Xref: utzoo sci.electronics:12976 rec.audio:22977
Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!sun-barr!newstop!sunaus.oz!softway!otc!damos
From: damos@otc.otca.oz (Daniel Amos)
Newsgroups: sci.electronics,rec.audio
Subject: Re: Digital/Analog converter help needed
Message-ID: <1810@otc.otca.oz>
Date: 19 Jul 90 23:57:53 GMT
References: <3550.26a1d2d7@ccvax.ucd.ie>
Lines: 32

in article <3550.26a1d2d7@ccvax.ucd.ie>, b_haughey@ccvax.ucd.ie (Brian J Haughey) says:
> Xref: otc sci.electronics:3089 rec.audio:747
> 
> [Repost of a query that died somewhere...]
> 
> Hi there.
> 
> I'm planning on doing some work with D-A converters, and I need some 
> info before I start.
> 
> 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 ?
> 
In all my experiences with DACs, I haven't seen one that could drive
speakers directly.  Generally, DACs are designed to produce a reasonably
accurate analog representation of a digital number - they don't include
high power amplifiers to drive low impedance loads.  A possible reason
for this is that amplifiers usually dissipate a fair amount of heat,
which is not really good for resistor chains inside DACs - you would
prefer temperature stability.

In practice, (ie if heat problems could be solved), a high resolution
DAC (eg 22 bits) could be used, and a digital multiplier would multiply
the bit stream from the digital source by a constant (the volume setting),
and the DAC would output the result.  Naturally, the DAC would require a
peak-to-peak output voltage of at least 50V (to provide a reasonable
output power).

Dan Amos
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