Class D "digital" amps. Opinions on performance

[Jerrold Tiers]

That's from a listener perspective, If I had to take a PSWAG as to why they sound different, I would think that the power stored / available in the led sled has something to with it. With the bigger transformer and caps they are built with they pull a whole lot more current than the class d's, having that current on tap to drive the output would be the difference one would think.

Curiously...... the usual class-D can do MUCH better than most class A-B units on current, unless teh current limits are set poorly......

A class-AB amp pulls one amp from the power supply for every amp on the output.....

BUT a class-D amp pulls LESS than one amp per amp for almost all output levels..... the difference is the efficiency. Sounds like some sort of "free lunch" but it isn't.

At a particular time, the output voltage of each amp may be the exact same, and that may be, let's say, 1/3 of the power supply voltage.

The class AB is supplying 3 amps output, which means it is drawing 3 amps average current from the power supply.

The class-D amp is ALSO supplying 3 amps output, but it is only drawing 1 amp average current. The reason is that the Class-D is about 95% efficient..... the class-AB is lmuch less efficient.

That means that if the voltage out is 24 volts, at 3 A, both are putting out 72 watts, from a power supply of about 72 volts.

But, the draw from the power supply of the Class AB is 3A x 72volts, or 216W. Since only 72 watts is coming out as signal, 2/3 of the power is being lost as heat in those massive heatsinks. That's 33% efficiency at that moment.

meanwhile, at 95% efficiency, the Class-D is drawing 76 watts, which is a draw on the supply of 1.05 A at the same moment. A considerable difference in the demand for supply current, for EQUAL output currents.

With equal power supplies, the class-D can generally make far better use of the power supply energy storage..... OR for equal performance, the class-D power supply can have less storage capability.

The only time the Class-D actually draws 1 amp per output amp is at the very peak of the signal at a level just before clipping.

The argument about power supplies can only be true if the Class-D designer went overboard in assuming how much could be cut out of the power supply on account of efficiency.

 

[c2thej2theizzo]

Getting back to the original topic, From a non-scientific perspective. There is something missing in the overall presence of bass in class D amps, It may not be measurable by dB meters or frequency analyzers, but there is an overall warmth and low end presence that just surrounds you like ur being spooned by a friendly grizzly bear when using transformers.

even when using a nice preamp on D power - it just doesn't compare to Toroidal Transformers- It is more noticeable to me when using 15's and 18's. I have A/B'd with about 6-8 amps from class A and class D crown amps using a nice Avalon (and others cheap and expensive) Preamps - to using a brand new Eden Wtx-500 and my old CXC110 combo with a WT-300 in it - and GK's Mb-200 and their old Backline amps. And everytime the Class D lacks depth. Although, In my opinion this doesn't outweigh the advantages of Class D- this low end warmth I'm talking about isnt really noticeable on stage next to a drummer. And its not really noticeable to the audience. It is noticeable in amps powering subs for mains though.

If you are just running a 2x10 or a 12 these amps are fine, I wouldn't get a 1000W class D for a pro rig. If you need to power a 2x15 or 8x10, ur gonna carry that weight , might as well get a heavy amp.

 

[seamonkey]

6 to 8 amps is not a large enough sample size to generalize a behavior.

Blind tests match the scientific measurements. Science works.

FOH is using class-d big time.
Class-d got a huge start in driving subs

 

[will33]

OK, subjectively, I might like the big amps too. Well, they're not big, or heavy, but I suppose we'll use that when comparing to something the size of a book.

Point is, all these "I played this, then I played that" comparisons DO NOT isolate the poweramp from the rest of the package, right? You're not "testing" power amp designs, you're hearing the whole package and all the variables that come with it. Google "scientific method" or something, it's not that difficult to understand the basic principles of it, meaning you don't have to be a scientist to see the flaws in your comparisons.

 

[Chef]

c2thej2theizzo:

I respectfully disagree. I've been gigging a long, long time, and have carried about every piece of big iron that was popular at any given time.

My former Eden Navigator/QSC-PLX1802 driving a Dr Bass 15/8/1+12/6/1 hit just as hard as any old heavy amps I've used.

