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Discussion Starter · #1 ·
I've been seeing some amps lately that have been putting out impressive dyno Rms numbers for their size. Namely alot of the Sundown sfb stuff.

But in just basic observation, there seems to be a wild swing I'm sizes of amps with similar footprints.

Other than case size being a better heatsink. What all are the tradeoffs of having larger vs smaller size amps that have the same power output?

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These new super-small amplifiers are commonly referred to as Brazilian amplifiers. In short, what the did was utilized full-bridge technology to reduce the voltage in the amplifier, allowing usage of lower performance parts. They are capable of putting out large amounts of power, but it's not without it's downsides, there's no free lunches. These fall under Class D amplifiers, which use switching technology to cycle the electronics on and off. Class A amplifers are on all the time, require a lot of power and create a lot of heat, but they sound great, like a tube amp... Class A/B is what us common-folk use for sound quality installations. Class D is commonly used for subwoofers, since distortion can't really be heard at low frequencies. Most of these "Brazilian" amplifiers are full range... They were designed for a different market, one where SQ isn't quite as important...

The design itself isn't completely horrible. The issue is, due to the reduced component count, they're inexpensive to begin with. Less than scrupulous companies copy the design and are forced to use even lesser components to hit a lower price point. There's a great example out there where the real-deal amp works just fine, but the copy doesn't work for crap because they didn't use a big thick PCB like the real-deal amp did.

It could be argued that the mainstream market will eventually shift to these amplifiers; the power/size/cost ratios are just too good. Pretty much every company has come out with a full-bridge amplifier; you just need to pick a good one. Engineering goes a long way... I'm personally planning to run one to drive passive 2-way front and sub in my beater as a test. If the snow would ever melt...
 

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Discussion Starter · #3 ·
These new super-small amplifiers are commonly referred to as Brazilian amplifiers. In short, what the did was utilized full-bridge technology to reduce the voltage in the amplifier, allowing usage of lower performance parts. They are capable of putting out large amounts of power, but it's not without it's downsides, there's no free lunches. These fall under Class D amplifiers, which use switching technology to cycle the electronics on and off. Class A amplifers are on all the time, require a lot of power and create a lot of heat, but they sound great, like a tube amp... Class A/B is what us common-folk use for sound quality installations. Class D is commonly used for subwoofers, since distortion can't really be heard at low frequencies. Most of these "Brazilian" amplifiers are full range... They were designed for a different market, one where SQ isn't quite as important...

The design itself isn't completely horrible. The issue is, due to the reduced component count, they're inexpensive to begin with. Less than scrupulous companies copy the design and are forced to use even lesser components to hit a lower price point. There's a great example out there where the real-deal amp works just fine, but the copy doesn't work for crap because they didn't use a big thick PCB like the real-deal amp did.

It could be argued that the mainstream market will eventually shift to these amplifiers; the power/size/cost ratios are just too good. Pretty much every company has come out with a full-bridge amplifier; you just need to pick a good one. Engineering goes a long way... I'm personally planning to run one to drive passive 2-way front and sub in my beater as a test. If the snow would ever melt...
Okay so what about two different Class D amps then. Both from reputable companies. Both of these amps put out 3k or more. Vastly different sizes.



Dynos for both ^
 

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That Sundown amplifier is a full-bridge amplifier, a "Brazilian" design, while the Wolfram is a half-bridge amplifier. A half-bridge amplifier only drives a signal into the + speaker terminal, the - speaker terminal is just "ground". Since the - channel is basically doing nothing, the output transistors need to drive the full voltage and current to hit the rated voltage. High voltage, high current transistors are not cheap.

