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What is a Digital Amplifier receiver


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#1 of 31 wes18

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Posted January 23 2005 - 02:07 PM

I'm having a difficult time understanding the difference between a traditional receiver (such as my Yamaha RXV 1200) and one that has digital amplification (such as the Panasonics). I can't find any article that describes the differences in a way that makes sense.

Thanks in advance.

#2 of 31 NickSo

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Posted January 23 2005 - 02:21 PM

IN a traditional analog reciever, when a digital signal is recieved it is first converted to an analog signal through a DAC (Digital-Analog converter). Then the ANALOG signal is amplified and the amplified signal is sent to the speakers.

In TI's PurePath digital amplification, the signal stays Digital all the way through, and is outputted as PWM. There is no Digital to Analog conversion whatsoever throughout the whole process.

Better explanation/detail here:
http://www.psaudio.c...ticles/sdat.asp


#3 of 31 Dave Moritz

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Posted January 23 2005 - 08:39 PM

The suposed advantage is that the signal stayes digital through the amplifier section. And that the ampifiers are supposed to be more efficent than standard analog amplifiers, if I am not mistaken. Companies like H/K and Sony ES are marketing digital recievers that are said to sound as good as more exspensive higher end models. Nick's explanation is very good and I hope the link he provided helps. I heard the Sony STR-DA9000ES digital reciever at the CES show in Vegas last year. Needless to say I was not impress as it had a slightly harsh cold sound to it, lacking warm and detail. These digital amplifiers have been compaired to high end brands, but imho. While they may be the future they need more refinement and can not touch a really nice analog high end amplifier. I personally would not own a digital amplifier or reciever with a digital amp section. Heck I would rather keep my Yamaha 995 over a new Sony ES digital reciever!
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#4 of 31 Ricky c

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Posted January 24 2005 - 01:01 AM

Would like to know does it mean that digital receivers wont do 2ch like traditional receivers can.

#5 of 31 Kent Y

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Posted January 24 2005 - 03:08 AM

Sure the digital recs will do 2 channel. The digital amps have nothing to do with processing/decoding. I think you're confusing the amps with the fact that digital source inputs are frequently used for multi-channel sources (Dolby Digital, DTS, etc.). Many CD players have digital outputs, and they are only two-channel.

#6 of 31 Ricky c

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Posted January 24 2005 - 03:25 AM

I always thought that when you went into 2ch stereo mode it was analog.I guess you learn something everyday.

#7 of 31 Sami Kallio

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Posted January 24 2005 - 03:28 AM

As I understood it, they are digital PATH amplifiers. There is no such thing as digital amplifier. How could there be?

#8 of 31 Brian Fellmeth

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Posted January 24 2005 - 04:13 AM

Quote:
There is no such thing as digital amplifier. How could there be?


There is such thing and here is how. Analog amp sends smooth AC current to the speakers. Digital amp sends discrete pulses of current. As long as the sample rate is high enough, the discrete pulsatile nature of the signal is inaudible.

#9 of 31 Sami Kallio

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Posted January 24 2005 - 05:09 AM

That's still analog signal, isn't it? How would you amplify digital signal? Shift by n bits? Posted Image

#10 of 31 NickSo

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Posted January 24 2005 - 05:52 AM

Quote:
That's still analog signal, isn't it?
Actually no, the signal thats being sent to the speakers is not an analog 'wave', but rather digital pulses, pulsing at 350,000 times a second whcih to the human ear hears a single smooth wave (kinda like how for movies its 24 frames per second, but we see smooth motion)

Read the link i posted in the first reply.


#11 of 31 AndersLS

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Posted January 25 2005 - 05:22 AM

Check out ICEpower amps...really, really cool!Posted Image

#12 of 31 Peter Fallon

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Posted January 28 2005 - 12:12 PM

Class D amplifiers are not digital amplifiers. They are PWM switching amplifiers. They function in a similar way to the switching power supplies you find in modern computers. The faster power transistors available today made it possible to apply the same ideas to amplifiers capable of covering the full audio range.

The first step in a Class D amplifier is generating a series of pulses through Pulse Width Modulation. The resulting waveform from the PWM process is the analogue audio on an analogue carrier. The series of pulses are amplified and then the carrier is filtered out with a low pass filter. The resulting output is amplified analogue audio, NOT a series of pulses.

