Digital, Amps, Signal Processing & More...

[clint e.]

Class-D audio power amplifiers (APAs) were first introduced nearly 50 years ago. Since then, they have been used sparingly in a relatively small number of applications with limited bandwidth, such as public address systems and telephony equipment. This will soon change as a new class of integrated Class-D APAs make their way into such mainstream applications as portable computers, battery-operated music systems, wireless communication devices, and other compact low-power systems.




The Truth About Digital (Class D) Amplifiers


" Firstly I'd like to point out that "digital amps" is a misnomer. There are two categories:

Analog-controlled class D. Switching amplifiers with an analog input signal and an analog control system. Normally some degree of feedback error correction is present.
Digitally controlled class D. Amplifiers with a digitally generated control that switches a power stage. No error control is present. Those that do have an error control can be shown to be topologically equivalent to an analog-controlled class D with a DAC in front.
Both use switching power stages and have high power efficiency as their most eye-catching feature.

Why Digital… Digitally controlled class D initially delivered a success in the form of the Tact Millennium. However, by its mere existence this device proves that obtaining good performance from such a contraption is largely an analog design exercise - a very complicated and expensive one at that. After all, the distortion phenomena that stand in the way between a perfectly formed digital control signal and a perfect analog replica are inherently analog. Similarly, cheaper digital class D's (such as Sony S-Master and TI's) go on to show that at practical price and complexity levels, performance is quite abysmal (better than 0.1% THD is unusual and be sure it aint just third harmonic!)

One should ask the question: would any D/A converter designer in his right mind build a DAC using power components? Probably not. Then how about the old argument that digital-to-the-end is best? Well, I should think the D/A barrier is best put precisely where it allows the whole signal chain to perform at its best and why should we believe that this is necessarily right at the end? Quite obviously the concept of a digital class D amplifier was dreamt up by DSP folks who presumed that the signal should be kept out of the big bad analog world as long as possible, at the same time expecting the power stage, power supply and filter (all highly analog in nature) to perform flawlessly.

…or Rather, Why Not?
Analog controlled class D is quite a different story. Although most commercially available implementations are well short of this ideal, proper error control can be used to make analog class D amplifiers with performance figures giving the digital variety a run for their money, at a price well below that of even the cheapest digital class D's. They can have vanishingly low output impedance right across and beyond the audio range (which the digital ones can't!) while frequency-independent distortion (for that "zero-feedback sound") is actually easier to achieve than with digital ones.

To the Ear
So how about sound? The output filter's highish HF output impedance, when uncorrected (in amplifiers without post-filter-feedback, ie. all digital ones and many analog ones too) is responsible for the oft- quoted tube-like warmth and air. At low frequencies the filter impedance is low, resulting in a commanding, dynamic bass. Because switching amplifiers previously had a reputation for sounding harsh (due to people who hadn't heard them but presumed that switching couldn't mean anything else), about every modern entry in the field was heralded as the "first audiophile class D". Read a review about the Bel Canto Evo or the Sharp 1-bit (which is analog, btw) to see what I mean. Keep in mind that if a device sounds radically different from what you've held in high esteem previously, there's usually something fishy going on.

Unfortunately, while warm and airy is nice, it isn't all you need for real audiophile sound. I like to think audio components should sound neutral and transparent too. A frequency response that wanders 10dB off the line at 20kHz isn't conducive to neutrality. High THD isn't good for transparency, especially when it goes up with frequency. Ergo the Tact Millennium (which has flat and low THD but a nonflat frequency response) sounds transparent but not neutral, and your average transistor amp (which has a low output impedance but sharply increasing THD) sounds neutral but not transparent.

Now, the technology (if you can call a circuit with 16 transistors that) to deliver low output impedance with frequency-independent low distortion in class D exists. Built with audiophile-grade parts it'll scare the pants off any high-end amp (while I'm the designer of that circuit and thus some care reading this statement is warranted, I do have a lot of serious folk to back up my claims). Of course, having these characteristics it sounds more like other high-end amps than that it sounds different, in the same vein as that the best tube gear and the best solid state gear don't differ by miles in sound.

