(Oops, forgot to CC the list. Chuck: There's a small update - search for "minidsp") On Thu, Dec 15, 2011 at 18:37, Charles Henry <czhenry@xxxxxxxxx> wrote: > On Wed, Dec 14, 2011 at 7:59 PM, Johan Herland <jherland@xxxxxxxxx> wrote: >> I'm planning a hobby project to build an all-digital surround/hi-fi >> system. Regular surround/hi-fi systems convert digital input sources >> to analog in the surround processor/preamp, but I want to keep the >> signal in the digital domain as far as possible (by using all-digital >> class D power amps, aka. "PowerDACs" [*] that convert a PCM signal to >> an amplified PWM signal that is feeds the speaker directly through an >> LPF. > ... >> [*]: Examples of all-digital power amps include the NAD Direct Digital >> amps (M2 and C390DD), the Tact True Digital Amplification series, etc. > > I have previously looked for such a product, with no luck--I started > to believe that no such thing existed! Do you have any more examples > that I could check out? There certainly aren't many products available. Here's what my (probably incomplete) research has found so far: In the late nineties, Toccata Industries developed a technology called Equibit <URL: http://en.wikipedia.org/wiki/Equibit >, which is - AFAIK - the first implementation of a digitally driven PWM amplifier (i.e. the first "true" digital class D amp). Toccata and Equibit were acquired by Texas Instruments in 2000, and Equibit has since become available in TI's "PurePath Digital" products: <URL: http://www.ti.com/corp/docs/landing/tas5261/index.htm?DCMP=hpa_amp_tas5261&HQS=Other+PR+tas5261-pr >. Along the way, a few companies have built products on top of Equibit: - TacT Audio has a whole series of digital amps using their "True Digital Amplification" technology: <URL: http://www.tactlab.com/tact_products.html#digital_amplifiers > - Lyngdorf (closely associated with TacT) has the Millennium Mk4 and the TDAI 2200: <URL: http://www.lyngdorf.com/content/view/16/36/ > - Panasonic SA-XR series amps (now abandoned, AFAICT): e.g. <URL: http://shop.panasonic.com/shop/model/SA-XR700?support > - I've just discovered a new company called "minidsp" that produces a DIY kit called "miniAMP", based around the Equibit chip: <URL: http://www.minidsp.com/products/minidspkits/miniamp >. At some point, Sony also did a full digital amp series called "S-Master PRO", based on their own technology: <URL: http://www.docs.sony.com/release/ES_STR_05_Final.pdf >. Here are a couple of product names: STR-DA9000ES, STR-DA7100ES. I don't know if Sony is still pursuing S-MASTER. Finally, we have the DDFA (Direct Digital Feedback Amplifier) technology started in 2005 by Zetex (now a subsidiary of Diodes Inc.). Technical information available at <URL: http://www.diodes.com/applications/audio/ddfaa/ >. NAD (in collaboration with Zetex) first launched the M2 Direct Digital Amplifier a couple of years ago: <URL: http://nadelectronics.com/products/masters-series/M2-Direct-Digital-Amplifier >, and they are just now launching the follow-up model - the less expensive C 390DD: <URL: http://nadelectronics.com/products/hifi-amplifiers/C-390DD-Direct-Digital-Powered-DAC-Amplifier >. It seems there are currently no other users of the DDFA technology. I've seen press releases for a Theta Digital "Virtu PowerDAC" product, but there's no trace of it on TD's own webpages, so I assume it's abandoned. AFAIK, that covers the market for all-digital amplifiers. I hope you find it useful. I should emphasize that I'm a software professional, and not an electronics expert, so I only have a high-level understanding of how these devices work. That said, from what I've read, I find the Zetex DDFA technology the most promising so far, and I'd probably go for the NAD M2 or C 390DD if I were to buy a hifi stereo amp today. On the other hand, the miniAMP may be a very interesting option for putting the amp directly into (or next to) the speaker, thus maintaining a digital signal all the way to the physical speaker. If we're extra lucky someone might even produce a monoamp (or DIY kit) based on DDFA... Have fun! :) ...Johan -- Johan Herland, <jherland@xxxxxxxxx> www.herland.net _______________________________________________ Linux-audio-user mailing list Linux-audio-user@xxxxxxxxxxxxxxxxxxxx http://lists.linuxaudio.org/listinfo/linux-audio-user
