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

[bassinflorida]

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

You are incorrect. They ARE NOT DIGITAL power sections. You just think they are. Study. A lot!

 

[DJ Bebop]

NO SUCH THING AS A DIGITAL AMP!! Stop spreading misinformation!

To quote an Earth Wind & Fire song title...

 

[Element Zero]

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

I dunno dude… most music purchased through iTunes sounds baller through my AirPod Pros and usually better than my Beyer Dynamic DT770s. Even most music videos on YouTube sound really good through my little earbuds.

 

[E2942]

If the President of Roland or Boss said Digital = Class-D, I want to see that video.

 

[Killing Floor]

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

Springy. Best for bread and potato chips. The olde fashioned non springy ones are the best clothespins for metal.

 

[Rolling Thunder]

Class D amps are not digital, so my BS alert is already tripped.

Not tube = digital (at least to some people)

 

[Plastalmonus]

It seems he is talking more about the overdriven/saturation aspects of Class AB vs Class D where he feels that Class D needs higher headroom as the overdriven aspects aren't as musical.

It is the American guy who says you need 5 times the power.

 

[Rolling Thunder]

If the President of Roland or Boss said Digital = Class-D, I want to see that video.

 

[mbell75]

It seems he is talking more about the overdriven/saturation aspects of Class AB vs Class D where he feels that Class D needs higher headroom as the overdriven aspects aren't as musical.

It is the American guy who says you need 5 times the power.

Yea, watch from the 5:51 mark to about 8:40

 

[Grinderman]

This thread is still happening, really?

 

[fdeck]

To be fair... sometimes "bad" technical terminology ends up in widespread use. For instance in the bicycle world, parts made from aluminum are referred to as "alloy," even though steel parts are also made from alloys... of steel. So, if mis-use of "digital" is the only crime committed by a commenter, I prefer to let it slide and focus on more serious issues.

Also, an amusing and pedantic factoid is that there are digital systems with more than two levels, such as some memory chips, and the signals transmitted by telephone modems and some other systems. With modems faster than 2400 baud, a connection would start with "arbitration" to determine the number of levels that could be reliably distinguished above the noise of the line. Cell phones also use arbitration AFAIK. For this reason, "binary" is not a necessary-and-sufficient criterion for whether something is digital.

 

[Iristone]

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

Why not? Vinyls degrade the sound quality so much, even AFTER converting to digital and compressed to MP3 there's a significant difference

 

[JimmyM]

[

Why not? Vinyls degrade the sound quality so much, even AFTER converting to digital and compressed to MP3 there's a significant difference

I feel the same way.

 

[DJ Bebop]

Very different design choices. The GK is much brighter and many players associate this with "quicker and more dynamic", but in fact this is a perception and is not shared by all players.

Plus that thing you taught us that the Mesa SW line uses ( I hope I get this right ) linear potentiometers whereas most others use audio taper. If I have a linear pot amp Mesa and a taper pot amp. I can set my input or gain at 9:30 on both, the Mesa my seem to be quite than the taper pot amp. But if I turn up the Mesa to say 11:00 or noon, it will be as loud as the taper at 9:30, but the difference is I can turn up the Mesa pass that point whereas the taper pot amp has given all it's good power up before that point.

Is that right?

 

[agedhorse]

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

Ha! Actually, you reminded me of the comment made where it was supposed that class D was not as good at low frequencies. Actually class D is BETTER at low frequencies and are the foundation of the technology behind SMPS and continues to function at DC.

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.

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).

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.

The slew rate of those early devices were an issue in circuits where high open loop gain was necessary, specifically many eq and tone control circuits. Fortunately, those days are long gone.

The choice of linear over audio taper is generally a design decision, often driven by a marketing department's desire for "get loud early in the rotation" response. The cost is about the same regardless of the taper.

It seems he is talking more about the overdriven/saturation aspects of Class AB vs Class D where he feels that Class D needs higher headroom as the overdriven aspects aren't as musical.

It is the American guy who says you need 5 times the power.

Again, it's all about the choices made by the designers. I can (and obviously have) been able to overcome the perceptions that overdriven class D amps aren't musical... in fact that's one of the primary applications with the output tube emulation and damping circuitry wrapped around a class D platform. It's similar to what I have done with class AB amps as well.

 

[JimmyM]

Again, it's all about the choices made by the designers. I can (and obviously have) been able to overcome the perceptions that overdriven class D amps aren't musical... in fact that's one of the primary applications with the output tube emulation and damping circuitry wrapped around a class D platform. It's similar to what I have done with class AB amps as well.

The first micro I got couldn't overdrive worth a crap. I think that since it was such a popular amp at one time, it gave people the perception that it was par for the course with micros.

 

[brianrost]

Wow, I go out for a few hours and come back to 8 pages full of total confusion.

 

[esoxhntr]

Wow, I go out for a few hours and come back to 8 pages full of total confusion.

That'll teach you.

 

[esoxhntr]

Ha! Actually, you reminded me of the comment made where it was supposed that class D was not as good at low frequencies. Actually class D is BETTER at low frequencies and are the foundation of the technology behind SMPS and continues to function at DC.



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).



The slew rate of those early devices were an issue in circuits where high open loop gain was necessary, specifically many eq and tone control circuits. Fortunately, those days are long gone.

The choice of linear over audio taper is generally a design decision, often driven by a marketing department's desire for "get loud early in the rotation" response. The cost is about the same regardless of the taper.



Again, it's all about the choices made by the designers. I can (and obviously have) been able to overcome the perceptions that overdriven class D amps aren't musical... in fact that's one of the primary applications with the output tube emulation and damping circuitry wrapped around a class D platform. It's similar to what I have done with class AB amps as well.

Once again, thank you for being the patron saint of sensibility on Talk Bass.

 

[wes stephenson]

A watt is a watt, regardless be it tube, A/B, Class D.

The better question is are modern manufacturers fudging their power ratings?
I can tell you through the same 8 ohm cab, my old mark III peavey bass head is a lot louder than my Trace Elliot Elf despite them having similar power ratings (actually I believe the old peavy is less powerful at 8ohm than the trace is rated)

Right! I had a 900w GenzBenz that was blown out of the water, as far as volume is concerned, by a 500w GK MB amp. These folks are out here fibbin!