The Upshot

Digitally controlled class D: dead end street.
Analog controlled class D: definitely the future, although you shouldn't expect it to flatten competition from traditional solid- state and tube amps by a tremendous margin.
In the very high-end segment the three are bound to coexist for a very long time. In mainstream gear, class D is certain to take over the scene completely, although one serious problem remains: building a good class D amp is an order of magnitude tougher than a linear amp, and the knowledge required is much more diverse. It may take long before each large company has at least one knowledgeable designer. It won't stop them from putting class D based products on the market, but until then and unless they buy completed amplifier modules from specialist vendors (which eastern companies rarely do, they'd rather commit harakiri than having to swallow their pride), they will be putting out seriously substandard products for years to come. "

"Quote from Bruno Putzeys, Chief Engineer Class D Audio at Philips Digital Systems Labs"


This post has been edited by clint e. on April 25, 2007 11:50 am

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[clint e.]

Here's a list of some Digital Amplifiers

Acoustic Reality http://www.acoustic-reality.com/
eAR202, etc (ICEPower)

Analog Research Technology http://www.analogresearch-technology.com/

AudioArt (NL) http://www.audioart.nl/
Van Medevoort MA240 (Hypex UcD)

AudioResearch http://www.audioresearch.com/
150.2, 300.2, 150M (Tripath)

B&O http://www.icepower.bang-olufsen.com/sw1067.asp
(ICEPower)

BelCanto http://www.belcantodesign.com/products.html
Evo 2, Evo4, Evo6, Evo2i integrated (Tripath)

Bertram http://www.audiokabel.dk/eng-main.htm
(ICEPower)

Cary Audio http://www.caryaudio.com/
A 306 power amplifier

Channel Islands Audio http://www.ciaudio.com/
D100, D200 (Hypex UcD)

Egosys http://www.egosys.co.jp/
Audiotrak DrAMP (Tripath)

Elan http://www.elanhomesystems.com/
D1200, D1600 (12 and 16 channel power amps, Tripath)

Flying Mole http://www.flyingmoleelectronics.com/
(proprietary class-D)


H2O Audio http://www.iceh2oaudio.com/
M250, M500 (ICEpower)

Halcro http://www.halcro.com/logic/home.asp
Lyrus

Hypex http://www.hypex.nl/
Manufacturer of UcD modules

Integra /Onkyo http://www.integrahometheater.com/
DTA 9.4 7x120W 8Ω

Hypex Electronics, http://www.hypex.nl/

Jeff Rowland http://www.jeffrowland.com/
(ICEPower)

Jjaz Audio http://www.jjaz.dk/
(ICEPower)

Kharma http://www.kharma.com/
MP150

LC Audio http://www.lcaudio.com/
Predator SE (ZapPulse)

Medius [DK] http://www.medius.cc/
A II, A III

Midgard Audio http://www.midgardaudio.no/www/
(ICEPower)

MindCraft (NL) http://www.mindcraft.nl/
Media Amp One (Hypex UcD)

Nuforce http://www.nuforce.com/
Ref 8, Ref 8b, Ref 9 (proprietary class-D)

Onkyo A-933

PSAudio http://www.psaudio.com/
GCA, GCMC

Red Dragon Audio http://www.reddragonaudio.com/
(ICEpower)

RedWineAudio http://www.redwineaudio.com/
Clari-T, Lotus (Tripath)

Rotel http://www.rotel.com/
1077 (ICEPower)

Sharp http://www.sharpusa.com/
SM-SX1, SM-SX100

Sonneteer http://freespace.virgin.net/sonneteer.audio/bronte.html
Brontë (Tripath)

Sony http://www.sony.com/
TA-DA9000ES (S-Master)

Spectron http://www.spectronav.com/
Musician, Troubador (int amp w digital inputs)

TactAudio/Lyngford http://www.tactaudio.dk/ http://www.lyngford.com/
Millennium & others (Equibit)

TEAC Esoteric http://teac.co.jp/av/esoteric/
AZ-1 pre-main (translated)

Trends Audio TA-10 http://www.musical.ca/catalog/item/4377302...CFQMgUAodemczmA
(Tripath)


UniwaveTek http://www.uniwavetek.com/
Anaco II

Yamaha http://www.yamaha.com/
MX-D1


This post has been edited by clint e. on April 25, 2007 11:37 am

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[clint e.]

Sonic T-Amp.

some linteresting links about it :

http://www.tnt-audio.com/ampli/t-amp_e.html

http://www.tnt-audio.com/clinica/t-amp_tweaks_e.html

http://www.michael.mardis.com/sonic/start.html

http://mywebpages.comcast.net/ampbox/page2.html

http://www.6moons.com/audioreviews/sonicimpact2/t2.html

http://www.auricles.com/t__amp_upgrade.htm



This post has been edited by clint e. on April 25, 2007 11:40 am

[clint e.]

