JFETs in ASM-1 VCO

Dr Steve Grainger s.grainger at staffs.ac.uk
Tue Nov 2 12:29:02 CET 1999


Dear All,

	Thanks for the individual responses (Paul, Magnus, Paul, Romeo,
	Jorgen).

	Tried an experiment last night by increasing the comparator the 
	comparator ON time by changing the recommended 18pF capacitor
	for a 33pF - and yes the sawtooth amplitude increased !

	Conclusions:-

	1.	Use a JFET with a lower Rds (ON) - will try the J112 from
		Siliconix

	2.	Could increase the comparator time constant (will probably
		need to recalculate the series resistor value in the integrator
		feedback to compensate)

	3.	Use paralleled 2N3819 JFETs - perhaps as costly as an
		alternative with a lower Rds (ON)

	Is this why Moog used BJTs for discharging the capacitor in his
	VCOs ?

	Regards

	Steve Grainger


Dr Steve Grainger
Midlands ED and MiB Support Centre Manager
School of Engineering and Advanced Technology
Staffordshire University
Beaconside
Stafford
ST18 0AD

Tel.   +44 (0) 1785 353636    
Fax.  +44 (0) 1785 353551    
 



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