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From: bill@vrdxhq.verdix.com (William Spencer)
Newsgroups: sci.electronics,rec.audio
Subject: Re: Digital/Analog converter help needed
Message-ID: <35906@vrdxhq.verdix.com>
Date: 20 Jul 90 16:01:59 GMT
References: <3550.26a1d2d7@ccvax.ucd.ie>
Followup-To: sci.electronics
Organization: Verdix Corporation, Chantilly,  VA
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in article <3550.26a1d2d7@ccvax.ucd.ie>, b_haughey@ccvax.ucd.ie (Brian J Haughey) says:

> What I am looking for is info on D-A converters that can directly drive
> speakers. My query is : would the scaling factors of such a D-A have
> to change as the volume went from very low to very high ?

AND most important:
> Any advice, tips, or references welcome. Thanks a lot.

What are you trying to accomplish? Low cost? Amplifier chips start about 
50 cents. This does bring up a good subject though... first, no, it's hard
enough to do 16 bit D/A, much less put power handling into the same chip.

But a higher output D/A would be nice. Best would be a high voltage output.
This output would be essentially passive: a resistor ladder connected to the
output by (FET) switches. Digital volume contol could be used but
controlling volume in analog would be better. Passive filters could be used.
If the voltage was high enough no voltage amplification would be required.
Current amplification would be needed in ther form of unity gain buffers.
Merely increasing the voltage ratings of a D/A chip is very possible.

If digital could provide a means of eliminating almost all analog 
circuitry this would answer many audiophile concerns. Digital is
complicated enough on its own without following it with complex analog.

A "digital speaker" has been built (Meridian). All it really eliminates
is analog cabling. This is not enough to justify it, especially if
there's any chance of using analog sources.

ANOTHER POSSIBILITY: "One bit" conversion at power. This is simialar 
to a "switching"  or "class D" amplifier but there's also big differences.
Despite the high effieciency and power output possible this type of 
amplifier is not popular and for good reason. Analog type switching
amplifiers rely on loop feedback. "One bit" D/A conversion if a forward
only process. Don't know what this would do with a complex load though.
"One bit" conversion could also be used for the high voltage D/A 
concept above.

Hope someone can benefit from these ideas. I'm not finished mucking
with conventional analog yet.

bill S.