Jitter


http://www.altmann.haan.de/jitter/english/engc_navfr.html

https://cdnav.sslpowered.com/shared/Jitter%20DBT.pdf - it's in pdf.

This post has been edited by clint e. on April 09, 2007 06:49 am

[clint e.]

An Introduction to Delta Sigma Converters

http://www.beis.de/Elektronik/DeltaSigma/DeltaSigma.html

This post has been edited by clint e. on April 09, 2007 06:51 am

[clint e.]

CD vs. DVD-A vs SACD

http://sound.westhost.com/cd-sacd-dvda.htm

This post has been edited by clint e. on April 09, 2007 06:54 am

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[clint e.]

Sonic T-Amp Gallery
http://www.octopusamps.com/gallery/

There is a new T-Amp dealer on the Web.
http://www.audiomagus.com/

Sonic Impact Super-T Amp.
http://www.michael.mardis.com/sonic/super.htm

Trends Audio TA-10 Amplifier Modifications
http://www.michael.mardis.com/trendamp/mods-1.htm



This post has been edited by clint e. on April 25, 2007 11:42 am

[clint e.]

This post has been edited by clint e. on April 25, 2007 11:44 am

[Charivari]

jitter

Attached File ( Number of downloads: 140 )
 Jitter_20DBT.pdf

[clint e.]

Retro-Digital-iTube

Not only Fatman have a tube amp for users of Apple iPod or any other portable mp3 device, there's a new kid in town :

The Roth Audio MC4 Music Cocoon.
It's an Hybrid machine, with 2x12AX7 and 2x12AU in preamp stage and Mosfets in the power stage.

http://www.rothaudio.co.uk/docs/products/mc4.shtml



iPodding a classic table radio

Here's a link to a flickr set full of pictures documenting the transformation of a vintage 1947 National Union G-619 table radio found at a flea market into an iPod amplifier.

Ken pulled out the original tube-based radio chassis and replaced it with a modern transistor amp and speakers.

http://www.flickr.com/photos/obeyken/sets/72157594170289282/

This post has been edited by clint e. on April 27, 2007 06:39 am

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[clint e.]

Digital Audio Basics

"Nyquist determined that if a signal is sampled at twice its maximum frequency, the samples will contain all the data required to reconstruct the original signal. In audio, the original signal is a complex wave shape and there is debate as to what frequency band is essential...."

http://www.amek.com/oldsite/datashee/aesebu.htm

This post has been edited by clint e. on May 11, 2007 06:47 am

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[clint e.]

The Importance of Digital Filtering

"What is the role of a digital filter? It's a common misconception that the (digital) filter in a CD player or D-A processor chiefly exists merely to filter out ultrasonic spuriae and thereby also reduce aliasing distortion. If this were true, then it would be optional to even have the filter at all."

http://www.iar-80.com/page25.html


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[clint e.]

Something wrong with your cdp ?

Notes on the Troubleshooting and Repair of Compact Disc Players and CDROM Drives

How to Fix Your CD Player


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[clint e.]

Sorry.

This post has been edited by clint e. on May 20, 2007 03:37 pm

[clint e.]

USB Turntables

Not long ago it was impossible to me think of writing something about this subject...but, the late technology developments allow us now, to plug a turntable via an USB cable directly into your computer or any mp3 device.
Technology runs fast...
Of course you can't expect an "audiophile" sound from these audio devices, but some of them are close to that; because like in analog audio, everything matters: Good cables & computer power supply, a good soundcard & amp or digital amp (witch are cheap and great sound) and of course a good pair of speakers. And if you're using a comp. as an audio source you need also a good dvdr/cdp.
With these things in mind and with a possibility of having an USB TT - witch are cheap, practical and simple to use and came with a lot of audio software - you're very close to have a great sound.
Well, maybe not that "audiophile" sounds, but imo an "audiolover" kind of sound.

So, here's a list of some USB Turntables available in the market:

Price range between 100 and 150 USD.

Stanton T.60

Numark TT1650

Sony PS-LX250H

Audio Technica AT-PL50

iTTUSB

Portable Turntables Yes, they are back again!

Numark PT-01

Vestax Handi-Trax

In this digital age, Vinyl rules again.

This post has been edited by clint e. on June 02, 2007 07:44 am

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