times per second) of typically 5000uF at 100V for a total of 75J. In reality, most SMPS that are used in the amps we are talking use primary bulk caps of between 1,000 and 2,000uF which makes an SMPS FAR superior in terms of energy storage, and explains why you can't just compare the values of caps and draw valid conclusions without knowing a whole lot more about the circuit. I know comparing cap values or comparing transformer weight or any number of hair-brain internet ideas is a popular theory, but it's simply wrong.



The area under the curve is very important to power measurement and perception. In reality, using this concept is part of how distortion and overdrive algorithms are developed, it's one variable in the check & balance equations.





Agreed, there is so much perception of loudness associated with voicing of different amps (and speakers) that it's easy to develop opinions that do not generally apply (but may in some cases)



No, it's not a mistake (for the Subway amps anyway). We were looking at the challenges of getting parts for the Carbine and Big Block models and the D-800/800+ were developed considering those platforms. Later, when developing the WD, I asked specifically what folks would want if we were to consider a re-imagination of the Walkabout and one of the most common needs was for more power since the Walkabout ran out of power too quickly for enough users that it was a real issue (for those applications). Even if I would have re-designed the Walkabout using class AB technology (which was one of the considerations), it would have been about the same power as it is in the current class configuration. This doesn't man that we won't do a smaller amp, but that was not a priority at the time.


Name a high end bass amp released in the past 5 years that is class AB.

(Hint: there are a couple but pretty obscure)

I'm not one of the A/B vs D guys. Whether there is a tonal difference is subjective to one's ear, but I totally feel like A/B watts work more or less like D watt for whatever purpose they serve to a consumer. Which in of its self is problematic as this thread shows.

 

[Bassamatic]

Is it though? A 50 watt all tube guitar amp is A LOT louder than a 50 watt digital guitar amp. A 50 watt tube Marshall guitar amp can be played at a large gig. A 50 watt digital amp? No...Its not even close. Why is that?

Guitar amps are louder with the same wattage because our EARS are more SENSITIVE in the mid-range where guitars live. As you can see from the well-known Fletcher-Munson curves, the human ear is nearly 60dB (1 Million times) more sensitive to 3K than 100 Hz. That's one reason we need BIG amps and speakers. Also, one amp can seem louder than another because it contains a bit of distortion (tube amps, maybe) that our ears are more sensitive to.
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ALSO WATTs are not always WATTS - there are many ways to measure Watts. We have all seen battery powered boom boxes advertised as 1000 and 2000 Watts, right? To be accurate, 2 amps must use the same method for comparison. It go so out of hand that a measurement spec was developed by the IHF so that Hi-Fi amps could be compared. RMS is normally considered to be the most common REAL measurement, but the distortion level must be specified also and could vary from 0.1 to 10-20 percent affecting the spec.

 

[blowinblue]

Didn't read the entire thread, but having grown up listening to the Rolling Stones I thought that watts were a measurement of drum volume.

M. M.

 

[mcnach]

Hence the name, Digit.

I do dig it.

 

[mbell75]

hmmm. if we're talking about bass amps, i see more aguilar than both of those other brands combined. so, less than 50% ... is what i see.

You see twice as many...Aguilar bass amps than Ampeg and Fender combined? Ummm, what kind of shows are you watching? I just watched dozens of bands over two weekends at Coachella. Saw lots of Ampegs and some Fenders, zero Aguilar. I watch lots of live performances on Youtube, same thing.

 

[bdplaid]

I do dig it.

 

[yodedude2]

You see twice as many...Aguilar bass amps than Ampeg and Fender combined? Ummm, what kind of shows are you watching? I just watched dozens of bands over two weekends at Coachella. Saw lots of Amps and some Fenders, zero Aguilar. I watch lots of live performances on Youtube, same thing.

mostly jazz and jazz-related acts.

 

[bdplaid]

the human ear is nearly 60dB (1 Million times) more sensitive to 3K than 100 Hz.

Not anymore.

 

[5StringBlues]

A horse can lead you to water, but he can't make you think