Alternative to MIDI-CV

Kimmo Koli kimmo at
Thu Feb 8 17:02:42 CET 1996 wrote:
> Hi Kimmo,
> Thanks for the Frequency-to-CV schematic.  I have two questions.
> 1.  What value resistor should be used?
> 2.  What is connected at the top of that resistor? (5V, 15V?)
> Bill Fox        wbf at

Actually, that schematic was only a principle to input a exponential CV
to a
VCF or a VCO that has linear CV control and uses the typical exponential

The Frequency-to-CV converter can be built for example from a LM2907 or
Or simply by chaining these blocks:

   comparator       pulse generator       filter
      or        ->     for ex. 555   ->  10-100Hz
  zero-cross det.                        low pass
If the zero-cross detector triggers both at rising and falling edges,
input frequency is doubled and ripple is reduced.

If the pulse generator uses accurate pulses (Xtal-clock synchronous)
and the amplitude is accurate, accurate F-to-V conversion should be

If the input frequency is high enough, also the filter corner frequency
can be higher and the response time is faster. Otherwise filter should
be 12 db/oct or even steeper.

Hope this helps,
  Kimmo Koli      			     Email: kimmo at 
  Helsinki University of Technology          URL:
  Electronic Circuit Design Laboratory
  Otakaari 5 A 
  FIN-02150 Espoo     			     Tel:  +358 0 451 2273
  Finland      				     Fax:  +358 0 451 2269

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