There are different ways to handle the PWM process, including controlling it with the digital audio you wish to amplify. This doesn't make the amplifier a digital amplifier though. The process is a form of digital to analogue conversion and it's still an analogue waveform that's getting amplified in the end. It's just pushing the digital to analogue conversion to the very end.

#13 of 31 FeisalK

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Posted January 28 2005 - 03:59 PM

For the sake of simplicity and nomenclature, lets call PWM amplifiers digital, the same way we call PCM audio digital, when effectively PCM is only a storage/transport medium and not really audio, at least not until it comes out of your speakers.

not only is there such a thing as digital amplifiers - but there are a few different ways of doing it by different companies. Check out
http://www.tripath.com
http://www.ti.com (Equibit)
http://www.bang-olufsen.com (ICEPower) http://www.d2audio.com
http://www.flying-mole.co.jp/ and a couple of other companies I can't remember the addresses to.
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#14 of 31 Peter Fallon

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Posted January 28 2005 - 05:21 PM

That's just it, PWM in this case is the process of placing the analogue audio onto a carrier. The analogue audio is still there, it hasn't been converted into anything else. It's just riding on a higher frequency carrier. Place it through a low pass filter and you have your original analogue audio signal.

PCM is a way to carry a numerical representation of the original analogue audio. That numerical representation needs to be turned back into real voltages before our speakers can play it back and our minds can interpret it as music.

Yes real digital amplifiers do exist, I have quite a few devices that can function as such. I usually call them calculators though.

#15 of 31 FeisalK

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Posted January 28 2005 - 08:05 PM

IIRC The TI Equibit converts PCM to PWM - don;t ask me how they do it, tho Posted Image
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#16 of 31 Peter Fallon

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Posted January 28 2005 - 10:11 PM

As I mentioned it is indeed possible to use a PCM bitstream to control the PWM. The process is a digital (PCM) to analogue (PWM) conversion. It still doesn't make it a digital amplifier though, rather an analogue amplifier with a built in DAC.

Keeping the signal in the digital domain until the last moment isn't inherently better though. Going directly from PCM to PWM requires a more complicated design and seems to have an inherent flaw in that it impedes the use of feedback. A switching power transistor is also going to make a lot of noise, so now the final digital to analogue conversion takes place in the middle of the lion's den.

The aim of these switching amplifiers should be on it's efficiency. Smaller, lighter and less expensive (as a whole unit) while supplying the same output. The potential is there but so far too much effort has been placed into marketing these amplifiers as some sort of holy grail of signal purity wich they are not.

#17 of 31 David Judah

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Posted January 29 2005 - 11:46 AM

The negatives you mention, Peter, are worse case scenarios. The reason we are hearing so much about digital amps is because we now have the ability to overcome alot of the negatives you mentioned with proper implementation. In addition, there are advantages, besides efficiency, to keeping the signal in the digital domain until the very end.

The lack of large amounts of negative feedback is considered by many a good thing(as audiophiles have been touting for years). I won't go as far to say it is the reason there has been so much positive buzz about the Equibit solution, but it certainly is a possibility.

There are always compromises in the design of both digital and analog amps. The beauty of many of the digital amps is that even with alot of those compromises, they can sound great and they are inexpensive to produce. They will only continue to improve and offer more bang for the buck for consumers.

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#18 of 31 FeisalK

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Posted January 30 2005 - 07:45 PM

The Sound of Change: From analog to digital audio amplifiers (From eet.com)
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#19 of 31 Karl_Luph

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Posted January 31 2005 - 02:16 AM

Is this the same technology used in the Line 6 guitar amps? I think they've been out since around 1997, maybe earlier.

#20 of 31 Dave Moritz

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Posted January 31 2005 - 09:49 AM

As for myself I dont feel that digital amps in most casses can compete with analog amps. At least not when we are talking about very good quality analog amps. This will most likely change as the digital amps are improved. I personally would not purchase and current recievers with digital amps inside. Last year at CES I heard the Sony ES flagship that had digital amps and while it shound decent. I was not really impressed enough with it to place one in my own home theater system that currently has a Yamaha RX-V995 in it. Which I am looking to upgrade to ether a Denon AVR-4806 reciever or a pre pro. Just depends on my income at the time and what I can afford to invest.
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