[sdiy] CV offset question.

[René Schmitz]

Hello Harry and all,

harrybissell wrote:
> Engineering is usually about trading cost/complexity for performance. 

Well said!

If you're using a 7805 as a voltage reference, then the money for an 
expensive opamp is thrown away. The drift of the 7805 will most likely 
exceed that of the 1013. The offset can always be trimmed away, and in 
case of a pitchwheel, you will iron that out by hand.

I'm not trying to say that the 7805 wouldn't be good enough, but if one 
goes for "motm territory" then one needs to consider that the 
performance will always be determined by the weakest link.

One gold plated part lumped together with other el cheapo components 
will rarely deliver high end performance.

Either one starts with choosing the reference and uses a matching (i.e. 
good enough not to cause additional errors) opamp, or the other way 
round. In that case I would suggest using at a LM336-5.0 or something 
similar as the reference. Then the LT1013 can really play out its 
properties. An alternative to that would be to use an OP 07, even lower 
drift, and these are a little cheaper. Besides the LT1013 is a dual, but 
you only need a single here.


Cheers,
  René

-- 
uzs159 at uni-bonn.de
http://www.uni-bonn.de/~uzs159