Cgs synth

>The first schematic is the buffer stage. I've built many a buffer
>stage like this except without the 1K resistor. What purpose does this
>1K resistor serve?

Protection for the chip. It allows the chip to deal with anything odd that
gets plugged into it by restricting current flow. As we are using this as a
voltage follower, limiting the current flow has virtually zero effect on
normal operation.

>The second schematic (column mixer) op amp output stage. I'd like to
>know more about what's going on here. I've seen an Oakley design that
>uses a 75R (instead of 220R) and a 22K (instead of 47K)in the feedback
>loop. In the Oakley user guide it explains that this enables it to
>drive larger capacitive loads. So, I think I get that part of the
>circuit.

220R restricts the maximum drive output from the op-amp, again to protect
the op-amp from whatever it gets plugged into - such as accidently plugging
it into another output. the 47k is arbitary. You could replace them all with
100k.

>My question is: What are the parallel diodes and 4.7K and 390R that
>are in the lower feedback loop doing? This is very interesting.

Output clipper. It merely limits the maximum swing of the output. It can be
left off with no ill effects. I don't know why I bothered to include it in
the first place.

Ken
_______________________________________________________________________
Ken Stone sasami@...
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