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

[drumvsbass]

Through same 8x10" cab both are sufficiently loud that folks find no need to test their headroom limits under any practical circumstance.

I've been in a situation where the SVT was necessary. I guarantee you the PF350 couldn't do this gig. For everything else, yes I agree, unnecessary artillery. But for the loudest drummer and 3 guitarists...

 

[DeepHz]

AS Always... Thank you Andy!

 

[JakobT]

I'm always amazed at the sheer length of these threads. They usually run as follows:

• Thread started, with initial post containing wildly inaccurate or completely wrong information.
• @agedhorse weighs in, and puts everything straight after several pages of nonsense.
• Nonsense persists for X number of further pages.

It's a paradigm for the cosmos.

 

[andrus108]

I suggest checking Dave Rat's YT channel, he compared two PA amps with A/B and D power sections.

Interestingly he found out class D amp drops the power when pushed, compared to A/B. He also noted it is possible one simply has a limiter to avoid overheating, while the other gives it all until it breaks, so might not be related to class type at all.

 

[baxter_x]

Nonsense persists for X number of further pages.

That's the best part actually.

 

[Boneless]

Actually, the weight of an amp or transformer is nowhere in any of the amp/power supply design equations. It's about voltage, current and the transfer function between voltage and current with respect to load (related to output impedance).

A transformer is heavy because the core can't saturate at the power line frequency (50 or 60Hz) especially at high line conditions (this is part of the safety testing). The weight is due to the amount of cross-sectional area required to support the flux density at full load, the number of primary windings, the gauge of the primary wire.

Why are SMPS lighter? Because the AC input is first converted to high voltage DC (primary low frequency rectification and bulk capacitance), then this is turned into a PWM signal at high frequencies, this high voltage low current PWM signal is then converted into a low voltage high current PWM signal by the high frequency transformer which is then converted back to DC (secondary high frequency rectification and L-C filtering) for use by the amp.

The high frequency transformer can be much smaller and lighter because at higher frequencies there's no need or benefit to a large core (and there are disadvantages to a large core as well), and because the frequency is high the number of primary windings is much lower which makes the wire lengths shorter which decreases the copper losses. This is why SMPS are better than linear supplies, lower output impedance (which we have always struggled to obtain with conventional supplies).

Yes, I wrote that "good amps weigh a ton" in quotation marks because that's what the popular wisdom was once upon a time. Basically you really needed larger transformers with linear power supplies (even if it's not about weight, but there is a certain correlation). With SMPS technology, there is no need for this and the efficiency and effectiveness of the power supply is also greater. Still, there are many amps that are still made with traditional linear power supplies, so I'm guessing there must be something at which they are better. (I doubt that it's noise).

 

[teemuk]

Still, there are many amps that are still made with traditional linear power supplies, so I'm guessing there must be something at which they are better. (I doubt that it's noise).

Well, for starters, one doesn't have to be a rocket scientist to design one. It's rather trivial to come up with a decent, hum free layout for a bridge rectifier and two filter capacitors whereas an incorrectly laid out SMPS design won't only have inspectors knocking at your door searching for device that interferes with the automation systems of the factory next door but also EXPLODES violently!

My hat's off to all engineers with traits to design systems that switch high power at radio frequencies. Even their "LF" is above hearing range.

 

[DWBass]

I would argue that. I made some digital copies of a vinyl record and found that those that profess to have golden ears couldn't differentiate between the original and the digital copy.

I've done the same.

 

[teemuk]

• Nonsense persists for X number of further pages.

And then, after 3-4 days restarts in yet another thread with the same topic.

 

[Boneless]

Well, for starters, one doesn't have to be a rocket scientist to design one. It's rather trivial to come up with a decent, hum free layout for a bridge rectifier and two filter capacitors whereas an incorrectly laid out SMPS design won't only have inspectors knocking at your door searching for device that interferes with the automation systems of the factory next door but also EXPLODES violently!

My hat's off to all engineers with traits to design systems that switch high power at radio frequencies. Even their "LF" is above hearing range.

