Cgs synth

>I'm getting ready to put the Sequential Switch together (on the
>breadboard first). I noticed that there are diodes at the power supply
>and ground inputs. Can someone shed some light as to what their
>function is? Are they essential to the circuit? I'm very curious.

They are essential. What they do is more the 4051 so it is operating in the
-0.6 to +14.4 volt range instead of the 0 - 15V range. This is needed
because the chip is coupled to a summing null (virtual ground) of an op-amp.
WHen operated in this mode, the voltage across the active 4051 channel is
always zero, held there by the op-amp. This means positive and negative
voltages can be switched, without the positive negative voltage ever
actually having to pass through the 4051. All the diodes at the inputs
prevent the not-selected channels from being taken negative.

This is also explained in the article.

Ken
_______________________________________________________________________
Ken Stone sasami@... or sasami@...
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