[sdiy] Voltage references in VCO

[Ian Fritz]

ARGHHH!!!!!

As I have shown in great detail, residual drift can be zeroed out with 
appropriate active circuitry.  The "character" introduced by temperature is 
not acceptable to me.  I have had several recording sessions ruined because 
I didn't retune often enough.  If you want frequency variations, then add 
them electronically.  That way you can have whatever "character" you want.

   Ian

http://home.earthlink.net/~ijfritz/sy_cir9.htm
http://home.earthlink.net/~ijfritz/sy_cir7.htm



At 04:45 PM 4/13/06, Rob wrote:
>Hi
>Agreed, I'll add some more info! All the components need to be carefully
>considered, with low drift OP177/LT1013 Op Amps, and 0.1% 15ppm resistors in
>the critical places. And yes temperature drift is still going to be an issue
>even when the voltage reference and line regulation has been sorted out. If
>you are building a new VCO you might as well make it high quality one...
>
>Regards
>Rob
>
>No disagreement there, with careful notice of the big "IF". That is if
>the stuff that gets these stable references really good enough to really
>benefit from that. In a VCO that is peppered with TL084s the money for a
><1ppm reference is just thrown out money. For that a Tl431, LM336
>(20-50ppm) is way better than the rest of the circuitry can handle.
>
>Besides nobody is going to toss their old synths because they did use a
>LM7xxx style regulator... It was good enough for rock and roll back
>then, so why not anymore?
>
>You might want to add a paragraph about choosing the right components to
>make the most out of these references. The performance should match.
>It is very easy to spoil the performance. Opamp drift exceeding that of
>the reference for example.
>
>Don't forget that you can't use metal film resistors anymore, since
>their 100ppm temperature coefficient even does exceed the precision of
>your reference. Even with the 25ppm types.
>
>Cheers,
>   René