[sdiy] question on JFETS in vco of MS series

[David Ingebretsen]

More intelligent people than I will give the right answer :), but I think it
all depends on voltage potentials. Ground is an arbitrary reference against
which we measure other voltage potentials. Turning Q5 on or off depends on
the potential difference between the gate and source/drain, not the voltage
of the gate with respect to ground. All this circuit does is keep the gate
at a constant potential. You change the voltage at the drain/source to turn
it on/off.

David


>>> -----Original Message-----
>>> From: synth-diy-bounces at dropmix.xs4all.nl [mailto:synth-diy-
>>> bounces at dropmix.xs4all.nl] On Behalf Of dan snazelle
>>> Sent: Saturday, August 27, 2011 9:02 AM
>>> To: synth DIY
>>> Subject: [sdiy] question on JFETS in vco of MS series
>>> 
>>> 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.
>>> 
>>> 
>>> I thought that ground shut off a transistor. obviously this circuit
works,
>>> so my guess is that ground is NOT in fact OFF, so it must be acting as a
>>> constant of some sort.
>>> 
>>> could anyone help me with this? usually when I see JFETS in vcos, the CV
>>> signal is going into the Gate so this is new to me.
>>> 
>>> 
>>> thanks!
>>> 
>>> 
>>> 
>>> 
>>> 
>>> _______________________________________________
>>> Synth-diy mailing list
>>> Synth-diy at dropmix.xs4all.nl
>>> http://dropmix.xs4all.nl/mailman/listinfo/synth-diy