Yes, but I'm not talking about hobbyists or small companies here (and even small companies can just buy ready-made SM power supplies and incorporate them into their designs). I'm also guessing that linear power supplies are better for "the road" since they tend to be more dependable (they hardly ever break down, and when they do, it may be trivial to repair them), but on the other hand, SM power supplies are also available off the shelf.

 

[Stan_da_man]

Morons who believe that Class A/B is better (louder) are great.

Just drives down the prices of quality secondhand class D amps.

 

[sxaxsx]

Ok, I have asked 3 people and none have replied, maybe you can help. Name me at least one Class D combo bass amp that has an analog power section rather than digital.

The better question would be what do you think digital means?

 

[jw23mind]

How the wattage is measured (peak, rms, program, continuous or time-limited); in context with how the signal is pre-processed (clipped, compressed, or not). I have a 1KW Class-D amp which can put out continuous uncompressed power, and another which compresses the signal by reducing peak power with a continuous signal. Very different responses, but both class-D and put out full rated power on transients.

This:

QUOTE="Boneless, post: 26455358, member: 85545"]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.[/QUOTE]

 

[IanStephenson]

From what I have seen, the biggest complaint about class D seems to be in the delivery of lows

At the risk of jumping into a thread that I really should stay away from...

Class D is most likely reproducing the lows perfectly. If your class D is clipping then you would know about it... In fact its your old A/B tube amp that's messing up the lows. The tube amp is pushing into clipping/compression which is gently distorting those low frequencies and adding in higher frequencies that shouldn't be there.

Thing is - you (quite reasonably) LIKE those extra frequencies - they're the "heft" and "thump" you talk about.That those are missing from the Class D is theoretically a good thing. However once you get into preference then its up to you what you like.

If you want that "heft" from the class D then you'll need to introduce that at the pre-amp stage, and then let the Class D do its job and make it louder.

 

[Mingo Sanders]

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.

Can you describe or identify the digital to analog converters in any digital Class D bass amplifiers?

 

[ThinCrappyTone2]

All I know is I plug my bass in and heavy metal comes out

love this quote

 

[HolmeBass]

There are very few class D amps that use a processor to control (and/or generate) the PWM signal. It's not that it "can't" be done, but that the ways we do it currently works so well.

Thank you for that clarification. I think I heard that from Eden's own copy about their initial class D offering, an amp which I bought and still own. WTX-260 IIRC. Since then I have come to realize not all messaging from Eden was completely accurate. They were trying to use the lack of a processor in their amp as a marketing differentiator.

 

[Dominic D]

Well, because streaming sounds like absolute garbage unless you have a very nice quality DAC to run Hi-Res streaming. Even then, I'll still take vinyl. To me, its like the difference between a good old fashion tube amp and something like a Kemper modeling amp. Sure, the stream/Kemper is technically superior quality to vinyl or tube amp, but we dont hear technicalities like that. Just like a tube amp, vinyl has a depth, warmth and presence that no digital audio file can touch.

What you call "depth, warmth and presence", I call "distortion".

 

[Michael Favata]

Be sure to watch this people it's hilarious!
Thanks @patrickhowell !

 

[teemuk]

I'm also guessing that linear power supplies are better for "the road" since they tend to be more dependable (they hardly ever break down, and when they do, it may be trivial to repair them)...

I guess repairing is certainly easier, no proprietary ICs, etc. but I'm not sure how many cheap consumer items like musical instrument amps are really designed from principle of easy serviceability. Often service may be as costly as the amp itself. These are not $10k items one most definitely repairs instead of just replacing with a new unit.

But are the SMPS really that fragile? I don't believe it. They are all around us, everywhere and they don't fail all that often. My hunch tells me that a lightweight SMPS is more roadworthy than a power supply with a huge transformer that weighs 1 - 3 kg and is ready to get torned apart the chassis from the slightest bumb. I have certainly seen more tube amps that have failed this way in shipping vs. millions of shipped SMPS wall warts for mobile phone chargers, laptop and DVD player power supplies and whatever common household items with a SMPS power supply adapter.