[sdiy] Which opamp pins wiring is best for CV out ?? A , B or C ???

[Dave Kendall]

Hi.

Interesting thread... If going with "A", what is the minimum resistance 
that is useful? 1K seems to be popular, although I've seen plenty of 
circuits with 330R, or even as low as 100R.
Can anyone throw some light on this?

cheers,
Dave
On Nov 9, 2010, at 15:06, Neil Johnson wrote:

> Hi,
>
> Harry wrote:
>> hmmm... when that input is on the end of a shielded cable. I've had 
>> LOTS of TL07x (08X)
>> opamps go NUTS when driving even a reasonably short cable, if there 
>> is no series resistance.
>> Even 10 ohms is enough to decouple the capacitive load...
>
> Yes indeed, those darn cables!  If we imagine a typical example:
> output goes to a connector on the front panel.  This then goes into a
> cable, lets assume shielded cable for those who like to use jacks.
> Now I've seen cables a good couple meters long on modular systems
> here.  Then that plugs into something else, which might be a passive
> multi, that then breaks out to a couple more one-metre cables.  So,
> load capacitance?  Looking at the VanDamme catalogue I see something
> of the order of 100-160pF/m.  How many metres?  Lets say 4 (2+1+1).
> So that's 400-640pF.
>
> That's a lot of capacitance for a lowly op-amp to drive without going 
> "NUTS".
>
> Cheers,
> Neil
> -- 
> http://www.njohnson.co.uk
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