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Digital Receivers

Discussion in 'Receivers and amplifiers' started by Mattrage, Mar 4, 2004.

  1. Mattrage

    Mattrage Regular member

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    Lately I have seen what are being advertised as "Full Digital Receiver/Amplifiers." I have no idea what this means. The spec sheets on them don't look any better. They are cooler, quieter, and smaller, but is there any advantage sound-wise? Fundamentally, what makes a receiver "digital"? You're going to have to use a DAC at some point, right? I'm extremely skeptical of this stuff. Somebody set me straight!
     
  2. Damon1

    Damon1 Regular member

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    Man, I'm not too sure, either.

    But I think It just means an amp that can playback digital audio + digital video, which would just mean an amp with optic and coaxial connections for audio + composite or similar digtal video connections for video. but I think it would also have to have digital video outputs as well as inputs for full intergration with HD tv set top boxs, digital cable, DVR's, etc.

    If I'm wrong someone please Iluminate us as I'd like to know.

    p.s. something tells me that to be "fully" digital those digital video inputs and outputs would have to be HD compatible( accept 1080i). So something might? have to different for that.
     
    Last edited: Mar 5, 2004
  3. Mattrage

    Mattrage Regular member

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  4. Damon1

    Damon1 Regular member

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    Thanks for the link, looks like this is some cutting edge stuff. Straight digital conversion, heh! I gotta look into this! So that means no DAC, no converter. This may be the future?
     
  5. Oriphus

    Oriphus Senior member

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    Firstly ill address the website:
    This only applies if you are taking the digital signal and converting it to anologue (such as playback) and then converting it back to digital.

    What they mean by digital receivers is that once the signal has entered the Receiver in digital format, via CD, DVD or any other digital means, it will stay in digital. Some amplifiers convert the digital signals to anologue before processing them with a digital sound processor. All this means, which is the norm in good amplifiers now, is that the Digital Sound Processor, processess the raw digital material from the sender (DVD player), before sending it to the converter for anologue for output to the speakers (in sound waves and frequencies). Its no big deal really.

    My advice, think about what money you want to spend on an amplifier. Think what you are going to use it for. Think whether you should include in your budget, speakers (usually recommended) and cable (expensive stuff is good). Then when you've done that, come back here, tell us yuor needs nad we'll help and give you advice as to what we would get in your shoes with your budget. Then you can make your own choice.

    Chris
     
  6. Mattrage

    Mattrage Regular member

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    I already know what I would buy if I had money for such things, and that's not on the list. I was just wondering if this technology has any real validity, or if it was more just a gimmick. I've heard several in person and they have no audible advantage over their normal, less expensive counterparts. Also, the fact that they have started incorporating this technology into cheap HTIB (Home Theatre in a Box) products leads me to believe that there's really not much to it anyway. Thanks for the replies!
     
  7. jeff-o

    jeff-o Member

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    Actually, many of these digital amplifiers use what's called a class-D amplifier. Most traditional amplifiers use high-power transistors or FETs that are not very efficient at all, dumping 50% of the energy they draw as heat. That's why your amp needs all that ventilation and heatsinking.

    A Class-D amplifier is up to 90% efficient, so they give off far less heat. If you see a 500W amplifier in a package the size of your DVD, you know that it's using a class-D amplifier inside.

    So what's the catch? Class D amplifiers still use FETs to amplify the sound, but do so differently from traditional amps. Instead of feeding a steady signal from the source, the sound is broken up and sent as very high frequency pulses to the FET amplifier. The frequency is well over 100kHz. This results in less heat produced, with about the same sound reproduction. Of course, the signal is averaged out before it hits the speakers using capacitors and inductors. In the beginning, digital amplifiers did not have as good THD and SNR specs as their traditional cousins. They also produced a lot of EMI radiation, which is not good for your CRT TV.

    As far as I know, manufacturers have worked hard to eliminate these problems. The sound reproduction specs are much better, comparable to mid-range amps for less money. The EMI problem is solved with adequate shielding.

    As was stated in a previous post, using a class-D amplifier allows manufacturers to skip the step of converting a digital signal to analog for amplification. This step increases size, design complexity, and ultimately cost.
     
  8. Oriphus

    Oriphus Senior member

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    All true, but i cant see the audio enthusiasts (Audiophiles) using Class D amplification with Class A around. It will be interesting to see where this goes to...

    However, is Class D amplification really truely all-digital? The answer i guess is no. They are not driven directly by coherent binary data. They do act digitally in that the output drivers operate either in the fully ON-region or fully OFF-region. I was once told to think of the Class D amplifiers as being similar to a switch mode power supply,but with audio signals modulating the switching action.

    When you say Class D amps still use FET's, it is true, but i think they are MOSFET's, with the MOS meaning Metal Oxide Semiconductor


    The obvious advantage to Digital Amplifiers (Class D) is the decrease in the consumption of power they use. I think the figures are something Class A/B - efficiencies of around 20-30% for the power they use, whereas Class D is about 80-98%. Obviously this means, as you stated, that there is far less heat generated and so the bulky power packages and heatsinks can be eliminated. All this means smaller and cheaper receivers - which cant be a bad thing.

    Does it compare to Class A or A/B in terms of sound quality? Class D amplifiers have been criticized as lower quality than Class AB systems with use limited to lower performance applications such as public address systems. Through recent advances in power semiconductor devices and the need for better efficiency under battery power, Class D now sees a new length of interest. It is now possible to develop a Class D design that may rival most AB amplifiers. Though, to be honest, i wouldnt change from Class A A/B, would you?
     
  9. Mattrage

    Mattrage Regular member

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    Great posts guys! As to the last question, I certainly wouldn't, given the difference in sound quality. As a guitar player, I see the difference as being very much akin to the age-old comparison of a tube amplifier to a solid state amplifier: try as they might, they can't make a solid state amplifier that will please my ear like a good ole' tube amp. Again, thanks for the info and commentary, that's just what I was looking for when I started the thread.
     
  10. jeff-o

    jeff-o Member

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    I think that for the average consumer, class D amplifiers are fine. Most people I talk to have no idea what THD+N and SNR are, they are content knowing that their amplifier has more inputs then their neighbour's does. Manufacturers know this, and so they cater to both ends of the spectrum just like almost every other company in the world.

    Class D amps really are an excellent thing for battery powered devices. Things like MP3 players, cell phones and even laptop computers are already benefiting from class D amps.
     
  11. Oriphus

    Oriphus Senior member

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    Definitely agreed, the obvious advantage has got to be mobility...

    On the THD, do you know what the Marantz SR5400 is? What do you deem as resonable, anything under 1%? I've seen figures of around 0.05%, but havent seen anything concrete on Marantz...
     
  12. jeff-o

    jeff-o Member

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    A review on Marantz's website, from Sound & Vision magazine, says that the SR5400's THD+N is 0.03% in nearly all cases. I consider anything below 0.05% to be great for nearly everyone.

    You can get a review here:

    http://www.marantz.com/hifi/america/news/review_.zip
     
  13. Oriphus

    Oriphus Senior member

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    Cheers Jeff, was wondering what it was. Thats a good figure as well.
    Thanks
     

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