My current 12/6/1+12sub rig, powered by a GK MBFusion hits as hard in the low end as anything I've ever played. Same thing for the GK MB800>GK 2x212 rig.


I don't at all miss carrying around 60-100lb amps when 4 lbs will do nicely, even a tiny little bit.

 

[seamonkey]

Oh, and we bought the Bryston as snob appeal amongst many engineers runs deeper than the actual sonic value some days.

Brian Russell, president of Bryston Ltd

"This is worth it. This is worth it, This is worth it, ...." --------- Pop!


Go visit their new class-d line

 

[Bob Lee (QSC)]

Getting back to the original topic, From a non-scientific perspective. There is something missing in the overall presence of bass in class D amps, It may not be measurable by dB meters or frequency analyzers, but there is an overall warmth and low end presence that just surrounds you like ur being spooned by a friendly grizzly bear when using transformers.

even when using a nice preamp on D power - it just doesn't compare to Toroidal Transformers- It is more noticeable to me when using 15's and 18's. I have A/B'd with about 6-8 amps from class A and class D crown amps using a nice Avalon (and others cheap and expensive) Preamps - to using a brand new Eden Wtx-500 and my old CXC110 combo with a WT-300 in it - and GK's Mb-200 and their old Backline amps. And everytime the Class D lacks depth. Although, In my opinion this doesn't outweigh the advantages of Class D- this low end warmth I'm talking about isnt really noticeable on stage next to a drummer. And its not really noticeable to the audience. It is noticeable in amps powering subs for mains though.

If you are just running a 2x10 or a 12 these amps are fine, I wouldn't get a 1000W class D for a pro rig. If you need to power a 2x15 or 8x10, ur gonna carry that weight , might as well get a heavy amp.

You're mixing up "class D" and "toroidal transformer." That's like mixing up "round-wound" and "bolt-on neck."

 

[R Baer]

If there is an audible problem with a module, and so with all units using it, that isn't the "fault" of the type of amplifier, it is the "fault" of the SPECIFIC MODULE....... You will be able to find someone's amplifier that doesn't HAVE that specific problem.

So it really is NOT a "class-D problem" it is still a "design" problem

Getting people to understand that is, as with anything actually factual, is hard. Almost everyone wants to avoid thinking, and responds better to a well-told lie than the truth, which is usually more complicated. Politicians and salespeople have been using that fact for thousands of years.

...Point is, all these "I played this, then I played that" comparisons DO NOT isolate the poweramp from the rest of the package, right? You're not "testing" power amp designs, you're hearing the whole package and all the variables that come with it...

Jerrold, I don't mean to imply that I think there is a "problem" inherent with class D modules. My opinion on the "sound" of class D comes from my experience with choosing a power section for our amp. The preamp was designed first and once done, we set out to find a power section. We tried various class D modules set up in a "blind test" where we auditioned three different off the shelf class D modules, along with a class H and two class A/B modules built from the ground up by our engineer. Everything was gain matched, so I was just hearing the exact same pre amp with each power module. Our engineer insisted that we do the test twice, on different days to see if I came up with the same preference. On both test, I preferred the sound and feel of the class A/B amps first, followed by the class H and then the class D's. There was a certain heft and body to the notes from the class A/B that wasn't present in the class D's.

Now, knowing what sound and characteristics I liked in the amp, our engineer said that given some additional R&D time, he could probably get the class D modules to get pretty close sounding to the class A/B. But, size and weight were never part of the design considerations for this amp, so I made the decision to go with a power section I already liked, rather than to spend time taking a design I didn't like as much and developing it further. I certainly don't mean to go against the engineering experience of someone like yourself, Andy from GB, or Bob from QSC, but I it's just been my experience, that there are some inherent differences in the sound and feel of various amp topologies. Does that mean, as some have suggested that I have some kind of beef against class D, or that I'm "pushing" class A/B simply because that what is in our amp? Of course not. I think class D has it's applications and I'm certain we will do a class D at some point. All I'm saying is that I've yet to try a class D power section that has the sound and feel of, say a Crest CA9.

 

[echidna]

There is something missing in the overall presence of bass in class D amps

Maybe the something is a low damping factor?

 

[Chef]

I do concede this.

