[sdiy] question on JFETS in vco of MS series

[lanterma at ece.gatech.edu]

On Aug 27, 2011, at 12:02 PM, dan snazelle wrote:

> there is a JFET in the MS20 VCO which connects to the CV source...on the schematic it is called Q5
> 
> see here:
> 
> http://www.korganalogue.net/korgms/images/service/ms20/circ1.gif
> 
> the drain connects to ground and the source to a 10k resistor
> 
> the odd thing (from my understanding) is that the gate is connected to GROUND.

This came up a few month ago, when some of my students were working on building the Korg MS-10/20 VCO. I seem to recall folks on the list who know more about these things than I do noted that it's essentially acting as a *current* buffer (instead of a voltage buffer), so the bits of circuitry in the main VCO core down load down the expo converter in weird ways. I think most of the common VCO cores don't need something like that.

If you dig into the SDIY list archives you may find some relevant posts.

- Aaron