Frequency shifter

[gstopp at fibermux.com]

     Ya know this is *exactly* the problem with my unit - the exponential 
     15-25 KHz VCO drifts. I've a tempco resistor in mine, but it still 
     wanders like crazy. I too have considered building a more precise VCO 
     for this. I think the problem is that the VCO is not really drifting 
     *that* much percentage-wise, it's just that a "little" drift at that 
     frequency produces a pretty noticeable hetrodyne around the zero-shift 
     point so that it's difficult to control there.
     
     Perhaps a linear VCO would be drift-free. Of course it is possible to 
     get rid of the fixed osc/VCO setup, and two of the ring modulators, 
     and just stick the two outputs of a quadrature LFO into the PDN 
     mixers. Whilst this would provide the stability that is difficult 
     using the hetrodyne method, it would take away the "through-zero 
     shift" feature. Seems too much of a sacrifice - I think the stable 
     20KHz VCO is the best pursuit.
     
     - Gene
     gstopp at fibermux.com
     
     p.s. I used AD532's and the envelope follower/VCA approach, per the 
     original design, and I have no carrier feed-through problems. Whether 
     or not these are related, I don't know. I suppose I could just open up 
     my VCA's and listen...


______________________________ Reply Separator _________________________________
Subject: Frequency shifter
Author:  Christopher_List at Sonymusic.Com at ccrelayout
Date:    1/7/97 10:48 AM