I've yet to try a class D power section that has the sound and feel of, say a Crest CA9.

 

[seamonkey]

With the right testing procedure many amps match sonically,

i.e. many discussions ago:
http://www.talkbass.com/forum/f15/crest-ca9-lovers-speak-up-489784/index2.html#post6573906

Pickles: "The CA6, CA9, PLX2402 (and up) sound identical to my picky ears when gain matched, and any of them can make a great bass rig when matched with a preamp of appropriate gain and a cabinet that can handle their power.

If the gains are off by even a TINY margin when A/Bing, they will sound very different. I was really surprised by this, but the gain matched testing opened my mind a lot.
Reply With Quote"

Don't let a little thing like gain matching get in the way of a good test. And that's just one variable to keep in check.

 

[agedhorse]

Maybe the something is a low damping factor?

Damping factor can be even lower on some well designed class D amps but overall, damping factors are pretty even between good class D and good class AB amps.

 

[wcriley]

Sound companies wouldn't be powering their subs with class D amps if damping factor was a problem.

 

[bryanspkr]

Damping factor can be even lower on some well designed class D amps but overall, damping factors are pretty even between good class D and good class AB amps.

Do you find these good, well designed amps in the smallest micro heads?

 

[projectMalamute]

Sound companies wouldn't be powering their subs with class D amps if damping factor was a problem.

I don't think very many do. The I-Tech stuff is a variation on class D, so probably the closest you see out there powering big rigs. But that's a radically different amp than what people are talking about in this thread.

The big boy Crest stuff is all class H, so are the PLX amps and I'm pretty sure all but one of the Powerlights.

I see class D amps in DJ rigs and band PA's, not at jobs where sound is hired out to a reputable company.

 

[bongomania]

Sound companies wouldn't be powering their subs with class D amps if damping factor was a problem.

Also bear in mind that large-scale pro sound companies are not concerned about size or weight. Their rigs are either bolted in place, or in the case of touring companies the rigs are hauled in trucks and maneuvered in large rolling racks. So since size and weight are not factors, what does that leave? Sound, reliability, and price. Price is not so different overall between amp classes, so we're left with sound and reliabilty--and the sound pros are choosing class D (and related technologies).

 

[projectMalamute]

Also bear in mind that large-scale pro sound companies are not concerned about size or weight. Their rigs are either bolted in place, or in the case of touring companies the rigs are hauled in trucks and maneuvered in large rolling racks. So since size and weight are not factors, what does that leave? Sound, reliability, and price. Price is not so different overall between amp classes, so we're left with sound and reliabilty--and the sound pros are choosing class D (and related technologies).

Who are these companies with racks of class D amps?

This notion seems to get repeated a lot around here and it is contrary to my experience.

 

[greenboy]

Who are these companies with racks of class D amps?

This notion seems to get repeated a lot around here and it is contrary to my experience.

Well, what one person sees and another might sees makes it largely anecdotal, but a friend in the greater LA area works a large venue and sees a lot of touring acts come in with big amp racks stuffed with lots of Class D. They actually scale how many of the amps in the racks are in use depending on the size of the venues and how much of their entire systems are flown and arrayed at each stop-off.

Another person mentioned touring company weight concerns. Actually the industry has weight concerns too. It costs a lot less in fuel to move lighter stuff across the globe, and companies seem to want to apply that not only to amp racks but also the enclosures/arrays, since that means there is a greater margin of safety for rigging.

 

[bryanspkr]

My Hypex class D subwoofer amp is a beast. I have no question about that. The question is, what are they squeezing into these tiny micro heads? How does this relate to that part of the market?

 

[projectMalamute]

That sounds a lot like anecdotal evidence as well...

What amps are they using? I don't think QSC or Crest or Crown are even making a flagship touring class type amplifier with a class D output. Did everybody start using something else while I wasn't paying attention?

Just googling around I see lots of Powerlights and lots of 200 series amps and lots of I-Techs. I don't see anybody that you would call a 'big sound company' using Crown XTi or XLS or Peavey IPR or any of the other class D amps everybody talks about on talkbass.

Can somebody give me a link to a real deal rig being powered with class D amps? I'm sure they exist, but this notion that all the pros are using class D amps is just not true.