Deal Extreme amplifiers?

[ThyDntWntMusic]

I just stumbled across these...

DealExtreme: $18.10 VMA2015 15W Stereo Audio Amplifier Evaluation Module (EVM) Board

there's a few other varieties, but the 2X15 watt was the highest power I saw...

anyone have any experience with them?

[star882]

No experience with that particular module, but it looks like a hybrid given its small size.

[pacificblue]

If you wonder what hybrid means in this context, whether a hybrid car, a hybrid of different amp types (e. g. tube pre + chip power amp) or a hybrid of whatever, star882 refers to class D amps without integrated digital signal processing as hybrids. He refuses to acknowledge that class D amps are in fact analog amplifiers (PWM) and not digital amplifiers (PCM).

And indeed it is a fully integrated class D amp that does not need any further components. It is a pity that the manufacturer only gives a rudimentary set of specs. By the description those amps are rather intended for low-cost, lo-fi music reproduction.

[star882]

Originally Posted by pacificblue

If you wonder what hybrid means in this context, whether a hybrid car, a hybrid of different amp types (e. g. tube pre + chip power amp) or a hybrid of whatever, star882 refers to class D amps without integrated digital signal processing as hybrids. He refuses to acknowledge that class D amps are in fact analog amplifiers (PWM) and not digital amplifiers (PCM).

And indeed it is a fully integrated class D amp that does not need any further components. It is a pity that the manufacturer only gives a rudimentary set of specs. By the description those amps are rather intended for low-cost, lo-fi music reproduction.

Class D can be analog input (which makes it a hybrid) or digital input (which makes it a true or pure digital). The one here is a hybrid since it accepts analog input. The Delta Sigma modulator takes the analog input and outputs a digital bitstream, which drives the output stage. Hence it is a hybrid since it uses both analog and digital. If the modulator took digital input instead, the entire modulator would be a digital circuit.
An Introduction to Delta Sigma Converters

[pacificblue]

from Class-D Amplifiers
Figure 3 shows a typical PWM signal modulated by a sine wave. Notice that it is designed so signals between –1 and 1V will produce 0% to 100% duty cycles, 50% corresponding to 0V input. The 'digital' output uses standard logic levels, where 0V is a logic '0' and 5V is a logic '1'. Because of this digitisation of the signal, PWM amps are sometimes erroneously referred to as digital amps. In fact, the entire process is far more analogue than digital.

from Class D Amplifier - Wikipedia, the free encyclopedia
The term "class-D" is sometimes misunderstood as meaning a "digital" amplifier. While some class-D amps may indeed be controlled by digital circuits, the power stage deals with voltage and current in function of time. The smallest amount of noise, timing uncertainty, voltage ripple or any other non-ideality immediately results in an irreversible change of the output signal. A digital circuit also uses physics to operate, but those same errors will only lead to incorrect results when they become so large that a signal representing a digit is distorted beyond recognition. Up to that point, non-idealities have no impact on the transmitted signal. The difference between digital and analogue signals is that digital signals are subsequently interpreted as numbers whereas in analogue signals the exact waveform matters.

from http://users.ece.gatech.edu/mleach/e...01/ClassD2.pdf
The “D” in class-D is sometimes said to stand for “digital.” This is not correct because the operation of the class-D amplifier is based on analog principles. There is no digital coding of the signal.

[star882]

In the real world, everything is analog. Ideally, the output of the modulator would be either 0 or 1, with no in between state. It's just that the laws of physics forces a finite transition time. (We're also ignoring the output stage and gate drives.)

It is possible to "build" a purely digital Delta Sigma modulator in Verilog, which would only consist of digital signals.

So a "pure digital" class D amplifier is as digital as any real world "digital" chip. In the real world, digital is just a form of analog where the transistors spend most of their time fully on or fully off. At high power levels, you generally want your transistors to efficiently control power as opposed to wasting it on trying to imitate Tiffany Yep, as a friend of mine has said.

[mace1337]

Originally Posted by star882

Class D can be analog input (which makes it a hybrid) or digital input (which makes it a true or pure digital). The one here is a hybrid since it accepts analog input. The Delta Sigma modulator takes the analog input and outputs a digital bitstream, which drives the output stage. Hence it is a hybrid since it uses both analog and digital. If the modulator took digital input instead, the entire modulator would be a digital circuit.
An Introduction to Delta Sigma Converters

What the hell?

Class-D is not purely digital.

The A/D converter you describe converts to pulse code modulation, whereas Class-D operates on principle of pulse width operation.

All you need to conver the PWM output to AC is a lowpass filter.
A class-D amplifier operates in the analog domain, no A/D needed.

@ThyDntWntMusic:

For that money, I'd say try one, see how it works.

[ThyDntWntMusic]

it seems they only give 8ohm ratings, which confuses me?

also, they give a voltage range, but don't say what voltage gives what power...

they rate them upto 24volts... surely more voltage equals more power?

[mace1337]

Not really, since at lower voltages it just draws more current.

[wwenze]

VMA2013/2015 6W/15W Audio AmplifierProduct Details

Max power increases with load impedance... baby has limited output current, not surprising for its size and cost.