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<DIV><FONT face=Arial size=2>I wanted to share some interesting chips found by
Tim "Servo" Parkhurst. The chips are the Maxim DG212, DC508A and DC509A. If you
like the 405x analog switch/mux chips, you should really like these -- they look
great on paper, anyway. If any of you happen to have experience with these
(particularly the 508) please let us know what you think of them.</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>The background: I got interested in modifying the
Oberheim OB-X VCF to provide BP and HP outputs in addition to LP, as provided by
the very similar SEM filter. My interest was simply in modifying 2 voice cards
that are not in an OB-X, but "AnalogueJeff" wanted to make this mod to his
actual OB-X. Having tested the basic filter mod and loved it, he decided to
modify his OB-X to save the filter settings in the presets. Jeff was willing to
forego the Noise source in favor of programmable filter modes. The OB-X has
limited control of noise: off, half, or full; the "half noise" and "full noise"
control signals are separate, so he had 2 bits to play with, enough to select
from 1 of 4 options. Having only 3 filter modes to choose from, this was great.
The next step was to find a switch of mux chip to do this
selection.</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>The OB-X has a number of 4053 8-into-1 mux chips in
the audio path, so I figured that we could use the similar 4052 dual 4-way mux.
Bzzzzz! Wrong! The switch configuration was perfect, but apparently the signal
levels are too high coming out of the filter -- as much as +/- 10V -- and the
405x can only handle 15 volt swings (the levels are apparently lower in other
parts of the voice circuitry). Bottom line: The 4052 was overloading. Not good.
We needed a new chip, and Tim may have found it.</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>So, now that I've made a short story long, you can
see Tim's findings, below.</FONT></DIV>
<DIV><FONT face=Arial size=2>--</FONT></DIV>
<DIV><FONT face=Arial size=2>john</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2><SPAN
style="FONT-SIZE: 10pt; FONT-FAMILY: Arial"></SPAN></FONT> </DIV>
<DIV><FONT face=Arial size=2><SPAN
style="FONT-SIZE: 10pt; FONT-FAMILY: Arial">(Quoted without permission.
;-)</SPAN></FONT></DIV>
<DIV><FONT face=Arial size=2><SPAN
style="FONT-SIZE: 10pt; FONT-FAMILY: Arial"></SPAN></FONT> </DIV>
<DIV class=Section1>
<P class=MsoNormal><FONT face=Arial size=2><SPAN
style="FONT-SIZE: 10pt; FONT-FAMILY: Arial">Maxim DG212CJ Quad SPST switch at
$3.45</SPAN></FONT></P>
<P class=MsoNormal><FONT face=Arial size=2><SPAN
style="FONT-SIZE: 10pt; FONT-FAMILY: Arial"><A
href="http://pdfserv.maxim-ic.com/en/ds/DG202-MAX332.pdf">http://pdfserv.maxim-ic.com/en/ds/DG202-MAX332.pdf</A></SPAN></FONT></P>
<P class=MsoNormal><FONT face=Arial size=2><SPAN
style="FONT-SIZE: 10pt; FONT-FAMILY: Arial"></SPAN></FONT> </P>
<P class=MsoNormal><FONT face=Arial size=2><SPAN
style="FONT-SIZE: 10pt; FONT-FAMILY: Arial">I got this price by checking for
"DG212CJ" at Digi-Key. This is simply a set of four analog switches. They would
have to be controlled by a 4052 or a similar mux. Basically the two select lines
from the noise switch would go to the mux, and one of the outputs from the mux
would turn on the proper switch in the DG212. This would require a little board
to hold all the parts, but it would be a very simple mod. The neat thing about
this part is that it will accept + and - 15V supplies, and will handle the
signal levels you're looking at. It's a little pricey, but it's cheaper than a
handful of resistors and discrete JFETs (good JFETs anyway), and also cheaper
than three relays (and probably more reliable).</SPAN></FONT></P>
<P class=MsoNormal><FONT face=Arial size=2><SPAN
style="FONT-SIZE: 10pt; FONT-FAMILY: Arial"></SPAN></FONT> </P>
<P class=MsoNormal><FONT face=Arial size=2><SPAN
style="FONT-SIZE: 10pt; FONT-FAMILY: Arial"></SPAN></FONT><FONT face=Arial
size=2><SPAN style="FONT-SIZE: 10pt; FONT-FAMILY: Arial"></SPAN></FONT><FONT
face=Arial size=2><SPAN
style="FONT-SIZE: 10pt; FONT-FAMILY: Arial"></SPAN></FONT> </P>
<P class=MsoNormal><FONT face=Arial size=2><SPAN
style="FONT-SIZE: 10pt; FONT-FAMILY: Arial">Maxim DC508ACJ single 8-channel
(<SPAN style="FONT-SIZE: 10pt; FONT-FAMILY: Arial">1-of-8) analog mux</SPAN> at
$5.70</SPAN></FONT></P>
<P class=MsoNormal><FONT face=Arial size=2><SPAN
style="FONT-SIZE: 10pt; FONT-FAMILY: Arial">(also the Maxim DC509A differential
4-channel (2-of-8) mux)</SPAN></FONT></P>
<P class=MsoNormal><FONT face=Arial size=2><SPAN
style="FONT-SIZE: 10pt; FONT-FAMILY: Arial"><A
href="http://pdfserv.maxim-ic.com/en/ds/DG508A-DG509A.pdf">http://pdfserv.maxim-ic.com/en/ds/DG508A-DG509A.pdf</A></SPAN></FONT></P>
<P class=MsoNormal><FONT face=Arial size=2><SPAN
style="FONT-SIZE: 10pt; FONT-FAMILY: Arial"></SPAN></FONT> </P>
<P class=MsoNormal><FONT face=Arial size=2><SPAN
style="FONT-SIZE: 10pt; FONT-FAMILY: Arial">Here's another analog switch chip
that can run on +-15V and handle these monster signals. Again, the price is from
Digi-Key and they show it as available. This chip is a little more expensive,
but it doesn't require a separate mux like the DG212. Just feed the two select
lines into A0 and A1, ground A3 and the enable line and you're off and running.
HOWEVER... this chip is NOT pin compatible with the 4051 or the 4052. You'd have
to build a little board to hold it, but this would be pretty
simple.</SPAN></FONT></P>
<P class=MsoNormal><FONT face=Arial size=2><SPAN
style="FONT-SIZE: 10pt; FONT-FAMILY: Arial"></SPAN></FONT> </P>
<P class=MsoNormal><FONT face=Arial size=2><SPAN
style="FONT-SIZE: 10pt; FONT-FAMILY: Arial"></SPAN></FONT> </P></DIV></BODY></HTML>