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Here are some sites that have information on the LM1973 audio mixer
chip.
http://search.dogpile.com/texis/search?q=LM1973&geo=no&fs=web
Timothy Stockman wrote:
>
> >|3. Adjust levels *before* the A/D to prevent overload while maximizing dynamic
> >| range. Most modern MD recorders have fixed gain *berfore* the A/D; not a
> >| good thing!
>
> >Absolutely. So you use the LM1973's you mentioned in a programmable gain
> >configuration, right? Are these parts quiet enough to work with
> >microphone-level signals?
>
> I was planning on using a topology that had the LM1973 in the *feedback* loop
> of the microphone preamp stage. Therefore, it would get its drive from the output
> of the mic preamp, after 40 dB or so of gain and attenuate it back to microphone
> level before feeding it to the inverting input. They spec these chips at over 100 dB
> S/N, and this configuration exploits the available S/N to the max, so my guess is
> that it would be quite acceptable. This topology is what I was refering to when I
> was talking about channel trim.
>
> The LM1973 contains three pots; I'd use the first one for level trim as described\
> above, and the other two as conventional attenuators, one feeding the left
> channel and one feeding the right. That would allow the controlling microprocessor
> to emulate channel gain and pan, all the while maintaing an optimum gain
> structure to maximize S/N while minimizing overload.
>
> >you're well over
> >1/2 watt--roughly 20 hrs. with 3-4 AA cells-- is this what you have in mind
> >for a portable MD system?
>
> That would be great... I'd planned to use NiHM AA cells...
>
> >Also, I would think that some MD titling interface built into the mixer
> >might be a nice feature that would distinguish your mixer from anything else
> >that's commercially available.
>
> A great idea! I'd probably use an 8051 derivative (we've had great success
> here at work with the Philips 87c552 in battery powered equiopment; it has
> some nifty power-save and sleep modes). This CPU would probably have
> enough resources left over to run a titling program.
>
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--
Jim Coon
Not just another pretty mandolin picker.
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If Gibson made cars, would they sound so sweet?
My first web page
http://www.tir.com/~liteways
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