If you read the description for that Wolfram, it says "Linkable at 2 ohm (1 ohm to each amp), the AW-3000.1 allows multiple amps to be synced together perfectly as one." A full-bridge amplifier is basically two amplifiers linked together, creating a full-bridge amplifier. Rather than the - terminal doing nothing, in a full-bridge amplifier, the - terminal drives a signal 180° out of phase from the + signal, essentially cutting the power requirements on the output transistors in half. Rather than the + side needing to generate full voltage, the - side now carries it's weight. Additionally, as mentioned in that exert from the Wolfram site, the load that each half of the amplifier sees is half of the actual load. So compared to a half-bridge amplifier, the output transistors now need to output half the power into half the load. Hopefully it's obvious that these will be much cheaper than the high voltage, high current transistors required for half-bridge amplifiers. The power supply only needs to create 1/2 the voltage it did before, allowing it be smaller and therefore less expensive.

Another reason that half-bridge amplifiers have to be much larger than full-bridge amplifiers is power supply pumping. "Since the energy flowing in the Class D switching stage is bi-directional, there is a period where the Class D amplifier feeds energy back to the power supply. The majority of the energy flowing back to the supply is from the energy stored in the inductor in the output LPF. Usually, the power supply has no way to absorb the energy coming back from the load. Consequently the bus voltage is pumped up, creating bus voltage fluctuations. Bus pumping does not occur in full bridge topologies because the energy kicked back to the power supply from one side of the switching leg will be consumed in the other side of the switching leg. " Half-bridge amplifiers need more capacitors to keep the bus voltage fluctuations in check...

Beyond that, you into the difference in crossover circuits, protection circuits, difference in size between SMD and wire wound resistors, quality caps, etc. At about the limit of my knowledge at this point....
 

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Used to be heat sink requirement, a long time ago. Then, someone had the bright idea that in order to save money on aluminum, just roll back the power supply voltage to reduce the current output when things get hot. That used to be a last resort, but now it's often how this is managed entirely. When designs become really small, board layout becomes more difficult as switching parts need to be isolated somehow from analog audio sections. Moving them farther apart is one way to achieve that.
 

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Discussion Starter · #6 ·
So different technologies and more expensive parts but...if they both put out the same amount of power without thermal shutdown. Why would you ever pick a bigger amp?

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Because you can fit more letters in a bigger amp and "SQ" has 2 letters and AB also has 2 letters. So, since SQ and AB both have 2 letters, AB has more SQ and you need a bigger amp to fit them inside. D has only 1 letter so it can be smaller but SQ cannot fit inside because there is only room for one letter?
 

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Discussion Starter · #8 ·
Because you can fit more letters in a bigger amp and "SQ" has 2 letters and AB also has 2 letters. So, since SQ and AB both have 2 letters, AB has more SQ and you need a bigger amp to fit them inside. D has only 1 letter so it can be smaller but SQ cannot fit inside because there is only room for one letter?
Sir. Why are you not pouring me whatever you're drinking

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After a bit more digging, it appears that another trick that's used to reduce size is to implement a filterless output stage. Rather than using a passive LC filter circuit to smooth out the PWM waveform from the output transistors, through the power of computing and the ability to drive both "sides" of the signal, the PWM signal to the transistors is adjusted in real-time to eliminate the need for the passive filter components. Quality inductors and capacitors aren't cheap, and take up a lot more space, compared to a generic programmable chip. A key point to take away is that custom programming is key to the performance of these amplifiers. Not saying that a "rip-off" cann't end up with better programming than the original, but it's unlikely. Engineering makes a HUGE difference and it doesn't come cheap. There are only so many people in the world with the knowledge and interest to do this stuff and they could make a lot more money elsewhere.

The trouble is, "For very cost-sensitive or smaller form factor requirements, filterless solutions may be feasible, but these can lead to EMI problems and high-frequency power dissipation due to the switching waveforms. A filterless design is not practical in a “noisy” automotive environment. As with all things engineering, there are trade-offs in performance vs. size and cost of the LC filter components." It can basically be summed up as "This modulation scheme relies on the intrinsic inductance of the loudspeaker and the bandpass filter characteristic of the human ear to recover the audio signal." There's nothing "SQ" about that... Whether it matters for a sub is another conversation.

Other reason's you should get the "old skool" Class D? Due to the lack of that LC filter, if any of the speaker terminals gets grounded out, the magic smoke escapes if the protection circuit isn't up to snuff. On the same token, you just dumped X number of amps into your chassis... Another reason to buy quality, pretty much all of the brands have a solution in these small form factors now-a-days...

