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From: firstname.lastname@example.org (Tom Bruhns)
Subject: Re: Polyphase network loss
Date: 12 Sep 2002 14:24:31 -0700
References: <email@example.com> <firstname.lastname@example.org> <email@example.com>
NNTP-Posting-Date: 12 Sep 2002 21:24:31 GMT
"Richard Hosking" wrote in message news:<firstname.lastname@example.org>...
> The problem is that there are 4 paths which need preamps from the Tayloe
> mixer to the network.
> Also I would like to avoid dual power supplies and have +12 V only with low
> current drain.
There are other op amps that are pretty low distortion and reasonably
low noise over the audio range. One example is the OPA2134 (or
OPA2132). You can certainly do better for noise than their about
8nV/rtHz, but their distortion is very low, and that may be the more
important thing. The mixer should be limiting the output bandwidth to
the audio range, so you shouldn't have to handle significant signals
above that. I'd assume it's only on receive that there's an issue.
Those amps will easily run on 12V total supply voltage, at about 4mA
per amplifier. You may be able to find a better part with respect to
the current-distortion product, but generally, really low distortion
costs current. The numbers I gave are duals; you can get quads and
singles too. OPA627's will run on 12V too, but are almost twice the
current (not to mention a LOT more money). Lower noise, and rather
lower distortion. Only available in singles. The typical design
tradeoff! You want zero distortion, zero noise, infinite bandwidth,
at 100% power efficiency, but you have to settle for less, and decide
what's most important to optimize your design.
> I tried to model it on my old version of Microcap (3!!)
> but it wouldnt allow enough nodes - I have the free student version
> Do you have pointers to a cheap/free simulator which could model a 6-8 pole
> network? This would be about 36 nodes.
You can try the file spice3f4.zip at
ftp://ftp.heise.de/pub/ct/spezial/, if you don't mind entering your
circuit as a Spice netlist. I've tried some others and had trouble
with them, so I tend to keep using this "raw" version. You might also
try the Spice available from the Linear Technology web site; it's
deceptively named SwitcherCAD III. Try
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