JH's VCO, wavetable source

[mbartkow at ET.PUT.Poznan.PL]

A pre-tuned PLL !

Cool. This was my idea for a VCO tandem. The input voltage 
was intended to control two VCOs. A special "detune" switch
was supposed to offset the voltage of each VCO by a constant
number of volts (which would result in operating of the VCO
at n*basic frequency). Both VCO were intended to be kept in
phase by the phase loop which would add a small "correction"
(proportional to their eventual drift) voltage to their input
voltages. The loop phase detector was intended to be driven from 
the pulse outputs of the VCO through a frequency divisor. 
The division factor of each VCO frequency had to be set 
proportionally to the added "detune" voltage. See the block
diagram attached.

I tried to build this circuit using two 8038s with simple
expo converters and an edge sensitive phase detector 
(from the book of Tietze and Schenk). This worked so-so, because
the frequency of both the VCOs drifted, but I did not give up
yet. I think it is a good idea and will return to it later
(probably for a polysynth). I must admit the setting time was
very acceptable.

mb


--

Maciej Bartkowiak, PhD
========================================================================
Institute of Electronics and Telecommunication     fax: (+48 61) 8782572
Poznan University of Technology          phone: (+48 61) 8791016 int.171
Piotrowo 3A                             email: mbartkow at et.put.poznan.pl
60-965 Poznan POLAND               http://www.et.put.poznan.pl/~mbartkow
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