Next up, input voltage. This varies model by model and there's really not physical limitation to it, purely engineering choices for the low-cost, locally sourced market these amps were originally intended for. Often times these amps are not designed for much above 15V; think low cost, small engine vehicles... Even more troublesome, the original designs didn't like too low of a voltage either. But again, with Engineering for different markets with different components, this isn't always the case.

And lastly, what happens when it clips. In a regular ol' amplifier with the passive LC filter circuit smoothing the output, when the voltage required exceeds the supply voltage, the peak of the sine wave gets cut flattened out. Sounds weird, but generally not the end of the world. With a full-bridge amplifier utilizing filterless technology, due to the usage of signal summing, when one or both signals can't keep up, the combined output goes all to hell; it turns into a nasty square wave.

The question is, should you ever be clipping? Sure, if you don't have the $$$, get an amp rated for less than your sub and believe you need to run your amp at full gain, clipping might be an issue. The proper way to set your gains is to set them just a little bit higher than is required to achieve your desired listening volume (need a bit more than normal for when your drunk...) when your source is turned up to it's maximum volume before it distorts. You want to get the maximum voltage out of the source, and then amplify it as little as possible to get the desired listening volume. Reason being, ANY noise introduced into the system after the source is also amplified by the EXACT same amount. The stupidest f'ing thing you can do is crank the gains up until just before it clips, and then only turn your volume up a little bit for normal listening. Why on earth would you ever want to put out small voltage from your source? Any small voltage spike is a much larger percentage of the single than if you were outputting 2,4,6,8+ volts...

To be continued...
 

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Let's dive a bit deeper shall we; hopefully someone who know's WTF they're talking about will come along and set us straight; just a hick from the sticks over here... If you ignore that fact that this video is manipulated to show a particular effect, it does raise some other concerns about these amplifiers with regards to "SQ"


First thing to keep in mind, the Taramp is a $200, full-range 3000W amplifier, true "Brazilian" design. But it gets the mind churning, right? You read a couple of the comments about how switching to a old-skool Class D improved their bottom end and it gets you thinking, "Is there a fundamental reason for the varying response or is it just lack of Engineering?" I am by no means even remotely knowledgeable in the stuff we're talking about; a hick from the sticks. But lets look at


First thing to note is that the old-skool amps are referred to as "Korean" amps... But anyway, without going off topic, let's focus on the description of half-bridge Class D amplifiers being current source devices and full-bridge amplifiers being voltage source devices. Maybe I'm reading it wrong, not sure I fully understand why any Class D would be considered a current-source device given the usage of PWM to create the signal waveform, but I'm going to take a "hick from the sticks" guess that it's due to the LC filter circuit. With enough capacitance and a low enough resistance, a capacitor is going to be able to dump a bunch of current quickly. With a filterless output configuration, the transistors are driving the output directly. "Pushing" current through a transistor is going to be nowhere near as efficient as a capacitor "dumping" the current. This is a double edge sword for the half-bridge Class D. The pumping of the power supply bus is due primarily to this capacitor. "Big" output capacitor(s) to have plenty of charge to be able to quickly "dump" current into that sub requires "big" capacitors in the power supply to handle them dumping back through the transistors. Quality "big" capacitors are also physically large. The small little SMD capacitors, while potentially "big" capacitance, are crap in comparison.

As they're saying in the comments on that video I believe, too much time into this response already :), this lackings of the filterless, full-bridge amplifier for subwoofer usage is most apparently at 50hz and below IIRC off the top of my head. Luckily, our hearing is crap down low and we can often times handle near 100% distortion at those frequencies. I know for sure my hearing is crap and I have no room in my vehicle to spare. Quality, name brand filterless, full-bridge mini-amps all the way for me... Take a look at every single DSP/Amp combo; filterless, full-bridge mini-amps... Engineering goes a long way... YMMV.

I beg y'all to correct me if I'm wrong; just trying to help, hopefully it does...
 
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