Ang: [sdiy] Moog/Bode type frequency shifter design in EDN europe magazine

[Scott Bernardi]

If you were interested in turning this circuit into an exponential 
through-zero VCO:
Instead of driving linear voltage to current converters, you could drive 
the linear FM inputs of two expnential converters; i.e., on the servo 
opamp that usually drives the emitters of the exponential transistor 
pair, you would DC couple the modulation signals, one inverted and one 
non-inverted, into the inputs of the servo opamps where the voltage 
references usually go. If you used a quad pnp array like the THAT120 for 
the exponential pairs, the exponential tracking should be pretty good 
between the two current sources. You would have a single CV summing amp 
that would drive both of the exponential pairs.  The rest of the 
quadrature circuit would be the same as in the article
I think this would give you the benefit of the smooth through-zero 
transition that the article purports, but with an exponential CV 
response.  Does this make sense or am I missing something?

Daniel Araya wrote:

>Nice one!
>
>http://www.reed-electronics.com/ednmag/article/CA341451
>
>/d
>
>  
>
>>>>Peter Blackett <dragon.servicing at virgin.net> 2004-01-21 14:12:21
>>>>
>>>>        
>>>>
>Hi,
>I just thought you might be interested to know that in the latest
>issue
>of EDN Europe , Jan 2004 ,
>there is an article in the design idea's section for a VCO that
>produces
>positive and negative output frequencies.the article mentions that
>this
>is traditionally done in analog music effect units such as they
>Bode/Moog frequency shifters.
>Article is written by Henry Walmsley from Farnborough .
>edn's web address is www.edn-europe.com 
>but I don't know if they have the article on line .
>regards Peter
>
>
>  
>

-- 
Scott Bernardi
sbernardi at comcast.net

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