[sdiy] exponential converter

[James Patchell]

One problem with doing what you said is dynamic range...although...It might 
be helpful to know exactly what your application is.  Here are some of the 
issues I see....

If you are talking about VCO's and VCF's....generally, the modules are 
controlled by a current...rather than a voltage...which is fortunate.  And 
the core of both is inherently linear...ie they respond by so many 
micro-amps/Hz.  What is generally done is to create a converter that 
converts an input that is the log of the desired frequency in volts to a 
current...(and this is done with the so called exponential current 
converter that we have all come to both love and hate)...

Now...if it is the above you want to do...circuits are abundant all over 
the internet....

On the other hand...if what you are actually looking for is a way of 
controlling a VCO module that has a voltage input that controls the 
frequency linearly (i.e. V/Hz)...well, it is still possible to use our good 
friend the exponential current converter to do this job...however, you are 
going to have dynamic range problems.  This is because it is a lot easier 
to deal with current over a large dynamic range as opposed to 
voltage.  Doing a voltage exponential converter you might...if you are real 
careful, get about 5 octaves of range out of it.  Problems arise at the 
lower ends of the scales because the change in voltage from one note to the 
next is very small and it can get swamped out by offset drifts and what not....

At 02:35 PM 6/5/2005 -0700, Jeeves quimby wrote:
>I've been feeling the need to build a v/Oct to v/Hz
>converter.
>Any suggestions would be greatly appreciated.
>
>Thanks,
>
>JPQ
>
>
>
>
>
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         -Jim
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