[sdiy] Maxim analog switch ICs

[jhaible at debitel.net]

I did this modification on my OB-8 some years ago:
http://home.debitel.net/user/jhaible/hjob8mod.html
Hey, even sacrificing the "Noise" function sounds
familiar! (;->)

In the OB-8, you really can use standard 15V CMOS
switches (positive-only signal voltages),
because the CEM chips *also* work with positive signals.
(They only have a small auxiliary negative voltagefor
the biasing / expo / current mirror stuff).

But if the OB-X uses larger signals, you need a switch that
can handle these voltages, *or* some special signal handling
or level shifting. Fortunately, today there are
plenty CMOS switches which can handle 30V. So I'd expect
no problem if you use one of these.

Speaking of the Maxim DG409, I just received two samples
which will be used in a slightly changed version of
Don Tillman's brilliant trapezoid QVCO. I need the 30V
feature there, too.

JH.


> 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.
> 
> 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.
> 
> 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.
> 
> So, now that I've made a short story long, you can see Tim's findings,
> below.
> --
> john
> 
> 
> (Quoted without permission.  ;-)
> 
> Maxim DG212CJ Quad SPST switch at $3.45
> 
> http://pdfserv.maxim-ic.com/en/ds/DG202-MAX332.pdf
> 
> 
> 
> 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).
> 
> 
> 
> 
> 
> Maxim DC508ACJ single 8-channel (1-of-8) analog mux at $5.70
> 
> (also the Maxim DC509A differential 4-channel (2-of-8) mux)
> 
> http://pdfserv.maxim-ic.com/en/ds/DG508A-DG509A.pdf
> 
> 
> 
> 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.
> 
> 
> 
> 
> 




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