Odp: [sdiy] 1/8th inch questions

[Tim Ressel]

Grant,

Why would you want to passively mix CVs? My modules
have CV mixing built in. 

I must point out that 100 ohms is too small to protect
some opamp from short-circuit damage. 

--TR

--- Grant Richter <grichter at asapnet.net> wrote:
> Not to contradict you, but...
> 
> According to Bernie Hutchins in an article about
> input and output
> structures. The 1K value was chosen to make passive
> mixing of outputs
> possible.
> 
> Also the 1K output impedance is taken from Analogue
> computer where the
> coefficient potentiometers are 1K in value.
> 
> The 1K/100K combination gives an error of 1%
> (1V/Octave voltage sources
> don't have 1K resistor). The 100/100K reduces the
> error to 0.1% and could be
> useful in some configurations.
> 
> > From: John Blacet <john at blacet.com>
> > Date: Tue, 22 Oct 2002 15:54:28 -0700
> > To: synth-diy at dropmix.xs4all.nl
> > Subject: Re: Odp: [sdiy] 1/8th inch questions
> > 
> > I believe that this refers to the practice of
> including the output
> > resistor (1K) in the feedback loop of the op amp.
> For example, if you
> > have a 100K feedback R and a 1K output R, the
> actual output is taken
> > from the junction of the two, not the output pin
> of the amp. Of course,
> > this changes the actual gain, so you have to
> figure the Rs for that. I'm
> > not sure if this is something you can do with a
> buffer configuration.
> > 
> > In practice, we have opted to use a 100 ohm
> resistor for the output. The
> > 074X series for example, is rated for indefinite
> short circuits to the
> > supplies and ground. The 100 ohm is just extra
> current limiting, but
> > gives us 10X the "fanout" of the 1K typically
> used.
> > 
> > --
> > Regards,
> > --/////--
> > John Blacet
> > Blacet Research
> > http://www.blacet.com
> > 
> > 
> > 
> 


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