Re: [LAU] What audio interface to use for a Linux-powered surround preamp?

(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@email-addr-hidden> wrote:
> On Wed, Dec 14, 2011 at 7:59 PM, Johan Herland <jherland@email-addr-hidden> 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@email-addr-hidden>
www.herland.net
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